Historical timeline
Photography’s chronology is quoted more often than it is checked. Schulze is dated to 1717 or 1719 in most accounts and belongs in 1727. Fabricius is credited with discovering the light sensitivity of silver chloride in 1565 and recorded nothing about light at all. Bunsen and Roscoe are given as 1862 and are 1855 to 1859. Each of those errors is a nineteenth-century summary quoted at second hand, and each of them is repeated in print every year.
This timeline is built from the pages of this course, entry by entry. Nothing appears here that a written lesson has not verified, every entry names the lesson that owns it, and every entry carries the sources it was checked against. Where the course could not settle a date, the entry says so instead of choosing.
227 entries, owned by 47 lessons. 47 of them are contested and say so; 9 correct a date or an attribution that circulates widely and is wrong.
How to read a date here
- Exact67A specific day, established by the sources.
- Year120Established to the year, or the month, and no finer.
- Span14The event occupies a stated range of years.
- Circa11Approximate. Somebody else’s estimate, or a century rather than a year.
- Contested15The sources disagree, or the date usually given could not be sourced at all.
A contested entry always carries a note saying who holds which position and what this course states. An entry may be firmly dated and still contested about something else — who was first, what it signifies, or whether the attribution is sound — and those are marked separately from the date.
Before silver
The instrument exists and nobody can keep its picture.
- 4th century BCDate precision: Circa
Eder writes that mention of pictures formed through a small aperture is found in the words of Aristotle, without naming the work.
Contested: the attribution.Eder attributes the earliest mention to Aristotle without naming the work. The passage usually cited is in the Problemata, whose attribution to Aristotle is itself disputed, and the course could not settle that from the sources it read. The entry therefore says 'the Aristotelian corpus' rather than 'Aristotle'.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter I, on Aristotle and Ibn al Haitam
- Late 4th to mid 3rd century BCDate precision: Circa
The Mohist Canons record inquiries in geometry, mechanics, optics and economics. They are widely quoted as containing a description of the inverted pinhole image; this course states what the Canons are and when, and does not quote what they say about pinholes.
Contested: the attribution; unverified by this course.The dating is the Stanford Encyclopedia of Philosophy's, which confirms the Canons record inquiries in optics but gives no detail of the optical passages. The course has not read them in translation and therefore does not repeat the pinhole description that is usually attached to this row.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Chris Fraser, 2024§ Opening section on the dating and scope of the Canons
- c. 1038Date precision: Circa
In an essay Eder gives as 'On the Form of the Eclipse', Ibn al-Haytham describes the crescent sun cast through a narrow round hole onto a plane, and states the condition under which it appears: only when the hole is very small. Widen it and the crescent gives way to the shape of the hole itself.
This is an experiment rather than an observation: the whole aperture argument of the lesson, written a thousand years ago, followed by a discussion of varying the aperture-to-wall distance. Eder spells the name Ibn al Haitam.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter V: The History of the Camera Obscura; Chapter I on Aristotle and Ibn al Haitam
- d. 1344Date precision: Year
Levi ben Gerson used the camera obscura for eclipses of the sun and moon, as his predecessor had.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter V: The History of the Camera Obscura
- c. 1500Date precision: Circa
Leonardo da Vinci gives the first clear description: images entering a small hole into a darkened room and appearing on the opposite wall, upside down.
Written in mirror script and not printed for centuries, so it influenced nobody at the time.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter V: The History of the Camera Obscura
- 1540Date precision: Year
Erasmus Reinhold and his pupils, among them Gemma Frisius, observed a solar eclipse with a pinhole camera.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter V: The History of the Camera Obscura
- 1550Date precision: Year
Girolamo Cardano proposes putting a glass disc in the aperture, in De subtilitate, page 107.
Cardano's glass disc precedes both editions of Della Porta's Magiae naturalis. The lens clause that Porta announced as something he had kept silent about until then was inserted into the second edition of 1588, and Eder points out that Barbaro had published the lens twenty years before that. Where the popular account gives Della Porta the lens, the dated documents put two other people in front of him.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter V: The History of the Camera Obscura
- 1553 and 1588Date precision: Contested
Giovanni Battista della Porta's Magiae naturalis gives the first widely read description of the camera obscura: a concave mirror in the first edition, a convex lens added in the second.
Contested: the date; who was first.Eder gives the first edition as 1553 and supports it by adding that Porta wrote it in his fifteenth year, which fits a birth in 1538; 1558 is the date more often quoted elsewhere. The course has not examined the book and shows both. On priority, Eder points out that Barbaro's account of the lens was published twenty years before Porta described it as his own secret, and that Liesegang's comparison of the two editions shows the lens clause was inserted into the older sentence: Porta's famous 'something I have kept silent about until now' originally announced the concave mirror.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter V: The History of the Camera Obscura
1565–1800: two centuries of nearly noticing
Capable people watch silver salts darken and ask the wrong question.
- 1565Date precision: Year
Georg Fabricius describes horn silver, native silver chloride, in De metallicis rebus as a translucent mineral the colour of leather. He records nothing about any change in light.
Often given as:Fabricius discovered the light sensitivity of silver chloride in 1565.Eder traces the light claim to Arago's 1839 report, copied at second hand ever since. The 1565 date is right for the book and wrong for the discovery. When a date here looks suspiciously early, a nineteenth-century summary quoted at second hand is the usual explanation.
Contested: the attribution.Fabricius is often credited with discovering the light sensitivity of silver chloride in 1565. Eder is emphatic that De metallicis rebus says nothing about light, and traces the claim to a sentence in Arago's 1839 report on the daguerreotype which later writers copied unchecked.
Verified in:Part 1 — Silver Salts and Light: Schulze to Ritter
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Fabricius 1565
- 1568Date precision: Year
Daniele Barbaro, in La pratica della perspettiva page 192, puts the spectacle lens of a long-sighted man in the hole and then stops it down with a diaphragm to sharpen the result. This is the first stop.
The brightness-against-sharpness trade the lesson derives, being made by hand in Venice.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter V: The History of the Camera Obscura
- 1575Date precision: Year
Francesco Maurolico, in Photismi de lumine et umbra, explains why the sun's image is round through a square hole.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter V: The History of the Camera Obscura
- 1614Date precision: Year
Angelo Sala writes that powdered silver nitrate exposed to the sun turns black as ink, and that silver nitrate wrapped in paper for a year had blackened the paper.
Verified in:Part 1 — Silver Salts and Light: Schulze to Ritter
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Sala 1614
- c. 1620Date precision: Circa
Johannes Kepler used a revolving tent with a convex lens in a tube, in which he traced landscapes with a pen.
Reported in Sir Henry Wotton's letter to Bacon.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter V: The History of the Camera Obscura
- 1663Date precision: Year
Robert Boyle records the white precipitate and its darkening, and blames the air.
The lesson body gives 1663; the citation of Eder in the same page's front matter labels the passage 'Boyle 1667'. The body's date is the one carried here.
Verified in:Part 1 — Silver Salts and Light: Schulze to Ritter
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Boyle
- 1665 or 1685Date precision: Contested
Johann Zahn's Oculus artificialis teledioptricus describes a portable box with lenses in a tube and a slanting mirror throwing the image upward, which is the reflex camera.
Contested: the date.Eder gives the first edition as Wuerzburg 1665, reinforcing it by dating the book four years before a publication of Boyle's from 1669; Wall's Dictionary of Photography gives Wuerzburg 1685. The course has not examined the book and states both.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter V: The History of the Camera ObscuraE. J. Wall, edited by F. J. Mortimer, 1912§ Camera
- 1671Date precision: Year
Athanasius Kircher's Ars magna lucis et umbrae describes a camera large enough for the artist to climb into through a hatch in the floor and draw.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter V: The History of the Camera Obscura
- 1694Date precision: Year
Wilhelm Homberg shows the Paris Academy a box turned from beef bone, soaked in silver-bearing aqua fortis, blackened in the sun and cut back on a lathe to expose the pale bone as a marbled pattern. He never separated light from heat, and laid no stencil on it.
Verified in:Part 1 — Silver Salts and Light: Schulze to Ritter
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Homberg 1694
- 1727Date precision: Year
Johann Heinrich Schulze publishes the scotophorus memoir in the first volume of the Acta physico-medica at Nuremberg: chalk moistened with silver-bearing nitric acid darkens on the side facing the sun and not on the side turned from it. He held the tube to a fire until the glass was almost too hot to hold and nothing changed colour, then wrote words into the sediment with a waxed paper stencil.
Often given as:The experiment was made in 1717 and published in 1719.The course could not find a source for either date. The Latin memoir sits in the Acta physico-medica volume published at Nuremberg in 1727, and Eder, who reprinted that Latin text and wrote a monograph on Schulze, dates the work to 1725-1727. Until someone produces the 1719 printing, this course states 1727.
Two details matter more than the picture. A single shake erased the writing and reset the material, so the permanence problem is present in the first photographic image ever made; and calcium nitrate alone proved insensitive, so the effect belonged to the silver.
Verified in:Part 1 — Silver Salts and Light: Schulze to Ritter
Sources:Johann Heinrich Schulze, 1727§ Scotophorus pro phosphoro inventusJosef Maria Eder, translated by Edward Epstean, 1945§ Chapters IX-X: Schulze
- 1757Date precision: Year
Giacomo Battista Beccaria, in Turin and apparently unaware of Schulze, runs the same test on silver chloride alone and concludes that the agent is light, not air as he had believed.
Verified in:Part 1 — Silver Salts and Light: Schulze to Ritter
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Beccarius 1757
- 1777Date precision: Year
Carl Wilhelm Scheele establishes four things at once: light and not heat causes the darkening; the black product is metallic silver; the chlorine is released; and the response is strongest at the violet end. Washing the blackened powder with aqueous ammonia removed the silver chloride light had not acted on and left the image silver behind.
The ammonia step is the first fixing operation anyone performed, and nobody recognised it, Scheele included. He had no picture to preserve, so the answer to the permanence problem sat in print for decades before Wedgwood and Davy gave up.
Verified in:Part 1 — Silver Salts and Light: Schulze to Ritter
Sources:Carl Wilhelm Scheele, translated from the German by J. R. Forster, with an introduction by Torbern Bergman and notes by Richard Kirwan, 1780§ Sections 60 to 66Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter XIII: Priestley to Senebier
- 1782Date precision: Year
Jean Senebier, librarian at Geneva, puts times to the spectral ordering: horn silver visibly changed in 15 seconds under violet, 29 under blue, about 5 minutes under yellow and 20 minutes under red, with the three slowest never reaching the depth violet produced.
The figures reach us through Eder and were judged by eye. Treat them as an ordering, which is robust, not as ratios, which are not.
Verified in:Part 1 — Silver Salts and Light: Schulze to Ritter
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Senebier 1782
- 1794Date precision: Year
Elizabeth Fulhame, in An Essay on Combustion with a view to a New Art of Dying and Painting, describes silk soaked in a solution of gold and hung in the sun, where a purple tinge and specks of reduced gold appear over days. She ran a control, the same silk in a dried atmosphere, which produced nothing in three months, and applied the method to maps, drawing rivers in silver and cities in gold.
Contested: what it signifies.Larry Schaaf has argued that this earns Fulhame a place among the forerunners of photography, and Herschel named her in his first written account of the subject in 1839. Whether light-drawn maps are photography is a question about definitions; that she did the experiment, and the control, is not.
Verified in:Part 1 — Silver Salts and Light: Schulze to Ritter
Sources:Mike Ware, 2020§ 2.4 Elizabeth Fulhame
- 1798Date precision: Year
Vauquelin finds that chromic acid forms a carmine-red silver salt that darkens in light. Because it is a silver compound, the reaction belongs to silver photochemistry rather than to the chromate family.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Discovery of the photographic processes with chromates by Ponton (1839)
- 1800Date precision: Year
William Herschel, measuring the heating power of the colours with thermometers, finds the effect continuing past the red where there is no colour at all, and so discovers infrared.
Verified in:Part 1 — Silver Salts and Light: Schulze to Ritter
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Herschel and Ritter 1800-1801
- In the years before 1802Date precision: Contested
Thomas Wedgwood makes profiles, copies of paintings on glass and contact prints from leaves and insects' wings on paper and leather moistened with silver nitrate. When the experiments were done is not established.
Contested: the date.Mike Ware puts the first recorded contact images at around 1797 and describes the photograms as made about 1800; the paper itself gives no dates at all, and Wedgwood was in poor health throughout the period. The course writes 'the 1802 paper' for the document and 'in the years before 1802' for the work, and does not give a year for the experiments.
Verified in:Part 1 — Wedgwood, Davy and the Problem of Permanence
Sources:Mike Ware, 2019§ 2.1 Silver compounds and the tawed-leather explanationRobert Hunt, 1854§ Chapter I, sections 31 to 33: the Wedgwood and Davy memoir of 1802, transcribed
1801–1838: the three problems take shape
Wedgwood fails, Niepce succeeds at something else, and the answer to permanence sits unread in a chemistry journal.
- 22 February 1801Date precision: Exact
Johann Wilhelm Ritter lays a spectrum across silver chloride on damp paper in a dark room and finds the darkening beginning beyond the violet, where nothing can be seen, so discovering ultraviolet. He notices too that already-darkened paper goes darker still at the violet end and lighter at the red.
Red light undoing what violet had done is an antagonism Part IV returns to.
Verified in:Part 1 — Silver Salts and Light: Schulze to Ritter
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Herschel and Ritter 1800-1801
- c. 1802Date precision: Contested
Hunt reports that at about the same time the French physicist Jacques Charles proposed, in his Paris lectures, to make black profiles on a prepared paper by the action of light, and died without disclosing the preparation.
Contested: the date; who was first; unverified by this course.Hunt adds that Charles's own countryman the Abbe Moigno conceded he left no authentic document to attest the discovery. Eder offers a deflationary explanation: Charles was librarian of the Institut de France, whose library carried the Journal of the Royal Institution, so he could simply have read Wedgwood and Davy. The course states that Wedgwood and Davy published the first account; an undocumented claim is not evidence, and it is also not a refutation, it is a gap.
Verified in:Part 1 — Wedgwood, Davy and the Problem of Permanence
Sources:Robert Hunt, 1854§ Chapter I, sections 31 to 33Josef Maria Eder, translated by Edward Epstean, 1945§ From Vauquelin to Davy
- June 1802Date precision: Year
An Account of a Method of Copying Paintings upon Glass, and of Making Profiles, by the Agency of Light upon Nitrate of Silver, invented by T. Wedgwood, Esq., with Observations by H. Davy is published in the Journal of the Royal Institution of Great Britain, volume one, page 170. It reports four kinds of picture, and states that camera obscura images were too faint to act on the nitrate of silver in any moderate time.
The title says invented by one man and observations by the other, and the two voices are distinguishable in the text. Eder is emphatic that although the work is routinely attributed to both, the credit for the conception belongs to Wedgwood. Davy's own contribution is the solar-microscope copy, and his condition on it - that the paper be close to the lens - is the sensitivity problem stated from the other side.
Verified in:Part 1 — Wedgwood, Davy and the Problem of Permanence
Sources:Robert Hunt, 1854§ Chapter I, sections 31 to 33: the Wedgwood and Davy memoir of 1802, transcribedLeonard Darwin, 1899§ Wedgwood, ThomasJosef Maria Eder, translated by Edward Epstean, 1945§ From Vauquelin to Davy: Wedgwood and Davy 1802
- 1814Date precision: Year
Humphry Davy produces silver iodide and recognises that it is sensitive to light.
Eder points out that this is of particular interest to the history of photography precisely because both Niepce and Daguerre later worked with it.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ From Vauquelin to Davy: Davy on iodide of silver 1814
- 5 May 1816Date precision: Exact
Nicephore Niepce reports his first exposure in a miniature camera he had built himself, giving a negative image on white paper coated with silver chloride which he could not fix. The values came out reversed and the objects reversed left to right, and he had to explain to his brother why the pictures looked so strange.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Joseph Nicephore Niepce: the 1816 letters to ClaudeMusee Nicephore Niepce, Chalon-sur-Saone§ Essais et realisations: 1816
- 2 June 1816Date precision: Exact
Niepce writes that it was impossible to find a substance of greater light sensitivity, and describes trying to fix images on metal plates with the aid of certain acids, finding that light did not noticeably influence the action of those acids. Letters of 16 June and 12 July show him continuing on stone, without success.
Contested: the attribution.The received account says Niepce tried to fix his 1816 silver chloride images with nitric acid. The course could not confirm the specific acid: Eder, working from the Fouque edition of the letters, says only 'certain acids', and describes the intent as etching the plate by the action of light rather than fixing a print. Nitric acid appears in Niepce's practice unambiguously, but as the etchant that bites the metal where the resist has been washed away. The outcome is not in dispute, and it is what the chemistry predicts: an acid strong enough to attack anything on that sheet attacks the image silver and leaves the silver chloride.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Joseph Nicephore Niepce: the 1816 letters to ClaudeRobert Hunt, 1841§ Processes on metallic and glass tablets, I: Heliography
- 1818Date precision: Year
Niepce settles on bitumen of Judea dissolved in oil of lavender. He is no longer looking for a substance that darkens but for one whose solubility light changes, because a solubility difference can be developed with a solvent and then used to protect a metal from acid.
The list he worked through first is a research programme in itself: iron chloride in alcohol, yellow iron oxide fumed with chlorine, manganese dioxide, guaiacum resin, and phosphorus, which he abandoned after burning his hands. Bitumen is not a compound; Ware calls its structure a chemist's worst nightmare, and this course writes no formula for it.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Musee Nicephore Niepce, Chalon-sur-Saone§ Essais et realisations: 1818Mike Ware, 2019§ 2.6 Bitumen; 2.7 Resins
- 1819Date precision: Year
John Herschel publishes 'On the Hyposulphurous Acid and its Compounds' in the first volume of the Edinburgh Philosophical Journal. Among the general characters of the class: 'One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver, and retaining it in considerable quantity in permanent solution.'
The answer to the permanence problem was in print, in a well-read journal, seventeen years after Wedgwood and Davy said they had nothing and twenty years before anybody applied it to a photograph. Herschel was not thinking about pictures; he was characterising a new class of salts, and the investigation began with a bitterness he could not account for in a jar set aside for a few days.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:John Frederick William Herschel, 1819§ Article II, general characters of the hyposulphites; Hyposulphite of silver
- 1822Date precision: Year
Niepce makes copies of engravings on glass plates good enough to give away, including a portrait of Pope Pius VII.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Musee Nicephore Niepce, Chalon-sur-Saone§ Essais et realisations: 1822
- 11 July 1822Date precision: Exact
Daguerre and the painter Charles-Marie Bouton open the Diorama in a purpose-built showroom in Paris: enormous translucent paintings, lit from in front and from behind, in which the light is changed while the audience watches so that a scene passes from day to night.
This is the background a showman brought to Niepce's problem, and it explains the result: Daguerre was not looking for a scientific record but for an image with the qualities of the Diorama, and the process he arrived at has exactly those properties and few of the ones a scientist would have optimised for.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Malcolm Daniel, Department of Photographs, The Metropolitan Museum of Art, 2004§ Daguerre and the Invention of Photography, whole essayJosef Maria Eder, translated by Edward Epstean, 1945§ The Life of Daguerre
- 1823Date precision: Year
Renewed attempts on lithographic stone, which Niepce tries to etch so that the stone can serve as a printing matrix.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Musee Nicephore Niepce, Chalon-sur-Saone§ Essais et realisations: 1824
- 1823-1824Date precision: Span
On Italian journeys Talbot tries a camera obscura throwing its image onto tracing paper laid on a pane of glass, and finds that the pressure of the hand shifts the instrument and that the detail defeats his patience.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:William Henry Fox Talbot, 1844§ Brief Historical Sketch of the Invention of the Art
- 1824-1825Date precision: Span
On copper the etching finally works, producing the plates now known by their subjects, among them a man leading a horse and a girl at a spinning wheel.
From 1825 Niepce corresponds with the Parisian engraver Lemaitre, who pulls proofs from his plates and tells him what is wrong with them, and with the optician Vincent Chevalier about lenses. That correspondence is the reason the work can be dated at all.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Musee Nicephore Niepce, Chalon-sur-Saone§ Essais et realisations: 1824, 1825
- 1825Date precision: Year
Herschel describes the actinometer in the Edinburgh Journal of Science, an instrument that turns a chemical effect into a measurement. At the close of 1836 he made with it the first satisfactory measurements of direct solar radiation.
Part XV builds the modern descendant of that instinct.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Agnes Mary Clerke, 1891§ Herschel, Sir John Frederick William: photography, the actinometer, and the photograph on glass
- 1826-1827Date precision: Span
Daguerre writes to Niepce in 1826 and meets him in Paris in 1827.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ The Life of DaguerreMalcolm Daniel, Department of Photographs, The Metropolitan Museum of Art, 2004§ Daguerre and the Invention of Photography
- May 1826Date precision: Year
Niepce names the invention heliographie, sun-writing, and switches from copper to pewter, which he finds gives much better results because the support is whiter.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Musee Nicephore Niepce, Chalon-sur-Saone§ Essais et realisations: 1826
- 1827Date precision: Year
Niepce gives up etching his camera views. The acid either bites or does not, and a continuous-tone camera view has no way of instructing it, so the half-tones cannot be rendered.
Turning a continuous tone into something a printing press can carry is a nineteenth-century industry in itself, and Part XXVI picks the thread up.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Musee Nicephore Niepce, Chalon-sur-Saone§ Essais et realisations: 1827
- 1827Date precision: Contested
View from the Window at Le Gras: a heliograph on pewter, 16.7 by 20.3 by 0.15 cm, made by coating a polished plate with bitumen dissolved in oil of lavender, putting it in a camera obscura at a second-storey window and leaving it. It is the earliest photograph produced with the aid of the camera obscura known to survive.
Often given as:The View from the Window at Le Gras is 1826.The holding institution, Ware and the Musee Niepce all give 1827. 1826 is the year Niepce switched to pewter and named heliographie, which is probably where the older date comes from.
Contested: the date.The Harry Ransom Center, which owns the plate, dates it 1827 in its object record and its exhibition text; Ware gives 1827; the Musee Nicephore Niepce's chronology places the Point de vue du Gras under 1827. Many older accounts give 1826, and some give the range. This course writes 1827 because that is what the holding institution states, while noting that the evidence is circumstantial in every version: there is no dated inscription, and the argument runs through the correspondence and through which support Niepce was using when. The exposure is separately unsettled: Niepce's own directions as Hunt translated them give six to eight hours, while Jean-Louis Marignier's reconstruction, with the pre-1828 lens at f/4, concluded about five days, and the Harry Ransom Center's text says 'several days'. The course reports both and combines neither.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Harry Ransom Center, University of Texas at Austin§ The Niepce Heliograph, exhibition text and object recordMusee Nicephore Niepce, Chalon-sur-Saone§ Essais et realisations: 1827Mike Ware, 2019§ 3.8 exposure of the heliographic process
- December 1827Date precision: Year
Niepce travels to England to his sick brother Claude and spends four months trying to interest London's scientific societies in heliography, writing a Notice sur l'heliographie dated at Kew in December 1827. Because the method was not disclosed, the Royal Society declined to hear the paper and never printed it.
Niepce would not give up the secret and the Society would not take an undisclosed process, and both positions were reasonable. He left several heliographs with his host at Kew, Francis Bauer.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Niepce exhibits asphaltum photographs in England in 1827Musee Nicephore Niepce, Chalon-sur-Saone§ Biographie: 1827-1828 England
- 1829Date precision: Year
Moving from pewter to silver-plated copper on Lemaitre's advice, Niepce exposes the bared silver to iodine vapour to darken it and improve the contrast of the finished plate, then dissolves the bitumen off with spirit of wine. Exposures are still three to four hours in the sun.
Hunt, writing in 1841 while everyone involved was still alive, saw where that led: the practice 'appears to have led the way to Daguerre's beautiful process'. The step that made the daguerreotype possible was invented for its cosmetic side-effect by a man who did not want its photographic one.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Robert Hunt, 1841§ Processes on metallic and glass tablets, I: HeliographyMusee Nicephore Niepce, Chalon-sur-Saone§ Essais et realisations: 1829
- 14 December 1829Date precision: Exact
At Chalon-sur-Saone, Niepce signs a ten-year association with Louis Jacques Mande Daguerre, a Parisian painter and proprietor of the Diorama, who is charged with perfecting the invention.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Musee Nicephore Niepce, Chalon-sur-Saone§ Biographie: 1829-1833Josef Maria Eder, translated by Edward Epstean, 1945§ Daguerre and Isidore Niepce
- 1832-1834Date precision: Span
Hercules Florence, having no printing shop within reach, scratches label designs into dark varnish on flat glass and prints them by contact onto paper sensitised with silver and gold chloride, devising a fixing method using urine. He began in 1832 and his surviving notebooks show good results in 1833-34. The Getty Conservation Institute's atlas states that these pharmaceutical labels appear to be the oldest photochemically produced images on paper still extant.
Contested: who was first.Ware reports, on Kossoy's authority, a claim that Florence used the French word photographie in 1833, six years before Wheatstone, Herschel or the Vossische Zeitung. Ware gives 1833; 1834 is also commonly quoted; the Getty atlas, which does not discuss the word, dates Florence's good results to 1833-34. The course could not settle the year and reports the claim with Ware's date attributed rather than asserted. The larger claim, that Florence should be counted an independent inventor, rests on better ground. What he did not have is a reader: his work was virtually ignored by historians until Boris Kossoy's research recovered it in the 1970s, which is a fact about the history of communication rather than about him.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Dusan C. Stulik and Art Kaplan, 2013§ Historical background, Hercules Florence and TalbotMike Ware, 2019§ 3.2 Proto-photography
- 1832Date precision: Year
Suckow finds that chromate salts mixed with organic substances are light-sensitive without any silver. Eder: 'He must be recognized as the first discoverer of this light reaction.'
Often given as:Ponton discovered the light sensitivity of chromates in 1839.Suckow, 1832, for the effect without silver; Ponton, 1839, for the first photographic application of it to printing on paper; Talbot, 1852, for dichromated gelatin. Where a source says simply 'Ponton discovered it', read that as shorthand for the middle claim. Eder adds that Ponton's own explanation of the chemistry was quite incorrect.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Discovery of the photographic processes with chromates by Ponton (1839)
- June 1832Date precision: Year
Working together in Burgundy, Niepce and Daguerre produce the physautotype, in which the sensitive coating is not bitumen but the residue left when oil of lavender is evaporated, dissolved in alcohol and laid on in an extremely thin wash. The image is visible by differential light-scattering, rather in the manner of the daguerreotype.
Contested: who was first.The June 1832 date for the physautotype is not itself in question. What is in question is whether the process existed earlier: a Getty Conservation Institute analysis of Niepce's Un Clair de Lune found not bitumen but a photohardened resinous gum whose infrared spectrum strongly resembles the physautotype, on a plate dated five years before 1832. Ware notes the conflict and says that in the light of further research this episode may yet be rewritten. Analysis of the object is capable of overturning the documentary record, and here it may have done.
Ware records Marignier's finding that the residue is a resin - colophony, chiefly abietic acid - that light-hardens without any inorganic sensitiser.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Mike Ware, 2019§ 2.7 ResinsMusee Nicephore Niepce, Chalon-sur-Saone§ Essais et realisations: 1832
- 5 July 1833Date precision: Exact
Niepce dies suddenly, aged 68, without having made his invention public. His son Isidore inherits the partnership with Daguerre.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Musee Nicephore Niepce, Chalon-sur-Saone§ Biographie: 1829-1833
- October 1833Date precision: Year
On the shores of Lake Como with a camera lucida, Talbot is failing with it - 'the faithless pencil had only left traces on the paper melancholy to behold' - and writes down the idea that the medium turns on: how charming it would be if it were possible to cause these natural images to imprint themselves durably, and remain fixed upon the paper. He writes down with it the experiments he thinks most likely to realise it.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:William Henry Fox Talbot, 1844§ Brief Historical Sketch of the Invention of the ArtGeorge Clement Boase, 1898§ Talbot, William Henry Fox
- June 1834Date precision: Year
Talbot finds that a lesser quantity of salt produces a greater effect. Patches near the edges of a badly brushed sheet, which had taken up less salt, blackened much faster than the rest; a much weaker salt solution gave a sheet whose whole surface turned black uniformly and rapidly. Ware's chronology dates this discovery of the excess-silver sensitiser and Talbot's first fixer, potassium iodide, to the same moment.
Orthodox stoichiometry demands 34.4 per cent of the silver nitrate's own weight in salt, and a paper prepared at that ratio fails dismally. The heresy is the whole chemistry of the page.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Mike Ware, 2019§ 6.1 Invention of photogenic drawing; 8 chronologyWilliam Henry Fox Talbot, 1844§ Brief Historical Sketch of the Invention of the Art
- 8 February 1835Date precision: Exact
Talbot adds a strong sodium chloride solution to his stabilising treatments, following the potassium iodide of June 1834. Both leave the silver salt in the sheet.
Talbot and Herschel called the halide treatments fixing and called Herschel's thiosulfate something else entirely, washing out. The modern habit of using fixing for the second and stabilisation for the first has blurred a distinction they intended, and this course keeps them apart.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Mike Ware, 2019§ 7.5 Fixation: chemistry and etymology; 8 chronology
- 28 February 1835Date precision: Exact
Talbot's Notebook M: 'In the Photogenic or Sciagraphic process if the paper is transparent the first drawing may serve as an object to produce a second drawing, in which the lights and shadows would be reversed.' The negative-positive principle, written down before the window negative and five years before Herschel supplied the words for it.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Mike Ware, 2019§ 1.8 Negative-positive processes; 8 chronology
- Summer 1835Date precision: Year
Talbot attacks the camera with repeated alternate washes of salt and silver, uses the paper moist, and cuts a bright-day camera exposure to ten minutes. The pictures are 'very pretty' but 'quite miniatures', made in the small boxes his wife Constance later called mousetraps.
Ware lists six conditions Talbot had to satisfy at once - excess silver, a small format, a wide aperture, patience, a bright subject rich in blue and ultraviolet, and some way of stopping the image changing - and observes that neglecting any one of them makes the attempt fail.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Mike Ware, 2019§ 6.1 Invention of photogenic drawing
- August 1835Date precision: Year
The Latticed Window at Lacock Abbey, 36 by 28 mm, made in a mousetrap camera with a lens of around f/4. The National Science and Media Museum, which holds it, describes it as the earliest known surviving negative.
Contested: the attribution.The Getty Conservation Institute's atlas goes further and calls it the earliest photographic image on a paper substrate still in existence - but the same atlas, three paragraphs earlier, says the oldest photochemically produced images on paper still extant appear to be Hercules Florence's pharmaceutical labels of 1833-34. Both sentences cannot be right as they stand. The museum's narrower claim, earliest known surviving negative, is the one this course repeats.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:National Science and Media Museum§ Latticed Window at Lacock Abbey, 1835Dusan C. Stulik and Art Kaplan, 2013§ Historical background
- Before June 1837Date precision: Contested
Daguerre finds that a plate carrying an exposure far too short to darken it visibly can be made to yield a complete picture by exposing it to the vapour of mercury, which forms an amalgam with the silver where light had acted. This is the discovery of development, and of the latent image.
Contested: the date; the attribution.No source the course read dates the discovery. The 13 June 1837 contract's claim of sixty to eighty times Niepce's speed is the earliest dated evidence that development was working, so the entry is placed immediately before it. The received story - blank plates left in a cupboard, an image found days later, the contents removed one at a time until only a dish of mercury remained - is marked as hearsay in Eder's first words, and his source is not Daguerre but Liebig, writing in the Cornhill Magazine, by way of Vogel's 1878 textbook. The broken thermometer does not appear in Eder's version at all and the course could not find a source for it. Treat the account of how he found it as folklore rather than testimony.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Development with Mercury VaporsPrints and Photographs Division, Library of Congress§ The daguerreotype medium; exposure times; the camera
- 13 June 1837Date precision: Exact
A new contract is signed with Isidore Niepce. Daguerre gains the right to attach his own name alone to the new process; in exchange Isidore gets a document acknowledging that the process has been communicated to him, and that it reproduces objects sixty to eighty times more rapidly than the one his father invented.
That ratio is the earliest quantitative statement of the amplification the daguerreotype achieved.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Daguerre and Isidore Niepce
1839–1840: the eighteen months
Two announcements, a fixer, a vocabulary, and every claimant at once.
- 1839Date precision: Year
Daguerre's manual states the purpose of the last operation in one clause: to remove the iodine which, if the picture were exposed too long to light, would go on decomposing and destroy it. His first answer is a hot saturated solution of common salt, which Eder calls an imperfect fixation giving the plates a mottled appearance; the manual already offers a weak solution of pure sodium hyposulfite as preferable, because it removes the iodine entirely.
Ware's summary is that by the end of 1839, having adopted Herschel's method, the process was enjoying widespread initial success.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Louis Jacques Mande Daguerre, 1839§ Cinquieme operation: removing the iodine with saturated salt solution or hyposulfite of sodaJosef Maria Eder, translated by Edward Epstean, 1945§ Iodized Silvered Plates
- 1839Date precision: Contested
Friedrich Gerber, of Bern, is regularly named among the 1839 claimants.
Contested: the date; unverified by this course; who was first.The course found no account of Gerber's work in the sources it read. This entry exists to record that the claim is made and that this course did not verify it; nothing about what he did, or when, is asserted here.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Bayard's direct paper positives in the camera and analogous methods
- 1839Date precision: Year
Mungo Ponton reports that paper soaked in bichromate of potash is 'powerfully and rapidly acted on by the sun's rays', and that to fix it all that is required is careful immersion in water, the unexposed salt dissolving out while the exposed portions stay on the paper.
A third answer to the permanence problem, neither Herschel's nor Talbot's: light does not reduce a metal here, it makes an organic layer insoluble, so plain water separates the image from the rest. Hunt is realistic about it - bichromate paper is not sensitive enough for the camera obscura, but it answers well for copying prints and dried plants, and its recommendation is cost: two shillings a pound against five shillings an ounce for silver nitrate.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Robert Hunt, 1854§ Section I: Mr Ponton's process (bichromate of potash)Josef Maria Eder, translated by Edward Epstean, 1945§ Discovery of the photographic processes with chromates by Ponton (1839)
- January 1839Date precision: Year
Hippolyte Bayard, a clerk at the Ministry of Finance who experimented after hours, begins experimenting in the same month as both announcements, and invents the direct positive process on paper: silver chloride paper blackened all over in daylight, soaked in about 4 per cent potassium iodide, and exposed while still moist in the camera, so that light bleaches rather than darkens.
Its virtue is its defect. It is a positive, which is what everybody said they wanted, and because it is a positive it cannot be printed from. Bayard's process solved the third problem by abolishing it.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Getty, 2024§ Exhibition announcement, April 2024Josef Maria Eder, translated by Edward Epstean, 1945§ Bayard's direct paper positives in the camera and analogous methods
- 6 January 1839Date precision: Exact
The Gazette de France publishes a notice of the invention, without details.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Commercialization of Daguerreotypy
- 7 January 1839Date precision: Exact
Francois Arago reports Daguerre's invention to the Academie des sciences in Paris, without the method.
This is the announcement that set Talbot and Herschel moving within days, and the start of the eighteen months in which photography acquired most of its inventors.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Commercialization of DaguerreotypyMalcolm Daniel, Department of Photographs, The Metropolitan Museum of Art, 2004§ Daguerre and the Invention of Photography
- 22 January 1839Date precision: Exact
A note from Captain Beaufort first calls Herschel's attention to Daguerre's concealed process. At that time, Herschel writes, he was ignorant that it had been considered by Mr Talbot, or by any one in this country.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:John Frederick William Herschel, 1839§ Abstract of the paper read 14 March 1839, pages 131-133
- 25 January 1839Date precision: Exact
Michael Faraday shows Talbot's photogenic drawings at the Royal Institution.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:George Clement Boase, 1898§ Talbot, William Henry FoxMike Ware, 2019§ 8 chronology
- 29 January 1839Date precision: Exact
Herschel first fixes a photograph with thiosulfate, a week after taking up photography at all.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Mike Ware§ January 1839Mike Ware, 2019§ 5.3 Herschel's versions of photography; 7.5.4 Thiosulphate fixation
- 31 January 1839Date precision: Exact
Talbot reads 'Some Account of the Art of Photogenic Drawing' to the Royal Society. It states that the two difficulties which defeated Wedgwood and Davy were sensitivity and permanence, claims both are solved, and says the paper can be made visibly affected by full sunlight in half a second. It gives no recipe.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:William Henry Fox Talbot, 1839§ Abstract of the paper read 31 January 1839, pages 120-121
- 1 February 1839Date precision: Exact
Herschel reveals thiosulfate 'washing out' to Talbot, showing him the result of the 29 January experiment. Talbot was using it himself by 1 May.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Mike Ware, 2019§ 5.3 Herschel's versions of photography; 8 chronologyMike Ware§ January 1839
- 1 February 1839Date precision: Exact
Kobell and Steinheil, in Munich, assert in the Nationalzeitung that they have made and fixed silver chloride images on paper, with a fuller description on 9 April.
Contested: who was first.Eder's dismissal is one line long and worth reading twice: 'this has no more to do with daguerreotypy than does the claim of the Reverend Hoffmeister.' He is not saying they did nothing; he is saying that the claim being staked was for a different invention from the one being announced.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Germany: Kobell and Steinheil
- 2 February 1839Date precision: Exact
Charles Wheatstone uses the word 'photographic' in a letter to Talbot, eight days before Herschel's first recorded use of it.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Mike Ware, 2019§ 5.9 Herschel's photo-etymology
- 5 February 1839Date precision: Exact
Bayard shows early specimens of his own process to Desprets.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Bayard's direct paper positives in the camera and analogous methods
- 10 February 1839Date precision: Exact
Herschel uses 'photographic' in a letter to Talbot, and his first known camera negative carries the same date, annotated J.F.W.H. Photog. Feb 10 1839.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Mike Ware, 2019§ 5.9 Herschel's photo-etymology
- 19 February 1839Date precision: Exact
Talbot writes to Herschel describing his own fixers: potassium iodide and sodium chloride.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Mike Ware, 2019§ 8 chronology
- 21 February 1839Date precision: Exact
Talbot discloses the method to the Royal Society in a letter to its Secretary: photogenic drawing paper, fixed with sodium chloride or potassium iodide. Ware notes that it makes no mention of Herschel's hyposulphite of soda at all, twenty days after Herschel had shown it to him.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Mike Ware, 2019§ 6.1 Invention of photogenic drawing; 8 chronologyWilliam Henry Fox Talbot, 1839§ Abstract of the paper read 31 January 1839
- 25 February 1839Date precision: Exact
The first appearance of 'photograph(y)' in print, in the Vossische Zeitung, a German provincial newspaper, over the initials 'J. M.' Eder identifies the anonymous author as the Berlin astronomer Johann von Maedler.
Contested: who was first.There are at least four claims and they are not all claims about the same thing. Wheatstone used 'photographic' to Talbot on 2 February 1839; Herschel on 10 February and in his Royal Society title of 14 March; Maedler's is the first appearance in print, on 25 February; and Boris Kossoy has argued that Hercules Florence used photographie in Brazil in 1833. Eder's qualification decides it for practical purposes: an unnoticed newspaper piece by an anonymous contributor made no difference, while Sir John Herschel's mention of it made the word known to the whole world. The course therefore says Herschel put the word into scientific circulation in the spring of 1839, not that he coined it.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Mike Ware, 2019§ 5.9 Herschel's photo-etymologyJosef Maria Eder, translated by Edward Epstean, 1945§ Scientific basis of photography: Maedler and the word photography
- 8 March 1839Date precision: Exact
The Diorama burns down, taking Daguerre's laboratory, his written records and most of his early work.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ The Life of Daguerre
- 9 March 1839Date precision: Exact
Samuel Morse, in Paris to sell his telegraph, having met Daguerre in the winter of 1838-39 and been shown the process in confidence, writes home describing it. In the same letter he recalls his own attempts at Yale, years before, to fix the camera obscura image on paper dipped in silver nitrate: he got different degrees of shade from different degrees of light, and gave up on finding that light produced dark.
Morse had the material, the instrument and the idea, and abandoned them over the tonal inversion that Talbot tolerated.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Daguerreotype portraits: Morse
- 14 March 1839Date precision: Exact
Herschel reads 'Note on the Art of Photography, or the Application of the Chemical Rays of Light to the purposes of Pictorial Representation' to the Royal Society, with twenty-three specimens. The paper is a specification before it is a recipe: preserve the blackened traces with any liquid capable of dissolving and washing off the unchanged chloride but leaving the reduced silver untouched, conditions best fulfilled by the liquid hyposulphites.
He also reports a second-best: pure water will fix the photograph by washing out the silver nitrate, but leaves a brick-red tint. One of the twenty-three specimens is a camera picture of his telescope at Slough, his father's instrument, fixed from its image in a lens.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:John Frederick William Herschel, 1839§ Abstract of the paper read 14 March 1839, pages 131-133
- 21 March 1839Date precision: Exact
Talbot reports that silver bromide paper is very sensitive.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Mike Ware, 2019§ 8 chronology
- April 1839Date precision: Year
Joseph Bancroft Reade exhibits pictures at the Royal Society made on writing paper soaked in a decoction of nutgalls, coated with silver nitrate and used moist in a solar camera.
Contested: who was first.Reade is regularly credited with the discovery of chemical development, and the DNB says outright that Talbot's priority claim for the calotype directly conflicts with Reade's. Eder judges the work extremely deficient for that purpose, because Reade saw the tanning substance only as an accelerator of ordinary blackening, did not recognise development of a latent image at all, and obtained images with silver nitrate and gallic acid rather than with a silver halide. A second, separate Reade claim concerns hypo, of which Eder's verdict is that there is at this time no way of verifying this belated story. The course credits Talbot with the calotype and treats the broader priority claim as unresolved, which is what the DNB, writing in 1898, also does.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ J. B. Reade; notes to pages 254-270George Clement Boase, 1898§ Talbot, William Henry Fox
- 10 April 1839Date precision: Exact
Lassaigne's communication of a direct-positive method appears in L'Echo du monde savant.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Bayard's direct paper positives in the camera and analogous methods
- 17 April 1839Date precision: Exact
Andrew Fyfe describes the same bleaching direct-positive method to the Society of Arts in Edinburgh, using paper prepared with silver chloride or phosphate. Eder notes separately that Fyfe fixed his photographs with ammonia.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Bayard's direct paper positives in the camera and analogous methods
- 11 May 1839Date precision: Exact
A letter signed H.L. in The Athenaeum proposes paper washed with equal parts white of egg and water, then sensitised with silver nitrate and fixed with iodide of potassium. It is the first published notice of albumenised paper in photography, three months after Talbot disclosed photogenic drawing, and it carried no chloride at all, so it depended solely on silver albumenate.
Contested: the attribution.The author of the letter has never been identified: Reilly gives only the initials H.L. as they were printed, and this course has found nothing in its corpus that puts a name to them. The entry therefore credits the letter and not a person, and it is the notice rather than the process that is being dated, since eleven years pass before Blanquart-Evrard turns the idea into the material photography actually used.
Verified in:Part 23 — Egg Albumen: A Protein Binder and What It Does to Silver
Sources:James M. Reilly, 1980§ Chapter Four, Albumen Paper - the letter of H.L. in The Athenaeum of 11 May 1839, the formula it proposed, and the observation that it carried no chloride and therefore depended solely on silver albumenate
- 14 June 1839Date precision: Exact
Preliminary agreement between Daguerre, Isidore Niepce and the Minister of the Interior, Duchatel.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Commercialization of Daguerreotypy
- 24 June 1839Date precision: Exact
Bayard exhibits direct positive prints publicly in Paris, and is favourably mentioned in the French journals of July and August 1839.
Contested: what it signifies.The show is very often described as the first public exhibition of photographs. Eder records the event but not that description of it, and the course could not verify the superlative. It is also awkward on its face: Eder notes that the Moniteur officiel of the same date carried a description of Bayard's pictures; the DNB has Faraday showing Talbot's photogenic drawings at the Royal Institution on 25 January 1839, five months earlier; and Talbot exhibited again to the Royal Society on 31 January. Whether Bayard's was the first public exhibition anywhere depends on what counts as an exhibition, and this course does not decide it.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Bayard's direct paper positives in the camera and analogous methodsGetty, 2024§ Exhibition announcement, April 2024
- 3 July 1839Date precision: Exact
Arago presents the commission's report to the Chamber of Deputies, which passes the bill buying the process for the French state.
The terms are a life pension of 6,000 francs a year to Daguerre and 4,000 to Isidore Niepce, half of each reverting to their widows, in exchange for a sealed package containing the history and a complete description, which Arago was to verify and which was not to be opened until the bill passed.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Commercialization of Daguerreotypy
- 30 July 1839Date precision: Exact
The upper chamber passes the bill, 237 votes to 3.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Commercialization of Daguerreotypy
- 14 August 1839Date precision: Exact
Miles Berry applies for English patent No. 8,194 on Daguerre's behalf, as a communication from a foreigner residing abroad, naming Daguerre and Isidore Niepce as inventors. Five days before the process was given to the world, it was patented in England.
Eder calls this a mark of Daguerre's well-developed business acumen. The rights were bought by Claudet, and the AIC's summary is that the French government offered the process patent-free to the entire world except England. Separately, the Metropolitan Museum notes that Daguerre retained the patent on the apparatus: the chemistry was a gift and the camera was for sale.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Amy Brost, Luisa Casella and Stephanie Watkins, for the American Institute for Conservation§ Historical factsMalcolm Daniel, Department of Photographs, The Metropolitan Museum of Art, 2004§ Daguerre and the Invention of PhotographyJosef Maria Eder, translated by Edward Epstean, 1945§ Commercialization of Daguerreotypy
- 19 August 1839Date precision: Exact
Arago gives the full description of the daguerreotype at a joint session of the Academie des sciences and the Academie des beaux-arts.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Commercialization of DaguerreotypyMalcolm Daniel, Department of Photographs, The Metropolitan Museum of Art, 2004§ Daguerre and the Invention of Photography
- 27 August 1839Date precision: Exact
Working with a concentrated solar spectrum on chloride-sensitised paper, Herschel finds the sheet whiter where the full red of the spectrum fell than the paper around it, which had been discolouring under stray daylight. The red rays, he writes in the paper the Royal Society read in 1840, are by no means to be regarded as inactive, but rather as exciting an action of an opposite nature to that of the blue, violet and lavender rays.
He found its limit in the same experiment. On paper already darkened, red light did not restore whiteness but turned the darkening a fiery red and would go no further, and his attempt at a positive copy of an engraving came out with highlights eaten out in red, the colour of venous blood. A powerful red ray could neutralise a feeble white one at the moment of action, but could not undo an effect already fully produced.
Verified in:Part 4 — Reciprocity Failure and the Life of the Latent Image
Sources:John Frederick William Herschel, 1840§ Articles 60 to 65: chemical properties of the red end of the spectrum, the observation of 27 August 1839, and the combined action of rays of different refrangibility
- 1839 or 1843Date precision: Contested
Herschel makes photographs on glass. The first is regularly given as a glass negative of the Slough forty-foot reflector in September 1839, often called the first photograph on glass.
Contested: the date; unverified by this course.The course could not verify the September 1839 date from the sources it read. What it did find is the DNB's notice of 1891, which states on Abney's authority that 'his reproduction in 1843 of an engraving of the Slough forty-foot reflector was the first example of a photograph on glass' - a different year, and a copy of an engraving rather than a camera negative. Ware separately records a camera negative of the same telescope annotated J.F.W.H. Photog. Feb 10 1839, which is on paper. The course states that Herschel made photographs on glass and that the DNB dates the first to 1843; the 1839 date is not asserted, and a reader who finds a museum record settling it should treat that record as better evidence than either.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Agnes Mary Clerke, 1891§ Herschel, Sir John Frederick William: photography, the actinometer, and the photograph on glassMike Ware, 2019§ 5.3 Herschel's versions of photography
- Autumn 1839Date precision: Contested
Portraits begin to be attempted on daguerreotype plates by giving enormous exposures. Eder credits John William Draper in New York with the first: his assistant, face powdered with flour, sitting facing the sunlight for half an hour.
Contested: the date; who was first.Eder supports Draper with Sir David Brewster's statement in the Edinburgh Review of January 1843 that he believed Draper was the first. Other candidates are widely named, in particular Robert Cornelius in Philadelphia in late 1839; the course could not verify those claims from the sources it read and does not adjudicate. What the evidence supports is narrower: that portraits were being attempted from the autumn of 1839 at the limit of a sitter's tolerance, and only became a business after the plates were accelerated and Petzval's lens arrived in 1840.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Daguerreotype Portraits
- 11 November 1839Date precision: Exact
Bayard deposits a description of his process with the Academy, in a sealed letter.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Bayard's direct paper positives in the camera and analogous methods
- 1840Date precision: Year
The Becquerel process: a variant in which the exposed plate is developed by red light instead of by mercury vapour. It needs no mercury and no bromine or chlorine sensitising, and the plates are around ten times slower in consequence, which makes portraiture difficult. It still requires iodine.
Named here and not taught. Whether and how the course would ever classify it is Part XXVI's decision.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Amy Brost, Luisa Casella and Stephanie Watkins, for the American Institute for Conservation§ Historical facts; process overview
- 1840Date precision: Contested
Hippolyte Fizeau finds that treating a finished plate with a bath of hyposulphite of soda containing gold chloride greatly improves both its beauty and its permanence. An ungilded plate is so delicate that the image can be wiped off with a finger, so the treatment is adopted everywhere.
Contested: the date.Eder dates the invention to 1840; the AIC's conservation page gives 1841 for the introduction of gold toning. The lesson follows Eder without claiming the year is settled.
The chemistry of the bath was worked out shortly afterwards by the Paris pharmacists Fordos and Gelis, who identified the double salt and called it hyposulphite of gold and sodium - later sodium aurothiosulfate, sold in the trade as sel d'or. Eder notes it became the basis of many combined toning-and-fixing baths for silver printing papers.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Development with Mercury VaporsAmy Brost, Luisa Casella and Stephanie Watkins, for the American Institute for Conservation§ Historical facts; process overview
- 1840-1855Date precision: Span
For fifteen years the salted paper print is the ordinary printing material of photography, used almost exclusively for printing calotype negatives until about 1850 and then more widely, before albumen takes the market and holds it to 1895.
The handover is a decade rather than a date, and the sources put different events inside it: the AIC give 1847 for Blanquart-Evrard's simplified formula, the Getty atlas gives 1850 for his albumen process and says the replacement had happened by the middle of the 1850s, and Reilly's identification chart gives 1855 as the handover. The course uses Reilly's chart and states the spread.
Verified in:Part 22 — The Variants of the Salt Print and How a Conservator Identifies One
Sources:James M. Reilly, 1980§ Appendix C Guideline IV, the identification chart giving salted papers 1840 to 1855, albumen paper 1855 to 1895, gelatin and collodion printing-out papers 1895 to 1905 and develop-out papers from about 1905; and the PrefaceDusan C. Stulik and Art Kaplan, 2013§ Historical background - the salt print as the dominant printing process of the 1840s and early 1850s and its replacement by albumen by the middle of the 1850s
- 20 February 1840Date precision: Exact
In the paper received and read on 20 February 1840, Herschel writes: 'To avoid much circumlocution, it may be allowed me to employ the terms positive and negative, to express respectively, pictures in which the lights and shades are as in nature, or as in the original model, and in which they are the opposite.'
The paragraph before it explains why he needed the vocabulary: the important line of inquiry is the exact reproduction of indefinitely multiplied facsimiles of an original, by which alone the publication of originals could be accomplished. Herschel is naming the parts of a machine for making many pictures from one.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:John Frederick William Herschel, 1840§ Paragraphs 1 to 10: recapitulation of the 1839 note, multiplied fac-similes, and the terms positive and negative
- 24 February 1840Date precision: Exact
Bayard's process is finally published. Verignon presented a similar one to the Academy on the same day.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Bayard's direct paper positives in the camera and analogous methods
- 16 March 1840Date precision: Exact
Arago reports to the Academy on the priority of the direct-positive process, and finds that the methods of Verignon and Bayard do not differ from Lassaigne's.
Contested: who was first.Four people in two countries with the same idea inside twelve months. Bayard showed specimens privately from February 1839, exhibited in June and deposited a sealed description in November; Verignon presented a similar process on the day Bayard's was published; Lassaigne claimed to have communicated it earlier, in L'Echo du monde savant of 10 April 1839; Fyfe described the same bleaching method in Edinburgh on 17 April 1839. Eder, agreeing on Arago's criterion, extends the list: 'If priority of publication of the process is to decide whose claim is valid, Lassaigne must be mentioned first, then Fyfe, and only then Bayard and Verignon.' The course reports that order without endorsing publication dates as the right criterion: they measure access to a learned society rather than who did the work.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Bayard's direct paper positives in the camera and analogous methods
- May 1840Date precision: Year
Josef Petzval in Vienna calculates a portrait objective of far greater light transmission than anything then available; Voigtlaender builds the first one; and Anton Martin, at Petzval's request, makes the first portraits with it in May 1840. Eder dates the boom in portrait photography from that lens.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Daguerreotype Portraits
- 23 September 1840Date precision: Exact
In the days following 20 September 1840 Talbot finds the way past printing out. Ware dates the invention of the calotype to 23 September: a latent image in silver iodide, developed with gallo-nitrate of silver, using four chemicals and no more - silver nitrate, potassium iodide, acetic acid and gallic acid.
The gain was about a hundredfold: Ware puts the calotype's first camera exposures at about half a minute at f/4 in bright sun against the hour or more photogenic drawing needed. Print-out on paper had reached its ceiling in 1835 and stayed there; development moved it in a fortnight, and paper photography became viable even for portraiture.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Mike Ware, 2019§ 6.2 Development of the calotype; 8 chronologyWilliam Henry Fox Talbot, 1841§ Preparation of the paper; Use of the paper; The fixing process
- 12 December 1840Date precision: Exact
John Frederick Goddard publishes, in a letter dated 12 December 1840, that using bromine in combination with iodine instead of pure iodine vapour considerably increases the sensitivity of the plate.
Contested: who was first.Eder is careful to add that Goddard must share the credit with Franz Kratochwila in Vienna, who had the same result in September 1840 and published it in the Wiener Zeitung on 19 January 1841, reporting at least a fivefold gain, exposures of a few seconds, and portraits made on cloudy days in eight seconds. Goddard published first; Kratochwila did it first.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Daguerreotype Portraits
1841–1846: the medium settles
Development, the patent, the blue, and the first books.
- 1841Date precision: Year
Herschel tells the British Association that the anthotype, or phytotype - petals crushed in alcohol, the dye painted on paper, a print made by bleaching the exposed dye in sunlight - holds out 'no slight hope of a solution of the problem of a photographic representation of natural objects in their proper colours.' It is positive-working and it produces colour; it is also almost unusably slow and there is no way to fix it.
Ware notes that Herschel ran over a thousand such tests, and that the one durable result was a principle: a dye is bleached fastest by the light of its complementary colour.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Mike Ware, 2020§ 2.5 Anthotype and phytotype
- 8 February 1841Date precision: Exact
Talbot patents the calotype as No. 8,842, 'Improvements in obtaining Pictures or Representations of Objects'.
The patent did immediate damage that had nothing to do with money: the Royal Society refused to print the calotype paper in its Philosophical Transactions on the ground that Talbot had already made the method public in the specification, and for three years afterwards the process stagnated, transfixed by the patent, because it inhibited publication of any improvement. The patent did not hold sway in Scotland, where Talbot had not registered his claim.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Mike Ware, 2019§ 6.7 Patents; 6.6 Publications; 10.1 Innovations at Saint Andrews
- 10 June 1841Date precision: Exact
Talbot describes the calotype to the Royal Society, in three stages he calls iodising, exciting and bringing-out. The important sentence is the one about the invisible picture: 'the impression is latent and invisible, and its existence would not be suspected by any one who was not forewarned of it by previous experiments.'
After weeks of angry correspondence and Herschel's intervention the Royal Society compromised on the less prestigious Proceedings, and Talbot issued the text privately as a pamphlet.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:William Henry Fox Talbot, 1841§ Preparation of the paper; Use of the paper; The fixing process; the five closing experimentsMike Ware, 2019§ 6.6 Publications
- 10 June 1841Date precision: Exact
Antoine Claudet, who had bought the English patent rights, describes iodo-chloride sensitising in May 1841 and reads a paper before the Royal Society on 10 June 1841 comparing it with bromo-iodide.
Verified in:Part 1 — Daguerre and the Daguerreotype: A Mirror With a Memory
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Daguerreotype Portraits
- 1842-1847Date precision: Span
Draper in 1842, Lerebours in 1846 and Claudet in 1847 find the same red-light action on the latent image of the iodised daguerreotype plate that Herschel had found on visible print-out silver, and the work is later extended to collodion and to gelatine silver bromide.
Often given as:The Herschel effect is the thing Herschel saw in 1839.Herschel's own observation was of red light acting on visible print-out silver on paper. The effect that now carries his name is the quenching of the invisible latent image in an exposed but undeveloped emulsion, which Draper, Lerebours and Claudet established on the daguerreotype in the years after. Same physics at two very different scales, and the name travelled.
Verified in:Part 4 — Reciprocity Failure and the Life of the Latent Image
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Herschel Effect: Draper 1842, Lerebours 1846 and Claudet 1847 on the latent image of the iodised daguerreotype plate
- 23 April 1842Date precision: Exact
Herschel's memorandum: 'Smee's Red Ferrocyanate of Potash washed on paper gives it a fine pale green colour. When the paper is thrown onto water the impression becomes stronger, loses its Violet ruddiness and turns to a fine prussian blue. This paper will prove valuable.' His diary that day is blunter: 'Discovered the Photographic property of the Red Ferro sesquicyanuret of Potassm.'
Ware's comment is worth keeping: discovered seems the better word than invented. The salt, potassium ferricyanide, then called the ferrosesquicyanuret or red prussiate of potash, was sent by the surgeon Alfred Smee, who had learned to make it cleanly by electrolysis.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Mike Ware, 2020§ 2.6 Discovery of cyanotypeJohn Frederick William Herschel, 1842§ Articles 202 to 213: ferrosesquicyanuret paper, ammonio-citrate of iron, the two stages
- 10 May 1842Date precision: Exact
Smee's letter mentions two salts newly vamped up by the chemists and druggists as iron tonics, the ammonio-citrate and ammonio-tartrate of iron. Herschel tries the citrate photographically instead of medicinally, finds it highly sensitive, and writes back that it 'has furnished me with an infinity of beautiful photographic processes'.
Ferricyanide paper alone needs half an hour or an hour's exposure to sunshine, which Ware calls optimistic; ferric ammonium citrate brings a contact print down to minutes.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Mike Ware, 2020§ 2.6 Discovery of cyanotype; 2.7 Invention of siderotype
- 16 June 1842Date precision: Exact
Herschel's paper 'On the Action of the Rays of the Solar Spectrum on Vegetable Colours, and on some new Photographic Processes' is accepted on 15 June and partly read to the Royal Society on 16 June, with 43 specimen sun-prints attached. Article 219 coins the name for the whole class: any process in which cyanogen in its combinations with iron performs a leading part, and in which the resulting pictures are blue.
Four siderotypes in one summer: cyanotype (Prussian blue), argentotype (silver), chrysotype (gold) and kelainotype (mercury, which defeated him). He named the chrysotype in imitation of Talbot's calotype. The one he thought least of is the one that changed drawing offices worldwide.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:John Frederick William Herschel, 1842§ Articles 218 to 223: the two stages, chrysotype, and the naming of cyanotypeMike Ware, 2020§ 2.8 Publication of siderotype
- 29 August 1842Date precision: Exact
In the Postscript added to his Royal Society paper, Herschel gives the first iron-silver process: paper prepared as for the chrysotype, exposed, then washed over with silver nitrate, which the iron(II) the light has made reduces to metal. He calls it argentotype, and it is the ancestor of the kallitype, the Van Dyke brown and the argyrotype alike.
Four days' work in the summer of 1842 produced the whole of the invention. Part I owns the paper itself, read to the Royal Society on 16 June, at tl-1842-siderotype-paper; this entry is the silver variant added to it in August.
Verified in:Part 24 — The Siderotype Principle: Iron Reduces Silver
Sources:John Frederick William Herschel, 1842§ Article 218, in the Postscript added 29 August 1842, for the substitution of nitrate of silver applied after exposure to paper prepared as for the chrysotypeMike Ware§ History, for Herschel's argentotype of 1842 and its derivatives
- 1843-1853Date precision: Span
Photographs of British Algae is issued privately in parts over ten years. Ware puts the total at roughly 420 plates or more across twelve fascicles, varying between copies, and estimates that the edition demanded the hand-printing of over five thousand cyanotypes.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Mike Ware, 2020§ 5.4 Cyanotypes of British algae by Anna AtkinsNational Science and Media Museum§ Anna Atkins, British Algae
- 1843-1846Date precision: Span
Robert Adamson, taught by his brother John, is by May 1843 the first successful professional photographer in Scotland; Brewster introduces him to the painter David Octavius Hill. Between 1843 and 1846 Hill and Adamson make more than three thousand images, whose salt prints Ware describes as notable for rich colour, high density and good stability.
Ware's explanation for the stability is deflating and probably right: not a secret ingredient but dilute hypo and scrupulous washing. Cundell's 1844 account recommends a 2.5 per cent fixing bath where the manuals of the 1850s specify 10 to 30 per cent.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Mike Ware, 2019§ 10.1 Innovations at Saint Andrews
- 1 June 1843Date precision: Exact
Talbot's patent No. 9,753 covers hot thiosulfate fixation and the waxing of paper negatives.
Two further patents followed, in 1849 and 1851.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Mike Ware, 2019§ 6.7 Patents
- October 1843Date precision: Year
Anna Atkins distributes more than a dozen copies of the first fascicle of Photographs of British Algae: Cyanotype Impressions. A dried, pressed alga laid on sensitised paper is its own negative, and every plate carries its Linnaean binomial in Atkins' own handwriting, written on a translucent slip and printed with the specimen.
Contested: who was first.Three claims circulate about the first photographically illustrated book, and they are settled by reading the wording rather than the dates. Ware records the October 1843 distribution and that the first part of The Pencil of Nature did not appear until June 1844, so British Algae takes precedence, albeit as a privately published one; the Getty atlas agrees. The DNB, writing in 1898, calls The Pencil of Nature the first book ever illustrated by photographs produced without any aid from the artist's pencil, a formulation that quietly excludes a privately circulated part-work. Eder asserts that Talbot's Sun Pictures in Scotland of 1845 was the first, which cannot be right on his own chronology. The course states Atkins' first fascicle, October 1843, with the qualifier 'privately issued' in the sentence every time.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Mike Ware, 2020§ 5.4 Cyanotypes of British algae by Anna AtkinsNational Science and Media Museum§ Anna Atkins, British AlgaeDusan C. Stulik and Art Kaplan, 2013§ Historical background
- January 1844Date precision: Year
The Reading establishment is founded under Nicolaas Henneman: the first attempt at printing photographs in quantity.
Henneman washed each batch of twenty-five prints for ten minutes in each of three baths of hot water, and Schaaf traces the severe sulphide fading of The Pencil of Nature prints mainly to residual thiosulfate and to Reading's water supply.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:Mike Ware, 2019§ 8 chronology; 17.3 Deterioration by environment
- June 1844 - 1846Date precision: Span
The Pencil of Nature: six fascicles between 1844 and 1846 carrying twenty-four plates, every print made by hand, in sunlight, and pasted in. Talbot wrote a caption for each, and read together they are the earliest sustained attempt this course knows of to say what photographs are for.
Talbot is honest about the medium's difficulty in the remarks that precede the plates: the copies are almost facsimiles as to design but vary in tint, because each is separately formed by a sun whose strength is exceedingly variable even in serene weather.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:William Henry Fox Talbot, 1844§ Brief Historical Sketch of the Invention of the Art; Plate VI The Open Door; Plate VII Leaf of a PlantMike Ware, 2019§ 8 chronology
1847–1870: the medium industrialises
The patent fights end, the law of exposure is stated, and the lensless camera is described in a book about stereoscopes.
- 1847Date precision: Year
P. F. Mathieu publishes the first account of gold-toning a paper print, adapting to salted paper the gilding bath Fizeau had devised for the daguerreotype in 1840. Neither source says the technique caught on: both date its general adoption to after Le Gray publicised it in the 1850s.
Reilly calls the pamphlet Auto-Photographie and Ware Autophotographie; the spelling differs and the year does not. The Getty atlas dates general adoption of gold toning to after 1850, accelerating after 1855, which is to say after the Fading Committee reported.
Verified in:Part 22 — Gold Toning and the Permanence of a Printed-Out Silver Image
Sources:James M. Reilly, 1980§ Chapter Eight, Gold Toning - Fizeau's gilding of 1840 adapted to paper prints by P. F. Mathieu in 1847, and the technique not catching on until Le Gray publicised it after 1850Mike Ware, 2020§ Section 5.3, on Mathieu's Autophotographie of 1847 and the later publicising of gold toning
- 27 May 1850Date precision: Exact
Louis-Desire Blanquart-Evrard presents the albumen printing process to the French Academy of Sciences: egg white beaten to a froth with a salt solution, settled overnight, floated onto paper for a minute, dried, and sensitised on silver nitrate. In that form it becomes the material almost every photograph on paper is printed on for the next forty years.
Two Tier 1 sources agree on the day. Blanquart-Evrard's own account claimed the albumenised paper would keep indefinitely before sensitising; no source read for this course tests that claim, and the course states the coated-paper keeping time as good rather than indefinite.
Verified in:Part 23 — Egg Albumen: A Protein Binder and What It Does to Silver
Sources:Dusan C. Stulik and Art Kaplan, 2013§ Historical background - the process presented by Louis Blanquart-Evrard to the French Academy of Sciences on 27 May 1850 and published in the Comptes rendus des seances de l'Academie des Sciences 30, no. 21 (1850): 665James M. Reilly, 1980§ Chapter Four, Invention of the Albumen Printing Process - the communication of 27 May 1850 and the original recipe, egg white beaten to a froth with 25 per cent by weight of a saturated salt solution, settled overnight and floated one minute
- March 1851Date precision: Year
Frederick Scott Archer publishes his application of collodion to photography in The Chemist: a nitrocellulose film flowed onto glass, sensitised in a silver nitrate bath and exposed while still wet. He did not patent it, and a free process that was sharper than a calotype and cheaper than a daguerreotype displaced both within a decade.
Contested: who was first.The AIC records a claim for Gustave Le Gray between 1850 and 1851, notes that his method was received as theoretical at best and that he abandoned coated glass for paper. The Dictionary of National Biography, writing in 1885 with living witnesses available, separates the two questions: Archer does not seem to have been the first to suggest the application of collodion, but there appears no doubt whatever that he was the first to carry it into effect. The course repeats neither Archer invented photography on glass nor Le Gray got there first as a settled fact.
Collodion existed as a surgical preparation first: Schoenbein discovered gun-cotton in 1846 and Maynard of Boston prepared an ethereal solution of it for surgery in 1847. Archer published a book-length account in 1854, died in May 1857 having reaped no benefit, and the Crown granted his children a pension on that explicit ground.
Verified in:Part 26 — Wet-Plate Collodion: The Process That Made the Nineteenth Century Look Like That
Sources:Henry Trueman Wright Wood, 1885§ The whole entry: Archer's dates of 1813 to May 1857, Schoenbein's gun-cotton of 1846 and Maynard's surgical collodion of 1847, Archer applying collodion to photography in 1850 and his first account published in The Chemist in March 1851, the priority sentence, and the record that he did not patent the inventionAmerican Institute for Conservation, Photographic Materials Group§ Background and the claim recorded for Gustave Le Gray between 1850 and 1851
- 1852Date precision: Year
At the request of the presidents of the Royal Society and the Royal Academy, Talbot throws his discoveries open, keeping only portrait-taking for sale to the public.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:George Clement Boase, 1898§ Talbot, William Henry Fox
- 29 October 1852Date precision: Exact
Talbot patents photoglyphic engraving, the sensitivity of dichromate mixed with gelatin or gum, which Ponton had missed. The whole chromium(VI) family - carbon printing, gum bichromate, photogravure, dichromated gelatin - descends from this.
One of the two post-1846 dates Part I fixes for the rest of the course. Potassium dichromate's aggregated GHS classification is severe enough that no home procedure is on offer; Part XXVI carries the assessment and the argument.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Discovery of the photographic processes with chromates by Ponton (1839)
- 1854Date precision: Year
James Ambrose Cutting patents a method of sealing an under-exposed collodion negative on glass with Canada balsam behind a cover glass, and gives the object its name, taken from the Greek for imperishable. The name was his lasting contribution; the sealing was not, because plates made under the patent are known to deteriorate because of it, showing a yellowish-green hue.
Nothing about an ambrotype is positive: it is an under-exposed wet collodion negative that appears positive because of a dark backing or a dark support, so taking the backing off turns it back into a negative. The main period of use in North America is 1850 to 1870. This course found no citable date for the tintype or ferrotype patent.
Verified in:Part 26 — Wet-Plate Collodion: The Process That Made the Nineteenth Century Look Like That
Sources:Photographic Materials Group, American Institute for Conservation§ The definition of the ambrotype as an under-exposed wet collodion negative on glass, James Ambrose Cutting's patents of 1854 and the name taken from the Greek for imperishable, and the main period of use, 1850 to 1870 in North AmericaImage Permanence Institute, Rochester Institute of Technology, 2026§ The note on the Cutting-method ambrotype: that in 1854 Cutting developed a method of sealing the plate with Canada balsam, that plates made under the patent are known to exhibit deterioration caused by the technique, and that Cutting's lasting contribution was the name
- December 1854Date precision: Year
Talbot tries and fails in the courts to enforce his patent against a photographer the DNB names Sylvester Laroche, whose collodion development he held to infringe it.
Ware notes that Talbot's answers under cross-examination are themselves technically interesting.
Verified in:Part 1 — Talbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle
Sources:George Clement Boase, 1898§ Talbot, William Henry FoxMike Ware, 2019§ 6.7 Patents
- 1855-1859Date precision: Span
Bunsen and Roscoe's Photochemische Untersuchungen: exposure as the product of intensity and time, the reciprocity law that Parts XIII and XIV are built on.
Often given as:Bunsen and Roscoe's photochemical investigations are 1862.Eder dates the Photochemische Untersuchungen to 1855-1859, and records that Bunsen and Roscoe began the chlorine detonating gas work in 1854. The 1862 date is not only folklore: Mike Ware gives it, citing Annalen der Physikalische Chemie volume 117, which is a later paper in the same series. The disagreement is about which paper in a five-year run to name, and this course follows Eder. This is one of the two post-1846 dates Part I fixes, and every later page must respect it.
Verified in:Part 1 — 1839 and the Many Inventors of Photography
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Bunsen and Roscoe, Photochemische Untersuchungen
- 21 May 1855Date precision: Exact
The Photographic Society of London appoints a committee to consider the fading of positive photographic pictures upon paper. It reports on 21 November that the most ordinary cause of fading is sulphur, intrinsic from hyposulphite left in the print or extrinsic from the atmosphere, and much faster in the presence of moisture. Its two recommendations, thorough washing and gold toning, are still the two controls this course teaches.
Ware records that the recommendation that gold in some form should be used was not unanimous. Reilly credits the improvements in print stability made during the 1850s with letting albumen paper attain a better record of durability than the salted papers before it.
Verified in:Part 22 — Gold Toning and the Permanence of a Printed-Out Silver Image
Sources:James M. Reilly, 1980§ Chapter Eleven, The Era of Salted Papers 1840-1855 - the committee appointed 21 May 1855 and its report of 21 November, and the quoted finding on sulphur, intrinsic and extrinsic, and moistureMike Ware, 2020§ Section 5.3, on the Fading Committee and the recommendation of gold not being unanimous
- 13 December 1855Date precision: Exact
Poitevin's English patent turns the light-hardening of a dichromated colloid into two industries in one specification: wash the exposed layer and the pigment left behind is a carbon print, or dampen it and roll it up with greasy ink and it is collotype. Talbot had patented the mixture in 1852; Poitevin found what to do with it.
Poitevin's French licence is dated 6 August 1855, and Pretsch's English patent for a gravure process using the swelling property predates the English filing at 9 November 1854. Sutton and Pouncy reached a pigment process independently in England in 1858, and Cassell's 1911 encyclopaedia credits Pouncy with being the first actually to produce carbon prints.
Verified in:Part 26 — Light-Hardened Colloids: Bitumen, Dichromate and the Pigment Processes
Sources:Encyclopaedia Britannica (article by W. de W. Abney and others), 1911§ Printing with Chromates, Carbon Prints - Poitevin's English patent of 13 December 1855 for a direct carbon print by rendering gelatin insoluble, and the surrounding chronology from Ponton's May 1839 report onwardsJosef Maria Eder, translated by Edward Epstean, 1945§ Chromates - Poitevin's discovery of collotype and pigment printing in 1855, and his English patent of December 1855 recommending a mixture of albumen, fibrine, gum arabic and other colloids
- 1856Date precision: Year
Brewster's The Stereoscope describes an image formed through a small aperture in the side of a camera, records that pictures so made are accurate representations of the object, and names the one error he can imagine - the inflexion of light - adding that only experiment can ascertain its effect. He and the Rev. Mr Egerton had obtained photographs of a bust in ten minutes, with a very faint sun, through an aperture less than the hundredth of an inch.
Contested: who was first.The page calls this the passage usually cited as the first published description of lensless photography, and makes no priority claim of its own; nor has this course surveyed the earlier literature a claim of priority would need. What is recorded here is what Brewster wrote, not that nobody wrote it before him. The attribution of the term pin-hole to Brewster is repeated in the pinhole literature and is likewise not verified here.
His conclusion is a prediction and an objection in one breath: that when chemistry furnishes a more sensitive material a camera with only a pin-hole will be the favourite instrument of the photographer, and that at present no sitter could preserve his composure for the minutes required. Rayleigh did the experiment Brewster called for thirty-five years later.
Verified in:Part 7 — Seeing Like a Pinhole: The Image, Its Makers and Previsualisation
Sources:Sir David Brewster, K.H., D.C.L., F.R.S., 1856§ The chapter on stereoscopic portraiture: the small aperture H in the side M N of a camera, the inflexion of light, and the photographs of a bust
- 1856Date precision: Year
M. De Caranza recommends platinic chloride as a toner for silver prints, the first published mention of platinum toning. Very little notice is taken, and rightly: a platinum(IV) toner has only a slight toning action and a strong tendency to bleach the image, so it is useless on albumen.
Platinum toning only became practical downstream of the platinotype: potassium chloroplatinite was an obscure substance until Willis made it an article of commerce in 1879, J. Reynolds found in 1886 that it was an energetic toner of silver prints, and Stieglitz published a pioneering formula in 1889. The practice peaked between 1895 and 1925.
Verified in:Part 22 — Gold Toning and the Permanence of a Printed-Out Silver Image
Sources:James M. Reilly, 1980§ Chapter Eight, on platinum toning - De Caranza's platinic chloride recommendation of 1856 as the first published mention, the obscurity of potassium chloroplatinite until 1879, Reynolds in 1886, Stieglitz's 1889 formula and the 1895 to 1925 peak
- 1856Date precision: Year
Charles John Burnett of Edinburgh makes the first palladium prints, working not from iron but from a uranium(VI) salt reduced to uranium(IV) by light in the presence of the paper or its sizing, the uranium(IV) then reducing a noble metal salt to the metal. He obtained fine images in gold and silver too. None of his prints is known to have survived.
This anticipates Willis's Palladiotype of 1917 by sixty years, on entirely different photochemistry. It is the only place in this course where an element other than silver, iron or a noble metal carries the photochemistry, and the architecture is the argentotype's with uranium in iron's place.
Verified in:Part 26 — Uranium, Mercury and the Heavy-Metal Treatments
Sources:Mike Ware, 2017§ Section 1.4, Charles Burnett's experiments - the uranium(VI) to uranium(IV) photoreduction, the first palladium prints in 1856, the fine images in gold and silver, and the fact that none of his prints is known to have survived
- 1857Date precision: Year
Josef Petzval, reporting dioptric investigations to the Vienna Academy, gives the diffraction patch of a very small hole as A.lambda/rho, says the hole's own diameter must be added for a larger one, differentiates the sum and obtains rho = the square root of A.lambda/2 - the optimum-pinhole rule d = 1.41 times the square root of f.lambda. His worked case is a screen distance of 11 Vienna inches.
Contested: the attribution.The summed-blur derivation and its constant are usually quoted as Rayleigh's, and they are Petzval's. Rayleigh reproduced them in 1891, said the theory can hardly be regarded as sound because adding the two extreme cases is inadmissible, remarked that it is very remarkable that it nevertheless produces the right relation, and then did the diffraction properly from Lommel. Part VI states 1.41 as Petzval's constant and treats the 1.9 that circulates as Rayleigh's as his photographic measurement rather than his theory.
Petzval also supplies the viewing criterion this part uses - a blur spot stops being visible when it subtends about one minute of arc at the eye - and reckons a good 3-inch portrait objective of 11-inch focus about 180 times superior in sharpness to the camera obscura without glass. His wavelength scale does not survive conversion: his red is what we would call green and his violet is deep ultraviolet.
Verified in:Part 6 — Diffraction and the Optimum Pinhole
Sources:Joseph Petzval, 1857§ Sitzungsberichte volume 26, pp. 39-41: the diffraction patch D = A.lambda/p, the summed blur, the minimisation giving p = sqrt(A.lambda/2), and the worked case A = 11 Zoll
- 1858Date precision: Year
Abel Niepce de Saint-Victor, a cousin of the Niepce of heliography, publishes and seeks patent rights for uranium printing processes essentially identical to those Burnett had described a year earlier. Burnett accused him in the press of most monstrous and systematic plagiarism.
Contested: who was first.The course records the dispute and takes no side in it. What is documented is the publication dates - Burnett describing the processes in 1856 and 1857, Niepce de Saint-Victor publishing and seeking patent rights in 1858 - and the accusation Burnett made in the press. What is not documented anywhere the course has read is who knew what, and independent rediscovery is as consistent with these dates as plagiarism is.
Verified in:Part 26 — Uranium, Mercury and the Heavy-Metal Treatments
Sources:Mike Ware, 2017§ Section 1.4 - Burnett's priority challenged by Abel Niepce de Saint Victor (1805-1870), who published and sought patent rights in 1858 for uranium printing processes essentially identical to those Burnett described a year earlier, prompting Burnett's accusation of monstrous and systematic plagiarism
- December 1859Date precision: Year
Davanne and Girard report to the French Photographic Society that a 2 per cent solution of potassium cyanide removes all traces of silver from an albumen print while strong hypo does not. It is the first published notice that a fixed print retains silver in its whites, and the beginning of the whole yellowing problem.
Their own conclusion was that it is difficult to remove every trace of silver salt from albumenised proofs, which explains the difficulty photographers met in getting pure whites. Cyanide fixation bleached the image and was highly poisonous, so it was never a remedy.
Verified in:Part 23 — Egg Albumen: A Protein Binder and What It Does to Silver
Sources:James M. Reilly, 1980§ Chapter Eleven, Causes of Highlight Yellowing in Albumen Prints - Davanne and Girard's communication to the French Photographic Society, December 1859
- 1864Date precision: Year
Jacob Wothly patents the Wothlytype, a printing-out process whose sensitive salts were a mixture of the nitrates of uranium and silver dissolved in collodion, washed after exposure with acid and toned with gold chloride. It is the only commercial attempt to sell uranium as the light-sensitive material, and it failed.
Contested: what it signifies.Ware calls the Wothlytype egregious and unsuccessful; Cassell's 1911 cyclopaedia calls it practically the immediate predecessor of collodio-chloride printing-out papers. These are not in conflict: the first is a judgement about the process as a product, the second a claim about lineage, since a silver salt in collodion, printed out and gold-toned, is structurally the collodion printing-out paper of the 1890s minus the uranium. A process can be a commercial failure and a technical ancestor at once, and the course states both.
In 1866 Wothly used a similar uranium sensitiser to make feeble blue-black prints in platinum and palladium which had to be intensified by gold toning, and the process went no further. The Getty's analytical table confirms the composition from the objects: the Wothlytype row carries silver, gold and uranium in a collodion binder.
Verified in:Part 26 — Uranium, Mercury and the Heavy-Metal Treatments
Sources:edited by Bernard E. Jones, 1911§ The Wothlytype entry - the sensitive salts as a mixture of the nitrates of uranium and silver dissolved in collodion, the acid wash and the gold chloride toning, and the description of it as practically the immediate predecessor of collodio-chloride printing-out papersMike Ware, 2017§ Section 1.4 - the uranium sensitizer employed by Jacob Wothly in 1866 for feeble blue-black prints in platinum and palladium, and the egregious and unsuccessful Wothlytype of patent 1864Dusan C. Stulik and Art Kaplan, 2013§ The analytical table for collodion processes, whose Wothlytype row carries silver, gold and uranium in a collodion binder with a brown tonality
- 1865Date precision: Year
Eder's history credits Selle with the first use of potassium ferricyanide mixed with uranium nitrate, to intensify and brown-colour collodion negatives. The method met with little approval, and nobody investigated the reaction it depended on for another decade.
The order of events is the reverse of the order the formularies print: the scheme was found on uranium, understood on lead, and only then applied as a family. That is why the group is a list of metals rather than a list of processes, and why the exclusions in this part are about elements rather than techniques.
Verified in:Part 26 — Uranium, Mercury and the Heavy-Metal Treatments
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Lead intensification and invention of darkening of silver with ferricyanides - the first and earliest application of a mixture of potassium ferricyanide with uranium nitrate for intensifying and brown-colouring collodion negatives, credited to Selle in 1865
- 1866Date precision: Year
Jose Martinez-Sanchez and Jean Laurent introduce the baryta coating - barium sulfate dispersed in gelatin and calendered smooth - two decades before it has anything to do with a silver gelatin emulsion.
Verified in:Part 18 — The Structure of a Printing Paper: Base, Baryta, Emulsion and Supercoat
Sources:Dusan C. Stulik and Art Kaplan, 2013§ Historical background and timeline - the baryta layer traced to its introduction by Jose Martinez-Sanchez and Jean Laurent in 1866
- 1868Date precision: Year
The Pharmacy Act puts cyanide of potassium and all metallic cyanides and their preparations in Part 1 of the poisons schedule, the strictest part: the purchaser had to be known to the seller, sign a register naming the quantity and the purpose, and receive the salt labelled Poison. A legislature does not put a substance in the first schedule for a hypothetical.
The same law drew the boundary this page turns on. Cassell records that it was an open question whether all metallic cyanides covered the ferri-, ferro- and sulphocyanides, and that as a matter of fact these preparations were held not to be scheduled poisons - the same exclusion the Environment Agency's current waste guidance carries in modern language. This is the one dated regulatory milestone the course could establish for the heavy-metal and cyanide chemistry; no citable date was found for the removal of uranium or mercury from the photographic supply chain.
Verified in:Part 26 — Cyanide in the Historical Darkroom, and the Ferricyanide That Is Not Cyanide
Sources:edited by Bernard E. Jones, 1911§ The legal note on the Pharmacy Act 1868, recording that cyanide of potassium and all metallic cyanides and their preparations sat in Part 1 of the poisons schedule with the register and labelling requirements, and that the complex cyanides were held not to be scheduled poisons
- 14 January 1868Date precision: Exact
John Spiller, reading to the Photographic Society of Great Britain, names the retained silver: an argentic organic compound, colourless, unalterable by light, and comparatively insoluble in hyposulphites, held in the whites and indeed in all parts of the coating. His test for it was to moisten a white area with ammonium sulfide and watch a brown stain appear.
Matthew Carey Lea had confirmed the presence of the residual silver in 1866 and searched without success for a solvent. Spiller's ammonium sulfide test is the same chemistry as the residual-silver test this course still runs.
Verified in:Part 23 — Egg Albumen: A Protein Binder and What It Does to Silver
Sources:James M. Reilly, 1980§ Chapter Eleven - John Spiller's paper to the Photographic Society of Great Britain, 14 January 1868, with the quoted description of the argentic organic compound and the ammonium sulfide test
- c. 1870 - c. 1950Date precision: Circa
For roughly eighty years the cyanotype and its variants are the main way engineers and architects copy plans, until diazo processes replace them. The word outlived the technology by seventy years and now means a plan of any kind.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Dusan C. Stulik and Art Kaplan, 2013§ Main application of the cyanotype process
1871–1900: the dry plate, and the plate that could be measured
Gelatin makes photography a manufactured product; dye sensitisation gives it colour vision; and Hurter and Driffield, Schwarzschild and Rayleigh start measuring what everyone had been asserting.
- 1871Date precision: Year
Richard Leach Maddox publishes a gelatine emulsion - silver bromide, as Abney puts it, emulsified in a gelatine solution with which plates are coated. What he had was a binder that could be manufactured, stored and sold. What he did not have was speed.
Verified in:Part 5 — Precipitation, Nucleation and Crystal Growth
Sources:Captain W. de W. Abney, R.E., F.R.S., 1885§ Chapter VI, Introductory Remarks on Gelatine Emulsions: the gelatine emulsion as first made by Dr Maddox in 1871
- 1872Date precision: Year
The first commercial cyanotype paper is made by Marion et Cie in Paris as papier ferro-prussiate.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Dusan C. Stulik and Art Kaplan, 2013§ Historical background; Main application of the cyanotype process
- 1872Date precision: Year
The first ready-sensitised albumen paper is offered to the public by the Sensitized Paper Co. of Portsmouth, Ohio. It rests on Adolf Ost's publication of a citric acid preservative in Vienna in 1869, and it is what put albumen printing into the hands of people who would never have coated a sheet.
The problem it solved is the one the lab still meets: a sensitised albumen sheet keeps twenty-four to forty-eight hours, and in warm humid conditions may yellow in eight to twelve.
Verified in:Part 23 — Lab: Sensitising, Printing and Toning an Albumen Print
Sources:James M. Reilly, 1980§ Chapter Six, Preserving Sensitized Paper - Adolf Ost of Vienna publishing the idea in 1869, and in 1872 the first ready sensitized albumen paper, a product of the Sensitized Paper Co. of Portsmouth, Ohio, offered to the publicDusan C. Stulik and Art Kaplan, 2013§ Figure 2, dating the first presensitised commercial albumen paper to 1872
- 5 June 1873Date precision: Exact
William Willis patents Improvements in Photo-chemical Printing, for a platinum process that still carries silver, gold or lead. He had begun in 1872 with platinic chloride, platinum(IV), and failed, because platinum(IV) is thermodynamically reducible but far too inert kinetically to make an image in the minutes available; in 1873 he turned to the little-known platinous salts and made his own potassic chloro-platinite.
Willis also admitted that his attention had been directed to potassium oxalate as the developer by a note by a French chemist who has never been identified, and that he had to prepare the salt himself because he could not obtain it in London.
Verified in:Part 25 — Noble Metal Chemistry and the Platinotype
Sources:Mike Ware, 2017§ Section 1.6, William Willis's invention - the 1872 start, the platinic chloride failures, the turn to the platinous salts in 1873 and the patent of 5 June 1873
- 17 October 1873Date precision: Exact
Hermann Wilhelm Vogel exhibits his first spectrum photographs on colour-sensitised collodio-bromide plates at the Berlin Society for the Promotion of Photography. Photographing the solar spectrum, he had found that a plate carrying corallin - a dye put there to stop halation - showed a greatly increased sensitivity to the green, and he recognised that as a specific action of the admixed dye rather than an oddity of the plate.
The test is what turns the accident into a discovery. Corallin absorbs yellow and green and sensitised for yellow and green; green aniline dyes sensitised into the red. The sensitised region tracks the dye's own absorption band, which is the whole mechanism, stated as an empirical rule sixty-five years before anyone could explain it in terms of energy levels. The fuller account followed in Poggendorff's Annalen in 1874.
Verified in:Part 4 — Spectral Sensitivity and Colour Response
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter LXIV, Discovery of colour-sensitizing of photographic emulsions in 1873: corallin in Stuart Wortley's collodion dry plates and the exhibition of 17 October 1873
- 1874Date precision: Year
Edmond Becquerel finds extra sensitivity bands in chlorophyll-dyed silver bromide collodion. It is the first support for Vogel's result, and it ends the controversy in his favour.
Monckhoven in Ghent and Carey Lea had both repeated Vogel's experiments and got nothing, and Vogel spent years defending the result in print against them and Spiller. Eder records the explanation, and it is a lesson in experimental design: Monckhoven had better apparatus - spectrographs of greater dispersion, and therefore weaker spectra - while the sensitisers of the day were feeble enough that the effect showed plainly only in Vogel's small direct-vision instrument used in strong sunlight.
Verified in:Part 4 — Spectral Sensitivity and Colour Response
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter LXIV: the opposition of Monckhoven and Carey Lea, and Becquerel's endorsement
- 1875Date precision: Year
Abney works out the cause of halation: light that passes through the emulsion is reflected back into it from the far surface of the base, most strongly at the critical angle, so the image of a bright point develops as a ring shaded according to how much light was reflected at each angle. The nineteenth-century cure was to back the plate with an absorbing material in optical contact with the glass.
Modern films use an undercoat between emulsion and base, a backing on the far side, or a tinted base, and all of them must clear during processing: an absorber that stayed in place would add density everywhere and behave exactly like fog.
Verified in:Part 4 — Grain, Speed and Resolution
Sources:Encyclopaedia Britannica (article by W. de W. Abney and others), 1911§ Halation: Abney's 1875 investigation of reflection from the back surface of the plate, and the practice of backing a plate
- 14 December 1875Date precision: Exact
Eder, working with Captain Victor Toth, finds that mixtures of potassium ferricyanide with lead salts deposit silver ferrocyanide together with lead ferrocyanide, reports it to the Vienna Photographic Society, and states that the same scheme operates in the darkening of silver images with other metals. From here the cation in the bath is a free variable and the family is a shopping list.
Vogel's verdict on uranium in the same year is purely commercial and has nothing to do with toxicology: too rare and too dear to be employed generally in photography.
Verified in:Part 26 — Uranium, Mercury and the Heavy-Metal Treatments
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Lead intensification and invention of darkening of silver with ferricyanides - the work with Captain Victor Toth in 1875, the precipitate of silver ferrocyanide together with lead ferrocyanide, and the report to the Vienna Photographic Society on 14 December 1875Hermann Wilhelm Vogel, 1875§ The verdict on uranium as too rare and too dear to be employed generally in photography
- 1876Date precision: Year
The first commercial blueprint machine, built in Switzerland, reaches the United States at the Philadelphia Centennial.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Dusan C. Stulik and Art Kaplan, 2013§ Main application of the cyanotype process
- 1877-1883Date precision: Span
The British patent abridgments for photography are full of specifications that are recognisably Niepce's process: a metal plate coated with bitumen or asphaltum dissolved in benzene or turpentine, exposed under a negative in a printing frame, the unaffected coating cleaned off with a solvent, and the bared metal then etched with acid or built up in a galvanic bath.
Change the resin, change the solvent, keep the logic, and you have photolithography and photogravure, and a century later the manufacture of every integrated circuit ever made.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Patent Office, Great Britain, 1903§ Class 98 abridgments: bitumen and asphaltum resists on metal, 1877-1883
- 1878Date precision: Year
Charles Bennett publishes the first process which gives extreme rapidity: keeping the gelatine solution liquid at a temperature of about 90 degrees Fahrenheit, some 32 Celsius, for six or seven days. Abney's summary of the mechanism predates any of the chemistry - sensitiveness is attained by slow digestion at a low temperature instead of by boiling.
Bennett was performing an extremely long physical ripening and, without knowing it, a chemical sensitisation at the same time: the sulfur impurities in his gelatin were making silver sulfide specks throughout, and Sheppard would not identify them for another forty-six years. Abney names the cost in the same paragraph - in certain states of the weather the long emulsification risked decomposing the gelatine.
Verified in:Part 5 — Precipitation, Nucleation and Crystal Growth
Sources:Captain W. de W. Abney, R.E., F.R.S., 1885§ Chapter X, Bennett's gelatino-bromide process, first published 1878; Chapter VI on the long low-temperature digestion
- 1878Date precision: Year
Willis founds the Platinotype Company of London, which for sixty years made the best platinum papers anybody has made and left almost no technical record of how.
Often given as:The Platinotype Company was founded in 1879.Ware notes that all the general histories give 1879, and that 1878 is what the company itself printed on its own headed notepaper and embossed on its paper tins. A firm's own stationery is better evidence of the year it began trading than a secondary account written decades later, and the course follows Ware. What did happen in 1879 is the first commercial platinotype papers going on sale, which this timeline records separately.
Verified in:Part 25 — Noble Metal Chemistry and the Platinotype
Sources:Mike Ware, 2017§ Section 1.7, Willis's Platinotype Company of London - the founding of the company in 1878 rather than 1879, on the company's own headed notepaper and embossed on its paper tins
- 17 March 1878Date precision: Exact
Willis makes the first silver-free platinum print, annotated and witnessed on the verso, and patents it later the same year. From here the image is platinum metal and nothing else, which is the whole permanence argument for the process.
Verified in:Part 25 — Noble Metal Chemistry and the Platinotype
Sources:Mike Ware, 2017§ Section 1.7, Willis's Platinotype Company of London - the silver-free print of 17 March 1878, annotated and witnessed on the verso, and the patent of the same year
- 1879Date precision: Year
The first commercial platinotype papers go on sale in Britain, at a shilling for a demy sheet of 17 and three-quarter by 22 and three-quarter inches. The lead salt is removed from the sensitiser after Spiller's tests of 1880.
The same commercial availability of potassium chloroplatinite is what made platinum toning of silver prints practical: an obscure laboratory substance became an article of commerce.
Verified in:Part 25 — Noble Metal Chemistry and the Platinotype
Sources:Mike Ware, 2017§ Section 1.7 - the first commercial papers of 1879 at one shilling for a demy sheet, and the removal of the lead salt after Spiller's 1880 tests
- 1880Date precision: Year
Eder and Toth compare the three dihydroxybenzenes on gelatine dry plates and find that one formula develops three different ways. Hydroquinone, with its hydroxyls para, shows a very strong action on silver bromide in an alkaline developer; pyrocatechin, ortho, has great developing power; and resorcin, meta, has no energy as a developer at all.
Contested: the attribution.The generalisation drawn from this experiment - two electron-donating groups, hydroxyl or amino, standing para or ortho on the ring - is the Kendall-Pelz rule, named for J. Kendall and, in the later and more general form, for Pelz. This course has read neither Kendall's statement of it nor Pelz's: what it has read is Eder's account of the 1880 experiment the rule generalises, extended by Eder to para-aminophenol, and Kendall's 1941 patent, which is a different document about a different molecule. The rule also has a large and commercially dominant counterexample, phenidone, which is not a benzene ring with two donor groups on it and develops better than metol. The course presents the rule as a good guide and a poor law, and marks the general form as attributed rather than verified.
Verified in:Part 8 — The Classical Developing Agents: Metol, Hydroquinone, Phenidone
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Eder and Toth 1880 on hydroquinone, pyrocatechin and resorcin, and the extension of the rule to para-aminophenol
- 1881Date precision: Year
Leon Warnerke reports that only the unexposed parts of a pyrogallol-developed gelatine film remain soluble in warm water, the exposed and tanned parts being insoluble. For two generations after that, the tanning was the reason to use pyro at all.
Eder's history dates the discovery itself to the end of the 1870s and the report to 1881, and records that he had already pointed out that the relief left by alkaline pyrogallol without sulfite could be made high enough to mould from and used as a printing plate. The entry takes the reported date because that is the one the source fixes.
Verified in:Part 8 — Staining and Tanning Developers
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ The tanning action of pyrogallol: Warnerke's report of 1881 and the relief image
- 1882Date precision: Year
Pizzighelli and Hubl, two Austrian army captains in the photographic department of the military technical administration, publish the first detailed platinum recipes, including the drop-counted potassium chlorate contrast system that every kit sold today still uses. The publication won the Vienna Photographic Society's Voigtlander Prize and reached English in 1883.
Ware observes that British writers seem to have been careful not to publish platinum recipes, probably for fear of Willis's patents, which is why the detailed working knowledge of the process comes out of Vienna rather than London.
Verified in:Part 25 — Noble Metal Chemistry and the Platinotype
Sources:Mike Ware, 2017§ Section 1.16, Researches of Pizzighelli and Hubl - the 1882 publication, the Voigtlander Prize and the English translation of 1883
- 1884Date precision: Year
Lommel publishes the circular-aperture diffraction results that Rayleigh adapts seven years later to treat the pinhole rigorously, in place of Petzval's estimate of the blur as the plain sum of two extreme cases.
Cited at second hand. This course has not read Lommel; it has read Rayleigh, who names the work and uses it.
Verified in:Part 6 — Diffraction and the Optimum Pinhole
Sources:John William Strutt, Lord Rayleigh, 1902§ Article 178: the adaptation of Lommel's 1884 results to the pinhole
- 1884Date precision: Year
Vogel's azaline, a mixture of quinoline red with cyanine, sensitises green, yellow and orange together, and Eder calls him the creator of the first panchromatic plate in so many words. Erythrosine arrives as the standard orthochromatic sensitiser in the same year, Lowy and Plener in Vienna producing erythrosin-sensitised gelatine bromide emulsions on Vogel's own directions.
Contested: the attribution; who was first.Eder credits Vogel with the first panchromatic plate, and records azaline's shortcomings in the same breath: feebly sensitive, not very stable, needing strong filters to subdue the blue, and unable to compete in orthochromatic work with erythrosin or with the isocyanines of Miethe and Konig. The claim met far more often is that Wratten and Wainwright made the first commercial panchromatic plates in 1906. This course has found no source in its corpus that states that, and does not repeat it; Wratten and Wainwright certainly existed and made plates, since Hurter and Driffield used their material and name it repeatedly.
Verified in:Part 4 — Spectral Sensitivity and Colour Response
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter LXIV: azaline and the first panchromatic plate; erythrosin orthochromatic emulsions at Lowy and Plener 1884
- 1885Date precision: Year
Abney's Photography with Emulsions reports that silver bromide may be produced in several molecular states, all of which have different degrees of sensitiveness - identical in chemical composition, differing physically, the particles built up of a greater or less number of primary molecules. He also knew the halogen had to go somewhere, and used the phrase bromine absorbent for what would later be called a halogen acceptor.
This is the step between knowing that a plate is sensitive and being able to say what makes one plate more sensitive than another of the same composition. Sheppard's answer was still forty years away.
Verified in:Part 4 — The Latent Image
Sources:Captain W. de W. Abney, R.E., F.R.S., 1885§ Chapter I: the molecular states of bromide of silver; the bromine absorbent
- the 1880sDate precision: Circa
The gelatin dry plate displaces wet-plate collodion. The AIC gives the reason in one clause - equally sensitive, but with long-lasting portable plates - and dates the replacement to the 1880s; IPI's date band for collodion glass negatives runs from 1851 to about 1885. It is a statement about binders rather than about speed, because the speed had been matched rather than beaten.
A gelatin emulsion can be precipitated, ripened, chemically sensitised, washed, coated, dried, boxed, sold, stored and exposed months later. A collodion film can do none of those, because its permeability depends on solvents that are leaving. Part V exists because every one of those verbs is a separate piece of chemistry.
Verified in:Part 26 — Wet-Plate Collodion: The Process That Made the Nineteenth Century Look Like That
Sources:American Institute for Conservation, Photographic Materials Group§ The replacement of the wet collodion process in the 1880s by the gelatin silver process, described as equally sensitive but with long lasting, portable platesMaria Fernanda Valverde, Advanced Residency Program in Photograph Conservation, 2005§ Collodion Glass Plate Negatives, 1851 to about 1885
- 1887Date precision: Year
Pizzighelli, by then working alone in Bosnia, discovers the print-out platinotype: a sensitiser in which sodium ferric oxalate lets the image appear during exposure with no developer at all, humidity taking the developer's place. It is the ancestor of every modern print-out platinum and palladium process.
This is five years after the drop-counting publication he and Hubl made in 1882, and the two are frequently confused in secondary accounts.
Verified in:Part 25 — Noble Metal Chemistry and the Platinotype
Sources:Mike Ware, 2017§ Section 1.16 - Pizzighelli's 1887 print-out discovery using sodium ferric oxalate, and the frequent confusion with the 1882 publication
- 1888Date precision: Year
The Dresdener Albuminfabriken A.G. produces 18,674 reams of albumen paper in one year. A ream was 480 sheets, coating one took 9 litres of albumen solution and 27 dozen eggs, so a single company consumed over six million eggs in the year. The chemistry is why: albumen paper stayed a handicraft long after everything around it had been mechanised.
Six-million-egg figures circulate widely and usually without a source. This one is a named company's ream production in a named year multiplied by two stated trade constants, and it is not the same kind of claim as a national or global total.
Verified in:Part 23 — Egg Albumen: A Protein Binder and What It Does to Silver
Sources:James M. Reilly, 1980§ The production figure for the Dresdener Albuminfabriken A.G. in 1888, with the ream of 480 sheets at 46 by 58 cm, 9 litres of albumen solution per ream and 27 dozen eggs per 9 litres
- 1889Date precision: Year
In a British Association note Rayleigh gives 2.rho-squared = f.lambda for the best pinhole - the same 1.41 times the square root of f.lambda as Petzval's minimum - from an entirely different argument. A lens exists to correct the phase differences across an aperture, and he had shown that an extreme phase error of a quarter of a wavelength produces no appreciable deterioration in the definition; so open the hole until the error reaches a quarter wave and the lens is no longer missed.
Same constant, different criterion. Petzval minimises the width of the blur; Rayleigh asks for the largest hole a lens would not improve. His own example is a hole of a fifth of an inch, which puts the sun's image on a screen beyond about 66 feet as well defined as the direct view.
Verified in:Part 6 — Diffraction and the Optimum Pinhole
Sources:John William Strutt, Lord Rayleigh, 1902§ Article 178: the quarter-wave criterion and the relation 2r-squared = f.lambda
- 1889Date precision: Year
P. H. Emerson's Naturalistic Photography argues that photographic pictures should be made as the eye sees and not as the lens resolves: a picture should not be quite sharply focussed in any part, but made just as sharp as the eye sees it and no sharper, the great heresy of sharpness having lived so long because the art was practised by unphilosophical scientists.
Emerson's programme is differential softness - one thing rendered clearly because that is where the eye rests, everything else held back - which a pinhole cannot deliver, since it gives one blur circle the same size everywhere. He dealt with the pinhole in three sentences on page 131: the drawing would obviously be correct, but exposures of one to thirty minutes put it out of serious consideration, though in cases where the length of exposure is immaterial it would be a worthy field for experiment. The same book is categorical that head-rests must be entirely tabooed, against Wall's 1912 defence of a disciplined version.
Verified in:Part 7 — Seeing Like a Pinhole: The Image, Its Makers and Previsualisation
Sources:P. H. Emerson, B.A., M.B. (Cantab.), 1889§ The great heresy of sharpness; the rule on focus; the treatment of lensless photography on page 131; head-rests
- 1889Date precision: Year
W. W. J. Nicol patents the kallitype: an oxalate ligand instead of Herschel's citrate, a faint print-out image, and a chemical developer that decides both the colour and the contrast. It is the first iron-silver process to develop rather than print out, and the original patent developed the print in a silver nitrate bath, a revision of the early 1890s moving the silver into the sensitiser.
The developing-out route is what buys the kallitype its shadow depth: in a print-out process the shadows are fully exposed before the highlights have printed in. Nicol's stated motive was a silver printing process that would rival the expensive platinotype in simplicity and artistic effect, and unlike the faux-platinum papers it never claimed to be platinum.
Verified in:Part 24 — The Siderotype Principle: Iron Reduces Silver
Sources:Sandy King§ What is a Kallitype? And a Little History - the attribution to Herschel 1842 and Nicol 1889, Nicol's original patent developing the print in a silver nitrate bath, and the revision of the early 1890s moving the silver into the sensitiser
- 1890Date precision: Year
George Davison exhibits a picture of an onion field on Mersea Island in Essex that becomes the flashpoint of the argument about whether an unsharp photograph can be a good one. The Victoria and Albert Museum holds it in the Royal Photographic Society Collection, accession RPS.2369-2017, as a photogravure on paper, 155 by 205 mm.
Contested: the attribution.The claim that the picture was made with a pinhole is repeated in general reference accounts of Davison's work and throughout the pinhole literature, and it is why he appears in every pinhole history. The museum record is narrower: it gives title, maker, year, place and medium, and names no camera and no aperture; photogravure describes how the print was made rather than how the negative was exposed, so it neither confirms nor denies a pinhole. This course has not read the 1890 exhibition catalogue of the Photographic Society of Great Britain, the photographic press of that autumn, or Davison's own account, and therefore states the museum record as fact and the pinhole as a widely repeated attribution it has not traced to a primary source.
Two further Davison prints titled The Onion Field are in the same collection, dated 1890 and 1891. Davison went on to co-found the Linked Ring, the secessionist body through which Pictorialism did most of its arguing.
Verified in:Part 7 — Seeing Like a Pinhole: The Image, Its Makers and Previsualisation
Sources:Victoria and Albert Museum, London, 2017§ Collection record RPS.2369-2017: title, maker, date photographed 1890, place, and materials and techniques
- 1890Date precision: Year
Hurter and Driffield's photochemical investigations establish that density is proportional to the mass of silver per unit area - the other half of the chain that turns exposure into density - and, in Experiment 15, measure what a restrainer does to a whole characteristic curve: one plate, one pyro-soda developer, five bromide levels from nothing to 128 parts per thousand, three minutes of development for every strip.
Part VIII's restrainer lesson plots Experiment 15 in full, including their finding that the retarding influence of bromide can be fully compensated by time of development, so that the speed of the plate is not really altered. The precise date within 1890 is not established by the sources this course holds.
Verified in:Part 4 — Development as Amplification
Sources:Edited by W. B. Ferguson, K.C., M.A., F.I.C., Hon. F.R.P.S., 1920§ Photochemical investigations: density proportional to the mass of silver per unit area; The Latent Image and its Development, Experiment 15
- 31 May 1890Date precision: Exact
Hurter and Driffield's Photochemical Investigations and a New Method of Determination of the Sensitiveness of Photographic Plates is read at Liverpool before the local section of the Society of Chemical Industry. It plots density against log exposure, names the characteristic curve, divides it into under-exposure, correct representation and over-exposure, and defines inertia, from which their speed number follows as 34 divided by the inertia.
Part IV owns the same paper for what it establishes about development and restrainers, at tl-1890-hurter-and-driffield, where the precise date within 1890 was not established. This entry is the paper itself, with the date the memorial volume's contents list supplies. It is easy to miss how radical the construction was: the photographic press of the 1880s discussed plate speed without a curve at all.
Verified in:Part 13 — The Characteristic Curve
Sources:Edited by W. B. Ferguson, K.C., M.A., F.I.C., Hon. F.R.P.S., 1920§ Contents list, dating Photochemical Investigations and a New Method of Determination of the Sensitiveness of Photographic Plates to the Journal of the Society of Chemical Industry of 31 May 1890; Early Work, on the reading of the paper at Liverpool before the local section of the Society of Chemical Industry and on the definition of inertia; Relation between Negatives and their Positives, for the naming of the characteristic curve and its three periods
- 31 July 1890Date precision: Exact
Captain William de Wiveleslie Abney's paper On the Accuracy of the Grease Spot Photometer appears in the same journal two months after the classic paper, with Hurter and Driffield's first reply printed alongside it. The quarrel is about how a density is measured rather than about what the curve means, and it runs on into the following year.
Their dispute was over mutual reflection between paper and negative rather than over scattering in the silver image, but it is the same quarrel that ISO 5-2 settles by specifying a geometry, and the reason Kodak prints its densitometry condition on every published curve.
Verified in:Part 13 — The Characteristic Curve
Sources:Edited by W. B. Ferguson, K.C., M.A., F.I.C., Hon. F.R.P.S., 1920§ Contents list, dating Captain Abney's paper On the Accuracy of the Grease Spot Photometer and the authors' first Reply to it both at 31 July 1890
- 1891Date precision: Year
Lord Rayleigh's note On Pin-hole Photography sets the geometric shadow of the hole against the diffraction spread. He quotes Petzval's summed-blur derivation, says it can hardly be regarded as sound because adding the two extreme cases is inadmissible, does the diffraction properly from Lommel's results, and then pierces six apertures in sheet zinc from 0.0210 to 0.0366 inch and photographs a test object with each.
Often given as:The optimum-pinhole constant is Rayleigh's.The estimate of the blur as the sum of two terms is taken by Rayleigh from Petzval. Rayleigh himself objected that simply adding the two extreme cases is not a rigorous treatment, and worked the diffraction problem out properly. Part VI does the arithmetic.
His best photographic result gives (2r)-squared/f = 1.52 x 10^-4 cm, which with the photographically effective wavelength he back-calculated for his own plates, 4.2 x 10^-5 cm, is the constant 1.90 that circulates as the Rayleigh criterion. It is a measurement of what his plates and his eye preferred, not his theory; his theory, the quarter-wave criterion of 1889, gives 1.41. Part VI keeps the range 1.4 to 1.9 and uses 1.56 when one number is needed, because across that whole range the total blur varies by about three per cent.
Verified in:Part 6 — Diffraction and the Optimum Pinhole
Sources:John William Strutt, Lord Rayleigh, 1902§ Article 178, pp. 429-440: the quotation and criticism of Petzval, the adaptation of Lommel 1884, the zinc apertures of 0.0210 to 0.0366 inch, and the photographic determination (2r)-squared/f = 1.52 x 10^-4 cm
- early 1891Date precision: Contested
Hurter and Driffield's answer to Abney, The Sector and Grease-Spot Photometers, and their Results, admits that a photometer built on his principle reproduced his readings, and introduces the mutual-reflection term in the opacity of a combination. The dispute ends in a technical correction rather than a defeat.
Contested: the date.The 1920 memorial volume dates this paper twice and differently. Its contents list gives 31 January 1891; the reprint's own header line, printed at the head of the paper inside the same volume, gives 28 February 1891, No. 2, Vol. X. Both were set by the volume's editor, W. B. Ferguson. The course has not seen the original journal issue, takes no position between the two, and says early 1891 rather than picking the more convenient one.
Verified in:Part 13 — The Characteristic Curve
Sources:Edited by W. B. Ferguson, K.C., M.A., F.I.C., Hon. F.R.P.S., 1920§ Contents list against the reprint header for The Sector and Grease-Spot Photometers, and their Results; the section headed Reply to Captain Abney within that paper, for the admission about the photometer and for the mutual-reflection term in the opacity of a combination
- 27 January 1891Date precision: Exact
German patent 60174, of 27 January 1891, goes to Momme Andresen, chemist to the aniline company in Berlin that became Agfa, for paramidophenol - rodinal. Eder records that it was still in general use decades later, and a developer of the type is still sold today.
The type survives because the agent can be carried at a concentration the others cannot reach, so one bottle does about twice the work. The modern product's composition is not disclosed, and this course does not claim that what is sold now is the 1891 formulation.
Verified in:Part 8 — Alternative Developing Agents: p-Aminophenol, Ascorbate, Glycin, Catechol, Pyrogallol
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Momme Andresen and German patent 60174 of 27 January 1891 for paramidophenol
- 1892Date precision: Year
Willis announces before the Camera Club that he can make fine prints by development at room temperature rather than at the temperatures that had caused so many workers to scald their fingers, and then says that for reasons which will be understood he cannot make the method public. He never patented it.
No technical records of the Platinotype Company are known to have survived the London Blitz, so the manufacture of the most successful commercial platinum papers ever made is a lost secret. Ware infers from Willis's own wording that the answer lay in the sizing or the coating rather than in the sensitiser.
Verified in:Part 25 — Noble Metal Chemistry and the Platinotype
Sources:Mike Ware, 2017§ Section 1.8, Perfection of Platinotype - the 1892 cold-development announcement, the refusal to publish, and the loss of the company's records
- 1894Date precision: Year
Baryta layers are added to commercial developing-out papers, and to Kodak's from about 1900. From here the image sits on top of a smooth white barrier rather than partly inside the paper, which is what a fibre print's blacks, its wash time and most of its permanence depend on.
Papers of this structure were first used in the 1890s and were still being made in 2012, which is an unusually long life for a photographic construction.
Verified in:Part 18 — The Structure of a Printing Paper: Base, Baryta, Emulsion and Supercoat
Sources:American Institute for Conservation, Photographic Materials Group§ Chronology - baryta layers added to commercial developing-out papers in 1894 and introduced to Kodak papers in 1900; and the statement that in a developing-out print the image sits on top of a baryta layer rather than partly within the paper structureDusan C. Stulik and Art Kaplan, 2013§ Historical background and timeline - Kodak introducing baryta coating about 1900, and the statement that papers of this structure were first used in the 1890s and were still being produced in 2012
- February 1895Date precision: Contested
Hubl publishes the matte albumen formula, equal volumes of albumen and a 2 per cent arrowroot solution, giving a surface that resembles platinum rather than glass. It became the most commercially successful of the matte salted papers and the last of them in production, Trapp and Munch ceasing manufacture in 1929.
Contested: the date.Reilly dates the publication to Photographische Rundschau for February 1895, with Hubl's book Der Silberdruck auf Salzpapier following in 1896; the Getty atlas's own timeline dates the introduction of matte albumen to 1897. The disagreement is between a publication date and an introduction date and may not be a real conflict, but the course has not been able to close it, so it gives Reilly's 1895 for the formula and records the atlas's 1897 here.
Verified in:Part 22 — The Variants of the Salt Print and How a Conservator Identifies One
Sources:James M. Reilly, 1980§ Chapter Five, Matte Albumen Paper - the formula of equal volumes of albumen and 2 per cent arrowroot published in Photographische Rundschau for February 1895, and Trapp and Munch ceasing production in 1929Dusan C. Stulik and Art Kaplan, 2013§ The atlas timeline, which dates the introduction of matte albumen to 1897
- mid-1890sDate precision: Circa
Haddon and Grundy measure what Davanne, Girard, Lea and Spiller had only observed: a sheet sensitised, fixed and washed but never exposed still contained nearly 5 per cent of the silver applied to it. They then proved it theatrically, converting the residual silver back and printing an image out of a sheet that should have held none.
Reilly reports the work as a series of articles in the British Journal of Photography in the mid 1890s and gives no single year for the measurement itself; a Haddon and Grundy statement quoted elsewhere in his book is dated July 1897. The entry is therefore circa rather than a year. It is the quantitative foundation of everything this course says about albumen yellowing.
Verified in:Part 23 — Egg Albumen: A Protein Binder and What It Does to Silver
Sources:James M. Reilly, 1980§ Chapter Eleven - A. Haddon and F. B. Grundy, reported in a series of articles in the British Journal of Photography in the mid 1890s, with the figure of nearly 5 per cent of the silver left after sensitization remaining in a thoroughly fixed and washed sheet
- 1899-1900Date precision: Span
Karl Schwarzschild, having confirmed on stellar plates the deviation from the reciprocity law that astronomers could not explain, reproduces it under laboratory control at Eder's institute - the same plate cut up, the same developing bath, the same time, only the lamp distance changed - and gets one number out of it: equal blackening at I times t to the power p, with p = 0.86 for the Schleussner gelatine plates he tested. The paper appears in 1900.
The exponent is a property of the emulsion and not a constant of nature. Sheppard and Mees recorded in 1907 that Abney and Englisch both found p variable while Schwarzschild treated it as fixed, and three manufacturers today publish corrections differing by more than a factor of two for the same metered time.
Verified in:Part 4 — Reciprocity Failure and the Life of the Latent Image
Sources:Karl Schwarzschild, 1900§ The statement of the reciprocity law, the exponent 0.86, and the paired result at intensities 81 and 1
1901–1945: the theory catches up with the craft
Sheppard finds the impurity that had been making speed for fifty years, and Gurney and Mott say what a latent image is - a century after Daguerre developed one.
- 1901Date precision: Year
Luppo-Cramer finds that certain developers of the paramidophenol class, and ferrous oxalate, greatly reduce the sensitivity of unexposed silver bromide without destroying its capability of developing the latent image. Nineteenth-century photochemists had assumed the two must go together; they do not.
Verified in:Part 4 — Spectral Sensitivity and Colour Response
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter LXV, Discovery of desensitizing: Luppo-Cramer 1901
- 1901Date precision: Year
Germany bans the use of platinum in photography, on account of lamp filaments. It is the first of the interventions that ended the process, and none of them is about photography: platinum stopped being a photographic material because it became a strategic one.
Verified in:Part 25 — Noble Metal Chemistry and the Platinotype
Sources:Mike Ware, 2017§ Section 2.3, Price history of platinum - the German ban of 1901 on account of lamp filaments
- 1902Date precision: Year
Ostwald discovers that platinum catalyses the oxidation of ammonia to nitric acid. Nitric acid makes explosives, and from this point a photographer buying platinum is competing with a munitions industry. The catalysis is the same property the process itself may depend on.
Verified in:Part 25 — Noble Metal Chemistry and the Platinotype
Sources:Mike Ware, 2017§ Section 2.2, on Ostwald's 1902 discovery of the platinum-catalysed oxidation of ammonia to nitric acid
- 1904Date precision: Year
Flinders Petrie's Methods and Aims in Archaeology tells the excavator to stick to one small stop, say f/100, and learn exposures entirely on that basis, and describes small stops made from a strip of tin plate or blackened card and a pin-hole stop stuck in front of the lens so as to work at almost any nearness and scale with exposures of half a minute or a minute in full sunshine.
Often given as:Flinders Petrie photographed in the field with a lensless pinhole camera.Read the chapter and what he describes is a pinhole stop placed over a lens, not a lensless camera. He was buying the pinhole's freedom from a plane of focus - almost any nearness and scale - while keeping the lens in place, and paying the usual price in minutes. Petrie belongs in this history for what he did rather than for what he is usually said to have done.
Verified in:Part 7 — Seeing Like a Pinhole: The Image, Its Makers and Previsualisation
Sources:W. M. Flinders Petrie, 1904§ Photography: the one small stop discipline, and the pin-hole stop stuck in front of the lens
- 1907Date precision: Year
Sheppard and Mees's Investigations on the Theory of the Photographic Process measures what had until then been argued about: the low-intensity arm of reciprocity failure in Table 110, grain sizes under the microscope, the induction period of development, and the roll-call of oxidisers that destroy a latent image outright.
They also separated two things photographers still confuse: the survival of the latent image, and the ageing of the material it sits in. They had measured plates whose velocity coefficient of development fell to a third of its former value over six months of poor storage, which thins a negative without any latent-image decay at all.
Verified in:Part 4 — Reciprocity Failure and the Life of the Latent Image
Sources:S. E. Sheppard and C. E. Kenneth Mees, 1907§ Part II Chapter VI, The Nature and Destruction of the Latent Image: Failure of a Photo-chemical Law, Table 110; The Decay and Destruction of the Latent Image
- By 1911Date precision: Year
The eleventh edition of the Encyclopaedia Britannica describes panchromatic plates as now largely manufactured, distinguishes them from the older isochromatic plates most sensitive to yellow and green, and lists pinaverdol, pinachrom and pinacyanol as commercial dyes, noting that pinacyanol confers on a silver bromide plate as high a sensitiveness for red as erythrosin does for yellow.
This is a terminus and not a first. The course can show that panchromatic material was in ordinary commercial use by 1911; it cannot date the commercial introduction, and it declines to fill the gap with the 1906 attribution that circulates.
Verified in:Part 4 — Spectral Sensitivity and Colour Response
Sources:Encyclopaedia Britannica (article by W. de W. Abney and others), 1911§ Orthochromatic and panchromatic plates: pinaverdol, pinachrom and pinacyanol, and the description of panchromatic material as now largely manufactured
- Reported 1911Date precision: Year
The eleventh edition of the Encyclopaedia Britannica reports W. J. Russell's experiments: contact with substances such as wood makes a plate fog on development, the probable agent being hydrogen peroxide, and the same substance will destroy the effect light has already had. Russell's own conclusion is the practical one, that exposed plates should be stored only for brief periods.
The course holds the 1911 report and not Russell's own papers, so it can date the report and not the experiments. The date given here is the date of the account the course has read.
Verified in:Part 4 — Reciprocity Failure and the Life of the Latent Image
Sources:Encyclopaedia Britannica (article by W. de W. Abney and others), 1911§ The action of substances other than light on the sensitive plate: W. J. Russell's experiments and the hydrogen peroxide explanation
- 1911Date precision: Year
Rudolph Fisher patents in Germany a black-and-white paper whose response varies with the colour of the light. The paper is never marketed, and twenty-nine years pass before anybody sells one: the hard part was never the principle but the emulsion-making, three components matched in contrast and blue speed and differing only in green sensitisation.
Verified in:Part 18 — Variable-Contrast Papers: Three Emulsions, One Sheet
Sources:Dusan C. Stulik and Art Kaplan, 2013§ Variable Contrast Photographic Material - Rudolph Fisher's 1911 German patent for a paper with variable response to different colours of light, with the atlas's own note that this paper was never marketed
- 1911Date precision: Year
Platinum allergy is first identified, as an occupational disease of photographic factory workers handling platinotype paper. It is one of the few hazards in this course whose first recorded victims were photographic workers rather than chemists.
Verified in:Part 25 — Noble Metal Chemistry and the Platinotype
Sources:Mike Ware, 2017§ Section 6.4, Health warning, platinum allergy - the 1911 identification as an occupational disease of photographic factory workers handling platinotype paper
- 1912Date precision: Year
E. J. Wall's Dictionary of Photography records the working state of pinhole practice: a prolonged exposure of about twenty or thirty times the ordinary one for any given subject, and Alfred Watkins' table of needle sizes against plate distances, whose ratios run from about f/39 to f/60.
The rule survives the arithmetic. A period lens at f/11 against a pinhole at f/56 is 25.9 times, which is inside twenty or thirty and 4.7 stops, so the rule is the square law worked once by somebody and then remembered. It also shows how far the range has moved: Watkins' pinholes were four to six times faster than the ones this part pierces, because his plates were slower and his cameras longer.
Verified in:Part 6 — Pinhole Exposure and Reciprocity Correction
Sources:E. J. Wall, edited by F. J. Mortimer, 1912§ Pinhole Photography: the twenty-to-thirty-times rule and Alfred Watkins' table of needle sizes, plate distances and the resulting ratios
- 1912Date precision: Year
George Eastman installs a research laboratory at Rochester under C. E. Kenneth Mees. Among the scientists Mees gathers there is L. A. Jones, whose name the four-quadrant tone-reproduction diagram carries; Jones contributes to the first volume of the laboratory's Abridged Scientific Publications in 1913 and 1914.
The course holds none of Jones's own papers and therefore dates no part of the tone-reproduction work itself, nor the four-quadrant diagram, nor the Jones and Condit scene-luminance surveys. What the corpus supports is the laboratory he did that work in, and this entry states that and no more.
Verified in:Part 13 — Tone Reproduction: From Subject to Print
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Sensitizing Emulsions and Journals, Societies and Institutions - the account of the research laboratory George Eastman installed at Rochester in 1912 under C. E. Kenneth Mees, naming L. A. Jones among the scientists gathered there, and the record that Jones contributed to the first volume of the Abridged Scientific Publications of the Research Laboratories of the Eastman Kodak Company, 1913 to 1914
- 1916Date precision: Year
The British government embargoes platinum for anything but munitions, which stops Willis's manufacture and export. Ware's price history has the metal peaking in 1920 at 800 shillings, forty pounds, per troy ounce, five times the 1900 price, and falling in the Depression to 93 shillings in 1931.
The Getty atlas records that Kodak stopped producing platinotype material in 1916 for the same reason. The embargo was lifted in 1918, but the price never came back.
Verified in:Part 25 — Noble Metal Chemistry and the Platinotype
Sources:Mike Ware, 2017§ Section 2.6, Platinotype embargoed in Britain - the 1916 embargo and the 1918 resumption; Section 2.3 for the 1920 peak of 800 shillings per troy ounce and the 1931 minimum of 93 shillingsDusan C. Stulik and Art Kaplan, 2013§ Historical background - Kodak stopping production of platinotype material in 1916 and platinum becoming a strategic metal during the war
- 1917Date precision: Contested
Willis launches Palladiotype, replacing the embargoed metal with palladium, which Wollaston had discovered in 1803, Burnett had proposed for photography in 1856 and Willis himself had named in his 1878 patent, and which had been passed over then because it was more expensive than platinum.
Contested: the date.The Getty atlas states that the palladiotype process was invented by William Willis in 1916 and that the Platinotype Company introduced it in that year; Ware gives 1917, tied to named meetings, the Croydon Camera Club in January 1917 and the Camera Club of London on 8 March 1917, and to dated advertisements. No patent was ever issued for the process, so there is no filing date to settle it. The course follows Ware, because his date is anchored to specific dated events, and records the atlas's 1916 here.
Verified in:Part 25 — Noble Metal Chemistry and the Platinotype
Sources:Mike Ware, 2017§ Section 2.8, Palladiotype launched by Willis, for the 1917 date; Section 2.7, Palladium supplements platinum, for Wollaston's 1803 discovery and Burnett's 1856 suggestionDusan C. Stulik and Art Kaplan, 2013§ The palladiotype entry, stating that the process was invented by William Willis in 1916, that no patent was ever issued for it, and that the Platinotype Company introduced it in 1916
- 1920Date precision: Year
Luppo-Cramer finds far better desensitisers among the safranine dyes and publishes a method for developing highly sensitive and colour-sensitive plates in ordinary yellow light without fog - which, for anyone who had been developing panchromatic plates by touch, was a considerable improvement in life.
Verified in:Part 4 — Spectral Sensitivity and Colour Response
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Chapter LXV, Discovery of desensitizing: Luppo-Cramer 1920 and the safranine dyes
- 1924Date precision: Year
Three of the heliographs Niepce left with Francis Bauer at Kew come to the Royal Photographic Society's collection.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ the plates acquired by the Royal Photographic SocietyMike Ware, 2019§ 3.9 Niepce in England 1827
- 1924-1926Date precision: Span
S. E. Sheppard's Eastman Kodak patent, filed in June 1924 and published in March 1926, identifies the impurity that had been making photographic speed for fifty years. The sensitiveness of emulsion grains corresponds to nuclei of unstated chemical composition; those nuclei are silver combined with sulfur; and the sulfur came unbidden from the gelatin. Oxidise it out and you get emulsions of impractically low light-sensitiveness.
He states the mechanism as an attribution rather than a proof, and the patent's own wording records that the thing had been detected before it was identified. Thiosinamine - allyl thiourea - is singled out as especially useful. Once the impurity was identified the industry standardised on inert gelatin and added a measured sensitiser afterwards, which is why the modern buyer's problem is the opposite of the historical one.
Verified in:Part 4 — The Latent Image
Sources:Samuel E. Sheppard, assigned to Eastman Kodak Company, 1926§ United States Patent 1,574,944: nuclei of unstated chemical composition; thiosinamine; the oxidised-gelatin control
- 1926Date precision: Year
Work by L. A. Jones, E. Huse and V. C. Hall on the theory of photographic density, building on Kron's, puts Jones in print on density theory by the middle of the 1920s. It is the earliest of his own work that this course can date from its corpus.
Verified in:Part 13 — Tone Reproduction: From Subject to Print
Sources:Josef Maria Eder, translated by Edward Epstean, 1945§ Sensitizing Emulsions and Journals, Societies and Institutions - the reference to the later work of L. A. Jones, E. Huse and V. C. Hall of 1926 on the theory of photographic density
- 1928Date precision: Year
Kodak's Elementary Photographic Chemistry prints the American toning formulas that are still in circulation a century later, among them the hypo-alum sepia bath T-1a and the bleach-and-redevelop sulfide toner T-7a, with a paragraph saying what each ingredient of the bleach is answering.
Kodak still published the toner formulas in publication G-23 in 2006, at working strengths that differ from the 1928 printing - T-7a's toner is 10.4 g/L in 1928 and 22.5 g/L in 2006 - so a formula number on its own does not identify a bath.
Verified in:Part 20 — Sulfide and Sepia Toning: Bleach, Redevelop, Convert
Sources:Eastman Kodak Company, 1928§ Toning - the hypo-alum bath T-1a and the bleach-and-redevelop sulfide toner T-7a, with the account of what each ingredient of the bleach doesEastman Kodak Company, 2006§ The published toner formulas and their working-solution strengths, against the 1928 printing of the same numbers
- 1929Date precision: Year
E. J. Wall's Photographic Emulsions sets out commercial emulsion making at the scale it was then done - chloride and chlorobromide emulsions in forty-five-litre batches, with wash times and full finals sets - and rules formaldehyde out as an in-emulsion hardener on photographic grounds: under no circumstances, because in the writer's experience it leads eventually to fog on keeping.
Duffin reached the same conclusion independently thirty-seven years later. The photographic objection to formaldehyde was made twice, on photographic grounds, long before the health classification that would exclude it from this course anyway.
Verified in:Part 5 — Gelatin, the Photographic Binder
Sources:E. J. Wall, 1929§ The chloride and chlorobromide emulsions of pages 91 to 105; the rejection of formaldehyde as a hardener
- c. 1926 to 1929Date precision: Circa
Albumen paper ends as a trade. Trapp and Munch, the last maker, cease production of matte albumen paper in 1929, and the last glossy albumen paper was made about 1926, so the process stops over about three years rather than on a date.
Matte albumen outlived the glossy paper it was a reaction against. Reilly's account of the matte papers runs from the ready-sensitized paper of 1898 and Trapp and Munch's of 1902 through the half-matte paper of 1913 to the eighteen base stocks Trapp and Munch were still offering at the end.
Verified in:Part 22 — The Variants of the Salt Print and How a Conservator Identifies One
Sources:James M. Reilly, 1980§ Chapter Five, Matte Albumen Paper - Trapp and Munch ceasing production in 1929 as the last maker, and the last glossy albumen paper being made about 1926
- 1932Date precision: Year
Carroll and Hubbard, at the United States National Bureau of Standards, measure the silver compound of 6-nitrobenzimidazole against a silver electrode: more insoluble than silver bromide at pH 7.1, with the silver readily displaced by hydrogen in acid, and mol for mol about ten times the effect of soluble bromide in delaying after-ripening. That factor is what separates an organic antifoggant from a halide restrainer.
They were scrupulous about what the measurement did not prove: something more than the decrease in silver ion concentration must be involved, they wrote, and another method of attack would be needed to decide what. They pointed at adsorption without claiming it. Research Paper 525 is signed at Washington on 2 June 1932.
Verified in:Part 8 — Restrainers and Antifoggants
Sources:Burt H. Carroll and Donald Hubbard, of the National Bureau of Standards; the attribution on The Light Farm's emulsion literature list is Carroll, Hubbard and Kretschman§ RP525: the silver compound of nitrobenzimidazol, the silver-electrode measurement, and the tenfold effect on after-ripening
- 21 January 1938Date precision: Exact
R. W. Gurney and N. F. Mott publish The Theory of the Photolysis of Silver Bromide and the Photographic Latent Image in Proceedings of the Royal Society A 164 (917), 151-167. It is the origin of the alternating model: a photoelectron is trapped and reduces a silver ion, a mobile interstitial silver ion follows to the same trap, and the two steps repeat until a cluster of a few silver atoms makes the crystal developable.
Contested: what it signifies.The model is where every modern account starts and it was not accepted quietly. J. W. Mitchell, its principal critic, published a differing treatment in 1957 with Mott himself as co-author. This course has read neither original - the publisher's site refused access to the 1938 paper and no open copy was found - and takes the four steps it teaches from Ware's summary, which is what it has read. What is not in dispute is that absorption frees an electron, that silver ions move inside the crystal, that a small silver cluster makes the crystal developable, and that removing the halogen is necessary; the argument is about the route, not the destination.
Ware gives the minimum cluster as thought to be four silver atoms. The course keeps his hedge: four is the only figure it has read in a source it holds, and it is not presented as settled.
Verified in:Part 4 — The Latent Image
Sources:R. W. Gurney and N. F. Mott, 1938§ Bibliographic record only; the full text was not obtainable by this courseMike Ware, 2019§ 23.11 Gurney-Mott model of the latent image, in four numbered steps
- 1940Date precision: Year
The first variable-contrast papers reach the market: the US Defender Company's, and Ilford's first Multigrade in England at about the same time, which the war keeps off sale until 1950 and out of the United States until 1956. Kodak's Polycontrast follows in the spring of 1957.
Contested: the attribution; who was first.The Getty atlas prints the Defender product's name as Varigram; the name that circulates everywhere else, in printers' accounts, secondary histories and collectors' listings, is Varigam, and the course has found no Defender or DuPont publication, patent or advertisement in its corpus to settle which is right. On priority the atlas gives Defender the lead by a short head over Ilford's first Multigrade of about the same year, with Ilford's product delayed to market by the war. The date itself is not in dispute in either account, and nothing in the chemistry depends on the spelling.
Verified in:Part 18 — Variable-Contrast Papers: Three Emulsions, One Sheet
Sources:Dusan C. Stulik and Art Kaplan, 2013§ Variable Contrast Photographic Material - the 1940 introduction by the US Defender Company, the name printed as Varigram, Ilford Ltd's first Multigrade paper in England about 1940 with commercial availability only in 1950 and export to the United States from 1956, and Kodak's introduction of Polycontrast in spring 1957
- 1941Date precision: Year
T. Thorne Baker's Photographic Emulsion Technique is the manufacturing manual this course scales its emulsion work from: Trumm's bromide paper emulsion, the two per cent chrome alum dip after the final rinse racked without further rinsing, the glass subbing practice, and a bromide dose of about 170 milligrams per mole of silver.
Adopting Baker's chrome alum means the course alters no historical formula in order to be safe: chromium(III) is the hardener in Baker's finals, in Wall's finals and in Baker's glass subbing dip, and the British exposure limit for chromium(III) compounds is fifty times that for chromium(VI).
Verified in:Part 5 — Coating, Drying and Hardening
Sources:T. Thorne Baker, 1941§ Trumm's bromide paper emulsion; substratuming on page 140; the chrome alum dip
- 1941Date precision: Year
Commercial manufacture of platinum papers ends in Great Britain. The Platinotype Company had listed fifteen kinds of paper in 1911 and was wound up in 1937; American manufacture had already stopped in the 1930s. What eventually revived the process was not a paper but a kit of chemicals sold for hand-coating.
No citable date was found in this course's corpus for the twentieth-century revival itself. What the sources establish is the form it took - kits rather than papers - and not the year it began.
Verified in:Part 25 — Cost, Permanence and When a Platinum Print Earns Its Price
Sources:Dusan C. Stulik and Art Kaplan, 2013§ Historical background, for the commercial arc from the first papers of 1880 to the end of British manufacture in 1941 and the fifteen kinds of paper listed in 1911Mike Ware, 2017§ Section 1.8, for the winding up of the Platinotype Company in 1937 and the end of British commercial manufacture in 1941
- May 1941Date precision: Year
John David Kendall files a patent for Ilford whose declared objects are to provide a new series of photographic developing compounds and to provide a substitute for metol. The compound is 1-phenyl-3-pyrazolidone - phenidone - and the claim that made it famous is quantitative: replace the metol in a metol-hydroquinone developer with about one fifth to one sixth of its weight and you get a developer of similar development characteristics.
Contested: what it signifies.Phenidone is the standing counterexample to the structural rule that carries Kendall's own name. It is not a benzene ring with two donor groups on it, and it develops better than metol. One reading keeps the Kendall-Pelz rule as a guide with a known exception; the other holds that a rule with a commercially dominant exception is not a law. Kendall himself was on the second side by implication: his patent's stated object was a new series of compounds, not a variation on a phenol. The course takes the rule as a good guide and says why.
United States patent 2,289,367 issued in 1942. The ratio is what superadditivity has to explain, and it is the reason MQ gave way to PQ on every packet - with the skin of the person mixing the developer as the driver at every step.
Verified in:Part 8 — The Classical Developing Agents: Metol, Hydroquinone, Phenidone
Sources:John David Kendall, assigned to Ilford Limited, 1942§ United States patent 2,289,367: the declared objects, 1-phenyl-3-pyrazolidone, and Examples I and II
- March 1943Date precision: Year
T. Thorne Baker publishes a chloride emulsion in American Photography. It is the emulsion this course teaches for contact printing, in Denise Ross's KCl gaslight-paper adaptation for The Light Farm of 2012, which is the document the course has actually read.
Contested: the attribution.Baker's article survives in this corpus only as a page image that did not yield text, so the course has not read the original. Ross states that it contains two recipes, a developing-out paper and a printing-out paper, and the course teaches the developing-out one in her adaptation. Anybody citing Baker 1943 for a formula owes their reader that distinction: Baker owns the chemistry, Ross owns the scale, the vessels, the timings as she runs them, and the coating method.
Verified in:Part 5 — Project 1: A Silver Chloride Contact Printing Emulsion
Sources:Denise Ross§ The KCl Gaslight Paper Version of T. Thorne Baker's chloride emulsion, American Photography, March 1943, adapted 2012
After 1945: engineering, and the revivals
The sensitisers, the crystal habit and the developing agents become things a patent can specify; and the processes the industry left behind are picked up by the people who wanted them.
- 1946Date precision: Year
Ilford's patent by Waller, Collins and Dodd adds the second sensitiser. Small quantities of a soluble gold salt, added before or during digestion at a pH not greater than about 8, give a very considerable increase in the light sensitivity of the final emulsions.
The gold does not work alone. The patent states that all normal gelatin contains small proportions of sulfur compounds such as thiosinamine, that their presence is believed essential to the gold effect, and that inert gelatins benefit from a positive addition of one: sulfur and gold sensitisation are a partnership, not alternatives. Too much gold loses the speed gain rather than increasing it. The relative-speed tables are badly mangled in the scanned text and this course quotes no number from them.
Verified in:Part 4 — The Latent Image
Sources:Cecil Waller, Ronald Bernard Collins and Edward Cyril Dodd, assigned to Ilford Limited, 1946§ United States Patent 2,399,083: the gold salt, the pH limit, the thiocyanate addition, and the statement that sulfur compounds in the gelatin are essential to the effect
- 1949Date precision: Year
Kodak Limited prints formula D-173 under a heading that names its reason: an Elon-free paper developer, to eliminate the risk of discomfort to persons prone to metol dermatitis. It is a published formula whose stated purpose is what an ingredient does to the person mixing it rather than what it does to the negative.
Ilford now uses an agent it does not describe, and Kodak sells a developer whose headline benefit is the absence of the other one. MQ became PQ, and PQ is quietly becoming something with no quinol in it at all.
Verified in:Part 8 — The Classical Developing Agents: Metol, Hydroquinone, Phenidone
Sources:Kodak Limited, 1949§ Formula D-173, printed under the heading naming metol dermatitis
- 1949Date precision: Year
Kodak Limited's Chemicals and Formulae, a mainstream London trade handbook, still prints a uranium toner as T-9, a uranium intensifier, a mercury intensifier and the sulphide toner T-52, with the maker's own warnings set beside the formulas. Nobody publishing it was unaware of what was in it.
No citable date could be found for the withdrawal of uranium toning from mainstream practice. What can be dated is its last mainstream publication, and Vogel's purely commercial verdict of 1875 that uranium was too rare and too dear to be used generally in photography.
Verified in:Part 20 — The Toners We Study and Do Not Use
Sources:Kodak Limited, 1949§ The uranium toner T-9, the uranium and mercury intensifiers, and the sulphide toner T-52, with the warnings printed beside them
- 1952Date precision: Year
Kodak's patent by Davey and Knott describes a silver bromide emulsion containing some silver iodide in which the latent image forms inside the crystal on purpose. It is an early example of building a crystal so that its inside and its outside differ, and of putting the image where an ordinary surface developer cannot reach it.
Verified in:Part 4 — Grain, Speed and Resolution
Sources:Edward Philip Davey and Edward Bowes Knott, assigned to Eastman Kodak Company, 1952§ United States Patent 2,592,250: internal latent image emulsions and the iodide content range
- c. 1953Date precision: Circa
Optical brightening agents go into industrial production, and into general use after 1955, added to the paper base, the baryta layer or the emulsion. They move the white of a photographic paper, and their presence in a print dated much earlier than this raises a question about the date.
Developed in the late 1940s and tested after 1951 on Paul Messier's research. Their concentration can be reduced by extensive washing or quenched by later treatment, so a low reading is not proof of an early date.
Verified in:Part 18 — The Structure of a Printing Paper: Base, Baryta, Emulsion and Supercoat
Sources:Dusan C. Stulik and Art Kaplan, 2013§ Other analytical signatures - optical brightening agents added to the paper base, baryta layer or emulsion, dated to industrial production about 1953 and general use after 1955 on Paul Messier's research
- September 1957Date precision: Year
J. W. Mitchell, the principal critic of the Gurney-Mott model, publishes The nature and formation of the photographic latent image in the Philosophical Magazine 2 (21), 1149-1170, with Mott himself as co-author, nineteen years after the original.
Contested: what it signifies.This course has not read the paper and will not summarise an argument it has not read. It records that a differing account of the latent-image mechanism exists, by whom and where. That Mott co-authored a critique of his own model tells you how live the argument still was nineteen years on; it does not tell you which account is right, and neither does this entry. The modern position - which of the two the field settled on, or whether it did - is not something this course has established.
Verified in:Part 4 — The Latent Image
Sources:J. W. Mitchell and N. F. Mott, 1957§ Bibliographic record only; the full text was not read by this course
- 1960sDate precision: Circa
Contemporary photographers rediscover the cyanotype as an alternative to commercial silver gelatin materials. The Getty atlas notes drily that silver gelatin will itself soon be an alternative process.
Verified in:Part 1 — Herschel: Hypo, Prussian Blue and the Words of Photography
Sources:Dusan C. Stulik and Art Kaplan, 2013§ Historical background
- 1962Date precision: Year
Kodak's double-jet patent credits Berry and Skillman with the finding that the pAg of the solution alone decides crystal habit during precipitation: hold the pAg between 8.6 and 9.2 and the pH at 4.0 or less and the product is cubic-regular grains rather than the octahedra the usual methods of precipitation give.
Read at second hand. The course knows the finding through the 1972 Kodak patent that cites it - Berry and Skillman, 'Precipitation of Twinned AgBr Crystals', Photographic Science and Engineering 6(3), May-June 1962 - and has not read that paper itself. The Berry here is not the Miles Berry who took out Daguerre's English patent in 1839.
Verified in:Part 4 — The Silver Halides
Sources:Eastman Kodak Company, 1972§ The pAg range that selects the habit, credited to Berry and Skillman in 1962
- 1963Date precision: Year
The Harry Ransom Center purchases the Le Gras plate as part of the Gernsheim Collection, after what Ware describes as a five-year search by the photohistorians Helmut and Alison Gernsheim.
Contested: unverified by this course.The frequently quoted rediscovery date of 1952 the course could not verify from these sources, and does not assert. Only the 1963 purchase is stated here.
Verified in:Part 1 — Niepce and Heliography: Light That Hardens
Sources:Harry Ransom Center, University of Texas at Austin§ The Niepce Heliograph, exhibition text and object recordMike Ware, 2019§ 3.9 Niepce in England 1827
- 1966Date precision: Year
G. F. Duffin's Photographic Emulsion Chemistry states the physical chemistry of a make: the five stages, single-jet against double-jet emulsification, Ostwald ripening described as the crystals cannibalising each other, pAg as the variable behind the variable, and the ranges of active sulfur - one to two parts per million in inert gelatins against up to a hundred in active ones - that decide what a modern maker has bought.
He rejects formaldehyde as a hardener on the same photographic grounds Wall had given thirty-seven years earlier, and adds volatility, which loses the hardener during coating and contaminates other materials.
Verified in:Part 5 — Precipitation, Nucleation and Crystal Growth
Sources:G. F. Duffin, 1966§ Chapter IV, Emulsion Preparation, pages 57 to 74: the five stages, emulsification, ripening and the ten emulsion variables
- 1968Date precision: Year
Kodak sells the first commercial resin-coated paper. The material grew out of a military requirement for a base that would not absorb processing solutions; extruded polyethylene seals the fibres so that the emulsion never touches one, and the titanium dioxide filling the recto layer does baryta's job.
Early versions really were coated with thermosetting resins, which is where the name came from; the European designation PE paper describes the commercial material better than the American RC does.
Verified in:Part 18 — The Structure of a Printing Paper: Base, Baryta, Emulsion and Supercoat
Sources:Dusan C. Stulik and Art Kaplan, 2013§ RC photographs - the origin of resin-coated paper in a military requirement for material that would not absorb processing solutions, the first commercial RC paper from Kodak in 1968, the base sealed on both sides by extruded polyethylene with the recto filled with titanium dioxide, and the emulsion overcoated by a hardened gelatin supercoat
- 1971Date precision: Year
Matt Young's Pinhole optics appears in Applied Optics 10(12), 2763-2767, treating the pinhole as a useful and practical device rather than a curiosity and noting that its angular field can be made to exceed 90 degrees. From roughly this point the lensless camera becomes an artist's instrument again.
Contested: the attribution.A constant near 1.5 to 1.6 is widely attributed to Young. This course has read only the 1971 abstract, which confirms the paper's subject and states no constant, and has obtained the full text of none of the three papers usually cited. It therefore puts no number in his mouth, and instead derives the constant that follows from the modern criterion - geometric blur set equal to the true Airy diameter rather than to Petzval's cruder estimate - which gives 1.56, and labels it by its criterion rather than by a person.
Verified in:Part 6 — Diffraction and the Optimum Pinhole
Sources:Matt Young, 1971§ Abstract only; the full text was not available to this course
- 1990 or 1991Date precision: Contested
Ware re-visits Herschel's argentotype chemistry and publishes the argyrotype: the citrate ligand again, but silver sulphamate instead of silver nitrate, at pH 3.5, so that the whole sensitiser goes into one bottle and the print does not have to be cleared the way a Van Dyke does.
Contested: the date.Ware's own two accounts give different years for the same invention. His web article says he re-visited the underlying chemistry in 1990 and came up with the process he called argyrotype, and its footer records first publication in the British Journal of Photography on 13 June 1991; his workshop handout says the argyrotype version was devised in 1991. Nobody else is involved and the gap is small - an invention made in one year and published in the next is the ordinary shape of the thing - so the course writes it as devised about 1990 and published in 1991 and gives both of his statements rather than choosing.
Verified in:Part 24 — The Siderotype Principle: Iron Reduces Silver
Sources:Mike Ware§ Overview of Argyrotype, for the re-visiting of the chemistry in 1990 and the footer recording first publication in the British Journal of Photography on 13 June 1991Mike Ware§ The opening account, stating that the argyrotype version was devised in 1991
- 1992Date precision: Year
ISO 6846 gives the paper contrast figure that printers now read off a datasheet: the log exposure range the paper accepts, multiplied by a hundred. ILFORD attribute their published range figures for MULTIGRADE papers to this standard, and specify that the range meant is that of the image as projected on the enlarger baseboard rather than as read on a light box.
The date is ILFORD's own attribution on their own datasheet; the course does not hold the standard and quotes no part of it.
Verified in:Part 13 — Paper Sensitometry: Reflection Density, Grades and ISO(R)
Sources:HARMAN technology Limited (ILFORD Photo), 2020§ ISO Range (R) - the table of range figures by filter for MULTIGRADE RC papers, attributed on the sheet to ISO standard 6846-1992, with the instruction to multiply the effective negative density range by 100 and choose the nearest range figure, and the note that the range meant is that of the image as projected on the enlarger baseboard
- 1 February 1993Date precision: Exact
The second edition of ISO 6, Determination of ISO speed for black-and-white pictorial still camera negative film, is published. It is written for film and process systems together rather than for films alone, which is the structural reason a speed is never a property of a film by itself.
The course cites this standard by number only, buys no copy, quotes no part of it and states its own speed criterion instead, marking every figure derived under that criterion as its own measurement. It has also not verified whether this edition is still current.
Verified in:Part 13 — Film Speed and Exposure Index
Sources:ISO/TC 42, Photography, 1993§ Catalogue record and free preview: second edition, 1993-02-01; title and scope, which is written for film/process systems rather than for films alone
- 1994-1995Date precision: Span
Ware answers the seven documented faults of the classic cyanotype by changing the ligand: a crystalline ammonium iron(III) oxalate in place of the ill-defined ferric ammonium citrate. He develops the procedure in 1994 and publishes it as the New Cyanotype in Ag+ Photographic in 1995.
The course cites the 1995 article as bibliography only, not as a source it has read: what it has read is the Cyanomicon, Ware's website article and his 2009 workshop notes, all three of which print the same formula. An independent account by John Barnier followed in Photo Techniques in 1997.
Verified in:Part 21 — The New Cyanotype and the Other Ways to Make a Blue Print
Sources:Mike Ware, 2020§ Section 6.7.4, New cyanotype 1995 - the reasoning, the formula, and the endnote giving first appearance as A New Blueprint for Cyanotypes in Ag+ Photographic, volume 7, 1995, pages 74 to 80Mike Ware§ The account of the 1994 procedure for making the sensitiser in the beaker
- 14 December 2000Date precision: Exact
ISO 18915, Methods for the evaluation of the effectiveness of chemical conversion of silver images against oxidation, is released: a test method for exactly the claim toning makes. Its existence says the question is answerable; that the course cannot find the experiment published for the toners it teaches says how little of it has been answered.
Edition 1, sixteen pages, released 14 December 2000, and adopted by BSI as BS ISO 18915:2000 on 15 March 2001. The course cites it by number only, quotes no part of it, and no page will tell you that a print meets it.
Verified in:Part 20 — Toning, Permanence and What the Evidence Actually Supports
Sources:ISO/TC 42, Photography, 2000§ Title, scope and catalogue data: edition 1, 2000, sixteen pagesEuropean Standards s.r.o., 2026§ The two catalogue records read and cross-checked: ISO 18915:2000, edition 1, released 2000-12-14, 16 pages English; BS ISO 18915:2000, released 2001-03-15, 26 pages
- 2001 at the earliestDate precision: Contested
Worldwide Pinhole Photography Day, held on the last Sunday in April, is the pinhole community's annual event; its own site gives 26 April in 2026 and 25 April in 2027.
Contested: the date; unverified by this course.The site yielded no founding statement and names no founder, only organizers and volunteers. Its copyright notice runs from 2001, which is the earliest date this course can support, and the course prints that rather than asserting a first year. If a founding announcement can be produced, it should replace this entry.
Verified in:Part 7 — Seeing Like a Pinhole: The Image, Its Makers and Previsualisation
Sources:Worldwide Pinhole Photography Day organisers and volunteers§ The event's own site: the copyright range, the last-Sunday-in-April rule, and the 2026 and 2027 dates
- 2001Date precision: Year
David Hockney's Secret Knowledge and Philip Steadman's Vermeer's Camera put the strong version of the case that optical projection underlies a broad swathe of Western painting from the fifteenth century. They are the visible end of an art-historical re-evaluation that also runs through Doug Nickel's 1989 essay on drawing machines and Martin Kemp's The Science of Art of 1990.
Contested: what it signifies.That some artists used optical aids is not seriously disputed. What is disputed is who, and how much. The strong version - the Hockney-Falco thesis, and Steadman's reconstruction of a camera obscura in Vermeer's own room - is argued from the paintings rather than from documents that say so, and this course has read neither those arguments nor the published responses to them, so it takes no position on either. What it insists on is the distinction between the two kinds of sentence: 'Vermeer used a camera obscura' is an inference from the appearance of a finished work, and 'Barbaro described a diaphragm in 1568' is a page in a book with a date on it.
Entered as an interpretation rather than a fact, and the only entry on this timeline that is about a modern argument concerning old pictures rather than about something somebody did.
Verified in:Part 1 — The Camera Obscura: An Image Without Chemistry
Sources:Mike Ware, 2020§ Closing section on painters and optical aids, with its references to Kemp, Steadman, Nickel and Hockney
- 1 December 2009Date precision: Exact
The fifth edition of ISO 5-2, Geometric conditions for transmittance density, separates standard diffuse transmittance density from standard projection transmittance density and specifies a geometric mode, a sampling aperture and a light distribution for each. It exists because a silver image scatters as well as absorbs, so two instruments reading one negative disagree unless the geometry is stated.
This is the modern settlement of the quarrel Abney and Hurter and Driffield had from July 1890 into the following year. The course cites the standard by number only and reproduces no geometry, tolerance or value from it.
Verified in:Part 13 — Exposure, Density and the Logarithm
Sources:ISO/TC 42 Photography and ISO/TC 130 Graphic technology, joint working group, 2009§ Catalogue record and free preview: fifth edition, 2009-12-01; the contents list, for the separation of standard diffuse transmittance density from standard projection transmittance density and the specification of geometric mode, sampling aperture and diffuse and directional distributions for each
- 2012Date precision: Year
Pinhole Resource, run by Eric Renner and Nancy Spencer, donates 6,000 photographs from 500 photographers, 60 cameras and 200 books and catalogues to the Palace of the Governors Photo Archives at the New Mexico History Museum, where more than 1,300 of them are now in the digital database.
Founding years for Pinhole Resource and the run of the Pinhole Journal could not be sourced from the organisation's own site and are not printed here.
Verified in:Part 7 — Seeing Like a Pinhole: The Image, Its Makers and Previsualisation
Sources:Pinhole Resource (Eric Renner and Nancy Spencer)§ What the collection holds and the 2012 donation to the New Mexico History Museum
- 2019Date precision: Year
Ware answers the same question a second time with the Simple Cyanotype, building a well-defined ammonium dicitratoferrate(III) complex in the beaker from iron(III) nitrate and citric acid rather than buying an ill-defined citrate. The anion had been isolated and its structure determined by X-ray diffraction in 1998, three years after the New Cyanotype; the insight of 2019 is that a photographer does not need the solid.
Verified in:Part 21 — The New Cyanotype and the Other Ways to Make a Blue Print
Sources:Mike Ware, 2020§ Section 6.7.6, Simple cyanotype 2019 - the reasoning and the four benefits claimed for itMike Ware, 2022§ Ammonium Dicitratoferrate(III) Characterised 1998; Simple Cyanotype 2019, the reasoning and the benefits of the nitrate route
What is not here yet
Section titled “What is not here yet”The timeline is drawn from the eight parts written so far. Part I supplies most of it, because it is the densest historical material in the course and the part whose dates were argued hardest; Parts IV to VIII supply the rest, each owning the chronology of the mechanism it teaches — the dry plate and heat ripening, dye sensitisation, reciprocity failure, the latent image, the emulsion literature, the optics of the pinhole, and the developing agents.
The parts still to be written own the dates that are missing, and they are missing on purpose rather than by oversight. The collodion wet plate, albumen paper, the platinotype, the characteristic curve and the speed systems, the toners, and the twentieth-century regulatory events that removed uranium, mercury and cyanide from the photographic supply chain each belong to a part that has not yet done the verifying. None of them will appear here until it has.
Some things the written parts do teach still have no dated entry, because no source in this course’s corpus dates them. The tabular grain is the clearest case: Part IV teaches what it is and reads Kodak’s own published granularity figures, and no source it holds gives a year for its introduction. The origin of solargraphy, the founding of Pinhole Resource and the run of the Pinhole Journal, the conditions under which the Lainer effect appears, and the first commercial panchromatic plate are the others. Each of them is a gap this course would like filled and will not fill by guessing.
Image attributions are the last gap. The entry model carries a field for the holder and the licence of a public-domain image, and no entry uses it yet.