Overview: The Three Problems Every Photograph Must Solve

Photography was not invented by anyone who set out to invent it. The chemistry that made it possible was found by people looking for something else - a luminous stone, the constituents of air, a way of dyeing silk with gold - and for a century after the effect was understood, nobody could keep a picture made with it. This part is the account of how that changed.

Why the course begins here

Because the mechanisms arrive in a particular order, and each is easier to understand as the answer to a question somebody was actually asking. The sensitivity of silver salts to light was demonstrated deliberately, with a control against heat, in 1727; Eder’s history is the standard account of that work. Practical photography, the kind that produces a picture you can keep and show, belongs to the nineteenth century. The gap between the two is three unsolved problems.

Note the wording carefully. The eighteenth-century chemists established the effect; they were not trying to make pictures, and it misrepresents them to say they were. What they left behind was a material that darkens where light falls - which Kodak’s own 1928 primer describes as the earliest photographic material, and as far too insensitive to use in a camera.

The three problems

How this part is organised

1. 1SensitivityMake a material that responds fast enough to record a camera image, not just a shadow.
2. 2PermanenceRemove or neutralise what the light did not act on, so the picture stops changing.
3. 3ReproducibilityGet from one original to many prints.

Every process in this part attempts one of the three, and the failures are as instructive as the successes. Wedgwood and Davy solved none of them and said so. Daguerre solved the first two and not the third. Talbot’s answer was weaker at the first and decisive at the third. Herschel supplied the chemical that made the second routine. Each of those one-line verdicts is argued, with its sources, on the page that owns it; here they are only a map.

!This grouping is ours, not history's

Nobody in the eighteenth or nineteenth century wrote about “the three problems”. The framework is the course’s own way of organising material that its participants experienced as a tangle of private experiments, disputed priority and commercial secrecy. It is a teaching device, and a good one, but it is interpretation. When this course states a date, an attribution or a piece of chemistry, it cites where that came from; when it offers a frame like this one, it says so.

What you make, expose and keep

Three pieces, and you keep all three.

A camera obscura, built from a box or a blacked-out room, that gives you an image formed by nothing but light travelling in straight lines. No chemistry can be understood until you have seen that the image exists before any material records it.

An unfixed silver photogram, made by laying objects on ordinary photographic paper in sunlight. It appears without a developer, and then it keeps going: over the following week it darkens away while its twin, kept in an envelope, does not. That is the permanence problem, in your hands rather than in a paragraph.

A cyanotype photogram, made on paper bought already sensitised, which washes in plain water and then stops changing. It is the first piece of the assignment path, and the contrast with the silver photogram is the point.

Why no chemical is mixed here

Every material in this part is a finished article bought ready to use: photographic paper from a box, cyanotype paper or fabric already coated and dried. Nothing is weighed, dissolved, diluted or poured. The manufacturers publish safety data sheets for their processing chemistry, and ILFORD’s published guidance for domestic users in the United Kingdom treats small quantities of scrap film and paper as ordinary household waste; local rules govern, and they differ.

That does not make this part hazard-free, and the pages do not pretend otherwise. The real hazards here are the ones you would meet doing anything else outdoors or with a craft knife: solar ultraviolet on skin and eyes during long exposures in the sun, which ICNIRP’s guidance for outdoor workers addresses directly; cuts; blackout material near a lamp or a heater; and focused sunlight through any lens. Each practical page carries a safety classification and states which criteria of the rubric applied. All three are Level A. The daguerreotype, which depends on mercury vapour, is described as Level D: studied for its chemistry and history, never performed.

The habit to start now

One line per exposure, in a notebook you keep: the date, the material, the light, the time, and what you saw. Part II introduces the formal laboratory record. Start the habit here, where the stakes are a sheet of paper, and it will be automatic by the time it matters.

What you need first

Nothing. This is the first part of the course and it assumes no chemistry, no darkroom and no camera. The materials for the three practical pages are listed on each page and priced in the laboratory planner; what you need gives the stage-by-stage overview. Buy nothing before you have read the page that uses it.

Where this part leads

The unfixed photogram is deliberately left unfinished: it is retrieved in Part XI, where fixing chemistry finally explains what the envelope twin was waiting for. The printing-out silver you meet here is contrasted with developed silver in Part IV, on the latent image, and made properly in Part XXII, on salted paper. The camera obscura becomes the body of the pinhole camera in Part VI. The laboratory discipline this part deliberately does without arrives in Part II, and the daguerreotype and the cyanotype return for full treatment in Part XXVI and Part XXI.

The pages of this part

Part1 of 28Level1 — FoundationPages10Estimated time11.7 hoursHighest safety levelLevel D

0 / 10 lessons in this part completed

• BuildThe Camera Obscura: An Image Without ChemistryA150 min
• LessonSilver Salts and Light: Schulze to Ritter45 min
• LessonWedgwood, Davy and the Problem of Permanence40 min
• ExperimentExperiment: The Image That Would Not StayA120 min
• LessonNiepce and Heliography: Light That Hardens40 min
• LessonDaguerre and the Daguerreotype: A Mirror With a MemoryD45 min
• LessonTalbot: Photogenic Drawing, the Calotype and the Negative-Positive Principle50 min
• LessonHerschel: Hypo, Prussian Blue and the Words of Photography45 min
• AssignmentAssignment 1: A Botanical Cyanotype Photogram, After AtkinsA120 min
• Lesson1839 and the Many Inventors of Photography45 min