Salted paper print

Salted paper is the simplest silver print that can be made and the process against which every later paper is best understood, because the others differ from it in one variable: where the silver sits. Put the same chemistry in a protein layer on the surface and you have an albumen print; put it in gelatin over baryta and you have a modern paper. Here there is no layer at all. The chemistry is established on Talbot’s page, and the substances on the silver nitrate and sodium citrate pages.

The chemistry

Two coating steps, made independently, and that independence is the whole craft of the process.

Salting. A chloride goes into the paper first and dries there. It need not be sodium chloride: the Getty atlas records that a salting solution is often sodium citrate and ammonium chloride, and Reilly gives a plain variant of 20 g of sodium chloride, 20 g of sodium citrate and 2 g of gelatin per litre. The citrate is not a second chloride. It is a halogen acceptor, and it changes the print.

Silvering. Silver nitrate is floated or brushed on and meets the chloride in the fibres, so silver chloride precipitates in place with a large excess of unreacted silver nitrate around it. That excess is the mechanism rather than the waste: light splits silver chloride into silver and chlorine, and if nothing takes the chlorine out of circulation it recombines and the image goes backwards.

⚗What the halogen acceptor buys, and one thing the course cannot explain

Reilly reports the visible consequence of adding a neutral citrate: “the addition of a neutral citrate will cause the prints to be more reddish in color and slightly more ‘brilliant’.” Ware’s account of the printing-out papers describes the same job being done in the later materials by an added halogen absorber, and in albumen paper by the albumen itself, which acts as a scavenger for the chlorine.

Why absorbing the halogen should shift the colour towards red is not explained by any source this course has read, and the page does not supply a reason. Reilly’s own caveat belongs with the observation: the porosity of the paper stock remains the largest single factor in the result.

The exposure is printing out: light does the whole job and you stop when the print looks right. Two published figures bracket what that costs, and the course carries both rather than choosing. Reilly, from the practical side, puts printing out at up to 100,000 times the light energy of developing out — five orders of magnitude. Ware, from the photochemical side, puts the exposure needed to form visible photolytic silver at “in the order of a million” times that needed for a latent image — six orders. They differ by one order because they are measuring different things: Reilly compares two materials as used, Ware compares two photochemical end points in the same material. Part XXII takes the arithmetic apart and shows where the orders of magnitude go — not into absorption, which is much the same either way, but into what happens after the photon is absorbed.

Either figure gives the same practical verdict: every salt print is a contact print, and the process needs a negative of long density range rather than one made for an enlarging paper.

Historical workflow

Talbot explains it to a general reader in The Pencil of Nature, under a leaf: the first process gives a white image on a darkened sheet; that sheet is washed with a fixing liquid; it is then laid on a second sheet of sensitive paper, pressed into close contact and put in the sun, “this second process is evidently only a repetition of the first”. The second sheet comes out with the ground white and the image dark.

The mature nineteenth-century sequence adds two operations between exposure and drying, and both are load-bearing. Rinse first, in plain water, because a print-out paper is made with excess silver nitrate and thiosulfate meeting free silver nitrate throws down brown silver sulfide in the sheet. Then tone, which after 1847 usually meant gold, and which the Getty atlas ties to the visible change in the family’s colour. Then fix, and then wash properly.

The industrial scale of it is worth recording because it is where the permanence evidence comes from. Ware’s chronology dates the Reading establishment under Nicolaas Henneman to January 1844 — the first attempt at printing photographs in quantity — and the six fascicles of The Pencil of Nature between 1844 and 1846 carry twenty-four plates, every print made by hand, in sunlight, and pasted in.

The image

Colour. Untoned, the Getty atlas gives a tonality between light brown and reddish brown on prints made before gold toning became usual after 1847. Gold shifts it colder and more purple, and chloroauric acid explains the mechanism: the printed-out silver is nanoparticulate, so its surface area relative to its mass is enormous, and gold partially replaces the silver at the particle surface, coating it and shifting the colour.

Surface. Matte and sunken in, with the fibre visible, because the image is in the paper. On a light table there is enough translucency to read the watermark.

Sharpness. Softer than a plate process. The atlas notes that a print from a paper negative is less sharp because the negative’s fibres scatter the light passing through them, and that well-waxed negatives reduce the effect without abolishing it.

Variation between copies. Talbot was honest about this in print: 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” and on papers whose sizing differs between batches by secrets of the trade. Asked which tint was best, several persons of taste offered nothing approaching unanimity, so he printed them as they came.

Permanence

The permanence of a salt print is a fact about how it was processed, not about what it is. That sentence is the most useful thing in this entry, and the evidence for it is a controlled comparison history ran by accident.

At Reading, prints were fixed in the strong baths the manuals of the 1850s specify, 10 to 30 per cent, and washed in three changes of hot water for ten minutes each. Schaaf traces the severe sulphide fading of The Pencil of Nature plates mainly to residual thiosulfate and to Reading’s water supply. In Scotland, where Talbot’s patent did not run, the St Andrews group abandoned his halide fixing for Herschel’s hypo, Cundell published a 2.5 per cent fixing bath in 1844, and Ware describes Hill and Adamson’s salt prints as notable for rich colour, high density and good stability, comparable with the best Talbot made himself. Ware’s explanation is deflating and probably right: not a secret ingredient but dilute hypo and scrupulous washing.

Two failure modes follow from the chemistry rather than the workmanship. Over-fixing loses the image, because print-out silver is colloidal and easily oxidised in the presence of thiosulfate, and there is a colour cost as well — the rich print-out black shifts to a weaker dull brown on fixing, which the Getty atlas records as the reason printing-out papers are deliberately overprinted. Under-washing builds a slow bomb, because thiosulfate left in the paper converts image silver to silver sulfide over years, taking a rich brown down to a pale buff.

Gold toning is the countermeasure, and it was reached empirically: the Photographic Society of London’s Fading Committee of 1855 reported imperfect washing, an old or insufficiently acidic hypo bath, acidity in the mounting materials and atmospheric sulfur as the causes, and recommended thorough washing and toning with gold chloride — the two controls this course still teaches, arrived at a century before anyone could photograph a nanoparticle.

Hazards

Silver nitrate, at printing strength and handled wet, which the rubric names explicitly under Level B; thiosulfate fixing, which is mild; and gold toning, whose own level is set by chloroauric acid at Level B. The wash and the fixer are silver-bearing and belong to the silver recovery stream rather than to a drain.

One historical hazard is worth naming because a reader will meet it in period texts: nineteenth-century photographers made their own gold chloride by dissolving gold coins in mixed nitric and hydrochloric acids and evaporating. Reilly says plainly that because of the fumes and the concentrated acids this is not a procedure for a home laboratory, and this course agrees.

Where the course teaches it

Part XXII, Salted Paper: The First Silver Print, owns it, and it is a whole part rather than a lesson.

Printing Out: Silver Chloride Made and Darkened in the Paper is the chemistry this entry compresses: why a sheet is salted first and silvered second and why the order cannot be reversed, what the unreacted silver nitrate is actually for, photolysis without development, self-masking, the arithmetic of speed — and the one thing a reader of this page most needs, that what the fixer does here is unlike anything in Part XI, because it gives back part of the picture.

Lab: Salting and Sensitising a Sheet of Paper, Level B, is the first half of the practice: a batch of salted sheets that keep indefinitely, a silver bath made and labelled, five sheets sensitised under a working light you can see by, and a mass balance that says where every milligram of silver went. Lab: Printing, Toning, Fixing and Washing a Salt Print is the second: exposing by inspection until the print is visibly too dark, a first wash, a gold toner judged by eye, a fixer weaker than anything else in the course, and a wash you test rather than time.

Gold Toning and the Permanence of a Printed-Out Silver Image takes up this entry’s central claim and argues it properly: for a nanoparticle silver image colour and lifetime are the same subject, the four gold toner families are distinguished chemically, and the permanence argument is given in full alongside the half of permanence that no toner fixes.

The Variants of the Salt Print and How a Conservator Identifies One sets out the binder ladder from plain paper to pure albumen and the signatures — visual, microscopic and analytical — by which the results are told apart. And Break/Fix: The Printed-Out Image That Faded works six failures as diagnoses, on the question this entry’s permanence section turns on: what a faded print can and cannot tell you about its own processing.

Two earlier parts still bear directly on it — the fixing chemistry of Part XI and the washing and permanence work of Part XII, both of which this process depends on being understood before its own weak fixer makes sense.