Van Dyke Brown sensitiser

Three bottles of water, three weighed solids, and a silver print on any paper you like. The Van Dyke Brown sensitiser is the cheapest of the hand-coated silver processes this course teaches and the least demanding of them, and its cheapness is not a compromise: the picture is metallic silver among the paper fibres, exactly as in a salt print, made by a route that needs no halide, no developer and no strong fixer.

What has to be understood before anything else on this page makes sense is that the silver in it is not the light-sensitive part. Light acts on the iron. The iron(II) that light makes then reduces the silver, and everywhere the light did not reach, the silver simply washes away. Every characteristic fault of the process — the yellow highlights, the print that faded in a drawer, the image bleached away in the fixer — follows from that division of labour, and none of them is a speed problem.

Solution A — the light-sensitive half

Ingredient	Quantity	Form the source specifies
Ammonium iron(III) citrate	9 g	the green variety, which the kit supplies and which Ware's comparison table puts at 14 to 18 per cent iron against the brown salt's 19 to 28
Water	33 mL, added	at 20 °C; Distilled or demineralised water, and an added volume rather than a make-up volume: the sheet's instruction is "place the water in a mixing container and add the solid", so 33 mL is what goes in and not what comes out. The container for this solution must hold more than 100 mL, because the other two are poured into it.

Solution B — the acid

Ingredient	Quantity	Form the source specifies
Tartaric acid	1.5 g	the L-(+) acid, CAS 87-69-4, which is what the safety data sheet bundled with the kit covers
Water	33 mL, added	at 20 °C

Solution C — the silver

Ingredient	Quantity	Form the source specifies
Silver nitrate	3.8 g
Water	33 mL, added	at 20 °C

Mixed in this order — the sensitiser, mixed once and kept in a brown bottle

1. Start with the whole of Solution A — the vessel that receives the other two, so it must hold more than 100 mL
2. Then add the whole of Solution B — stirred in until the mixture is homogeneous
3. Then add the whole of Solution C — slowly, stirring while it goes in

In a darkroom using a red safety light, add Solution B to Solution A. Stir to ensure it is homogeneous. Slowly add Solution C to the combined mixture of Solutions A and B. Stir the mixture while Solution C is being added. A precipitate may or may not form. If a precipitate should form, disregard it. Store the resulting sensitizer in a brown bottle in a darkroom. It will remain active for months.

The sheet states no make-up volume for the combined sensitiser. It says only that the kit "makes about 100 ml of sensitizer solution", which is the three 33 mL portions of water plus whatever volume the 14.3 g of solids occupy. Every strength quoted on this page is therefore computed against that stated approximate 100 mL and is nominal, not a figure the source publishes — the shortfall recorded as open item 9 in docs/FORMULARY-SCHEMA.md, where a combined bath has no make-up volume the schema can hold. The order matters and the sheet gives it without a reason; the reason the course reads into it is under Mixing.

Purpose

To coat plain paper with a solution that will print out a brown silver image under ultraviolet light, and to do it with three chemicals that cost almost nothing. The sensitiser is the whole of the light-sensitive chemistry: there is no developer, because the image forms during the exposure, and the two baths that follow it — plain water, then a very dilute thiosulfate — remove what the light did not use rather than build anything.

Photographers’ Formulary’s own framing of the kit is worth having, because it names the family relationship precisely: the process “is similar to the Kallitype process in that the image is formed from silver metal. The Van Dyke process, however, uses ferric ammonium citrate as the sensitizer while the Kallitype process uses ferric oxalate.”

Recommended uses

Contact printing from a large-format or digitally enlarged negative, on to a cotton rag paper chosen for its surface as much as its purity. The sensitiser is far too slow for an enlarger, so the print is the size of the negative and the paper is part of the picture.

Proofing negatives made for the more expensive iron processes. A Van Dyke spends 3.8 g of silver nitrate on about twenty-five 8 by 10 prints where a palladiotype spends a platinum-group metal, and it uses the same coating rod, the same contact frame, the same ultraviolet source and a negative of broadly the same character. Ware makes this argument for the whole iron-silver group: they are useful “as an introduction to alternative printing for teaching workshops, for proofing large format negatives, and as a starting point for further toning of the colloidal silver image”.

Learning what printing out is, by watching it. The image appears during the exposure and is judged by eye, which makes it the clearest demonstration in the course that a print-out image and a developed-out one are two ways of finishing the same chemistry rather than two chemistries. The kallitype is the other half of that demonstration and differs by exactly one tray.

Work that is going to be toned. Bostick & Sullivan’s gold and palladium toner kits both name Van Dyke prints in their titles — “Gold Toning Kit for Printing Out Paper (POP)… also works for Van Dyke, Kallitype, Albumen and Salt Prints”, and “Palladium Toner Kit for POP, Vandyke, and Kallitype” — and in both the toning is done before the thiosulfate bath rather than after it. Ware makes that sequence a rule for the whole family.

When another formula is preferable

• For a print you intend to last without toning, Ware’s argyrotype is the better-reasoned formula and was designed to fix precisely this one’s two weaknesses. It replaces silver nitrate with silver sulfamate made in the beaker, on the grounds that nitrate is an oxidising anion which attacks the colloidal image during wet processing, and it runs the whole process at about pH 3.5 in a single bottle whose contrast is adjusted with more acid.
• For an image whose colour you choose at the development stage, the kallitype puts the silver in the same place by the same photochemistry but develops it out, and the developer chooses the tone. Wall’s 1912 dictionary lists four kallitype developers — built on borax, Rochelle salt and sodium tungstate — giving pure black, sepia, warm maroon and purple from one sensitiser.
• For the same photochemistry without any silver at all, the classic cyanotype sensitiser uses the same iron salt, with potassium ferricyanide in place of the silver, needs no fixer and washes in water. If the objection to a Van Dyke is the silver nitrate rather than the blue, that is the answer.
• For a silver image made directly from a silver halide, the salted paper sensitiser reaches the same warm brown by precipitating silver chloride in the sheet and printing it out. It is the older process, it needs no iron, and it needs a great deal more silver.
• For permanence above argument, print in platinum or palladium — and note that you cannot do it with this sensitiser. The iron(III)/iron(II) citrate couple that Ware puts at +0.372 V reduces gold at +1.00 V and silver at +0.80 V and does not reduce platinum at +0.73 V or palladium at +0.62 V under printing conditions. That is why the platinotype had to wait for ferric oxalate, and the citrate’s own page records that the potentials alone do not fully explain the division.

Mixing

Three solutions, made in the light; one mixture, made in the dark. The sheet is explicit that the separate solutions are not light-sensitive and may be mixed in strong light, and that the combination is, so the final step belongs under a red safelight or in very subdued light.

1. Solution A. 33 mL of distilled or demineralised water at 20 °C in a container holding more than 100 mL — everything ends up in this one — and 9.0 g of ferric ammonium citrate stirred in until dissolved.
2. Solution B. 33 mL of the same water, 1.5 g of tartaric acid, mixed the same way.
3. Solution C. 33 mL of the same water, 3.8 g of silver nitrate, mixed the same way.
4. Under a red safelight, add B to A and stir until homogeneous. Then add C slowly, stirring while it goes in.
5. Bottle in brown glass and keep it in the dark.

⚗Why B goes in before C, when the sheet does not say

The sheet gives the order and no reason. The reason the course reads into it comes from the closest published relative, and it is stated there in one sentence.

Ware’s argyrotype sensitiser is the same three things — a citrate of iron(III), an acid and a soluble silver salt — in different proportions with a different acid. His note on why it carries a 20 per cent excess of sulphamic acid over the amount needed to make the silver salt is this: the excess “gives a pH of ~3.5, which suppresses hydrolysis of the iron(III) and helps keep the silver in solution - otherwise silver citrate may precipitate out. This pH is also the optimum for the photosensitivity.”

Read that against the Formulary’s own next sentence — “A precipitate may or may not form. If a precipitate should form, disregard it” — and the order stops looking arbitrary. The acid goes in before the silver so that the silver never meets an unacidified citrate solution. Adding C first, or quickly, or without stirring, gives the silver a moment of exactly the local conditions Ware says throw silver citrate down.

What is inference and what is not. That acid suppresses iron(III) hydrolysis and holds silver against citrate precipitation in an iron-silver citrate sensitiser is Ware’s statement about his own formula, and it is evidence. That it is why the Van Dyke uses 1.5 g of tartaric acid, and why B precedes C, is the course’s reading and no source read states it.

Do not skip the “slowly”. It is the only word in the mixing instruction that is doing physical work. A silver nitrate solution poured in one go into a stirred citrate solution creates a transiently high local silver concentration at the point of entry, and that is where a precipitate forms if one is going to.

A precipitate is not a failure. The sheet says to disregard it, and the sensitiser is used as it stands. What it does mean is that some fraction of your silver is no longer in solution and will not coat evenly; if a batch throws down a great deal, the honest response is to make it again more slowly rather than to filter it and hope, because you now do not know the strength of what is left.

Distilled or demineralised water throughout, which the sheet specifies and which the wash instructions then explain: dissolved iron and alkalinity in a tap supply are the two things that spoil this process, and there is no reason to introduce either at the start.

Weigh in a room where nothing else is being coated. The silver nitrate is 3.8 g of an oxidiser and a caustic; see the SOP for weighing a solid and the one for handling silver nitrate.

🧮What the mixture actually contains

The sheet states no make-up volume, only that the kit “makes about 100 ml of sensitizer solution”, so every strength below is nominal and computed against that stated approximate hundred millilitres.

9.0 % w/v ammonium iron(III) citrate · 1.5 % w/v tartaric acid · 3.8 % w/v silver nitrate

Nominal strengths in the mixed sensitiser

That is the arithmetic a reader needs in order to compare this formula with anything else, and it is the course’s arithmetic rather than the supplier’s statement. It is also why the comparison in Variants is worth making: at 3.8 per cent silver nitrate this is a much weaker sensitiser than the argyrotype and a very much weaker one than a salt print’s silver bath, which Reilly gives at 12 per cent.

Behaviour

It prints out, and that changes how you work. There is no development stage, so there is no latent image to be uncertain about and no test strip that is strictly necessary: you look at the sheet in a split-back frame and stop when it looks right. What “right” means is the one piece of craft that has to be learned, because the print is nothing like finished when it comes out of the frame.

It darkens three times after the exposure. Bostick & Sullivan quantify the whole sequence: stop the exposure at about half the intended final darkness; the print will be about three-quarters of the way there when it leaves the fixer; and it darkens further as it dries. Ware puts the dry-down of the closely related argyrotype at “at least one Zone”, which is a stop. A print judged correct in the frame will be far too dark on the wall.

The first bath is a wash, not a developer, whatever the sheet’s heading calls it. Nothing is built there. The yellow that lifts off is unreduced sensitiser, and the print looks as though it is developing only because removing a yellow veil from a brown image makes the brown look stronger.

The two suppliers disagree about how long that first bath should be, and the disagreement is instructive rather than troubling. The Formulary says about one minute in running soft water; Bostick & Sullivan say three to five minutes in tap water, changed after eight to ten prints, and note that warm water at about 32 °C shortens it considerably. Neither explains itself. The course’s reading is that the two are optimising different risks: a longer wash removes more iron, which is what governs permanence, while a shorter one exposes the still-unfixed colloidal silver to less running water, which is what governs density. Ware, working on the same chemistry, resolves it by changing the water rather than the time — de-chlorinated water with a little citric acid, because chlorinated tap water attacks the silver nanoparticles while they are at their most vulnerable.

The fixer intensifies before it destroys. The print visibly darkens and shifts from red towards brown in the thiosulfate. That is not the fixer “bringing out” a latent image; it is a surface chemical change in the silver particles, explained under The mechanism. Both sheets warn in the same breath that going on too long bleaches the print, and the Formulary adds the sharpest instruction on the page: do not use an ordinary photographic fixer, because it will etch the finely divided silver off the paper.

Humidity is a working variable, not a nuisance. The reduction of silver by iron(II) needs the ions to be able to move, and in a “dry” coated sheet the only solvent is the few per cent of water the paper holds from the room. Ware demonstrates the consequence on the argyrotype: the image colour can be shifted from brown towards a purplish grey simply by humidifying the coated paper over water for thirty minutes before exposure, and he adds glycerol to his sensitiser as a humectant for the same reason. No source read for this page tests humidification on a Van Dyke; the chemistry is the same and the experiment is under Experiments.

Image characteristics

Colour. Warm brown, and the mechanism is particle size and surface chemistry rather than any added pigment. Ware’s account of nanoparticle silver is that pure particles of about 10 nm appear yellow-orange, that a thin coating of silver sulfide acquired in the thiosulfate bath “deepens the colour of nanoparticle silver to a more satisfying brown”, and that complete conversion weakens it again to a drab buff. The colour of a Van Dyke is therefore not one thing: it is set by how large the particles grew during the printing-out, which depends on humidity, and by how far the sulfiding went, which depends on the fixer.

Tonal scale. Long and self-masking. As the shadows darken they absorb the light that would darken them further, so a negative with a long density range can be accommodated by exposing longer — the opposite of the behaviour of an enlarging paper. The Formulary says a density range up to 1.85 can be used and calls the process “capable of an extremely long tonal range”; Ware wants 2 to 2.4 in the ultraviolet for the argyrotype. Either way the negative is a special negative.

Contrast. Low, in the sense that matters to a printer: a process that can accommodate a negative of 1.85 density range is a process of long exposure scale, and a negative made for an enlarging paper will print flat on it. Raising it is the difficulty. The only contrast control published for this sensitiser in any source read here is a chromium(VI) salt added to the first bath, which this course does not give as a procedure; see Safety. Ware’s redesign moved the contrast control into the sensitiser, where it belongs, by making it a function of added acid.

There is a third lever, and it costs nothing. Ware’s chapter on reciprocity in print-out silver records that high-intensity reciprocity failure is itself a contrast control: “exposure to bright sunlight brings about less photographic action than a proportionally longer exposure to a clear North sky; the shadow areas of a picture will not print as dark under an exposure to bright sunlight, as they will under the same exposure to a lesser illumination for a proportionally longer time, to produce the same highlight values.” He names Burton and Towler recommending the choice of illumination for exactly that purpose, and Crawford and Reilly describing the phenomenon explicitly. That chapter is written about salted paper rather than about Van Dyke, so the course reports it as a property of print-out silver and not as a measured figure for this formula — but it is testable in an afternoon, and it is under Experiments.

Surface. Metal among the fibres with no binder over it. The paper’s texture, colour and sizing are all visible in the finished print, and two papers will give two different pictures from one negative.

Sharpness. Set by the contact rather than by the chemistry, with one caveat that matters: Bostick & Sullivan recommend hot-pressed papers because they “produce a denser, sharper image with smoother transitions”, and Ware warns that a humidified sheet can damage a negative in contact unless a thin polyester film is interposed — which itself costs a little sharpness.

🧮How little silver is actually in the picture

Ware’s measurement is for salt prints rather than Van Dykes, and the extrapolation is the course’s, but the order of magnitude is worth having because it explains the whole permanence question.

Analyses of contemporary salt prints made in 1855 found that only about 2 per cent of the silver originally taken up by the sensitised paper remained in the final image, a coating weight of about 0.1 g per square metre. On that basis a whole-plate print carries about 3.3 mg of silver in total — “a piece of silver metal the size of a small pinhead weighs about 10 mg, so it would take three typical prints to supply even this much”.

Now the arithmetic for this formula. The molar mass of silver nitrate is 169.87 and that of silver 107.87, so 3.8 g of the salt carries 2.41 g of silver per 100 mL. At the sheet’s own brush-coating rate of 4 mL for an 8 by 10:

4 mL × 2.41 g / 100 mL ≈ 0.097 g of silver

Silver applied to one 8 by 10 sheet

An 8 by 10 inch sheet is 0.052 m², so at the salt print’s coating weight of 0.1 g/m² the image would hold about 5 mg — around five per cent of what was applied. The other ninety-five per cent leaves in the wash and the fixer. That is why those two baths are silver-bearing waste rather than rinse water, and it is why an image made of five milligrams of metal with no binder over it is as vulnerable as it is.

The mechanism

The process is a siderotype: light acts on iron, and the metal that ends up in the paper is whichever one the iron(II) was able to reduce. Ware’s summary of what every iron-based process has in common is the place to start — “under UV light, iron(III) reacts with oxalate to give iron(II) and carbon dioxide gas” — with the reaction written in dissected form so that the electron bookkeeping is visible.

2 Fe³⁺ + C₂O₄²⁻ → 2 Fe²⁺ + 2 CO₂

Ware's dissected form of the light reaction in an iron(III) carboxylate

Two electrons cross from the organic anion to two iron(III) ions, and the ligand is destroyed in the process, leaving as carbon dioxide. In this formula the ligand is citrate rather than oxalate, and Ware is explicit that the same principle holds with “a chemistry similar in principle, but rather more complicated with the citrate ion”. How much more complicated is set out on the citrate’s own page: the photo-active species is a dimer, the quantum yield peaks around 0.45 at 365 nm and pH 4, the organic photoproduct has been identified as acetone dicarboxylic acid — and the nature of the iron(II) photoproduct remains unknown, which is why no balanced citrate equation appears here or there.

The second step is the one that makes it a silver process. Ware writes it for platinum and states the rule that governs the stoichiometry: “it takes two iron(II) to make one atom of platinum, because two electrons are needed to balance the charges. These ratios are important in formulating the sensitizer solution correctly.” Silver(I) needs one electron, so the ratio is one to one.

Fe²⁺ + Ag⁺ → Fe³⁺ + Ag

The image, written as Ware writes the platinum step, with silver's single electron in place of platinum's two

Herschel found this in 1842 and described it as a development rather than a print-out. Having shown in article 210 that leaving the cyanide salt out of a cyanotype coating still leaves a paper “apparently little, but in reality highly sensitive” — four or five seconds of sun produce a change “quite imperceptible to the eye”, yet a subsequent wash of ferrosesquicyanate, which is ferricyanide, brings up “a considerable deposit of Prussian blue… on the part sunned, and none whatever on the rest” — he applied the same logic to metals. Article 212 is the chrysotype: ammonio-citrate paper, dried to “a good yellow colour, not at all brown”, exposed, then washed with a neutral gold solution “of such strength as to have about the colour of sherry wine”, whereupon “instantly the picture appears”. Article 218, in the postscript added on 29 August 1842, substitutes silver for the gold: “a very sharp and beautiful picture is developed, of great intensity. Its disclosure is not instantaneous; a few moments elapse without apparent effect; the dark shades are then first touched in, and by degrees the details appear… The picture may be fixed by the hyposulphite of soda.”

The Van Dyke’s one structural innovation over Herschel is putting the silver in the sensitiser. That is what turns a developed-out process into a printed-out one, and everything else on this page follows from it.

Deeper: why the paper must not be truly dry

Ware states the obstacle plainly for the traditional platinotype: the reduction of the noble metal “does not take place in the dry sensitizer, because the ions… are immobile and cannot encounter one-another. Only when dissolved in water are they free to roam.” A dry Van Dyke coating ought, therefore, not to print out at all.

It does, and the reason is that no air-dried sheet of paper is dry. Ware’s account of the modernised print-out platinum route gives the figure: “at normal relative humidity - around 70% - paper contains about 8% by weight of water”, and under those conditions the platinum image forms during the exposure and needs little or no development afterwards. The same water is what lets iron(II) and silver(I) meet in a Van Dyke.

Three consequences follow, and all three are practical.

• Over-drying costs you the image. Ware warns that over-rapid drying “may worsen loss of image substance in the wet processing”, and asks for an ambient relative humidity between 50 and 90 per cent for the argyrotype.
• Humidity changes the colour, because it changes the rate at which silver is deposited and therefore the size of the particles. Thirty minutes over water at 100 per cent relative humidity takes an argyrotype from brown towards purplish grey.
• A hair dryer is a variable you have not controlled. The Formulary permits one with a warning not to overheat; Bostick & Sullivan say their own testing found natural drying gives a superior image. Both cannot be optimal, and the difference between them is almost certainly this.

Deeper: the redox arithmetic, and how near this formula runs to stoichiometric

One iron(II) reduces one silver(I). It is therefore worth knowing how many of each the formula puts on the paper, and the answer is a surprise.

The silver is easy: 3.8 g of silver nitrate at a molar mass of 169.87 is 0.0224 mol. The iron is harder, because ammonium iron(III) citrate is not a compound and has no molar mass — its iron content runs from 14 to 28 per cent by weight depending on the grade, and Ware puts the green variety the kit supplies at 14 to 18 per cent.

9.0 g × 0.14 to 0.18 = 1.26 to 1.62 g of iron = 0.0226 to 0.0290 mol

Iron in 9.0 g of the green salt

So the molar ratio of iron to silver in this sensitiser is between about 1.0 and 1.3 to one — at or barely above the one-to-one the electron bookkeeping demands.

Ware’s argyrotype, designed from the chemistry upwards a hundred and fifty years after Herschel, carries 22 g of the same green salt and 7 g of silver(I) oxide per 100 cc. At his own stated 16 per cent iron that is 0.0630 mol of iron against 0.0604 mol of silver: 1.04 to one. Two formulas, arrived at independently, land on the same molar ratio while differing by a factor of 2.7 in concentration.

⚗What that near-equality does and does not tell you

It is tempting to read a one-to-one loading as meaning that all the silver is available to all the iron, and it does not. Only the fraction of the iron(III) that light actually reduces becomes iron(II), and that fraction is small: the exposure is a matter of minutes at a quantum yield of at most 0.45, and the arithmetic under Image characteristics says roughly five per cent of the applied silver ends up in the image. The one-to-one loading is a ceiling, not a yield.

What it does tell you is that neither component is present in the large excess a cyanotype’s iron is over its ferricyanide, and therefore that raising or lowering either one changes the ceiling directly. It also tells you that this is a formula with very little slack in it, which is consistent with the supplier’s report that the sensitiser keeps for months but not indefinitely: any dark reaction that consumes iron(II) or silver eats into a stock that has no margin.

This is arithmetic, not a source’s statement. No source read for this page computes the ratio, and the iron content of the salt in your bottle may not be the 14 to 18 per cent Ware gives for the green grade. Record your supplier and batch.

Deeper: what the thiosulfate bath actually does

The bath is 5 per cent sodium thiosulfate on both suppliers’ Van Dyke sheets, against 40 per cent in a plain hypo fixing bath and 15 per cent in Reilly’s alkaline bath for salt prints; Ware uses 2 to 2.5 per cent for the argyrotype. That descending series is not fashion. It is the accumulated recognition that a print-out silver image is dissolved by its own fixer.

One supplier contradicts itself, and it is worth knowing about. Bostick & Sullivan’s Van Dyke sheet gives 50 g of thiosulfate to the litre — 5 per cent. Its gold toning kit, whose title names Van Dyke prints, gives 100 g to the litre and a ten-minute fix. Its palladium toner kit, whose title also names Vandyke prints, gives “15% Sodium Thiosulfate (hypo) solution, 150 grams to one liter water… In practice, a 10-20% solution works fine”, for three minutes. Three figures spanning a factor of four, from one supplier, for the same kind of print. The course reports the discrepancy rather than picking a winner, and notes only that the two toning sheets are written for printing-out papers first and iron-silver prints second, and that the direction of the error a too-strong bath causes is the one this page has been describing.

It does three things at once, and only the first is fixing.

One: it removes the silver the light did not use. Unreduced silver is carried out as the soluble argentothiosulfate complex.

Ag⁺ + 2 S₂O₃²⁻ → [Ag(S₂O₃)₂]³⁻

What is left of the sensitiser leaving as a soluble complex

Two: it partially sulfides the image, which is why the print darkens. Ware’s explanation of the colour shift in the argyrotype’s thiosulfate bath is that the silver nanoparticles acquire a coating of silver sulfide “only to a depth of a few atoms, perhaps even a monolayer - but sufficient to modify their colour profoundly by its effect on the surface plasmon resonance absorption spectrum”. He records supporting evidence: energy-dispersive X-ray analysis of argyrotypes by Ellie Young at the Royal Melbourne Institute of Technology found sulfur as well as silver in the image. Because silver sulfide is very insoluble and stable, he reads the effect as mildly protective — a partial protective toning the process gets for free.

Three: given time, it destroys the image. The same reaction that coats the particles will convert them. Ware’s figure is stark: complete conversion of nanoparticle silver to silver sulfide “causes a drop in the optical density by a factor of about 30”, and the colour weakens from brown back to a drab buff. Add to that his separate observation that “the colloidal silver constituting the print-out image is easily oxidised by air in the presence of thiosulfate ions”, so that over-long immersion, too concentrated a bath, or oxidising impurities in the water all cost density, and the Formulary’s instruction not to exceed five minutes stops being arbitrary.

!The wash before the fixer is not optional

Ware names it as the first of three pitfalls in thiosulfate-fixing a print-out paper: “the excess silver nitrate present must be washed out with water, in which it is highly soluble, before applying the thiosulphate, otherwise the image will be seriously stained with brown silver sulphide resulting from the reaction of thiosulphate with silver nitrate.”

That is the entire justification for the plain-water bath that both sheets put first, and it is the reason a Van Dyke cannot simply go from the frame into the fixer. It is also, incidentally, the reaction on which the standard test for residual hypo is founded.

Function of every ingredient

Ammonium iron(III) citrate, green variety, 9.0 g in solution A, giving a nominal 9 per cent w/v in the mixed sensitiser. What it is: the ammonium salt of an iron(III)–citrate complex, and not a compound in any strict sense — a family of complexes made by precipitating ferric hydroxide and dissolving it in citric acid, whose iron content is found anywhere between 14 and 28 per cent by weight. The green grade the kit supplies is the acidic form Valenta first prepared in 1897; Ware puts its iron at 14 to 18 per cent against the older brown salt’s 19 to 28. Why it is here: it is the only light-sensitive substance in the formula. What it does: absorbs near-ultraviolet and blue light, and its iron(III) is reduced to iron(II) at the expense of the citrate ligand, which is oxidised and loses carbon dioxide. Photographic consequence: it sets the speed, and it sets the ceiling on how much silver can be reduced, because every atom of image silver required an iron(II) to make it. More of it: faster printing and a higher possible maximum density, at the cost of more iron to be cleared out afterwards — and residual iron is this family’s characteristic permanence fault. Less of it: slower, cleaner highlights, a lower ceiling. What it interacts with: the silver nitrate, which it must not meet on unacidified terms; the cellulose of the paper, to which iron(III) chemisorbs; alkali and hard water, which hydrolyse it; and humidity, because the solid is hygroscopic and the coating goes tacky. One warning from the kit sheet itself: the solid “is somewhat light sensitive. It should not be stored in bright light.”

Tartaric acid, 1.5 g in solution B, giving a nominal 1.5 per cent w/v and about 0.1 mol/L. What it is: the acid of grapes, 2,3-dihydroxybutanedioic acid, a dicarboxylic acid with two hydroxyls — a member of the small group of vegetable acids whose iron(III) salts are photosensitive. Photographic suppliers sell the natural L-(+) form, CAS 87-69-4. Why it is here: this is the honest gap on the page, and it is worth stating before the reasoning. The kit sheet gives the weight and says nothing whatever about the reason, and no manufacturer, standard text or conservation source read for this course states why the formula uses tartaric acid rather than more citric. What the chemistry of the family says it must be doing: three things, each of them stated by Ware for the directly analogous argyrotype sensitiser. It lowers the pH, which suppresses hydrolysis of the iron(III) — Ware’s clearing chapter records that above pH 4 iron(III) hydrolyses to a polymeric colloidal hydroxide that lodges in the fibres and eventually stains. It keeps the silver in solution, “otherwise silver citrate may precipitate out”. And the acid pH is itself “the optimum for the photosensitivity”. Photographic consequence, and how confident to be about it: in the argyrotype, adding a further gram of acid per 100 cc raises contrast, and Ware explains the mechanism — the extra acid “tends to dissolve silver in the highlights”. Whether the same holds for tartaric acid in this formula is untested in anything the course has read, and the claim is common in practitioners’ notes that are not evidence. More of it: on that reading, more contrast and cleaner highlights, bought by dissolving away some of the faintest values; less of it: the risk of precipitation in the bottle that Ware warns about when he reduces his own acid below the figure he gives. What it interacts with: silver, which Chemical Safety Card 0772 names among the substances it reacts with — the whole point of the mixing order is that the two are brought together deliberately and in sequence; and any alkali, which neutralises it to a tartrate. A historical footnote that is not evidence: Herschel’s article 210 records that “the ammonio- and potasso-tartrate fully possess” the same photosensitivity as the ammonio-citrate, so an iron tartrate is a perfectly good sensitiser in its own right. Whether any tartrate of iron forms in this mixture, and whether that is why the acid is tartaric, is unknown to this course.

Silver nitrate, 3.8 g in solution C, giving a nominal 3.8 per cent w/v and 0.0224 mol of silver. What it is: the standard soluble salt of silver, molar mass 169.87, colourless crystals that blacken in light and on contact with organic matter. Why it is here: it is the image, and it is here in this form for the least interesting of reasons — Ware’s judgement is that “without exception all the iron-silver processes to date have used the most commonly available soluble salt of the metal”. What it does: nothing at all until the exposure is over in the sense that matters, because it is not light-sensitive in this formula. It waits for iron(II) and is reduced to metallic silver, one silver per iron. Photographic consequence: it sets the maximum density, and the particle size it grows at sets the colour. More of it: a higher ceiling on density and more silver to wash and fix out; less of it: a weaker print. What it interacts with — and this is the criticism the argyrotype was built on: the nitrate anion is an oxidiser, and Ware’s objection is that it “tends to dissolve the colloidal image silver during wet processing, especially under acidic conditions”. A sensitiser that is deliberately acid is therefore a sensitiser whose own anion is attacking its image while it is being processed. That is a design fault in the formula, not a mistake in the darkroom, and the only fix is a different silver salt. It also reacts with thiosulfate to give brown silver sulfide, which is why the water bath comes first; with skin protein, giving a stain that is metallic silver and cannot be washed off; and with most metals, so nothing metallic goes near it.

Water, three times, and at a stated temperature. Why it matters: the sheet specifies distilled or demineralised water at 20 °C for all three solutions, and the reason appears later in the same document — dissolved iron and alkalinity are the two impurities that spoil this process, and a tap supply may carry both. What it does here: it is an added volume, not a make-up volume. Thirty- three millilitres go into each beaker; nobody measures what comes out, and the sheet’s only statement about the finished volume is that the kit makes “about 100 ml”. What happens with more or less: the proportions are the formula, and there is no development stage in which to compensate for a stock made up wrong. What it interacts with: everything, at every later stage — the wash water’s hardness and pH decide how much iron stays in the paper, which decides whether the print survives.

What the formula does not contain, and what each omission costs. There is no wetting agent. Ware states flatly that his argyrotype sensitiser “does not penetrate the cellulose fibres of paper effectively unless a surfactant is present”, and that without one the nanoparticle silver may not be retained by the fibres during wet processing — the bleeding that shows as a red-brown stain running off dense areas. There is no humectant; Ware adds glycerol to control the image colour through humidity, and calls the result the difference between a purplish brown and a more yellowish one. There is no contrast control in the bottle, which is the gap the supplier fills with a dichromate in the wash water and which Ware fills with acid in the sensitiser. And there is no preservative of any kind. Ware’s list of the classic cyanotype’s shortcomings records that a ferric ammonium citrate solution “proves to be an excellent nutrient medium for the growth of moulds, which will usually cover the surface within a week or two”, and that thymol will prevent it; the classic cyanotype sensitiser carries that remedy. Whether the acid and the silver in this mixture suppress the same growth, no source read for this page says, and the supplier’s “active for months” does not distinguish a solution that keeps from one that grows something.

Interactions

Tartaric acid with the iron(III) citrate, before anything else happens. Acidifying the citrate solution is the first thing the mixing order does, and on Ware’s account of the same system it is what keeps the iron(III) from hydrolysing and the silver, when it arrives, from coming down as the citrate.

Silver nitrate with the acidified citrate, which is the sensitiser. They coexist in the dark well enough to be sold as a mixture that “will remain active for months”, which is the supplier’s own phrase and the only keeping figure there is. What the sources read do not say is what limits it. Ware reports his own single-bottle argyrotype keeping for a year at least, and for several years in the workshop notes, and says that if it throws down a small black precipitate it should be re-filtered — black being the colour of reduced silver. The course records that observation for the argyrotype and does not transfer it to this formula as a mechanism.

Light with the iron(III), which is the exposure, and nothing else in the bottle is doing it. The sheet’s own claim that “the separate solutions are not light sensitive” sits oddly beside its warning that solid ferric ammonium citrate “is somewhat light sensitive”, and the resolution is Ware’s: light does reduce iron(III) citrate on its own, but “the result is not permanent, because the oxygen of the air will re-oxidise the iron(II) back to iron(III)”. With nothing to reduce, the exposure leaves no trace. Add silver and the iron(II) is consumed before the air can get it back, and the change becomes an image.

Iron(II) with silver(I), which is the picture, and it needs liquid water to happen. In a coated sheet that water is the several per cent the paper holds from the room, which is why humidity is a variable and why an over-dried sheet prints badly.

Atmospheric oxygen with iron(II), which is the competing reaction. Every iron(II) that the air re-oxidises before it finds a silver ion is an atom of image that never formed — Ware’s statement for the iron processes generally is that the photoreduction “is not permanent, because the oxygen of the air will re-oxidise the iron(II) back to iron(III)”. A back reaction of that kind is one of the mechanisms by which a photographic material fails the reciprocity law, and Ware documents reciprocity failure in both directions for print-out silver; whether it is the mechanism here is not something any source read for this page establishes, and Schaaf’s competing explanation — that slower printing simply grows smaller and more fixer-vulnerable particles — is recorded in the same chapter.

Thiosulfate with unreduced silver nitrate, which stains. Brown silver sulfide, immediately, if the print goes into the fixer without its water bath first.

Thiosulfate with the image silver, which is both the finish and the destroyer. A monolayer of sulfide deepens the colour and mildly protects it; complete conversion drops the density thirtyfold. The five minutes on the sheet is the interval between those two outcomes.

Iron(III) with cellulose, which is the permanence problem. Ware’s clearing chapter states that some of the iron(III) “may bind chemically to the hydroxylic functions of the cellulose”, and that above pH 4 it hydrolyses to a polymeric colloidal hydroxide which lodges in the fibres. Worse, if it is not removed before the print dries, it transforms irreversibly into iron(III) oxyhydroxide — the mineral goethite — which dilute acids will not touch. Residual iron then stains the highlights yellow and goes on oxidising the image silver for the rest of the print’s life.

Calcium with all of it. Ware names hardness in the washing water, and a chalk buffer in the paper, as promoting exactly that hydrolysis. This is the chemical reason both suppliers specify unbuffered cotton rag and soft or distilled water, and Ware goes further, soaking chalk-containing papers in dilute acid before coating.

Chlorine with the image, during the first wash. Ware’s instruction for the argyrotype is to avoid chlorinated water at the clearing stage, “when the silver nanoparticles are still highly vulnerable”, using rainwater, charcoal-filtered water, or water boiled and stood, with a little citric acid added to scavenge traces of chlorine and to give a slight acidity around pH 4.

Gold and palladium toners with the print, before the fixer. Bostick & Sullivan’s gold toning kit for printing-out papers states on its own title page that it also works for Van Dyke, kallitype, albumen and salt prints; the working bath is 50 mL of a 2 per cent ammonium thiocyanate stock and 50 mL of a 0.2 per cent gold chloride stock in a litre of water, and the print is fixed after toning, not before. Ware makes the sequence a rule for the whole family: “like all print-out silver images, the gold toning etc., if desired, should be done before the thiosulphate bath.”

Variants

⁇What is a Van Dyke, and who named it?

The disagreement is about the name and the boundary, not about the chemistry. Ware’s account is that “towards the end of the nineteenth century, Herschel’s argentotype process, which had long since fallen into desuetude, suddenly fathered a whole family of derivative iron-silver processes: Van Dyke Brown; Kallitype (kalli = beautiful); Sepiaprint; and Brownprint”, which he calls “the self-descriptive names for these essentially similar processes”. That is the course’s position: one chemistry, several trade names, and no meaningful line between Van Dyke Brown and brownprint.

What no source read for this page establishes is who first published the three-solution formula, when, or why it is called Van Dyke. The name is widely said to come from the brown pigment used by the painter Anthony van Dyck, and the course found no manufacturer, standard text, museum or conservation publication that documents the derivation — only practitioners’ accounts, which under this course’s research standard are for discovery and not for evidence. Wall’s 1912 dictionary and his 1924 Photographic Facts and Formulas both carry the kallitype at length and neither prints a Van Dyke; the American Institute for Conservation’s wiki page bearing the process name is an empty stub.

What the course therefore says: the chemistry and the family relationship are well attested and are set out above; the modern quantities come from a supplier’s kit sheet; and the origin of the name and of the particular numbers is an open question rather than a settled story. If a reader can point to a nineteenth- or early-twentieth-century printing of these quantities, this page should be rewritten around it.

Ware’s argyrotype. Not a variant of this formula but a redesign of it, and the most useful comparison on the page. Ware’s own dating is not quite consistent: his web account says he revisited the chemistry in 1990 and first published the process in the British Journal of Photography of 13 June 1991, while his workshop handout says it was devised in 1991. Sulfamic acid 7 g and silver(I) oxide 7 g are reacted in hot water to make silver sulfamate in the beaker — a soluble silver salt with a non-oxidising anion, which cannot be bought — then 22 g of green ammonium iron(III) citrate and about 1 cc of glycerol, made up to 100 cc.

	Van Dyke, this page	Argyrotype
Iron salt	ammonium iron(III) citrate 9.0 g	ammonium iron(III) citrate 22 g
Acid	tartaric 1.5 g	sulfamic 7 g, ~20 % more than reacts with the silver
Silver	silver nitrate 3.8 g	silver(I) oxide 7 g, as silver sulfamate
Silver content, per 100 mL	2.41 g	6.52 g
Molar Fe : Ag, at 16 % iron	about 1.15 : 1	about 1.04 : 1
Stated pH	none published	about 3.5
Contrast control	a dichromate in the wash water	more acid in the sensitiser
Wetting agent	none	Tween 20, about 0.5 %
Humectant	none	glycerol 1 cc
Bottles	three, then one	one
Fixer	5 % thiosulfate, 5 min	2 to 2.5 % thiosulfate, 2 to 3 min

The silver figures are the course’s arithmetic from the published weights: 3.8 g of silver nitrate at 169.87 g/mol carries 2.41 g of silver, and 7 g of silver(I) oxide at 231.74 g/mol carries 6.52 g. Ware’s own note that 7 g of sulfamic acid is a 20 per cent excess over the 5.87 g needed to react with 7 g of the oxide checks out to three figures, which is a reassuring sign that his stated quantities are the ones he meant.

Herschel’s silver siderotype, 1842. The argentotype is the ancestor and is not the same formula: the silver goes on after the exposure, so it is a developed-out process. Article 218 gives no strengths for the silver wash at all, and article 212’s citrate solution is specified only as “moderately concentrated… such as to dry into a good yellow colour, not at all brown”. Anyone reconstructing it is choosing numbers Herschel did not publish.

The kallitype. W. W. Nicol’s process is the developed-out version and uses ferric oxalate rather than the citrate. Wall’s 1912 dictionary credits it to Nicol without giving a date, states the principle in the same terms this page has used — “ferric salts are reduced by light to ferrous, and in this condition can reduce to the metallic state a soluble silver salt” — and prints a sensitiser of ferric oxalate, oxalic acid and silver nitrate in distilled water with four alternative developers giving pure black, sepia, warm maroon and purple from one coating. The quantities are not reproduced here: the course’s copy is an optically scanned text whose numeric column for that entry cannot be read with confidence, and a formula is not worth publishing at a guess. The Formulary’s kit sheet draws the family line in one sentence: same image substance, different iron salt.

Bostick & Sullivan’s premixed Vandyke solution. A 100 mL bottle whose composition the supplier does not publish, sold with 250 g of thiosulfate and said to make about fifty 8 by 10 prints. It belongs on a product page rather than here, and its instructions are cited on this one for the workflow they document rather than for a composition they do not.

☠The dichromate contrast route, which this course does not give as a procedure

Both the kit contents and the instructions include 5 g of potassium dichromate and a method for using it: a 10 per cent solution made up as 5 g in 50 mL of water at 52 °C, of which 9 to 10 drops are added to 500 mL of the first bath — of the order of 0.01 per cent w/v in the tray, if a drop is taken at the twenty-to-the-millilitre the other supplier’s coating figures imply — for a contrast increase the sheet quantifies as “equal to about the loss of 1 step of a Kodak No 2 Step Table”. The sheet is emphatic that it goes into the development water and not into the sensitiser.

Potassium dichromate is a chromium(VI) compound, and the course’s chromium ruling is that chromium(VI) is never used, at any level, anywhere. Its notified classification carries twelve hazard statements, among them H340 for genetic defects, H350 for cancer, H360 for reproductive toxicity, H330 for fatal by inhalation, H334 for asthma symptoms if inhaled and H410 for long-lasting aquatic toxicity; the chemical page classifies it safety level D, historical study only. The supplier’s own sheet acknowledges part of that — “all chromium salts are potential carcinogens”, and a spillage on skin “will cause a chemical burn, which will appear as ulceration” — and then directs excess solid dichromate and its solutions “down a drain with a large volume of water”, which is a disposal instruction this course does not follow and which the safety data sheets bundled inside the same PDF contradict.

So no dichromate procedure is given here. What to do instead, in order of how well attested it is: make a negative with a longer density range, which is the answer every source agrees on; print under a duller light for proportionally longer, which Ware’s reciprocity chapter describes as a contrast control that nineteenth-century printers used deliberately; or use the argyrotype, whose contrast is raised by adding acid to the sensitiser and whose author explains the mechanism. The course does not offer an untested tartaric-acid variant of this formula in place of the dichromate, because there is no evidence for one and Rule 6 forbids inventing it.

No course variant of these proportions is offered. There is nothing here to make safer by changing the weights — the hazard is the silver nitrate, and reducing it would simply give a weaker print — and the two better-documented alternatives, the argyrotype and the kallitype, already exist as separate formulas with their own evidence and their own pages.

Safety

Level B, and the classification comes from the silver nitrate alone. The course’s rubric names silver nitrate explicitly under Level B. Ammonium iron(III) citrate is Level A, an irritant; tartaric acid is Level B on its own page, chiefly for its eye hazard and the significant minority of notifiers who classify it as a skin sensitiser. The formula takes the level of the highest of them.

• Silver nitrate is both an oxidiser and a caustic, as the kit sheet puts it. Solid on the skin can give a chemical burn, to be washed with cold water and then soap and water and treated as a heat burn. Dilute solution on the skin gives a brown to brown-black stain which is “silver metal bound to the protein of the skin and cannot be washed off”; the sheet’s advice, which the course endorses, is to let it wear off rather than try to remove it chemically. The SOP for handling it and the one for a spill carry the procedure.
• Never put solid silver nitrate in a wastepaper basket. It is an oxidiser in contact with paper.
• Weigh all three solids without raising dust. The citrate’s safety data sheet asks for eye and face protection, gloves, and exhaust ventilation where dust is formed; the tartaric acid’s records that a harmful concentration of airborne particles is reached quickly when the powder is dispersed.
• Gloves are not optional at any stage. Bostick & Sullivan’s sheet is blunt about their own premixed solution: wear plastic or latex gloves while handling it, coating and processing; “the solution should be considered poisonous”; and do not store it in a refrigerator used for food or drink. The glove guidance covers the choice.
• This is an ultraviolet process, and the light is a hazard people forget. Ten to thirty minutes under a photoflood or a UV bank is a skin and eye exposure, and a UV lamp is worse than sunshine because it is closer and does not feel warm. Enclose the unit, use a timer, and follow the UV unit SOP. Ware’s own note is that “an ultra-violet lamp must of course be shielded from accidental viewing”.
• Heat. The Formulary’s photoflood method puts a 500 or 1000 watt lamp 24 to 30 inches from the frame and warns that considerable heat is generated; do not bring it closer to shorten the exposure.
• The dichromate the kit supplies is not used at all, under the course’s chromium ruling, and is dealt with under Variants; its own page classifies it safety level D. If your kit contains it, it still has to be stored and labelled as what it is and disposed of through a licensed route rather than down a drain, and it should be kept away from paper, wood and anything else reducing.

⚠What is not a hazard here, and why

There is no volatile solvent in this formula and nothing is heated: all three solutions are made with water at 20 °C. No step evolves a gas you could smell — the carbon dioxide from the photoreduction comes to a few tens of micromoles for an 8 by 10 sheet on the arithmetic above, and it is liberated inside the paper. Ventilation is therefore not the governing control here: an openable window or ordinary extraction is enough, and the reason to have it is dust while weighing rather than vapour while working. (The kit’s other solutions are a different matter: its fixing bath and its dichromate solution are both made with water at 52 °C.)

There is no cyanide chemistry, which distinguishes this sensitiser from the cyanotype it is so often bracketed with; the acid rule that governs a ferricyanide bench does not apply here, and tartaric acid is in this formula on purpose.

And the sensitiser is not a fire risk in solution, although the solid silver nitrate on the shelf above it is an oxidiser and must be stored as one. The distinction between a substance and its dilute solution is worth making deliberately: 3.8 g of an oxidising solid in a hundred millilitres of water, on a sheet of paper, is not the same object as the bottle it came from.

Storage

One brown bottle, in the dark, labelled with the date and the batch of citrate. The sheet’s own statement is that the mixed sensitiser “will remain active for months” kept that way. No number is given and none should be invented; what a reader can do is date the bottle and print a step tablet from it when it is new, so that a later loss of speed is measurable rather than suspected.

Keep the solid citrate dark, dry and stoppered. The kit sheet says it is somewhat light-sensitive and should not be stored in bright light; the safety data sheet bundled with it adds that it is hygroscopic and must be kept tightly closed in a dry, well-ventilated place. A citrate that has taken up water is a citrate whose 9.0 g is not 9.0 g of citrate.

Keep the silver nitrate away from everything. Dark glass, tightly closed, away from organic material, away from the tartaric acid — Chemical Safety Card 0772 names silver among the substances the acid reacts with — and never above a shelf holding paper or solvents. The storage rotation SOP covers the general practice and labelling the rest.

Coated paper: use it soon, and store it sealed if you cannot. Neither supplier’s sheet gives a keeping time for a coated sheet. Ware’s for the argyrotype is that the sensitised paper “is best used within a few hours of coating, although longer term storage in a dark desiccated box is quite possible”, and that a shelf life in a dry environment is at least a week. That is a different formula and the course does not transfer the number; what does transfer is the reason — a coated sheet holds its own humidity, and humidity is what the print-out reaction runs on.

Do not store the sensitiser or the coated paper in a food refrigerator. Bostick & Sullivan say so for their premixed solution and the reason is general.

Incompatibilities

Alkali, at every stage. Alkaline wash water will not remove the iron salts — the Formulary says so directly — and above pH 4 iron(III) hydrolyses to a colloidal hydroxide that lodges in the fibres. Ware’s separate warning about the alkaline route is that making a clearing bath distinctly alkaline at pH 9 to 10 does inhibit the dissolution of silver, “but may raise the level of residual iron in the image”, which is trading a visible problem now for an invisible one later.

Buffered paper. An alkaline reserve of calcium carbonate in the sheet is the same chemistry arriving before you have even coated. Both suppliers specify 100 per cent cotton rag, unbuffered; Ware decalcifies chalk-containing papers in dilute acid and washes them before coating.

Hard water, for the same reason and for a second one: the Formulary notes that hard water “usually contains dissolved iron salts, which will contaminate the print”.

Chlorinated water in the first bath, which attacks the silver nanoparticles while they are least protected.

Ordinary photographic fixer. This is the incompatibility most likely to destroy a print, and it is stated in capitals in effect if not in type: “Do not use a standard photographic fixing bath; the very finely divided silver metal of the Van Dyke print will be etched off the paper.” A rapid fixer, a hardening fixer and an ordinary acid fixer are all several times too strong to begin with, and the acid ones carry a second problem on top of the strength: Ware records that silver sulfide forms from thiosulfate and nanoparticle silver “especially under acidic conditions”.

Metal, in trays, tongs, clips, sinks and the caps of bottles. Silver nitrate carries H290, “may be corrosive to metals”, and the safety data sheet bundled with the kit names magnesium among its incompatible materials; the dichromate, if you have it, corrodes metal caps and the sheet says so.

Every other alternative process on the same brush. Bostick & Sullivan’s instruction is that a brush used for Vandyke should be used for nothing else, while a glass rod may be shared if washed properly. Cross-contamination between alt processes is a real and diagnosable fault.

Potassium ferricyanide and any silver bleach. A cyanotype bench and a Van Dyke bench share an iron salt and nothing else; ferricyanide is the oxidising half of Farmer’s reducer and will attack a silver image on contact.

Waste

Three streams, and two of them carry silver.

The first wash carries unreduced silver along with the iron(III) citrate and the tartaric acid. On the arithmetic under Image characteristics, of the order of ninety-five per cent of the silver you coated leaves the paper between this bath and the fixer; the sources do not say how it divides between the two, but Ware’s instruction that the excess silver “must be washed out with water, in which it is highly soluble, before applying the thiosulphate” implies the wash takes the bulk. It is the most silver-rich thing you will pour that day and it is the one people treat as rinse water. Collect it. The silver-bearing waste SOP covers the practice, and silver recovery is the reason.

The spent fixer carries the rest, as the argentothiosulfate complex, in a bath that is discarded after two or three prints. It is a small volume of a concentrated silver solution and belongs in the same container.

The final wash is dilute thiosulfate and dilute silver and should still not go on a garden, into a soakaway or into a watercourse.

Solid waste. Excess solid silver nitrate is never put in a bin, and the kit’s dichromate, if you have it, is a chromium(VI) waste requiring a licensed route. The kit instructions direct several solids and solutions down a drain with large volumes of water; this course does not follow those instructions, and the safety data sheets bundled inside the same PDF contradict them, the silver nitrate sheet directing that spillage be prevented from entering drains at all.

Jurisdiction governs. The course publishes no jurisdiction-specific disposal instruction anywhere, and makes no exception here. Label what is in the container, follow the general chemical waste SOP and the course’s disposal ruling, and comply with local regulation.

Troubleshooting

The highlights are yellow-brown and will not clear. The family’s signature fault, and it has two different residues in it that need two different treatments: unreduced silver, which the wash and the fixer remove, and iron(III) chemisorbed to the cellulose, which they do not. The full entry carries the EDTA clearing sequence and the reasons for each bath. Check first that the wash water is not alkaline and not hard.

The print faded, in a drawer, in a year. Residual iron oxidising the image silver is the leading cause, and it is a clearing failure rather than a fixing one. Ware’s diagnosis of the whole family is that “the inherent problem of the iron-based silver processes lies in the danger of leaving residual ferric iron in the print - to its ultimate undoing, because iron(III) will oxidise silver”. The nitrate anion and residual thiosulfate are the other two candidates.

The print bleached in the fixer. Too long, or too strong, or both. The dedicated entry covers it; the numbers to hold are five minutes at 5 per cent, or Ware’s two to three minutes at 2.5 per cent, and the fact that thiosulfate converts nanoparticle silver to silver sulfide and takes thirty times the density with it if allowed to finish the job.

Brown staining that appeared the moment the print entered the fixer. The water bath was too short or was skipped: thiosulfate meeting unwashed silver nitrate gives silver sulfide directly.

A red-brown stain running off the dense areas in the wash. Bleeding — the silver is not being held by the fibres. Ware’s diagnosis for the argyrotype is insufficient surfactant or an unsuitable paper, and his mitigation is to process face down, which reduces the staining of adjacent areas but not the density loss.

Blotchy, grainy or mottled coating. Paper and coating rather than chemistry. Blotchy and streaked hand coating covers the mechanics; the sheet’s own advice is not to over-brush, because it abrades the surface and clumps the fibres, and to reduce the volume by a quarter if you are still spreading after thirty seconds.

The sensitiser has gone cloudy in the bottle. Sensitiser gone cloudy is the entry. On this formula the first question is whether it was cloudy from the day it was mixed — the sheet permits a precipitate formed during mixing — or whether it has changed since, which is a different and more serious matter.

The print is dark and flat with no highlight separation. Over-exposed, most likely, because a print-out process gives you no second chance in a developer. Both sheets say to stop far earlier than instinct suggests. If the exposure was right, suspect a negative whose density range is well under the 1.85 the sheet says this process can take.

The print is weak however long it is exposed. Check, in this order: the age of the sensitiser; the iron content of the citrate batch, which may simply be a different substance from the last one; and whether the paper was over-dried, since the reaction needs the water the paper holds.

Two batches of the iron salt behave differently. They may genuinely be different substances. Iron content between 14 and 28 per cent is the published range for this material and no supplier is obliged to tell you which you have. Record supplier and batch beside your exposure times and re-test when either changes.

Yellow stains that appeared only after the print dried. The worst version of the residual-iron fault, because Ware’s clearing chapter states that iron(III) hydroxide left in the sheet transforms irreversibly on drying into iron(III) oxyhydroxide, which dilute acids will not dissolve. Clearing has to happen while the print is wet.

Experiments

Vary the tartaric acid, since nobody has published what it does. Mix three sensitisers from the same batch of citrate and the same silver, at 0.75 g, 1.5 g and 3.0 g of tartaric acid in solution B, coat one paper with all three on the same day and expose them together under one step tablet. Read maximum density, the number of steps separated, and the highlight clearing. Ware’s prediction, from the argyrotype, is that more acid raises contrast by dissolving silver in the highlights; this is the cheapest test of whether that transfers, and it is the gap this page has had to leave open.

Test the mixing order deliberately, once. Make a second 100 mL by adding solution C to solution A before solution B, and a third by adding C quickly rather than slowly. Look at all three bottles against a light after an hour, then coat and print them. This is the experiment that turns the sheet’s unexplained instruction into something you have seen.

Humidify a sheet before exposure. Two identical coatings from one bottle; leave one over water at 100 per cent relative humidity for thirty minutes, expose both together, process together. Ware reports a shift towards purplish grey on the argyrotype. Interpose thin polyester between the humid sheet and the negative, as he instructs, and expect the humidified one to be slightly less sharp.

Measure the dry-down. Read three steps of a step tablet print wet, again after an hour, and again the next morning. The number you get is the correction you apply to every future exposure, and it is specific to your paper.

Time the fixer against density. Four identical prints from one exposure, fixed for one, three, five and ten minutes in the same fresh 5 per cent bath, washed and dried together, then read on a densitometer. You should see the density and colour improve and then reverse. Finding your own turning point is worth more than the sheet’s five minutes.

Fixer strength against fixer time. The same test at 2.5 per cent, Ware’s strength, and at 5 per cent. If the argument on this page is right, the weaker bath should give a wider window between “finished” and “bleached”.

Water against water. One print washed in tap water, one in distilled, one in water with a pinch of citric acid to about pH 4 — all from one exposure. Judge highlight clearing at once, and again after the prints have been in daylight for a month. This is the permanence experiment of the whole family and it takes one afternoon plus one month of waiting.

Test the illumination as a contrast control. Two prints from one negative: one in bright direct sun, one in open shade or under a clear north sky for proportionally longer, matched on a highlight value rather than on the clock. Ware’s chapter predicts the shaded one will have the deeper shadows for the same highlights. This is the experiment that would put a contrast control on this page which is not a chromium(VI) salt, and it is the one the course most wants somebody to do.

Compare it with its cousins. One negative, four prints: this sensitiser, a classic cyanotype, a salted paper and, if you can reach it, an argyrotype. Measure the exposure scale of each. The comparison is the reason the process comparison atlas exists, and doing it yourself is the only way the differences stop being adjectives.