Lab: Printing a Van Dyke Brown

Every fixer you have mixed since Part XI was designed to dissolve silver halide without touching the image. Tonight’s fixer is designed not to dissolve the image, and that is a completely different problem, because the image is bare colloidal silver in paper with nothing over it. Photographers’ Formulary put the consequence in one sentence: do not use a standard photographic fixing bath, or “the very finely divided silver metal of the Van Dyke print will be etched off the paper.”

So the bath you will make is a fifth the strength of a paper fixer, is used for five minutes rather than ten, is never acid, and is thrown away after two or three prints. Understanding why is most of what separates a Van Dyke that lasts from one that does not — and the other part, the iron, this lab deliberately leaves unfinished for two pages’ time.

Purpose

To mix the Van Dyke Brown sensitiser from three separately dissolved solids in the order the source specifies, coat by rod and by brush, expose by inspection to a printed-out image, process through a first wash and a dilute alkaline thiosulfate bath, and measure the density the print loses between coming out of the frame and coming out of the fixer — a number nobody publishes for your paper.

Three things make this the right first iron-silver session: the sensitiser keeps for months, so a mistake tonight does not cost you the bottle; the image prints out, so every judgement is visible while you are making it; and the whole process needs no developer, which leaves the attention free for the two things that are genuinely new — the mixing order, and a fixer that has to be weak.

This page does not restate the formula. Its quantities, provenance, variants and the function of every ingredient are on the formulary entry, and the chemistry is the previous lesson’s.

!This lab does not finish the print, and that is deliberate

What comes off your drying line tonight is exposed, fixed and washed. It is not cleared. There is iron(III) left in the sheet — some of it chemisorbed to the cellulose — and iron(III) oxidises silver.

Two pages from now, the clearing and toning lab finishes it, tests it and tells you whether it worked. Do not mount tonight’s print, do not give it away, and do not treat it as archival. Keep it flat, in the dark, and label it as uncleared. Wynn White, who prints this process, abandoned a plain tap-water wash entirely after reading Ware on residual iron; the lab that follows is where you find out whether your water and your paper leave you in the same position.

Learning objectives

By the end of the session you will be able to:

• Dissolve three solids separately and combine them in a stated order, and say what the order protects against.
• Explain why a sensitiser containing silver nitrate is not light-sensitive because of the silver.
• Coat by rod and by brush and judge from the dry sheet whether the volume was right.
• Read a printing-out image and stop where three independent sources say to stop.
• Mix and use a fixer at one fifth the usual strength, and say what each of its three components does.
• Say why an acid or rapid fixer destroys this print, in terms of what the silver is and what it is sitting in.
• Measure the fix-down on your own paper, and record a run another person could repeat.

Prerequisites

• The siderotype principle — the mechanism this session is the craft half of, and the source of the fixer’s design constraint.
• Salting and sensitising the paper, for hand-coating with silver in the room, and printing-out silver, for the judgement of a print-out image. The comparison at the end assumes you have made a salt print from the same negative.
• Silver nitrate handling and the handling SOP. Read again rather than remembered.
• Negatives and papers for the alternative processes, whose paper rules are assumed and not repeated: 100 per cent cotton, unbuffered, no optical brightener, and the coating volumes for rod against brush.
• Concentration and dilution, for per cent w/v and the difference between adding water and making up to a volume.
• A negative of long density range. Photographers’ Formulary say the process is “capable of an extremely long tonal range” and that density ranges up to 1.85 can be used; a negative made for grade 2 enlarging paper is not one.

Safety classification

Level B, and one substance sets it.

Silver nitrate is the reason. Its notified classification, aggregated from 803 reports across 35 ECHA notifications, is signal word Danger with H272 as an oxidising solid at 97.4 per cent of reports, H314 for severe skin burns and eye damage at 99.9 per cent, H318 at 33 per cent, and H400 and H410 for acute and long-lasting aquatic toxicity at over 99 per cent. The kit’s own bundled safety data sheet — Columbus Chemical Industries product 4730, “Silver Nitrate, Crystal, ACS”, revised 31 August 2012 — classifies it skin corrosion 1B and serious eye damage 1, gives an occupational exposure limit of 0.01 mg/m³, and lists strong reducing agents, alcohols, ammonia, magnesium and strong bases among its incompatible materials. Record that version and date in your notebook under the SDS recording SOP; a sheet is a dated document and citing it without its revision is citing nothing.

The other two solids are Level A materials. Ammonium iron(III) citrate carries H315 and H319 in 89.8 per cent of the ECHA reports that classify it, with 161 of 1,576 reports saying it meets no GHS criteria at all, and its supplier sheet gives eye irritation category 2B and notes that the solid is deliquescent and light-sensitive. Tartaric acid is the more variably classified: signal word Danger across 4,731 reports, with H319 at 57.8 per cent, H335 at 55.4, H315 at 54.3, and H302, H317 and H318 each around 42 — a spread wide enough that the sensible reading is to treat it as an eye irritant and a possible skin sensitiser.

One raised step, declared here. Weighing 3.8 g of solid silver nitrate is the highest-hazard operation of the evening: a corrosive oxidiser as a dry powder, with a 0.01 mg/m³ exposure limit. Under the classification rubric’s raised-step rule that step carries its own controls, written out: chemical splash goggles rather than spectacles, nitrile gloves, the balance on a tray in still air, no sweeping motions, the jar opened and closed rather than left open, and the spill procedure read before rather than after. The rest of the session works with solutions at 3.8 per cent or less. Buying the sensitiser ready mixed avoids the step entirely, and the rubric prefers that.

⚠What is not a hazard here, and why saying so is part of the assessment

There is no chromium(VI) in this session. Photographers’ Formulary’s kit contains 5 g of potassium dichromate as a contrast booster and their sheet gives a procedure for it. This course does not use it, at any level, under the chromium ruling; the reasoning is on the contrast lesson. If your kit contains it, leave it sealed and dispose of it through the general chemical waste route rather than following the sheet, which tells you to wash it down a drain.

There is no hydrogen cyanide risk, and there is no acid rule of the Part XXI kind. No hexacyanoferrate is used in this session at all. The reason acid is kept away from this bench is a completely different one — an acid fixer dissolves the image — and it is a quality rule rather than a gas rule. Naming the difference matters, because a rule whose reason you have wrong is a rule you will break in the wrong direction.

Nothing here produces a vapour, which is why the Ventilation section below is about dust and about where the bench is rather than about airflow.

And the ultraviolet is a hazard even though nothing in the room smells of anything. A twenty-minute exposure is a twenty-minute exposure for your eyes and skin as well as for the paper, and it is why this page declares requiresUV.

Hazards

Hazard	Where it arises	Control
Corrosive solid, to skin and eye	Weighing 3.8 g of silver nitrate	The raised step above: splash goggles, gloves, no dust, the jar closed between scoops. Weighing SOP
Corrosive solution, to skin and eye	Solution C, the mixed sensitiser, the coating pool, the first wash	Gloves and eye protection from the first weighing to the last tray. Eyewash within reach and known about before you need it
Permanent staining of skin and fabric	Any contact with the sensitiser at all	The stain is metallic silver bound to skin protein and, on the kit sheet’s own advice, is best left to wear off. Gloves, an apron, blotting paper under everything
Dust of the two organic solids, to eye and airway	Weighing 9.0 g of citrate and 1.5 g of tartaric acid	No sweeping motions; goggles for the citrate, whose strongest statement is an eye one; treat tartaric acid as a possible skin sensitiser given H317 in 42.5 per cent of reports
Incompatible mixing	Silver nitrate meeting ammonia, a reducing agent or a metal	Nothing ammoniacal in the room. No metal spatula, tongs, clips or chipped enamel. The ammoniacal silver quench SOP exists because the failure mode is severe
Ultraviolet, to eye and skin	Every minute the source is energised, and all of a sunlight exposure	Part XVI’s enclosure and interlock, or outdoors shade, covered skin and eye protection. ICNIRP put personal protection last in the hierarchy and so does this page
Silver in the waste	Every bath, and the first wash most of all	Collect all of it. Silver-bearing waste SOP
Ingestion, hand to mouth	Any bench that has held food	Nothing that has touched this chemistry goes near food or a food refrigerator, which Bostick & Sullivan say in terms

Required PPE

Nitrile gloves throughout, from the first weighing to the last tray. HSE’s COSHH essentials sheet takes single-use nitrile at 0.2 mm as splash protection where the safety data sheet gives no more specific advice, and both supplier sheets simply say to wear gloves for handling, coating and processing. A glove is also what stands between you and a stain you will be explaining for a fortnight.

Chemical splash goggles for the balance and for making up solution C; safety spectacles for the trays. The distinction is deliberate. Silver nitrate’s strongest statement is H314, and the highest concentration of the evening is the dry solid and the 11.5 per cent solution you make from it before it is diluted into the mixture.

An apron, and old clothes under it. The stain is not a laundry problem; it is silver.

Sun protection if you take the sunlight route. Outdoors the personal protection is sun protection and not chemical protection: shade for the frame if you can arrange it, covered arms, a hat, and eyes off the sheet.

Ventilation

The controls here are dust management at the balance and separation from incompatible substances everywhere else. Airflow is not among them, because nothing in this session produces a vapour. Neither the sensitiser nor any of the four baths is volatile, and the only gas the process makes is the carbon dioxide of the photolysis, inside the closed frame — which matters because a sealed sandwich traps it into bubbles that blur the image, and is why the frame carries a porous backing.

Work in a room with the ordinary through draught HSE ask for wet photographic work, on a lipped, wipeable surface. A strong draught at the balance is worse rather than better, because it lifts powder: shut the window while you weigh and open it afterwards. And ammonia must not share a room with silver nitrate, household cleaning products included; ventilate and wipe the bench first if anything ammoniacal has been used on it.

Materials

• Six sheets of unbuffered 100 per cent cotton paper, hot-pressed, cut to 8 × 10 in — rod, brush, double-coat, dose strips, print, spare. Bostick & Sullivan specify at least 32 lb for a small sheet and hot-pressed at 47 lb or more for larger work, because heavier papers withstand wet processing better and a hot-pressed surface gives a denser, sharper image.
• A negative the same size as the print, of long density range — the standard negative from Part XXI, and the same one your salt print was made from.
• A brown glass bottle of 100 mL, three mixing vessels, and labels.
• Red or ultraviolet-opaque masking material, cut slightly larger than the negative. Its purpose is diagnostic as much as cosmetic: it leaves you a coated-but-unexposed border you can read afterwards.
• Blotting paper or clean newsprint, paper or masking tape, and a soft pencil.
• Distilled or de-ionised water, about 3 L, for the three solutions and for the first wash if your tap water is hard or above pH 7.
• A step wedge from Part XIII if you have one.

Chemicals

The formula is not restated here. The Van Dyke Brown sensitiser page carries the three solutions, their make-up volumes, the mixing order, the provenance and the function of every ingredient. What follows is what tonight consumes and what each bath is.

Chemical	Quantity	Form
Ammonium iron(III) citrate	9.0 g	Green variety. Record supplier and lot: the green grade’s iron content runs 14 to 18 per cent by weight and no supplier is obliged to tell you which
Tartaric acid	1.5 g	The natural L-(+) form, CAS 87-69-4, is what photographic suppliers sell
Silver nitrate	3.8 g	Crystals. The one raised step of the session
Distilled or de-ionised water	33 mL to each of the three	Not tap water. The kit sheet specifies it and the reason is later on its own page: dissolved iron and alkalinity are the two impurities that spoil this process

The baths:

Bath	Made from	Strength	Time
First wash	Running soft water, or three trays of distilled water where the supply is hard or alkaline	—	1 to 5 minutes, judged by the yellow
Fixer	Sodium thiosulfate pentahydrate, with the optional alkaline additions of the iron-silver fixer	5 per cent w/v	5 minutes, and not longer
Hypo clear	Sodium sulfite — 1 per cent on King’s figure, 2 per cent on White’s	1 to 2 per cent w/v	3 minutes
Final wash	Running water at about 20 °C	—	30 to 40 minutes

⚗Why the fixer is a fifth of the strength you are used to, and what the additions do

Every source in this part agrees on the strength, which is unusual enough to be worth saying. Bostick & Sullivan: 50 g of sodium thiosulfate crystals per litre. Photographers’ Formulary: 100 g in 2000 mL, which is the same 50 g/L. Wynn White: “a 5% solution of plain hypo”. Sandy King, for kallitype: 50 g/L. Ware, for the argyrotype, is the one outlier at 2 to 2.5 per cent, and he is using a different silver salt.

Compare that with a paper fixer. Kodak F-24 and its relatives run at 240 g/L of thiosulfate, so this bath is a fifth of one, and the reason is the siderotype lesson’s: the image is colloidal silver of about 20 nm with no gelatin over it, and thiosulfate dissolves silver as readily as it dissolves a halide once the particles are small enough.

The two additions, and where they come from. King’s kallitype fixer adds 10 g of sodium carbonate and 2 g of sodium sulfite per litre: the carbonate holds the bath alkaline, where atmospheric oxygen is a weaker oxidant of silver and where an accidental acid cannot decompose the thiosulfate, and the sulfite is an oxygen scavenger. Photographers’ Formulary’s kallitype kit reaches the same place with 12 mL of 28 per cent ammonia per litre, and their New Kallitype sheet gives the reason from the other side: “Acidic water accelerates the tendency of thiosulfate to bleach highlights.”

And here is the honest limit on all of that. No Van Dyke source read for this course specifies an alkaline fixer. Both Van Dyke sheets give plain thiosulfate in tap water. The extension of King’s alkaline bath to this process is the course’s own reading, made on the grounds that the silver salt, the particle size and the failure mode are the same; the fixer’s formulary page says so in its own dilution note. Ware supplies the counter-argument you should know about before you adopt it: making a bath “distinctly alkaline (pH 9 to 10) … inhibits the dissolution of silver, but may raise the level of residual iron in the image.” You are trading image loss against clearing difficulty, and this lab asks you to run both baths on split sheets rather than believe either.

Equipment

A balance reading to 0.01 g with a tray under it, checked by the balance and thermometer check; three 50 mL vessels and one of 100 mL or more, verified under the glassware SOP, one per solution and none of them metal; and a stirring rod for solution C that never goes into the others, because the mixing order only means something if the implements respect it.

A coating rod 6 to 12 mm across with a straight section wider than the image area, and a soft brush with no metal ferrule. Bostick & Sullivan’s rule is worth adopting: a brush used for Van Dyke is used for nothing else, while a glass rod can be shared between processes because it can be got genuinely clean.

A contact frame with a split back, which is not a convenience — a printing-out process is judged by opening the frame and looking. A UVA source, enclosed and interlocked, from Part XVI, or the sun. Four trays larger than the sheet, a timer, opaque card, and the reflection head of your densitometer if you built one.

Nothing metal touches anything. No metal tongs, clips, chipped enamel trays, ferrules or steel straight-edges. Silver nitrate is reduced by most metals and the mark it leaves is permanent.

A dim working light. Both Van Dyke sheets say the sensitiser responds to ultraviolet only and that ordinary incandescent lighting may be used throughout; Wynn White reports slight fogging until he began working under a 7 W red bulb about a metre above the coating area. Those are not in conflict — the sheets describe what the chemistry needs and White describes what his room turned out to require. Work under tungsten or warm LED, shade the window, keep fluorescent tubes off, and if fog appears on a coated-but-unexposed border, the light is the first thing to change.

Estimated cost

Band ££, and unlike Part XXI the chemistry is not the cheap part. The capital — balance, rod, frame, UV source, trays — is either already yours from Parts II and XVI or is on the planner’s list, and this session adds nothing to it. What it adds to the shelf is three jars, one of which is silver.

The overview’s arithmetic puts the silver in a single-coated 8 × 10 in sheet at about 36p to £1.72 depending on which of the two dated listings you can actually buy from, against roughly £1 for the sheet of cotton rag it goes on. Double-coating, which Wynn White treats as compulsory, doubles the first figure and not the second.

If weighing silver nitrate is not something you want to do at home, a premixed kit is a legitimate route: Bostick & Sullivan sell 100 mL of Vandyke solution said to make approximately fifty 8 × 10 in prints, and everything in this page from Stage 3 onward applies unchanged. What you give up is the ability to vary the formulation, which matters for the Further experiments and not for the print.

Estimated consumables cost

Every price with a number is the planner’s own dated UK figure and every quantity comes from the Materials and Chemicals sections above. Most of this table has no number in it, and that is the finding rather than a blemish.

Consumed	This session	Sourced price	Cost this session
Nitrile gloves	3 pairs	£6.64 to £14.99 per box of 50 to 100	£0.40 to £0.90
Ammonium iron(III) citrate, green	9.0 g into the bottle; about 1.5 g leaves on tonight’s sheets	£17.99 per 230 g, checked 7 September 2026; the listing does not name the grade, and this bottle wants the green	£0.70 into the bottle, about £0.12 onto the sheets
Tartaric acid	1.5 g	Not priced. It is one of the clearing-bath and sensitiser solids the file names as a single gap, and this row is among the reasons recorded against it	—
Silver nitrate	3.8 g into the bottle; about 0.6 g leaves on tonight’s sheets	£59.95 per 25 g, or £112.90 per 10 g	£0.09 to £0.43 for what the sheets carry away; £9.11 to £42.90 for the bottle
Sodium thiosulfate pentahydrate	25 g, for 500 mL of fixer	£14.70 per 1 kg of the raw salt. The rapid-fixer concentrate the file also prices is a different product and must not be used here	£0.37
Sodium carbonate, anhydrous, if the alkaline fixer is used	5 g	£7.20 per 500 g	£0.07
Sodium sulfite, anhydrous	5 g for the fixer and the hypo clear	£13.68 to £19.98 per kg	£0.07 to £0.10
Citric acid, if the wash is acidified	2 g	£10.00 per 250 g of the monohydrate	£0.08
Unbuffered cotton paper, 8 × 10 in	6 sheets	Not priced. Hot-pressed cotton rag is one of the gaps the price file already names	—
Distilled water	about 3 L	Not priced	—

The priced rows come to about £1.20 to £2.07 for what tonight’s session actually uses up, and that is a floor rather than a total: three of the ten rows have no sourced price, and the two largest costs of the session — the paper, and the whole 3.8 g of silver nitrate that goes into the bottle rather than onto these prints — are still one unpriced and one better read as a capital purchase. What the table does establish is the ratio that governs this cluster: on the cheaper silver listing the metal on a sheet costs about a third of the sheet, and on the dearer, nearly twice it. In Part XXI the sensitiser was 6p against 96p for the paper. That inversion is the economic argument of Parts XXII to XXV in one line.

Equipment is deliberately absent, because a balance is not consumed and neither is a coating rod.

Waste streams

Four streams, and every one of them carries silver. The spent sensitiser, mixing cup, blot and paper towel are small in volume and highest in concentration, and the solids go to the solid waste rather than the sink. The first wash is the one people underestimate: it is where the unreduced sensitiser leaves, so it carries more dissolved silver than the fixer does, along with all the iron. The fixer carries silver as thiosulfate complexes, which is the form Part XII’s recovery lesson is about. The hypo clear and the final wash are dilute, large in volume, and still not nothing.

The rule: collect all of it. Label each container with contents and date under the labelling SOP, follow the silver-bearing waste SOP and the general chemical waste SOP, and read the course’s disposal ruling. Silver’s aggregated classification carries H400 and H410 in over 99 per cent of ECHA reports, which is why this is not a proportionality argument. Check your local regulations; they govern.

One instruction in a source that this course does not follow. Photographers’ Formulary’s kit sheet tells the reader to clean up spilled solid silver nitrate with water and “dispose of any excess down the drain”. The safety data sheet bundled in the same supplier’s own 46-page PDF says the opposite — prevent spillage from entering drains, pick it up without creating dust. Where a document contradicts itself, the safety data sheet governs.

Alternative route

Without an ultraviolet unit, print in the sun. Both supplier sheets name sunlight in the same sentence as their lamps; Bostick & Sullivan list “a 1000 watt metal halide bulb, ultraviolet fluorescent lights or sunlight” without preference. The process is printing-out, so it is judged by inspection rather than by a dose, which makes it the most sunlight-tolerant page in this part. Photographers’ Formulary’s one complaint is that consistent results are difficult, and the answer is a record rather than a number: date, time, sky, orientation and elapsed time at each inspection, under the daylight exposure SOP and the outdoor exposure session SOP.

Without a split-back frame, plate glass on a board with clips holds the negative in contact and the frame page gives the geometry; what you lose is inspection without disturbing registration, and the workaround is a sacrificial coated strip beside the frame that you uncover instead. Without a balance, or without wanting silver nitrate in the house, take the premixed kit and run everything from Stage 3 unchanged. Without a densitometer, the fix-down still works as a comparison: cut the strip in two after the first wash, fix one half, dry both together and lay them side by side under one light. You lose the number, not the finding.

One thing has no alternative and it should be said plainly. There is no version of this session that makes a print without ultraviolet light, and no version that omits the wash. Photographers’ Formulary give 40 minutes of running water after fixing, or 24 minutes plus a hypo-clearing bath plus a further 15 to 20; Bostick & Sullivan give 30 minutes; Wynn White gives 30 minutes and then another hour after toning. If you have no running water and no way to change several litres of standing water repeatedly, this page cannot be run, and the honest thing is to say so rather than offer a substitute that produces a print which fades.

Preparation

The day before. Cut and mark the paper; choose a side; write the sheet number, the paper name and the intended coating method on the back in pencil, in a corner that will be trimmed. Check your tap water with narrow-range pH paper and find your supplier’s hardness figure. If the water is hard or above pH 7, plan the first wash in three trays of distilled water — that is Photographers’ Formulary’s own instruction, and their reason is exact: “If your wash water is slightly alkaline, the iron salts will not be removed. Hard water is not satisfactory; it usually contains dissolved iron salts, which will contaminate the print.”

Several days before, if you can: mix the sensitiser. Wynn White’s practice is to bottle it and “let it age for a few days before using”; the practical point is that mixing early costs nothing and mixing late may cost you the session.

Two hours before. Bring the paper into the working room — at least an hour to reach equilibrium, on Ware’s figure, because a sheet at a different moisture content from the room cockles when it is coated.

The bench. Blotting paper down, one end dry and one wet, a tray under the balance and the balance where neither wet hand can reach it. Trays laid out in sequence before anything is coated. Nothing ammoniacal in the room, nothing metal on the bench.

The reading. Both safety data sheets, under the SDS recording SOP, with version and date in the notebook: Columbus Chemical Industries 4730 of 31 August 2012 for the silver nitrate, and Spectrum Chemical F1001 revision G1 of 11 December 2014 for the green citrate. Read the second one for its oddity as much as its content — in the field where a molecular formula belongs it prints the sentence that the compound “is a complex salt of undetermined structure”, and that is what you are about to weigh to two decimal places.

Procedure

Eight stages. The attended bench time is about three hours; the session also contains an hour of drying you cannot hurry and a long final wash, so plan to read the result the next morning.

The session, end to end

1. 11. Three solutions, weighed and dissolved separately30 min — one vessel and one rod each, 33 mL of distilled water each
2. 22. Combine A, then B, then C — slowly, with stirring10 min — in subdued light, into a brown bottle. This is the step the order exists for
3. 33. Coat sheet 1 by rod, sheet 2 by brush, sheet 3 twice40 min — taped, masked, marked, blotted, rod rinsed at once
4. 44. Dry in the dark60 min unattended — no hair dryer
5. 55. Test strip: find the dose on your own source45 min — a stepped series, judged by inspection
6. 66. Expose the print, and stop at half the density you wantthe dose from stage 5, then look anyway
7. 77. Wet processing: first wash, fix, hypo clear, wash60 min — and the fix is the short one
8. 88. Dry, measure, recordnext morning — the fix-down number is the second product of the session

Stages 4 and the final wash are waits rather than work. Everything before stage 5 can be done under tungsten or warm LED; the sensitiser responds to ultraviolet, not to a domestic bulb.

Stage 1 — Three solutions, made separately (30 minutes)

Separately is the design of this formula. Each of the three vessels holds one solid and 33 mL of distilled water at about 20 °C. Photographers’ Formulary make the reason for the separation explicit in a way most sheets do not: “The separate solutions are not light sensitive; therefore they can be mixed in strong light. However, when they are combined, the resulting solution is light sensitive.”

1. Weigh 9.0 g of green ammonium iron(III) citrate under the weighing SOP. It is deliquescent: open the tub briefly and close it hard. If the contents have compacted into a mass, break off what you need rather than tipping. Dissolve in 33 mL and stir until clear. Use a vessel of more than 100 mL capacity, because the whole sensitiser will end up in this one.
2. Weigh 1.5 g of tartaric acid and dissolve in a second 33 mL.
3. Weigh 3.8 g of silver nitrate — this is the raised step declared above, so goggles on, gloves on, tray under, no dust — and dissolve in a third 33 mL, with its own rod.
4. Label all three by substance and strength, not by letter, under the labelling SOP.

📓Why the lot number is not bureaucracy

Ammonium iron(III) citrate is an ill-characterised substance: no single molecular formula, made by dissolving a polymeric iron hydroxide in citric acid, and an iron content across present-day green material running from 14 to 18 per cent by weight. Nine grams of one jar and nine grams of another are not the same amount of iron, and iron is what makes the picture.

Record the supplier and the lot in the batch record, with the date the tub was opened. When a batch behaves differently, that number is the difference between a mystery and a measurement.

Stage 2 — Combine them, in this order, and slowly (10 minutes)

Work in subdued light. The kit sheet asks for “very subdued light, or better, a darkroom with a red safety light” for this step and this step only.

The mixing order, and the reason for each move

1. 1A — ammonium iron(III) citrate, 9.0 g in 33 mL — the only light-sensitive component, and the vessel the whole sensitiser ends in
2. 2B — tartaric acid, 1.5 g in 33 mL — goes in first, so the mixture is acid before the silver arrives
3. 3C — silver nitrate, 3.8 g in 33 mL — added slowly, with stirring, so no part of the mixture is ever locally rich in silver
4. 4A precipitate may form — the kit sheet says to disregard it; what it is, and what to do if it is heavy, is under Expected observations

The order and the slow addition are the kit sheet's; the reasoning under each is set out in the text and, where it is the course's inference rather than the sheet's statement, said to be so.

1. Add the whole of B to A and stir to homogeneity.
2. Add C to the combined A and B, slowly, stirring the whole time. The sheet’s word is “slowly”, and it is the only instruction in the formula given twice.
3. A precipitate may or may not form. The sheet says to disregard it. See Expected observations for what it probably is and when to worry.
4. Into a brown bottle, labelled and dated. Photographers’ Formulary: stored in a brown bottle in a dark place, “it will remain active for months.”

⚗Why B before C, and how much of that is sourced

What the sheet states. The order, the slow addition and the stirring. It gives no reason for any of the three.

What the chemistry of the family says the acid is doing, and this is reasoning rather than a statement in a Van Dyke source. Ware, describing the directly analogous argyrotype sensitiser — an iron(III) citrate and a silver salt in one bottle — gives three functions for the acid he uses there: it suppresses hydrolysis of the iron(III), which above pH 4 would otherwise begin forming the colloidal hydroxide that stains; it keeps the silver in solution, “otherwise silver citrate may precipitate out”; and the acid pH is “also the optimum for the photosensitivity”, which his Cyanomicon explains as the photo-active dimer of the citrate complex predominating above pH 2. Every one of those is a reason to have the acid in before the silver rather than after it.

And what the course will not claim. No manufacturer, standard text or conservation source read for this page states why this formula uses tartaric acid rather than more citric, or what tartaric acid in particular contributes. The formulary page records that as an open gap and so does this one. The only evidence about the quantity is a practitioner’s: Wynn White reports that adding more tartaric acid “seemed to increase contrast slightly and move the image color to a more neutral gray but then graininess became a problem”. That is an observation from one printer on his own papers, it is consistent with what Ware says extra acid does in the argyrotype — it dissolves silver in the highlights, which raises contrast — and it is not a measurement.

The slow addition is the part that needs no source. Adding a concentrated silver solution in one pour makes a region of the mixture locally rich in silver, and where silver meets citrate at high local concentration you get silver citrate rather than a sensitiser. Slowly, with stirring, keeps the mixture homogeneous while the acid does its work.

Stage 3 — Coating, by rod, by brush, and twice (40 minutes)

Both supplier sheets describe the same technique the cyanotype used, and this page follows Part XXI’s coating lesson rather than repeating it. Three things differ.

The volume. Photographers’ Formulary give about 1 mL for a 4 × 5 and 4 mL for an 8 × 10, and add the caveat that “it is not necessary to use a measured amount of sensitizer because the amount needed will depend upon the porosity of the paper”. Bostick & Sullivan, who sell a premixed solution of unstated strength, give a drop table instead: 12 drops for a 4 × 5, 18 for a 5 × 7, 24 for a 6 × 9 and 40 for an 8 × 10, with half of that per solution in a two-bottle process. Ware’s rod-coating figure for the argyrotype is about 1.5 cc for a 10 × 8 in area. Those are not in agreement, and the reason is that they are measuring different things: a drop is not a defined volume, the papers differ, and a brush takes up more than a rod. Start from the Formulary’s 4 mL by brush and Ware’s 1.5 mL by rod and let your own sheets correct you.

The mask. Tape a piece of red construction paper or Rubylith over the sheet with a window cut slightly smaller than the coated area, so that the exposure leaves you a coated but unexposed border as well as an uncoated margin. Wynn White’s reason is the one to keep: a mask “makes it possible to see whether or not the print has completely cleared or if there is any fogging”. Those two regions are what the break/fix page reads, and a print made without them cannot be diagnosed.

The second coat. Wynn White is unequivocal: “I have tried single coating Vandyke prints but have found the dark areas of the print to be very weak. Double coating is a must.” His method is to coat, dry with a hair dryer, and coat again. Neither manufacturer’s sheet mentions double coating at all, which is exactly the sort of disagreement worth settling with a sheet rather than an argument — so coat sheet 3 twice and compare its maximum density with sheet 1’s.

1. Tape the sheet at its upper corners over blotting paper, lay the negative on it and mark the four corners in pencil, then set the mask.
2. Sheet 1, by rod, with Bostick & Sullivan’s two self-tests: more than six passes possible means reduce the volume by a quarter, and a line of solution still standing after ten passes is blotted off.
3. Sheet 2, by brush, wetted and hard-blotted first, spread horizontally then vertically. Still spreading after 30 seconds means reduce the volume by a quarter, and stop before the paper does, because over-brushing abrades the sizing and lifts fibre.
4. Sheet 3, twice: coat, dry, coat again in the perpendicular direction, dry again.
5. Blot the residual bead, because crystals formed there damage the negative pressed against them, and rinse the rod under the tap at once.

Stage 4 — Drying (60 minutes, unattended)

Lay the sheet flat until the reflective sheen has gone, then hang it in the dark for about an hour. Bostick & Sullivan give an hour in a dark spot and state that a hair dryer is not recommended because their own testing shows natural drying gives a superior image. Photographers’ Formulary permit a hand-held hair dryer with the instruction, in capitals, not to overheat the print. Wynn White uses one between his two coats.

Those are reconcilable if you read what each is for. Heat is not the objection; unevenness is, and an uneven dry is an uneven sensitiser distribution, which prints. Use a hair dryer between coats if you must, and let the final dry happen slowly and in the dark.

How long a coated sheet keeps. White reports coating the night before, sealing the sheet in a light-tight envelope and printing the next day with good results, while saying it is best used at once; no manufacturer’s sheet read for this page gives a keeping time at all. Coat what you will use tonight, and test anything older against a fresh strip before you commit a picture to it.

Stage 5 — The test strip, which is the point of the session (45 minutes)

!Why this page publishes no exposure time for your source, and what it publishes instead

Three sourced figures exist and all three belong to somebody else’s light.

• 10 to 30 minutes — Photographers’ Formulary, under a 500 or 1000 W photoflood at 24 to 30 inches, offered explicitly as a range to calibrate against with test strips.
• First inspection at 3 minutes, then every few minutes — Bostick & Sullivan, under a 1000 W metal halide bulb, UV fluorescent tubes or sunlight. They publish no completion time at all, because their whole instruction is to judge by looking.
• 4 to 12 minutes — Wynn White, under a home-made bank of five 60 cm BL fluorescent tubes about 8 cm from the frame.

Part XVI has already ruled on this and this page follows it: the course publishes no claim it has not measured, and it has measured nothing on your box. Two units built to one drawing, at different array heights, with emitters of different ages, are two different light sources.

So what this page publishes is a bracket, and the bracket is the course’s own derivation from those three figures: a stepped series of 4, 8, 16 and 32 minutes, which spans all of them and is centred between White’s lamp and the Formulary’s photoflood. If your source is the sun, run 2, 4, 8 and 16 and record the sky.

1. Cut one coated sheet into six strips, numbered in pencil on the back before anything is exposed, and lay a step wedge across each if you have one, so the series tells you about the tonal scale as well as the level.
2. Expose the series a stop apart — 4, 8, 16 and 32 minutes — each strip separately and whole rather than by sliding a card across one, because separate strips give four independent results and let you open the frame and look. Use the UV unit SOP, and give a fluorescent or mercury source its warm-up first.
3. Inspect one strip through the split back at three minutes and then every few minutes, so that you have watched the whole colour sequence at least once.
4. Process all four together and read them the next morning, taking the shortest exposure that gives full shadow density after the fix-down.

Stage 6 — Exposing the print

Negative orientation, and it is the one mistake that cannot be fixed afterwards. With the frame face down, lay the negative on the glass base side down, emulsion up, then the coated sheet face down on top, so that emulsion meets emulsion. Then apply Bostick & Sullivan’s check before you close the back: viewed through the glass the image must read the right way round.

Give it the dose from stage 5, and then look anyway, because that is the whole advantage of a printing-out process.

And stop early. This is the instruction everyone gets wrong the first time, and three sources give it independently: Bostick & Sullivan say to stop when the image “appears approximately half as dark as the desired final image”; Wynn White says the print out of the frame shows “approximately half of its final density”; Ware, for the argyrotype, says it is better to overexpose than underexpose “because a dense image can always be reduced”. Those are not quite the same instruction — the first two are about where to stop and the third about which way to err — and the resolution is that the density you gain in the fixer is large and the density you gain on drying is large again, so the print in the frame always looks wrong.

Stage 7 — Wet processing (60 minutes)

Into the first tray within a minute or two of leaving the frame, because until it has been washed the sheet is still a coated sensitiser and every second in the room light is unrecorded exposure.

What leaves the print in each bath

1. 1First wash — plain water, 1 to 5 minutesOut goes the unreduced sensitiser: iron(III) citrate, iron(II), and silver nitrate that never met an iron(II). The tray goes yellow. This bath carries more dissolved silver than the fixer does, and it is not a rinse
2. 2Fixer — 5 per cent thiosulfate, 5 minutes and no longerOut goes the residual silver salt, as thiosulfate complexes. The image darkens sharply, and Ware attributes most of that to partial sulphiding of the silver rather than to more silver
3. 3Hypo clear — 1 to 2 per cent sulfite, 3 minutesConverts and displaces retained thiosulfate so the final wash can carry it out in a third of the time
4. 4Final wash — 30 to 40 minutes runningOut goes the thiosulfate and the silver-thiosulfate complexes. What does not leave is the iron bound to the cellulose, and that is the next lab
5. 5What is still in the sheet when you hang it upIron(III), some of it chemisorbed to the paper. This print is not cleared

Four baths and one omission, and the omission is deliberate. Times from the two Van Dyke supplier sheets; the hypo clear is King's and White's.

1. First wash, face up, 1 to 5 minutes, and take the end point rather than the clock: the yellow leaving the highlights. Photographers’ Formulary give about one minute in running soft water at 20 °C, during which “the print will darken and become yellowish”; Bostick & Sullivan give 3 to 5 minutes “or until most of the yellow emulsion stain has been removed from the highlights”, and note that water at about 32 °C shortens it considerably. If your water is hard or above pH 7, use three trays of distilled water instead, which is the Formulary’s own instruction. Wynn White goes further — after reading Ware on residual iron he moved to eight trays acidified with citric acid to just below pH 7 — and this course records that as a practitioner’s choice rather than a rule, since he calls the eight trays “probably overkill” himself.
2. Fixer, 5 minutes, agitating periodically, using just enough to cover the print and discarding it after two or three. A bath loaded with silver fixes worse and bleaches no less.
3. Rinse 1 minute, then hypo clear 3 minutes in 1 per cent sodium sulfite on King’s figure or 2 per cent on White’s.
4. Final wash, 30 to 40 minutes in slowly running water at about 20 °C, agitating every five minutes. Photographers’ Formulary give 40 minutes plain, or 24 minutes then hypo-clear then a further 15 to 20; Bostick & Sullivan give 30 minutes.

✕The three ways to destroy the print in the fixer, and they are all the same mistake

Too strong. A rapid fixer, or a print fixer at working strength, is four to five times this concentration. Photographers’ Formulary: the very finely divided silver metal “will be etched off the paper”.

Too long. Both sheets warn about it and Ware gives the mechanism: overlong immersion transforms the silver nanoparticles completely into silver sulphide, “causing the image to become badly faded”. The same bath that gives you the rich brown at two minutes takes the picture away at twenty.

Too acid. An acid fixer is the ordinary photographic kind, and it is the worst of the three here because the acid attacks from two sides at once: it accelerates the bleaching — Photographers’ Formulary’s New Kallitype sheet says “acidic water accelerates the tendency of thiosulfate to bleach highlights” — and, as Ware’s argument for the argyrotype turns on, the nitrate anion already in the sheet dissolves colloidal silver “especially under acidic conditions”.

The consequence of reaching for the darkroom fixer already on the shelf is therefore not a slightly worse print. It is a print that comes out visibly thinner than it went in, with the highlights gone first, and there is no recovering it. Mix this bath fresh, label it, and keep it on a different shelf from everything else you own.

Stage 8 — Drying, and the measurement (next morning)

Drain for about fifteen seconds — Bostick & Sullivan’s figure — and air-dry hanging or flat on a plastic screen in a dust-free place. There is no binder to protect the surface.

Then measure, three times on the same marked patch: out of the frame before the first wash if you can do it quickly enough, out of the fixer blotted, and dry the next morning. The middle reading is the one this session exists to get.

The wet readings carry a caveat and the notebook has to carry it too. A reflection densitometer reads light coming back off a surface, and a wet paper surface has a specular sheen a dry one does not; blotting removes most of it and not all. So the wet figures are indicative and the dry figure is a measurement — the densitometer geometry page explains why the geometry matters more than the electronics here.

Expected observations

During mixing. Solutions A and B clear; A is a strong yellow-green. On combining, a clear solution that darkens; a precipitate may or may not appear, and the kit sheet says to disregard it.

=What that precipitate probably is, and what the course can and cannot say

What is sourced. Photographers’ Formulary: “A precipitate may or may not form. If a precipitate should form, disregard it,” with the instruction not to transfer it to the paper. Ware, for the argyrotype, states the analogous fact from the other direction: the acid is there partly to keep the silver in solution, “otherwise silver citrate may precipitate out”.

What the course therefore says, marked as an inference from Ware’s statement rather than as a finding about this formula: a light precipitate in a Van Dyke sensitiser is most likely silver citrate, formed where a locally silver-rich region met the citrate before the acid had done its work. That is consistent with the sheet’s own instruction to add C slowly and with stirring, and it predicts that a heavy precipitate means the addition was too fast.

When to worry. A trace that settles and can be left behind is what the sheet describes. A heavy, persistent precipitate, or one that reforms after you have decanted, means silver has come out of solution in quantity and the bottle is weaker than the formula says. The troubleshooting entry for a cloudy sensitiser separates the four different clouds, only two of which condemn a bottle.

On the dry sheet. An even yellow to yellow-brown, matte, with the sheen gone. Not grey, not brown all the way through, and no blue anywhere.

During the exposure, and this is the sequence to learn:

Stage	What you see	What it means
First minute	The coated area outside the negative begins to darken almost immediately	Iron(III) reducing, and silver following it. Bostick & Sullivan describe exactly this
Three minutes	A visible image, thin and orange-brown on a yellow ground	Enough to judge direction, not enough to judge exposure
Correct exposure	The image is about half as dark as you want the finished print to be, and the highlights are just beginning to show detail	Three sources give the same instruction. Stop here
Over-exposure	Shadows block up; on some papers and at high coating weights the deepest areas take on a metallic bronze sheen	The self-masking of a print-out process has run out of range

In the first tray, a yellow stain lifting off the sheet within seconds and clouding the water. This is the observation both supplier sheets describe.

=The milky cloud, and what the corpus does and does not establish

The manifest for this page asks about “the milky white cloud that comes off the print” in the first wash. No source read for this course describes a milky white cloud in a Van Dyke first wash, and the page will not assert one.

What the sources do describe. Bostick & Sullivan: “notice the yellow stain lifting off of the paper.” Photographers’ Formulary: the print “will darken and become yellowish” during the initial wash. Ware, for the argyrotype: “the yellow unexposed sensitizer of excess iron and silver salts should be completely washed out within this time.” All three describe a yellow effluent, and its composition is not in doubt: unreduced iron(III) citrate, iron(II), and silver nitrate.

Two other clouds are documented and neither is this one. Ware describes a red-brown stain running off the dense areas, which he identifies as colloidal silver bleeding out of the fibres and treats as a fault; and Bostick & Sullivan, writing about printing-out paper rather than Van Dyke, describe “a purple mist which will float off your paper” as excess silver meets the chlorine in tap water.

The course’s own hypothesis, marked as one. A genuinely white or milky cloud is most likely silver chloride, precipitated where the free silver nitrate leaving the sheet meets chloride in a hard or chlorinated supply — the same reaction Bostick & Sullivan describe for POP, at a different concentration. It costs one strip to test: wash half in tap water and half in distilled, and see whether the cloud follows the tap.

In the fixer, a rapid and substantial darkening, and a shift of colour from reddish or orange-brown towards a deeper brown. Bostick & Sullivan say the print emerges about three-quarters as dark as the final image.

On drying, more density again. Ware puts the dry-down of an argyrotype at “at least one Zone”, which is a large number, and Bostick & Sullivan note that these prints “will have a significant amount of ‘dry down’”. A print judged wet is a print judged wrong.

What is happening chemically

Three things, in order, and the middle one is the surprise.

Light reduces the iron, and the citrate pays for it. All the photochemistry belongs to the iron salt: near-ultraviolet light transfers an electron from the citrate ligand to the iron(III), giving iron(II) and an oxidised, decarboxylated organic fragment. Silver nitrate takes no part in this step and is not light-sensitive in this formula — which is why the separate solutions can be mixed in room light and the combination cannot.

The iron(II) reduces silver, and it does it where it stands. Because both are in the coating together and the citrate photoproduct is soluble, the second step needs no development:

Fe²⁺ + Ag⁺ → Fe³⁺ + Ag

One electron, one silver atom, and the iron is regenerated

The silver deposits as colloidal particles of about 20 nm among the paper fibres. That is why the print builds while you watch and why there is no developer on the bench.

And then the fixer changes the colour more than it changes the amount. Two things happen in that bath and they are easy to confuse. Thiosulfate dissolves the residual silver salt, which is the fixing proper:

AgNO₃ + 2 S₂O₃²⁻ → [Ag(S₂O₃)₂]³⁻ + NO₃⁻

Fixing: the unreduced silver leaves as the bis(thiosulfato) complex

Meanwhile the surface of the image particles acquires a coat of silver sulphide — Ware’s explanation for the dramatic shift from yellowish-red to a rich mahogany brown, supported by energy-dispersive X-ray analysis of argyrotypes that found sulphur as well as silver in the image, and by the fact that the same bath taken too far converts the particles entirely and fades the print. A layer perhaps a few atoms thick changes the surface plasmon resonance and therefore the colour “profoundly”, in his word, without adding a single atom of silver to the picture.

🔬Why a few atoms of sulphide change the colour of the whole print

The colour of a 20 nm silver particle is not a property of bulk silver. It is a surface plasmon resonance, a collective oscillation of the conduction electrons whose frequency depends on the particle’s size, its shape and the refractive index of whatever touches its surface — so change the surface and you change the colour. That is the same mechanism as gold toning, and it is why colour in these processes is chosen at the ligand, the humidity and the toner rather than mixed.

What the fixer does not do is remove the iron. Nothing in this sequence takes out iron(III) bound to cellulose. That is the whole of the next-but-one lab.

Data to record

Two records, and the second is the reason the first exists. Use the lab notebook and the batch record SOP.

The batch record, one entry for the bottle: the three weights and the three volumes; supplier and lot number of each solid, and especially of the citrate; the date and batch number; whether a precipitate formed and whether it was decanted; and the date the bottle was first used, so that the ripening question below can be answered from your own bottle.

The session log, one line. Date, room temperature, relative humidity. Paper: maker, product, surface, weight, size, which side. Sensitiser batch number and age in days. Volume per sheet, coating method, single or double. Drying method, temperature, time. Source: which unit, array height, warm-up, lamp hours — or, outdoors, date, time, orientation and cloud. Exposure per strip and per print. Every bath, its strength, its temperature and its time, and how many prints had been through it. Which waste went where.

The measurement table, one row per marked patch:

Column	What goes in it
Sheet and method	1 rod, 2 brush, 3 double-coated, S1 to S4 test strips
Patch	Numbered, marked in pencil on the back before exposure
Exposure	Minutes, and the source
D out of frame	Reflection density, dry, before the first wash — marked as indicative
D after fix	Blotted, straight out of the fixer — also indicative
D dry	The same patch the next morning
Δ fix-down	D dry minus D out of frame, signed
Notes	Bleeding, fog in the masked border, coating texture, edge quality, colour in words

And two things in neither table. The masked border, which is coated and unexposed, and the uncoated margin. Compare them with each other and with the picture before you throw anything away: almost every fault in this part is diagnosed by that comparison and by no other observation.

Analysis

First, decide what you may claim. One sheet per condition supports a comparison and not a measurement, so every conclusion tonight ends with the words “on this paper, from this bottle”.

Second, read the fix-down, which is what the session was for.

🧮The arithmetic, worked on constructed figures

The three densities below are constructed to show the method and are not measurements. No source publishes them, this course has not run the session, and copying them into a notebook would be recording somebody’s illustration as data. The procedure and the arithmetic are the page’s; the numbers are your paper’s.

Suppose a shadow patch reads 0.78 out of the frame, 1.12 blotted out of the fixer and 1.34 dry the next morning:

Δ = 1.34 − 0.78 = +0.56

Total gain

1.12 − 0.78 = +0.34

Gained in the wet baths

1.34 − 1.12 = +0.22

Gained on drying

What that would tell you. That the print in the frame carried about 58 per cent of its final density (0.78 ÷ 1.34), which is close to the “about half” that three sources independently give as the stopping point — so your judgement is calibrated. And that drying is worth a fifth of the final density on its own, which is why Ware calls the dry-down “at least one Zone” and why a print judged wet is judged wrong.

What it would not tell you. How much of the wet gain is more silver and how much is the colour change from sulphiding. A reflection densitometer reading visual density cannot separate them, and Part XV’s geometry page explains why. If your instrument has a blue channel, read the same patch in blue and in visual: a change that is mostly colour moves them differently.

Third, compare the three coatings on evidence: evenness of the mid-tones, the edge, any texture from the implement, and the maximum density. Does the double-coated sheet actually reach a higher Dmax than the single? Wynn White says it must; neither manufacturer mentions it. One measurement settles it for your paper.

Fourth, put the Van Dyke beside the salt print from the same negative, which is the comparison this part is built to make, and read four things off the pair: maximum density, measured, and which is deeper; where the tones sit, since both are self-masking print-out processes and the shape of the difference is not a foregone conclusion; colour, in words, in daylight, both dry; and surface, because both are silver in paper with no binder and they may still not match. Add the row to your comparison sheet — and note what the pair does not tell you, which is anything about permanence, because your Van Dyke is not cleared.

Fifth, ask what the exposure series says about the negative rather than the light. A series that goes from blank to blocked with nothing between means the negative’s density range is wrong for the process, and that is not a fault you can expose your way out of.

Troubleshooting

The formulary page carries the fault list for the formula itself, and the break/fix page works six failures as a diagnosis. What follows is what goes wrong at this bench.

The print bleached almost entirely away in the fixer. Three candidates: the bath was a standard or rapid fixer rather than 5 per cent plain thiosulfate; it was acid, or the water was; or the print was under-exposed. The break/fix page works the differential.

A grey or brown veil over the whole sheet, including the coated-but-masked border. Fog rather than stain, and the border is what tells you. Suspect the working light first — White saw exactly this until he went to a red bulb — then an old bottle.

Yellow highlights that will not wash out. Stain rather than fog, and the colour is the diagnosis: residual iron, which is exactly what this lab does not fix. See the atlas entry and then the clearing lab. If the yellow is also in the uncoated margin, your wet chemistry is contaminated and extra washing will not help.

A red-brown stain running off the dense areas in the first wash, and a weak print after it. Bleeding: the colloidal silver is not being retained by the fibres. Ware’s remedies are more surfactant in the sensitiser and processing face down, and his diagnosis is that the paper is unsuitable.

Blotchy or streaked coating, for which the atlas entry is the general treatment; the extra candidate here is a sheet coated too wet, because this sensitiser sits on a sized surface longer than a cyanotype’s does. Discrete dark spots unrelated to the negative are metal — a clip, a ferrule, a chipped tray, a nail on the drying line. A gritty surface, or fresh scratches on the negative, is crystals: blot the residual bead, and check whether the bottle has thrown a precipitate you have been carrying onto the paper.

Clean-up

Rinse the rod immediately, before anything dries on it, and wash the brush thoroughly — Bostick & Sullivan’s reason is that whatever is left on it will be exposed and will contaminate the next print. Wipe the bench; the blotting paper goes into the solid waste, not the sink, because it carries silver. Rinse graduates and the mixing cup into the silver-bearing waste container.

Gloves off last, under the PPE removal SOP, and hands washed. A brown stain on skin is metallic silver bound to protein; the kit sheet’s advice is to let it wear off, and its presence is a marker that a glove failed.

If solid silver nitrate was spilled, follow the silver nitrate spill SOP and the solid spill SOP: pick it up dry, do not wet it, do not raise dust, do not put it in a paper bin.

Storage

The mixed sensitiser: a brown bottle, in the dark, at room temperature, labelled and dated. This is the one formulation in the alternative-process cluster that genuinely keeps.

Source	What it says
Photographers’ Formulary	Stored in a brown bottle in a darkroom, “it will remain active for months”
Bostick & Sullivan	Their premixed solution is “stable at room temperature and will have a shelf life of at least 1 year from the date of purchase”
Wynn White	Pour into a brown bottle and “let it age for a few days before using”. Keeps it in a covered box. “I have used sensitizer that had been sitting around for a year or so and it was fine”

Those three agree, and the interesting disagreement is elsewhere. White ripens the sensitiser deliberately; neither manufacturer mentions ripening at all, and no source read for this course explains what ripening does. The course will not invent a mechanism for it. What is worth noting is that the same instruction appears in Photographers’ Formulary’s traditional kallitype sheet, where the sensitiser “must ripen for a few (2-3) days before use” with occasional stirring — so the practice is not White’s alone, and it is unexplained there too. It is the first of the Further experiments.

The solid citrate is deliquescent and light-sensitive: stoppered, dry, cool, opened briefly, in a light-resistant container, which both the supplier sheet and the kit sheet ask for. Silver nitrate: dark, dry, away from ammonia, alcohols, reducing agents and metals, on a different shelf rather than a different corner of one — see incompatibilities. Coated paper: sealed, cool, dry, dark, used within a day unless you have tested otherwise. The mixed fixer is not stored at all.

Finished prints, once cleared: unbuffered mounts. The alkaline reserve in ordinary archival board is the wrong environment for a plain-paper iron-silver print for the same reason it is wrong for a cyanotype, and it is the compatibility rule this cluster hands forward.

Disposal considerations

The chemistry first. The waste is dilute iron(III) citrate, iron(II), silver nitrate, silver as thiosulfate complexes, thiosulfate, sulfite and tartrate, and the two species that govern are the silver and the thiosulfate. Silver’s aggregated ECHA classification carries H400 and H410 — very toxic to aquatic life, with long-lasting effects — in over 99 per cent of reports, and the kit’s own safety data sheet instructs that spillage be prevented from entering drains. Thiosulfate’s own hazard is low, the pentahydrate being reported as not meeting GHS criteria in 277 of 281 ECHA reports, but it exerts an oxygen demand in water and it is the thing carrying the silver.

The general practice. Bottle each stream, label it with contents and date under the labelling SOP, never top up an unlabelled container, and follow the silver-bearing waste SOP. Nothing acidic goes into any of these containers, for the same reason nothing acidic goes into the process. And treat the silver as an asset rather than a nuisance — that is the framing Part XII prefers, and at the prices in the cost section it is the honest one.

And the caveat that is not a formality. The course publishes no jurisdiction-specific disposal instruction; local regulation governs, it differs, and it is the only document that can answer the question for your drain. In England and Wales a domestic worker’s route is the council’s household waste and recycling centre. Where a supplier’s sheet tells you to put silver nitrate or a dichromate down a drain, that is a manufacturer’s convenience and this course does not repeat it.

Questions

1. Why can solutions A, B and C be mixed in room light while the combination cannot? Name the light-sensitive substance and say what it is that makes the mixture different.
2. Your kit sheet says to add C slowly with stirring and gives no reason. Give two, and say which of them the sources actually state.
3. Why is this fixer a fifth the strength of a paper fixer? Answer in terms of what the image is made of and what it is sitting in, not in terms of tradition.
4. A print looks perfect through the split back after ten minutes. Why is that a reason to keep exposing, and by roughly how much?
5. The first wash carries more silver than the fixer does. Why? And what does that imply about which tray you collect first?
6. Your print comes out of the fixer visibly thinner than it went in, with the highlights gone first. Name three possible causes and the single differential that separates the fixer from the exposure.
7. You have a Van Dyke and a salt print from the same negative, both dry. Name three things you can legitimately compare and one you cannot, and say why the last one has to wait.

Further experiments

Ripening, settled with a densitometer instead of an anecdote. Coat and expose a strip from the fresh bottle, then strips from the same bottle at one day, three days, a week and a month, all on the same paper at the same dose and all processed together at the end. White says a few days improves it and neither manufacturer says anything at all; either result is a finding.

Single against double coating, quantified. Weigh the mixing cup before and after each coating so you know the mass on the paper rather than the volume poured, divide by the coated area, and read the maximum density of both. Put a number on White’s “very weak” for your paper.

Tap water against distilled, in the first wash, on two halves of one exposed sheet. This settles for your supply whether the Formulary’s warning about hard and alkaline water applies to you, and it is the test that would also identify the milky cloud discussed above.

Alkaline fixer against plain, on two halves of one sheet: King’s carbonate-and-sulfite bath against plain 5 per cent hypo, same time, same temperature. Read maximum density and highlight detail on both, then keep both prints — the real comparison is two years long, because Ware’s warning that alkalinity “may raise the level of residual iron in the image” is a prediction about the future.

And the one that connects forward. Put one strip of tonight’s print through the EDTA and sulfite clearing sequence before you read the lab that teaches it, and compare its highlights with the untreated half.

Recap

Three solutions, one order, and the order is doing work. The acid goes in before the silver and the silver goes in slowly, because the acid suppresses hydrolysis of the iron(III) and keeps silver citrate from precipitating — reasoning Ware gives for the analogous argyrotype, since no Van Dyke source explains its own formula.

The silver is not the light-sensitive part, which is why the separate solutions can be mixed in room light and why a Van Dyke is handled under tungsten rather than in a darkroom.

Stop at half the density you want. The print gains substantially in the fixer and substantially again on drying, and three independent sources give some version of the same instruction.

The fixer is a fifth the strength you are used to, runs five minutes, is never acid and is thrown away after two or three prints, because the image is colloidal silver of about 20 nm with nothing over it. And most of what happens in that bath is a colour change rather than more silver — partial sulphiding of the particle surfaces, on Ware’s reading, which taken too far is how the bath destroys the print.

The iron is still in the sheet. Nothing tonight removed it, and until the lab after next does, this print is not finished, not archival and not to be mounted.

Check your understanding

Question 1. Why must the Van Dyke sensitiser be made as three separate solutions and combined in the order A, B, C?

• Because silver nitrate will not dissolve in the presence of the citrate
• Because the separate solutions are not light-sensitive and the combination is, and because putting the acid in before the silver suppresses hydrolysis of the iron(III) and keeps silver citrate from precipitating
• Because tartaric acid decomposes if it meets silver nitrate directly
• Because the citrate must ripen before the silver is added

Show the answer and why

Answer: Because the separate solutions are not light-sensitive and the combination is, and because putting the acid in before the silver suppresses hydrolysis of the iron(III) and keeps silver citrate from precipitating

Photographers' Formulary state the light-sensitivity half explicitly: the separate solutions can be mixed in strong light, and the combined one is light-sensitive. The chemical half of the answer is not stated in any Van Dyke source; it is Ware's reasoning for the directly analogous argyrotype sensitiser, where the acid suppresses iron(III) hydrolysis, keeps the silver in solution against precipitation as silver citrate, and gives the pH at which the citrate system is most photosensitive. The course marks that as an inference wherever it uses it.

Question 2. You have run out of plain hypo and reach for the rapid fixer on the shelf, diluted for paper. What happens?

• Nothing much; the print fixes faster and needs a longer wash
• The image is visibly etched off the paper, highlights first, and there is no recovering it
• The print stains yellow because ammonium thiosulfate does not remove iron
• The print goes purple because the ammonium ion complexes the silver differently

Show the answer and why

Answer: The image is visibly etched off the paper, highlights first, and there is no recovering it

Photographers' Formulary say it in terms: do not use a standard photographic fixing bath, because the very finely divided silver metal of the Van Dyke print will be etched off the paper. A rapid fixer is four to five times the concentration of this bath and is usually acid as well, and Ware's objection to nitrate turns on the fact that acidic conditions accelerate the dissolution of colloidal image silver. Yellow staining is a real fault with a different cause - residual iron - and it is not what a fixer does.

Question 3. Bostick & Sullivan, Wynn White and Ware all describe the print leaving the frame at roughly half its final density. Where does the rest come from?

• Continued reduction of silver in the wet baths, which Ware puts at about half to one stop in the high values
• Partial sulphide toning of the image particles in the thiosulfate bath, which changes their colour rather than their number
• A substantial dry-down, which Ware puts at at least one Zone
• Aerial oxidation of the residual iron during drying, which deposits more silver

Show the answer and why

Answer: Continued reduction of silver in the wet baths, which Ware puts at about half to one stop in the high values, Partial sulphide toning of the image particles in the thiosulfate bath, which changes their colour rather than their number, A substantial dry-down, which Ware puts at at least one Zone

The first three are all documented and they add up to a large gain. The fourth is backwards and is worth being clear about: aerial oxidation turns iron(II) back into iron(III), which is the species that attacks the image rather than builds it. Nothing after the exposure deposits silver except the small amount of continued reduction Ware quantifies, and the biggest single visible change - the shift to a rich mahogany brown in the fixer - is a change of colour rather than of quantity.

Question 4. Which bath in this session carries the most dissolved silver, and why does that matter?

• The fixer, because that is where the silver salt is dissolved
• The first wash, because it is where the unreduced sensitiser leaves the sheet - and it is the tray most likely to be tipped away as "just water"
• The final wash, because it is the largest volume
• The hypo clear, because sulfite reduces silver complexes back to metal

Show the answer and why

Answer: The first wash, because it is where the unreduced sensitiser leaves the sheet - and it is the tray most likely to be tipped away as "just water"

Only a fraction of the coated silver is reduced to image silver; the rest is still silver nitrate when the sheet goes into water, and the first wash takes it out. The fixer then removes whatever the wash left behind, as thiosulfate complexes. The practical consequence is that the tray a printer is least likely to think of as chemistry is the one carrying the most recoverable and most aquatically toxic metal, which is why the waste section names it first.

Question 5. A print shows a faint grey veil in the border that was coated but masked from the light. What does that region tell you, and what does it rule out?

• It shows fog rather than stain, and it rules out the negative and the exposure as causes
• It shows stain rather than fog, and it means the clearing was inadequate
• It shows that the mask leaked ultraviolet, and it means a denser mask is needed
• It shows nothing useful, because a masked area receives no light and cannot record anything

Show the answer and why

Answer: It shows fog rather than stain, and it rules out the negative and the exposure as causes

Fog is unwanted image substance and reads grey; stain is unwanted residual chemistry, chiefly iron salts, and reads yellow. A grey tone in a region that was coated but received no light through the negative cannot be an exposure fault, so the negative and the dose are both eliminated and the candidates become the sensitiser, the working light, the paper and the wet chemistry. That is why Wynn White masks every print and why this lab asks for both a masked border and an uncoated margin: without them the diagnosis has nothing to compare.

Question 6. Your tap water is hard and reads pH 8.1. What does Photographers' Formulary say will happen in the first wash, and what is the remedy they give?

• The image will bleach; wash in distilled water only after fixing
• The iron salts will not be removed, and hard water usually carries dissolved iron of its own which contaminates the print; the remedy is three trays of distilled or demineralised water, about a minute in each
• The print will go blue; the remedy is to acidify the fixer
• Nothing, because the first wash is only a rinse

Show the answer and why

Answer: The iron salts will not be removed, and hard water usually carries dissolved iron of its own which contaminates the print; the remedy is three trays of distilled or demineralised water, about a minute in each

The sheet gives both halves: alkaline water leaves the iron salts in the sheet, and hard water brings dissolved iron of its own. Ware's clearing chapter supplies the mechanism - above pH 4 iron(III) hydrolyses to a colloidal hydroxide that lodges in the fibres, and calcium promotes that hydrolysis - and adds the sting, that once the print dries the hydroxide converts irreversibly to an oxyhydroxide dilute acids will not touch. Acidifying the fixer is the opposite of what this process wants, and the first wash is emphatically not a rinse.

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