Bostick and Sullivan cyanotype and toning kits

Four bottles, two boxes, one supplier, and a documentary situation that is the exact inverse of the one this page kind was built for. The usual bought product hides its composition behind a marketing description and discloses fragments of it on a safety data sheet, because the law obliges a maker to classify a mixture it sells. Bostick & Sullivan does the opposite. It publishes ninety safety data sheets and not one of them is for anything it sells premixed; and it publishes the composition of both kits in the last place a chemist would look for it, on the store page, in a parenthesis.

So the concentrations on this page were not read off a hazard document. They were read off a shop listing, which says “25% Ferric Ammonium Citrate in solution A and 10% Potassium Ferricyanide in solution B” and, on the toning kit’s listing, “14% potassium carbaonate solution” and “40% Tannic Acid Solution”, misspelling included. Those are the supplier’s own words about its own product, they are the only statement of composition it makes anywhere, and they are more than the maker of a premixed cyanotype usually gives. They are also all of it: no unit, no pH, no assay, no statement of whether anything else is in the bottle, and no sheet anywhere that classifies the liquid a printer actually pours.

That last gap has a sharp edge on this particular page, because the same company publishes, over the signature of Dick Sullivan, a classical cyanotype formula of its own that contains oxalic acid in both solutions and two-tenths of a gram of ammonium dichromate in solution B. Nothing in the company’s literature says the kit is that formula. Nothing says it is not. This page records the two documents side by side and declines to join them, which is the whole discipline of the exercise.

What follows is what the maker publishes — which for procedure is a great deal and for chemistry is four percentages; where the boundary falls; and the open formula this kit is a stronger printing of, which is the classic cyanotype sensitiser with a quarter more iron in it and no explanation of why.

Bostick & Sullivan, Inc. — sold as kit

Components the maker discloses — from the safety data sheet, which classifies hazards and does not state a formula

Component	Concentration as the sheet gives it	Hazard codes
Ammonium iron(III) citratenamed on the sheet as Ferric Ammonium Citrate-Green FlakesCAS 1185-57-5Part A, the light-sensitive half. The store page calls the whole thing the "Classic cyanotype formula" and the instruction sheet never mentions it; that light reduces the iron(III) in this salt is established chemistry rather than a claim the supplier makes anywhere	25 %
Potassium ferricyanideCAS 13746-66-2Part B, the precipitant, which reacts with the iron(II) that light has made and gives the print its blue. The supplier states the colour and the product name and does not state the reaction	10 %
Potassium carbonate (anhydrous)named on the sheet as potassium carbonateCAS 584-08-7Bleaching Solution A of the toning kit. The supplier says what it does to the picture — bright blue to red and then away to a shadow in three minutes — and does not say that the mechanism is alkaline hydrolysis of the pigment	14 %
Tannic acidCAS 1401-55-4Toning Solution B, which puts a new pigment where the bleached Prussian blue was. The supplier names the material and the colours it passes through and offers no chemistry	40 %

Not disclosed. Bostick & Sullivan publishes two percentages for the printing kit and two for the toning kit, on store pages rather than on any sheet, and publishes nothing else about what is in the four bottles. It does not say whether the percentages are weight in volume, weight in weight, or something else; it does not say whether anything besides the named salt is in any of the four solutions — no preservative, no wetting agent, no acid, no biocide is either named or ruled out — and that silence matters more here than at most suppliers, because the same company publishes, over the signature of its own founder, a house classical cyanotype formula that contains oxalic acid in both solutions and 0.2 g of ammonium dichromate in solution B, and never says whether the kit is or is not that formula. It does not state the grade or assay of the potassium ferricyanide, and it does not state the iron content of the green ferric ammonium citrate, which runs from 14 to 18 per cent by weight across present-day commercial material and is the single number that sets how fast the paper prints and how blue it goes. It publishes no pH for any of the four solutions, no coating volume in millilitres against which the drop table can be checked, no exposure time for any of the three light sources it names, and no sensitometry of any kind — no exposure scale, no maximum density, no speed, no curve. And the boundary that matters most is documentary rather than chemical: the company's safety data sheet library runs to ninety sheets, every one of them for a single substance sold loose by the jar, and there is no safety data sheet for this kit, for the toning kit, or for any premixed solution the company sells. A reader who wants to know what has been classified about the liquid in the bottle will find that the answer is nothing at all, and the four sheets cited on this page are the company's sheets for the solids, which is a different question.

Nearest open formula. Classic cyanotype sensitiser — Same two chemicals, same two bottles, same one-to-one mixing, and the ferricyanide half is identical: the kit's 10 per cent solution B is exactly the open formula's 10 per cent w/v stock B. The difference is all in the iron. The kit's solution A is 25 per cent where the open formula's is 20, so the mixed coating solution carries about 12.5 per cent of the citrate against 10 — a quarter more iron for the same ferricyanide. On this course's arithmetic from the same published figures and Ware's 14 to 18 per cent iron content for the green salt, that moves the iron-to-ferricyanide molar ratio from about 1.7-2.1 to about 2.1-2.7 to one, further from equivalence and further into the surplus iron(II) that bleeds out of a shadow into the highlight beside it. Curiously, that is the same ratio the Photographers' Formulary kit arrives at from the opposite direction, by cutting the ferricyanide rather than raising the iron. What the kit adds beyond the open formula is two premixed bottles, two droppers and a sheet of procedure with drop counts, a wash time and a peroxide bath on it. What the open formula adds is a stated iron content, a reason for every number, and a document that names the chemicals it is made of.

Purpose

To take a printer from a flat pack to a cyanotype without ever opening a jar of powder, and — in the second box — to take that finished blue print off blue again.

The printing kit is two premixed solutions and two droppers. There is no weighing, no dissolving, no making up to volume and no dark brown bottle to find, because the bottles arrive filled. That is a narrower offer than a kit of solids like the Photographers’ Formulary one, and a more valuable one to the particular buyer it is aimed at: somebody who owns no balance and does not intend to buy one. The price of the convenience is that the buyer never sees the material and cannot inspect it. A jar of green flakes can at least be looked at; a bottle of brown liquid cannot.

The toning kit is the same idea applied to the toned cyanotype: a bleach and a toner, premixed, at strengths chosen so that a twentyfold dilution of one and a ten- to twentyfold dilution of the other give working trays. It is sold as producing “a cool, deep magenta color”, which is a narrower claim than the brown-to-black that the same two-bath chemistry is usually sold as, and the sheet is honest about where the variety actually comes from: not from the toner but from how far the bleach is allowed to go.

	Cyanotype Printing Kit	Cyanotype Toning Kit
Sold as	250 mL	500 mL
Solution A	25 % ferric ammonium citrate, green flakes	14 % potassium carbonate
Solution B	10 % potassium ferricyanide	40 % tannic acid
Also in the box	two plastic droppers, instructions	instructions
Working dilution	equal parts A and B	50 mL A in 950 mL; 50–100 mL B in 900 mL
Stated yield	200–250 8 × 10 (sheet); about 200 (store); 250 (combo)	50–75 8 × 10 (sheet); 60–75 (store)
Stated keeping	about 1 year from purchase	10 years
Safety data sheet for the solutions	none published	none published

One point of housekeeping before anything else, because the register that commissioned this entry calls it “cyanotype and toning kits” and there is a third product with a claim on the same shelf. The company also sells The New Cyanotype Solution (Ware’s Formula) as a single premixed bottle in four sizes. It is a different sensitiser and a different process, it is not part of either kit, and it is treated here only under When another formula is preferable. Its store page publishes no composition at all, which makes it the ordinary case and these two kits the exception.

Recommended uses

A first cyanotype with the shortest possible run-up. Two bottles, two droppers, forty drops, an hour of drying and a lamp. Nothing in the printing kit’s route requires a measuring cylinder, a balance or a dark bottle, and the sheet’s instructions are written by somebody who has coated paper: the thirty-second rule for the brush and the six-pass rule for the rod are the kind of advice that only comes from having watched beginners flood a sheet.

Teaching, where the chemicals must not be handled as solids. A workshop that cannot open a jar of powder — no fume extraction, no balance, participants who have never worn gloves — can still run this kit end to end. Neither solution is a dust hazard once it is in solution, and both are handled in normal room light, which removes the other classroom obstacle. Read the Safety section first: the sheet’s phrase “the solution should be considered poisonous” is doing a lot of work with no chemistry behind it.

Printing on cloth. The store page recommends muslin and silk beside the cotton rag paper. The cyanotype process entry covers what changes on a textile support; the kit’s own sheet does not discuss cloth at all, which is one of the places where the Photographers’ Formulary sheet is the better document.

Toning a cyanotype without ammonia in the room. This is the toning kit’s real distinction and it deserves stating plainly. The published two-bath cyanotype toners bleach with ammonia, including this course’s own tannic acid toner, which is a Photographers’ Formulary formula. Bostick & Sullivan bleaches with potassium carbonate instead — a solid salt in water, not a volatile alkali. For a printer working in a kitchen, a shared studio or a room with no extraction, that substitution is the difference between a process that can be run and one that cannot.

Colour by clock rather than by formula. The toning kit’s own instruction is to vary the bleaching time rather than the bath — “Try bleaching for longer or shorter times to obtain many different colors in the toning bath” — and to pull the print from the toner whenever the colour is right. A printer who wants a range of colours from one box gets it here without mixing anything new.

Not where the sensitiser has to be the same next year. The unstated iron content of the green citrate is the variable that will move under a calibration, and no bottle carries an assay. If the work depends on repeatability across batches, buy the salt with a specification on the label and mix the open formula.

Not as a way of learning what is in a cyanotype. The instruction sheet does not name a single chemical in four pages. A student who reads only what comes in the box will finish the process knowing how to make a blue print and nothing whatever about why it is blue.

When another formula is preferable

• When there is a balance on the bench, the classic cyanotype sensitiser is this kit with the iron content stated, a chemist’s reason for each number, and a fifth less citrate. It is the same two bottles otherwise, and the comparison is set out in full under The nearest open formula below.
• When the classic sensitiser’s short scale is the actual problem, the New Cyanotype (1995) replaces the citrate with ammonium iron(III) oxalate and buys a longer exposure scale, a higher maximum density and a much shorter printing time. Bostick & Sullivan sells it premixed as a single solution and makes the claim in the softest possible form — “Users report faster exposure times and a deeper intensity” — with no figure attached and no composition published. As an object it is less documented than the classic kit, not more.
• When ammonia and a balance are both available, Mike’s Cyanotype and the Simple Cyanotype (2019) build the iron complex in the beaker and hand back the contrast control that the classic formula never had.
• When the question is what Herschel actually did, Herschel’s 1842 cyanotype gives the original proportions from his own account, and they are not these.
• When more contrast is wanted, this kit publishes no route to it and neither does this course endorse the one the same company publishes elsewhere. Ware’s improved classic cyanotype — the widely circulated formula that Ware’s own endnote traces to this supplier’s website — reaches its whiter highlights with ammonium dichromate, and is recorded at Level D for study only under the chromium ruling. The answers this course does give are a negative with a longer density range and a duller light for proportionally longer.
• When the toned print is to be brown or black rather than magenta, the open tannic acid toner is the same second bath with an ammonia bleach in front of it, and its published colour is brown to black. The difference in outcome between an ammonia bleach and a carbonate bleach at the strengths each supplier publishes is, as far as this course can establish, undocumented by anybody — see Experiments.
• When the comparison wanted is with the other kit of solids, the Photographers’ Formulary cyanotype kit publishes every weight in the box and ships four separately packaged solids with four substance sheets. It is the more transparent product on paper and the more troublesome one in the room, because one of those four solids is a dichromate.

What the maker publishes

Four documents, written at different times by different hands, and between them a great deal of usable procedure and almost no chemistry.

The composition, in a parenthesis on a shop page. “Classic cyanotype formula ( 25% Ferric Ammonium Citrate in solution A and 10% Potassium Ferricyanide in solution B)”. Lower on the same page, as a contents list: “Part A: 25% Ferric Ammonium Citrate-Green Flakes / Part B:10% Potassium Ferricyanide / 2 plastic droppers / Instructions”. The toning kit’s page carries the equivalent line: “Cyanotype Bleaching Solution A-14% potassium carbaonate solution / Cyanotype Toning Solution B- 40% Tannic Acid Solution”. Four numbers, four names, and that is the entire published composition of this entry.

The coating volume, in drops. This is the printing sheet’s best contribution and it is unusual: 12 drops in total for a 4 × 5, 18 for a 5 × 7, 24 for a 6 × 9 and 40 for an 8 × 10, half of each solution in every case, counted out with the supplied droppers into a shot glass. Most suppliers publish nothing of the kind, and the ones that do publish millilitres, which is less useful to somebody who owns no measuring cylinder.

Two self-correcting coating rules. For the brush: “If you are still spreading solution after 30 seconds, reduce the amount of coating solution by 1/4.” For the rod: “If you are able to make more than 6 passes back and forth, reduce the amount of coating solution by 1/4”, with a further rule that a line of solution still standing after ten passes should be blotted off with a paper towel corner. These are feedback rules rather than quantities, and they do a job that a millilitre figure could not: they correct for the paper, which the supplier cannot know.

A drying instruction with a reason attached. About an hour in a dark place, and no hair dryer — “Our testing has shown that allowing the paper to dry naturally results in a superior image.” The claim is the company’s own testing, unquantified, and it is at least attributed rather than asserted.

The exposure, entirely as an end point. No time is given for any of the three light sources the sheet names — a 1000 watt metal halide bulb, ultraviolet fluorescent tubes, or sunlight. Instead: “Cyanotypes must be over-exposed to create a permanent image”; “The blue color initially seen during exposure is non-archival and will wash away in plain water”; watch for the darkest areas to begin reversing and lightening; and “An exposed image that appears faded and ‘washed out’ will darken to a deep blue color after wet processing”. A first inspection at four minutes, then every few minutes. The sheet then says the thing most sheets leave out: “Judging the proper time to remove the print from the light is the most crucial part of the Cyanotype process.”

The wash, with an interval. Twelve to fifteen minutes with agitation, changing the water every two minutes, continuing until no yellow stain remains in the highlights, and a statement that some blue washing out is normal. A fifteen-second drain, then air drying, and then the sentence that saves a lot of beginners’ prints: a faded print left in the dark for two to four weeks will re-oxidise and go dark blue again.

The peroxide bath, optional and timed. A hundred millilitres of drugstore 3 per cent peroxide in 900 mL of water, 60 to 90 seconds with agitation, bubbles normal, then a further 8 to 10 minutes of washing. The bath is explicitly not necessary; it exists to let the printer see the finished colour at once rather than the next day.

Keeping times for both kits. The printing kit’s solutions, “approximately 1 year from the date of purchase if stored in their original separate containers”; the toning kit’s, “a shelf life of 10 years at room temperature”. Both are stated at room temperature, and both come with an instruction not to use a refrigerator that holds food.

The whole toning procedure, in numbers. Bleach at 50 mL in 950 mL, three minutes, gentle agitation every 20 to 30 seconds, and a description of what to watch — bright blue to red, then away to a shadow in two to three minutes except in the very darkest areas. Tone at 50 to 100 mL in 900 mL, agitating every 10 to 15 seconds, through salmon and eggplant to a deep burnt magenta, removable at any point. Fifteen minutes of washing. Replenish at 5 to 10 mL of Solution B per 8 × 10. That is a more completely specified toning procedure than most published toners have.

The papers. A hundred per cent cotton rag, unbuffered, to match the archival quality of the image; at least 32 lb for 8.5 × 11 and hot pressed at 47 lb or heavier for larger work, because heavier paper survives wet processing better and a hot-pressed surface gives “a denser, sharper image with smoother transitions”. Five specific papers are named on the store page. The advice to begin with a paper that has a proven record and experiment later is good advice and rarely printed.

What is not disclosed

Whether the kit is the company’s own formula. This is the first thing to say, because it is the question a reader arrives with. Bostick & Sullivan publishes, on its own website and over the signature of Dick Sullivan, a classical cyanotype formula it introduces with the words “The one we use is”: solution A of 27.2 g of ferric ammonium citrate with 0.5 of oxalic acid made to 100 mL, and solution B of 9.2 g of potassium ferricyanide with 0.5 g of oxalic acid and 0.2 g of ammonium dichromate made to 100 mL. The kit’s own store page says 25 per cent and 10 per cent and names no other ingredient. Those are not the same numbers, and 25 and 10 are also not in the same ratio as 27.2 and 9.2. No document in the company’s literature says whether the bottles contain the oxalic acid, and none says whether they contain the dichromate. A reader may find that reassuring or alarming according to temperament; what they may not do is treat either reading as established, and neither does this page.

Whether the four percentages are weights in volume. None of the four is given a unit. Twenty-five per cent ferric ammonium citrate could be 25 g in 100 mL of solution, 25 g in 100 g of solution, or 25 g made up with 100 mL of water, and the three are different solutions. This page reads them as weight in volume because that is the convention in every cyanotype formula the course has read, and that reading is an inference and is marked as one everywhere it is used.

The iron content of the green citrate. The same omission as on every cyanotype product page and the same consequence. Ammonium iron(III) citrate is not a defined compound — the supplier’s own substance sheet says so, printing in the formula field “This compound is a complex salt of undetermined structure, composed of Iron, Ammonia, and Citric Acid” — and the iron in the green form runs from 14 to 18 per cent by weight across present-day commercial material. Everything photographic follows from that number, and the buyer of a brown liquid has less chance of estimating it than the buyer of a jar of flakes.

The grade of the ferricyanide, and of everything else. No assay, no purity, no water content, no supplier, no lot. The substance sheets in the company’s library are for the material it sells loose, and nothing ties a particular sheet to a particular bottle of kit.

Any pH. Not for solution A, not for solution B, not for the coating mixture, not for the bleach and not for the toner. This is a larger gap in the toning kit than in the printing kit, because the bleach is an alkali whose whole function is its pH: how fast it destroys the pigment and how far it goes are both pH-dependent, and the only pH figure anywhere in the supplier’s documentation is on a substance sheet for the solid — potassium carbonate at 11.6 in a 10 per cent solution, which is fourteen times the strength of the working tray.

The life of the mixed emulsion. The printing sheet says to mix the drops and coat; it never says how long the mixture keeps. This is the one keeping time a cyanotype printer needs most often, because it decides whether a session’s leftovers can be used tomorrow, and the sheet that publishes a year for the bottles publishes nothing for the shot glass.

Coating volume in millilitres. The drop table is excellent and it is unconvertible, because no drop volume is given. That has a specific consequence: the yield claim cannot be checked. On the ordinary convention that a dropper delivers about twenty drops to the millilitre, 250 mL of each solution at 20 drops of each per 8 × 10 comes to about 250 prints, which sits at the top of the sheet’s own 200-to-250 range and matches the combo page’s 250 exactly. That arithmetic requires two assumptions the supplier never states — that a drop is a twentieth of a millilitre, and that a “250 ml kit” means 250 mL of each solution rather than 250 mL in total — and it is offered here as this course’s inference, not as the maker’s claim.

Any sensitometry. No exposure scale, no density range, no maximum density, no speed, no reciprocity note, no curve, and no exposure time for a named light source. The nearest thing to a measurement on either sheet is “after 4 minutes of exposure, remove the print from the light and inspect”.

Any contrast control. This kit publishes none. That is worth noticing rather than complaining about, because the two obvious ones would be dilution and a dichromate, and the supplier offers neither in the box.

Where the toning kit’s colours come from. The sheet describes red, salmon, eggplant and burnt magenta and attributes none of them to a substance. Something is formed in the second bath and the supplier does not say what.

!Why the concentrations here come from a shop listing, and what follows

Every other product page in this formulary reads its disclosed components off a mixture safety data sheet, because a maker that sells a classified mixture must publish one. This page cannot, and the reason is worth being precise about.

Bostick & Sullivan maintains a safety data sheet library on its own site. It is not thin: ninety sheets, alphabetically from aluminium potassium sulfate to Tween 20, enumerated in full for this course through the site’s own data endpoint. Every single one of them is a single-substance sheet for a chemical the company sells loose by the jar or the bottle — and several are republished sheets from LabChem and Spectrum Chemical rather than the company’s own documents. There is no sheet for the cyanotype kit, none for the toning kit, and none for any other premixed solution the company sells.

That is not necessarily a failure of duty, and this page does not assert that it is; classification obligations depend on where a product is sold and how it classifies, and a dilute solution of two substances that are themselves unclassified or mildly classified may fall outside the requirement. But the practical consequence for a printer is exact and unavoidable:

Nothing anywhere states the hazard classification of the liquid in the bottle. Not the strength at which it is classified, not its pH, not its ecotoxicity, not its incompatibilities as a solution. The Safety section below is assembled from the company’s four substance sheets for the solids, from this course’s own classification rubric, and from the chemical encyclopaedia. It is not a manufacturer’s assessment of the thing in the tray, because no such assessment has been published.

And the concentrations in the table above are therefore sourced to a store page. That is a weaker kind of document than a safety data sheet in every respect but one: it is the maker stating, in its own words, what is in its own bottle, and it is the only such statement that exists.

Disclosed components

Four, from two boxes, each with the percentage the supplier prints and none with a hazard code, because none of the four documents behind them prints one. The hazard column is empty on purpose and the reason is worth stating once: the company’s sheets are US-format and give their classifications in words rather than in GHS H-numbers, and in any case they classify the solid, not the solution. Translating “Causes eye irritation” into H320 and hanging it on a 25 per cent aqueous solution would be two inferences dressed as a citation. The words are quoted below instead.

Ferric ammonium citrate, green flakes, CAS 1185-57-5, 25 per cent, solution A of the printing kit. The light-sensitive half, and the one the supplier is least forthcoming about. The store page names it; the instruction sheet does not mention it once in four pages. The company’s substance sheet for the solid is Spectrum Chemical F1001, revision G1 of 11 December 2014, and three things on it are worth reading. Its classification is Serious eye damage/eye irritation Category 2B, signal word Warning, hazard statement “Causes eye irritation”, with “Causes mild skin irritation” printed separately under Other hazards — a mild classification that is nonetheless the strongest thing said about anything in the printing kit. Its formula field is printed not as a formula but as a confession: “This compound is a complex salt of undetermined structure, composed of Iron, Ammonia, and Citric Acid”, which is a reagent supplier saying in its own notation that the substance has no fixed composition — precisely the point the section above makes about the missing iron content. And its incompatibility list names, among strong oxidising agents and iodides, tannins — a fact with no consequence at all until you notice that the company’s other cyanotype box contains a 40 per cent solution of one. Elsewhere the sheet gives solubility as 25 g per 100 mL at 20 °C, specific gravity 1.8, no pH, an oral LD50 in the rat above 2000 mg/kg, “Not considered carcinogenic”, and the oddly specific chronic note that prolonged eye contact may cause a brownish discoloration of the eyes.

Potassium ferricyanide, CAS 13746-66-2, 10 per cent, solution B of the printing kit. The precipitant, and at 10 per cent it is exactly the open formula’s stock B. The company’s sheet for the solid is LabChem SDS ID 75436, version 1.0, revised 19 August 2013, and it is the flattest document in this entry: section 2 reads “Not classified” with “No labelling applicable” and no hazard statement whatever; section 3.1 gives one mono-constituent at 100 per cent, also not classified; the NFPA panel in section 16 reads health 1, fire 0, reactivity 1. It gives pH 6 in a 5 per cent solution, water solubility 33 g per 100 mL, density 1.85 g/cm³, decomposition at 200 °C, an oral LD50 in the rat of 2970 mg/kg, an LC50 to fish of 1869 mg/L, and an ACGIH time-weighted average of 1 mg/m³ counted as soluble iron salts. What it does not give is the one thing a photographer must know. Section 10.5 names strong acids among the incompatible materials, and section 10.6 lists the hazardous decomposition products as potassium oxide, carbon monoxide and carbon dioxide. The sheet nowhere mentions hydrogen cyanide, and nowhere carries the “contact with acids liberates very toxic gas” statement that other suppliers print for the same substance. The hazard is real, it is on this course’s chemical entry, and a printer who read only the document in the company’s own library would not meet it.

Potassium carbonate, CAS 584-08-7, 14 per cent, Bleaching Solution A of the toning kit. The alkali, and the substitution that makes the toning kit worth owning: an ammonia bleach does the same job and fills the room while doing it. The company’s sheet is Spectrum Chemical P1235 of 18 April 2016, and it carries the strongest classification of the four — hazardous under the 2012 OSHA standard and a dangerous substance under GHS, Acute toxicity Oral Category 4, Skin corrosion/irritation Category 2, Serious eye damage/eye irritation Category 2A and STOT single exposure Category 3, signal word Warning, with the statements “Harmful if swallowed”, “Causes skin irritation”, “Causes serious eye irritation” and “May cause respiratory irritation”, and the storage instruction “Store locked up”. Read that against the working bath: 50 mL of the 14 per cent stock in 950 mL of water is roughly 0.7 per cent carbonate in the tray, which is a very different proposition from the granular solid the sheet describes. The concentrate in the bottle is the one to respect. The sheet gives pH 11.6 in a 10 per cent solution, solubility 105 g per 100 mL, specific gravity 2.29, deliquescence, and an incompatibility list of oxidising agents, metals, acids, chlorine trifluoride, calcium oxide and magnesium. Its synonym list is a small pleasure — pearl ash, potash, salt of tartar — and a reminder that this is one of the oldest alkalis in the trade.

Tannic acid, CAS 1401-55-4, 40 per cent, Toning Solution B of the toning kit. The strongest solution in either box by concentration and the mildest by classification. Spectrum Chemical T1010 of 4 October 2016 states that the chemical is not considered hazardous under the 2012 OSHA standard and is “Not a dangerous substance or mixture according to the Globally Harmonized System (GHS)”, with no hazard statement and no signal word. It gives the formula as C76H52O46 at molecular weight 1701.28 — a plant polyphenol rather than a defined compound, so the formula is a representative one — pH 3.5, colour light tan to light brown, taste astringent, melting point 218 °C, and an oral LD50 in the rat of 2260 mg/kg. Its storage instructions are stricter than its classification: sensitive to light, kept in light-resistant containers, and stored under inert gas with a nitrogen flush, which is a laboratory precaution against slow air oxidation of the phenols and is plainly not what happens to a bottle in a kit. Its incompatibility list names strong oxidising agents, heavy metal salts, and strong bases and alkalis — which is to say, the other bottle in the same box.

Behaviour

It prints out, and the sheet is unusually firm about what that means. The image appears during the exposure, going bright yellow to brilliant blue within a few minutes, and the sheet immediately warns that this blue is not the image: “The blue color initially seen during exposure is non-archival and will wash away in plain water.” The print that survives is made further along, and the only way to know you have reached it is that the darkest areas have begun to reverse and lighten.

A correct exposure looks wrong in the frame. “Cyanotypes must be over-exposed to create a permanent image”, and a print that comes out looking faded and washed out is the one that will darken properly in the wash. This is the classic sensitiser’s known behaviour, and the sheet handles it by repetition rather than explanation.

It is not finished when it is dry, either. The image oxidises as the paper dries and goes to a dark Prussian blue over hours. The peroxide bath does the same job in ninety seconds. A print judged wet is not the print you will have tomorrow, which is the single most common cause of a beginner over-correcting the exposure in the wrong direction.

A faded print is often recoverable, and the sheet says how. “If the image should ever fade, simply place it in a dark place for 2-4 weeks and it will re-oxidize and turn dark blue again.” That is the reoxidation of the reduced pigment by atmospheric oxygen, stated as a practical remedy, and it is a better piece of advice than most kit sheets contain.

The sensitiser is one-shot; the toner is not. Nothing about the coating solution is replenished or reused: it goes onto the paper and is gone, and any surplus in the shot glass has no published life. The toning kit is the exception in this entry and the only place a bath is kept: working solutions go into light-tight containers for future use, and the toner is replenished at 5 to 10 mL of stock per 8 × 10 when it slows.

Speed is unstated and variable, and the sheet’s silence is defensible. No exposure time is given for the 1000 watt metal halide bulb, the fluorescent tubes or the sun. Between the three sources, the distance, the paper, the humidity of the drying room and the unstated iron content of the citrate, a published figure would be a fiction, and the four-minute first inspection is the honest substitute.

The bleach moves fast and then stops. Two to three minutes takes the whole image down to a shadow except in the very darkest areas, and the sheet’s “continue bleaching for 3 minutes” is therefore close to the end of the useful range rather than the middle of it. This is why the sheet’s advice about colour is about time in the first bath: a short bleach leaves more pigment for the toner to work around.

The toner has no fixed end point at all. Salmon, eggplant, deep burnt magenta, and “you can remove your print at any time during the toning process”. A printer wanting repeatable colour has to supply the clock, because the supplier has supplied only the sequence.

Image characteristics

Colour: Prussian blue, named and never explained. The store page promises “brilliant Prussian Blue” and the instruction sheet “stunning Prussian Blue”, and neither document says what Prussian blue is. The chemical entry does. The practical colour sequence a printer will see is the one the sheet describes: bright yellow, then blue during exposure, then a washed-out olive at the correct end point, then weak and pale from the wash, then dark blue as it dries.

Contrast: no control published, which is unusual and worth reading twice. Every other cyanotype kit in this formulary publishes at least one way to change contrast. This one publishes none — no dilution instruction, no ferricyanide first wash, no dichromate. The absence of the dichromate is the notable part, given that the same company’s own house formula on the same website contains one and that Ware’s endnote traces the widely circulated dichromate-bearing “improved classic” to this supplier. Whatever the reason, the kit as sold and as documented is a chromium-free product, and this course prefers it that way.

Tonality: the short scale of the classic process, managed by over-exposure. No exposure scale, density range or maximum density is published. Ware’s figure for the classic process — an exposure scale of about 0.9 — is the nearest independent number, and it is a fact about the formula rather than about this kit. The practical expression of that short scale is the whole of the sheet’s exposure advice: go past where it looks right, because the top of the scale will be washed away.

Toned colour: magenta, by the maker’s account. “A cool, deep magenta color”, reached through red in the bleach and salmon and eggplant in the toner. That is a narrower and more specific claim than the brown-to-black usually attached to a tannic acid toner, and this course records the difference without resolving it: the two suppliers publish different bleaches at different strengths, and neither publishes a measurement.

Surface and support: set by the paper, and the paper is specified. A hundred per cent cotton rag, unbuffered, hot pressed and heavy for the sharpest result. Unbuffered matters chemically rather than aesthetically — a buffered paper carries an alkaline reserve, and alkali is what destroys Prussian blue — and the sheet asks for it without giving the reason.

The mechanism

Almost nothing below is the supplier’s statement, because the supplier makes almost no chemical statements. The store page names two salts and a colour; the instruction sheets name nothing at all. Everything that follows is the open literature applied to the two names on the shop listing, and every step of it is an inference from the composition the maker publishes rather than an account the maker gives.

⚗What the printing kit's two bottles do

Light reduces the iron, and the citrate is what pays for it. All the photochemistry belongs to ferric ammonium citrate. Ultraviolet reduces iron(III) to iron(II) at the expense of the citrate ligand, which is oxidised and loses carbon dioxide. The potassium ferricyanide takes no part in the light reaction; it filters some of the printing light and waits.

The iron(II) then meets the ferricyanide. The two exchange an electron —

Fe²⁺ + [Fe(CN)₆]³⁻ → Fe³⁺ + [Fe(CN)₆]⁴⁻

The oxidation states switch

— and the resulting iron(III) and hexacyanoferrate(II) precipitate together in the paper as Prussian blue. This is why the wash both develops and fixes: it carries away the unreacted citrate and ferricyanide from the unexposed areas, which is the yellow stain the sheet tells you to wash out, and leaves the insoluble pigment behind.

The blue that appears during the exposure is not that pigment. In the excess of iron(II) that heavy exposure creates, the print carries a reduced form of the pigment, and atmospheric oxygen turns it back over hours. That is the whole basis of three separate instructions on the sheet — that the exposure blue washes away, that the dried print darkens, and that a faded print recovers in the dark over two to four weeks — none of which the sheet connects to a mechanism. The peroxide bath is the same oxidation performed deliberately and quickly, which is why bubbles form: the peroxide is decomposing as well as oxidising.

Is this kit a “PQ developer” equivalent — that is, can the class of thing be read off the disclosed components? Yes, and only as far as the class. Two salts at 25 and 10 per cent mixed one to one is a classic cyanotype sensitiser by any published definition, and the supplier calls it one. What cannot be read off the disclosure is anything about the third and fourth ingredients, if there are any. The company’s own house formula puts oxalic acid in both solutions, and oxalic acid is not decorative: it holds the pH down, and the sensitivity of an iron citrate sensitiser has a maximum in the region of pH 3 to 4. If the kit contains it, the kit is a slightly different sensitiser from the one the two percentages describe. This page does not assume either way, and a printer who wants to know can find out empirically — see Experiments.

⚗What the toning kit's two bottles do, and how confident this course is about each

The bleach is alkaline hydrolysis, and the confidence here is high. Prussian blue is destroyed by base: the pigment hydrolyses irreversibly, the iron ends up as hydrated iron(III) oxide-hydroxide and the hexacyanoferrate goes into solution. Ware records Holtzman’s result that a buffer at pH 9.4 completely decolourises a cyanotype in one to ten minutes, and a 0.7 per cent potassium carbonate bath sits comfortably above that — the supplier’s own substance sheet gives pH 11.6 for a 10 per cent solution of the solid, and a dilution of that order does not fall below 9.4. That the bleach works by pH is this course’s reading of the maker’s stated composition, not a claim the maker makes; what the maker states is only the colours and the times. The transient red the sheet describes is worth noticing and this course cannot account for it with confidence — it is most likely an intermediate stage of the hydrolysis rather than a distinct compound, and that is an opinion rather than a finding.

The toning step is less securely understood, and this page says so. What the second bath leaves is an iron-polyphenol complex: tannic acid is a hydrolysable tannin whose gallic acid units chelate iron(III), and the iron(III) left in the paper by the bleach is exactly what they find. That much is the chemistry of iron gall ink and it is not in doubt. What is not established is why this particular route gives the magenta the supplier claims, where the same two-bath idea with an ammonia bleach is published as giving brown to black. Bleach strength, bleach time, how much hexacyanoferrate is left in the sheet and how much tannin is present all plausibly matter, and none of them has been measured in anything this course has read. The open tannic acid toner records the same gap from the other side.

🧮The arithmetic on the maker's own numbers, and what it is worth

Both kits publish concentrations and dilutions, so the working strengths can be calculated. Every figure in this box is this course’s arithmetic on the supplier’s published percentages, and every one of them additionally assumes that the unlabelled percentages are weight in volume, which the supplier does not state.

The coating emulsion. Equal parts of 25 and 10 per cent gives about 12.5 per cent ferric ammonium citrate and 5 per cent potassium ferricyanide. The open classic sensitiser at Ware’s weights gives 10 and 5. The ferricyanide is the same; the iron is a quarter higher.

The iron-to-ferricyanide ratio. Taking Ware’s 14 to 18 per cent iron for the green salt, 12.5 per cent of it carries 17.5 to 22.5 g of iron per litre, or 0.31 to 0.40 mol/L, against 50 g/L of potassium ferricyanide, which is 0.15 mol/L. The molar ratio is about 2.1 to 2.7 to one, where the open formula’s is about 1.7 to 2.1. Both are well clear of the one-to-one that would consume both reagents, and this kit is further into the surplus.

A coincidence worth recording. The Photographers’ Formulary kit reaches the same 2.1-to-2.7 ratio by cutting the ferricyanide to 4 per cent while leaving the iron at 10. Two suppliers, two different departures from the same open formula, one identical outcome — because 12.5 to 5 and 10 to 4 are the same proportion. Neither publishes a reason.

The toning trays. The bleach comes out at about 0.7 per cent potassium carbonate and the toner at about 2 to 4 per cent tannic acid. The weak end of that toner range is within rounding of the 20 g per litre the open tannic acid toner uses, which means the supplier’s difference from the published toner is not really the toner at all — it is the bleach.

The nearest open formula

The classic cyanotype sensitiser, and the comparison is unusually clean because one of the two variables is identical.

Solution B is the same solution. The kit’s 10 per cent potassium ferricyanide is exactly the open formula’s stock B, which Ware states as “make up to 100 cc of a 10% w/v solution”. There is nothing to compare.

Solution A is a quarter stronger. Twenty-five per cent against twenty. Mixed one to one, that is 12.5 per cent of the citrate in the coating solution against 10, and on the arithmetic above it moves the iron-to-ferricyanide molar ratio from about 1.7-2.1 to about 2.1-2.7 to one. The predicted consequences are the ones a surplus of iron(II) always brings: a little more density available in the shadows, and a greater tendency for iron(II) to migrate out of a dense area into the highlight beside it before it can react. Nobody has published a measurement of the difference at these two strengths, and the honest statement of the direction is that it is small and known while its size is not.

What the kit adds. Two bottles already made up, two droppers, and a procedure sheet that is better than the open formula’s own account in three specific places: it publishes coating volumes for four print sizes, it publishes self-correcting rules for both coating methods, and it publishes a wash time with a water-change interval. None of those is in Ware’s section 7.1.

What the open formula adds. A stated iron content for the salt, so the sensitiser can be reproduced next year. A reason for every number, including why a more dilute sensitiser than the historical average is chosen. An account of what the wash is doing and what happens if it goes too far, which the kit sheet omits entirely. And a document that names the chemicals it is made of, which no document in either Bostick & Sullivan box does.

And the second comparison, for the toning half. The open tannic acid toner is the same second bath — tannic acid at 20 g per litre, which is the weak end of this kit’s own range — behind a different first bath. The open formula bleaches with ammonia at 10 mL of the 28 per cent solution per litre; this kit bleaches with about 0.7 per cent potassium carbonate. Both are alkalis and both destroy Prussian blue by the same hydrolysis, but one of them evaporates and the other does not, and the published outcomes differ: brown to black in the open formula, magenta here. That is either a real difference in the chemistry or a difference in how far each supplier bleaches, and nothing this course has read distinguishes the two.

Safety

⚠The four bottles, and the sentence that stands in for a hazard assessment

The printing kit’s instruction sheet says: “The solution should be considered poisonous.” No chemical is named, no route of exposure is given, no first aid is offered, and no document in the box tells the reader what the solution is. That sentence is doing the work of a safety data sheet, and it cannot.

Treat the four solutions as follows, on this course’s classification rubric rather than on any manufacturer’s assessment, because none has been published:

• Gloves for all four, as the sheets themselves require — nitrile or latex, and see glove selection. The printing solutions stain skin blue and the stain is only cosmetic; the staining of wood, metal and plastic that the sheet warns about is not.
• Eye protection for the toning kit’s concentrates, which its own sheet asks for along with an apron. The 14 per cent carbonate stock is the most hazardous liquid in this entry: its substance sheet classifies the solid as causing serious eye irritation and being harmful if swallowed.
• Normal room lighting throughout, for everything. Both processes are sensitive to ultraviolet only. This removes a whole class of darkroom risk and it is the strongest practical argument for cyanotype as a first process.
• Neither kit goes in a food refrigerator. Both sheets say so, and it is the one storage instruction they agree on.

The hazard that is on none of the documents in either box. Potassium ferricyanide is a stable, low-spin iron(III) complex in which the cyanide is bound to the metal and is not free to act as a poison — which is why the substance sheet in the company’s library reads “Not classified”. But strong acid liberates hydrogen cyanide from it, and that hazard appears nowhere in Bostick & Sullivan’s literature: not on the instruction sheet, not on the store page, and not on the LabChem sheet the company republishes, which lists strong acids only as an incompatibility and gives the decomposition products as potassium oxide and the oxides of carbon. The rule is simple and absolute and this course states it here because the box does not: nothing acidic goes near solution B or anything that has held it. See potassium ferricyanide and incompatibilities.

The dilution is doing most of the safety work, and it should be understood as doing it. The substance sheets classify solids at 100 per cent. The liquids in the boxes are at 10 to 40 per cent, and the liquids in the trays are at roughly 5, 12.5, 0.7 and 2 to 4 per cent. The concentrate is the thing to be careful with; the tray is comparatively benign. That is a normal state of affairs and it is worth saying explicitly, because the reverse mistake — being careful of the tray and casual with the bottle — is the common one.

Ferric ammonium citrate is an eye irritant and a mild skin irritant on the company’s own sheet for the solid, with the additional note that prolonged eye contact may cause a brownish discoloration. Splashes get flushed; see first aid.

Potassium carbonate is the one that needs respect in the bottle. Harmful if swallowed, causes skin irritation, causes serious eye irritation, may cause respiratory irritation, and “Store locked up” on the sheet for the solid. The 14 per cent stock is not the solid, but it is an alkaline concentrate and it should be poured, not splashed. An alkali splash is an alkali spill.

Tannic acid is the mildest thing in either box — not classified as hazardous under either the OSHA standard or GHS on the company’s own sheet — and it will stain everything it touches a tan brown that darkens with time.

Hydrogen peroxide is bought separately and is not innocuous at strength. The 3 per cent drugstore solution the sheet asks for is dilute; if a stronger stock is substituted it is a different hazard. See hydrogen peroxide.

The chromium question, answered by absence. Nothing in either box is a chromium compound, on the supplier’s own published composition. The company’s separate house formula is another matter, and this course does not use it: the chromium ruling is that chromium(VI) is not used at any level, anywhere, and Ware’s improved classic is recorded at Level D for that reason. If the kit does contain the dichromate of the house formula — which nothing states and nothing rules out — the buyer has no way of knowing, and that is the strongest practical reason on this page for wanting a composition on a sheet rather than in a parenthesis.

Storage

The bottles as sold, at room temperature, separated. The printing kit’s own instruction is “approximately 1 year from the date of purchase if stored in their original separate containers” — note separate, which is the supplier saying without saying it that A and B do not keep together. The toning kit’s is “a shelf life of 10 years at room temperature”, which is a remarkable claim to print and comes with no evidence attached.

Away from light, on the evidence of the substance sheets rather than the kit sheets. Neither kit sheet says to keep the bottles dark. The company’s own sheet for the green citrate says “Protect from light. Sensitive to light. Store in light-resistant containers”, and its sheet for tannic acid says the same and adds an inert-gas blanket. A brown bottle in a cupboard costs nothing and is what this course recommends for all four.

Not in a refrigerator that holds food. Both sheets say so, and it is worth obeying for the reason they do not give: an unlabelled bottle of brown liquid in a kitchen is exactly the situation the unlabelled or unknown container procedure exists for.

The mixed emulsion has no published life, so give it none. Mix what the drop table says for the sheet in front of you and coat it. If there is a surplus, treat it as spent rather than as stock; there is no figure to keep it against.

Working toning solutions may be kept, and the sheet says how. “Store working solutions in light tight containers for future use.” No time is given, so date the container — see labelling a container — and judge it by the replenishment behaviour rather than by the calendar.

Label everything the moment it leaves the original bottle. The kit’s own bottles say “Cyanotype Solution A” and “Cyanotype Solution B” and not what is in them, so a decant into an unlabelled jar produces a container that nobody, including its owner, can identify. Write the substance name and the percentage from the store page onto the label.

Incompatibilities

The unusual thing about this entry is that three of the four solutions appear on one another’s incompatibility lists, on the supplier’s own substance sheets. Used in the order the sheets prescribe, with a wash between, that is harmless. Kept carelessly, it is not.

Ferricyanide and acid: the absolute one. Strong acid liberates hydrogen cyanide from potassium ferricyanide. Neither kit contains an acid, so the risk is entirely one of housekeeping: an acid stop bath from another process in the same sink, a bottle of acetic acid on the same shelf, a tray used for both. Keep solution B and everything that has held it away from acids of any strength, and never pour a ferricyanide solution into a drain that has just taken one.

Tannic acid and the alkali in its own box. The company’s sheet for tannic acid names strong bases and alkalis among its incompatible materials, and the other bottle in the same kit is a 14 per cent alkali. In the tray sequence they never meet — bleach, wash, tone — and the sheet’s own instruction to transfer the print “from the wash bath” is the only thing standing between them. Do not mix the two concentrates, do not use one tray for both, and do not pour them into the same waste container.

Tannic acid and the iron salt in the other box. The company’s sheet for green ferric ammonium citrate names tannins among its incompatible materials, which is the same reaction the toning kit uses on purpose: iron and polyphenol form a dark complex. Nothing bad happens on a finished print. Something useless happens if a tannic acid solution gets into a bottle of sensitiser, and something staining and permanent happens if a tannin-loaded brush or rod is used to coat.

Potassium carbonate and acids and metals. The carbonate sheet names oxidising agents, metals and acids. Acid plus carbonate is carbon dioxide and a mess rather than a hazard at these strengths, but the metals matter for equipment: aluminium trays, an unanodised metal squeegee or a steel funnel do not belong in an alkaline bath.

Both iron salts and strong oxidising agents, on both sheets. The relevant oxidising agent in a darkroom is hydrogen peroxide, which is used in this process on purpose and only ever on a washed print. It has no business near a bottle of sensitiser.

Brushes and rods are shared at your peril, and the sheet agrees. “If you are coating with a brush you should only use it for Cyanotype printing. Avoid using a brush that has been used to coat other alternative process chemistry.” A glass rod may be shared if it is washed properly. The reason is contamination rather than reaction: iron(II) from anywhere will fog a cyanotype coating, and a silver process brush will do worse than that.

Buffered paper. An alkaline reserve in the sheet is a slow version of the toning kit’s first bath. The store page’s instruction to use unbuffered cotton rag is a compatibility requirement, not a preference.

Waste

The wash water is the bulk of it and it is not nothing. The first tray carries away the whole of the unexposed sensitiser: ferric ammonium citrate and potassium ferricyanide at whatever the coating left behind, plus the yellow stain the sheet tells you to wash out. The ferricyanide’s own aquatic figures are mild — LC50 to fish 1869 mg/L on the company’s sheet — and home darkroom volumes are small, but mild is not nothing. The standing arrangement is on the disposal page and in general chemical waste, and the first thing to establish is what your local authority accepts.

Never into an acidic drain. This is the incompatibility restated where it is most likely to be broken. A ferricyanide solution and an acid stop bath must not meet in a waste container or a trap.

Spent concentrates, if a bottle has to be discarded. Solution A at 25 per cent and solution B at 10 per cent are the concentrated case of the paragraph above. Keep them separate, keep them labelled, and do not combine them for convenience: mixed, they are a sensitiser that will precipitate pigment in the container.

The supplier’s own disposal claim for the toning kit, which this course records and does not adopt. The toning sheet says: “Depleted solutions may be poured down the drain, with plenty of water. Bleaching and Toning Solutions are safe for septic systems and the environment.” Two observations. First, it is a claim with no data behind it, made about two solutions whose composition appears nowhere on the sheet making the claim. Second, and more concretely, a depleted bleach bath is not the solution the claim describes: it carries the iron and the hexacyanoferrate that came off the prints. The course’s position is the standing one — check with the local authority, and treat the used baths as darkroom chemical waste rather than as household drainage — and the reason for stating it here is that a beginner reading only the box will be told otherwise.

Tannic acid stains and does not rinse away. A depleted toning bath will mark a sink, a bench and a plastic tray permanently. That is cosmetic rather than hazardous, and it is a reason to keep a dedicated tray.

Paper and packaging. Sensitised offcuts, test strips and blotters carry iron and ferricyanide. Dry them, keep them out of the compost and put them in general waste rather than in recycling. Empty kit bottles should be rinsed into the wash-water stream rather than into a sink and then discarded.

Troubleshooting

The coated sheet is blue before it is exposed. Iron(II) is already present, from stray ultraviolet or from contamination — a shared brush, a dirty rod, a tray that held something else. See blue fog in cyanotype highlights. The kit sheet gives no diagnostic of its own here, which is a real gap: the competing kit publishes the greenish-yellow test for a correctly dried sheet and this one does not.

The print is weak and the highlights have gone. Almost always under-exposure, because the correct exposure looks over-exposed and the shadows should have begun to reverse before the frame comes out of the light. See weak cyanotype maximum density, and before concluding anything, dry the print: it is not finished when it is wet.

All the blue washed out in the first tray. The sheet’s own warning, stated in advance: the blue seen during exposure is non-archival. This is under-exposure in its most dramatic form.

The print faded weeks later and the paper looks fine. Alkali. Check the mount board, the sleeve and whether it has been handled, and read cyanotype bleached by an alkaline wash. Before assuming the worst, try the sheet’s own remedy: two to four weeks in the dark will bring back a print that has merely been reduced.

Coppery, metallic shadows. Bronzing, from the heavy exposure this process needs. See bronzing and reversal; it is usually a sign of being at the right end of the exposure rather than the wrong one.

Blue has crept out of a shadow into the highlight beside it. Surplus iron(II), which this kit’s sensitiser carries a quarter more of than the open formula does — see the arithmetic under The mechanism. It is worse on a heavily sized sheet and worse after a long exposure.

Blue came off in the wash and coloured the water. Some is normal and the sheet says so. A lot is peptisation of the pigment out of the paper; see Prussian blue bleeding by peptisation.

A yellow stain in the highlights that will not wash out. Residual iron. See yellow iron stain in cyanotype highlights. Note that this kit publishes no clearing bath at all, where the Photographers’ Formulary sheet publishes an oxalic acid spot treatment; extending the wash is the only remedy in the box.

Streaks, brush marks or a patchy coating. Apply the sheet’s own rules before anything else: if you are still spreading after thirty seconds, or making more than six passes with the rod, you are using too much solution and should cut it by a quarter. Then see blotchy and streaked hand coating and mottled coating from humidity; if the solution beaded rather than wetted, repellency spots.

Small paper fibres balled up in the image. The sheet’s own diagnosis: over-brushing has abraded the surface. Lighter pressure, fewer strokes, and a paper with a harder size.

Soft or doubled edges on the image. Registration, not chemistry. See uneven contact print; the sheet’s split-back frame exists to let you inspect without disturbing it, and opening the wrong leaf will undo the alignment.

The toned print is brown where magenta was expected. The likeliest variable is the bleach: a short bleach leaves pigment behind and a long one does not, and the sheet’s own advice is to vary that time. Second likeliest is the toner strength, where the sheet gives a two-to-one range and expects the printer to choose.

The toner has slowed down. Replenish at 5 to 10 mL of Solution B per 8 × 10, which is the sheet’s own figure and the only replenishment number in this entry.

Two prints from the same box do not match. Ask how long the coating solution stood before it went onto the paper — the supplier gives no life for it — and how old the bottles are against the one-year figure. If neither explains it, the unstated iron content is the variable nobody can check, which is the argument of this whole page.

Blue fingers. Gloves next time, and strong soap for what is already there.

Experiments

Find out whether the bottles contain oxalic acid. This is the experiment this page most wants somebody to do, because it would settle the question the documentation leaves open. Measure the pH of solution A and of solution B straight from the bottle with a calibrated meter — see pH meter calibration — and compare against a 25 per cent solution of green ferric ammonium citrate and a 10 per cent solution of potassium ferricyanide that you make up yourself from bulk chemicals. The company’s own substance sheet gives pH 6 for a 5 per cent ferricyanide solution; a bottle sitting well below that is carrying something acidic. A null result is as publishable as a positive one, and either would be the first independent statement about this product’s composition.

Put the kit against the open formula, one variable apart. Mix the classic sensitiser at 20 per cent and 10 per cent from bulk chemicals, coat two strips of the same paper from the same batch, expose them together under the same source and read both on a densitometer. The predicted difference is a quarter more iron for the same ferricyanide, and nobody has published what that is worth.

Measure the life of the mixed emulsion, which the supplier declines to state. Mix twenty drops of each, coat a strip immediately, then at one, two, four, eight and twenty-four hours, keeping the mixture in the dark. Expose all six identically. You will have a number the maker does not publish and a curve where it publishes nothing.

Calibrate the drop. Count drops from the supplied dropper into a tared weighing boat until you have a gram, and repeat ten times — see weighing a solid for the technique and balance and thermometer check for the instrument. That single number converts the whole drop table into millilitres, lets the yield claim be checked against 250 mL, and tells you which of the supplier’s three different yield figures is the honest one.

Test the “no hair dryer” claim. The company says its own testing showed natural drying gives a superior image and publishes nothing else about it. Two identical coatings, one air dried for an hour and one dried warm, exposed and processed together, read on a densitometer. This is a manufacturer’s claim that can be checked in an afternoon.

Map the bleach. The toning kit’s whole colour range is controlled by time in the first bath, and the sheet gives one number and an invitation. Bleach six identical prints for 30 seconds, 1, 2, 3, 5 and 8 minutes, tone them all identically, and photograph the set. That is the colour chart the supplier does not print.

Compare the two published bleaches. This is the open question at the end of The mechanism. Take matched prints, bleach one set in the 0.7 per cent potassium carbonate this kit gives and the other in the ammonia bath the open tannic acid toner gives, then tone both in the same tannic acid bath at the same strength. One supplier publishes magenta and the other brown to black from what is nominally the same chemistry; a careful printer could establish whether the difference is real.

Time the reoxidation, with and without peroxide. One print through the 60-to-90-second peroxide bath, its twin left to dry in the dark, both read at ten minutes, one hour, six hours and twenty-four. This measures the process the sheet describes three separate times and never explains, and it will also show how much of the “it looks weak when wet” effect is real.

Test the recovery claim. Deliberately reduce a spare print — a few minutes in a very dilute alkali — then put it in the dark for the two to four weeks the sheet promises and read it before and after. The supplier makes a specific, checkable claim about permanence recovery, and it deserves checking.

Record all of it. A bought product earns a line in the formula version record as much as a mixed one does: the kit size, the purchase date, the date each bottle was opened, the water used, and what the first sheet off each box did. On a product whose composition is two percentages in a parenthesis and whose materials are not specified at all, your own record of the bottles is the only specification that will ever exist.