Moersch MT3 Variotoner

This is a product page, not a formula page. It is here because the sepia toner most European printers actually buy is a bottled thiourea kit, and no maker publishes what is in one. What follows is what Moersch publishes, which is an adjustment table, a bleach dilution range and thirty pages of plates; what his three safety data sheets disclose, which is four substances and the pH and density of every bottle in the box; what the two together still do not say; and the open formula the course teaches that comes nearest.

Two warnings before the detail, because this page differs from every other product page in the library. First, the bought product does not buy its way down the safety rubric. A bought selenium toner does — the reader who buys HARMAN’s bottle has bought their way out of weighing a Level C powder. Here the mixture as sold is still classified a suspected carcinogen and a suspected reproductive toxin, and it is still an open tray. This course gives no home procedure for thiourea toning, and that ruling is made on the thiourea page and in Part XX, not here. Second, the maker’s own guide is the best account of indirect toning in this corpus and is worth reading whether or not you buy anything: it was written by somebody standing at a tray, and it contains a disagreement with itself that nobody has resolved.

Moersch Photochemie (Wolfgang Moersch) — 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
Potassium ferricyanidenamed on the sheet as Potassium hexacyanoferrate(III)CAS 13746-66-2The oxidant of Part 1. The maker's own guide describes a bleach's job as transferring the image silver into a silver salt and names potassium ferricyanide as what most bleaches contain; the sheet itself assigns no function	<20%	H319, H411
Sodium bromideCAS 7647-15-6Recorded on the sheet as not classified, and given no function there. That it is the halide half of a ferricyanide-bromide bleach is the course's reading, marked as an inference, and the substitution of the sodium salt for the potassium bromide of the free formulas is the maker's own and unexplained	<6%
Thioureanamed on the sheet as ThioharnstoffCAS 62-56-6The sulphur source of Part 2, named in German on an otherwise English sheet. Moersch calls the product an odourless thiourea toner for indirect sulphur toning and states in his guide that a thiourea toner converts bleached silver bromide to silver sulphide; the sheet assigns no function, and every hazard statement the mixture carries comes from this line	<1%	H302, H351, H361d, H411
Potassium carbonate (anhydrous)named on the sheet as Potassium carbonateCAS 584-08-7The alkali of Part 3, which the maker calls the activator and which is the control the whole product is built around: the toner part is held constant and the shade is chosen by how much of this goes into the litre. The sheet assigns no function and does not mention the toner it activates beyond calling itself the activator for part A	35 %	H315, H319

Not disclosed. Moersch publishes no composition for any of the three bottles. What the three safety data sheets give is one or two substances each, and two of the four figures are upper bounds rather than quantities: potassium hexacyanoferrate(III) at under 20 per cent w/w and sodium bromide at under 6 per cent in the bleach, thiourea at under 1 per cent in the toner, and potassium carbonate at 35 per cent in the activator. Nothing else in the bleach or the toner is named at all. Neither the guide nor the product page nor any sheet gives a pH for a working bleach, a working toner or any of the five settings in the adjustment table; a working temperature for any step; a capacity in sheets per litre or per print for either bath; a keeping figure for the toner once it has been mixed with the activator; the thiourea concentration of a working bath at any setting; a conversion fraction or any measure of how much of a bleached image a given setting actually sulphides; or any account of why the maker's own adjustment table runs from brown-black at the least alkali to bright yellow at the most while the same document's text says that the higher the pH the darker the brown. A reader who wants to know how alkaline the tray in front of them is, or to change that number and watch the hue move with it, cannot get there from Moersch's literature — and here, unusually for this library, the open formula that would answer it is one the course is willing to print in full and still asks nobody to make at home.

Nearest open formula. Kodak T-7a — The same process, published in full seventy-nine years earlier, with a different sulphur donor and a different smell. Both bleach a finished print in ferricyanide and a bromide until the image is a faint yellow-brown, wash it, and put it into a bath that converts the silver halide to silver sulphide. Kodak prints every quantity — 75 g of ferricyanide, 75 g of potassium bromide, 195 g of potassium oxalate and 40 mL of 28 per cent acetic acid in two litres for the bleach stock, 45 g of sodium sulphide in 500 mL for the toner stock — and gives one bleach time, one toner time and one result. Moersch prints no quantity for anything, and gives instead five settings, a bleach dilution range of 1+10 to 1+200, and a hue the printer chooses. So the trade is the formulary's usual one inverted twice over. The open formula is the one with the numbers and the one whose bath stinks: sodium sulphide releases hydrogen sulphide, which is why the odourless toner exists at all. The bought product is the one that removes the gas and substitutes a suspected carcinogen and reproductive toxin, so it does not buy its way down the safety rubric the way a bought selenium toner does — both pages sit at Level C, and this course gives a home procedure for neither. What the bought kit really sells is control: T-7a has one colour and MT3 has a table of them, and the table is the thing no published sulphide formula in this library offers.

Purpose

To turn a bleached silver print into a silver sulfide print odourlessly, and to let the printer choose the hue rather than accept the one the formula gives.

The maker’s own description is one sentence: “Odourless thiourea toner for indirect sulphur toning.” Everything else on this page follows from the three words in it that matter.

Indirect. The print is bleached first, in ferricyanide and a bromide, until the metallic silver has become silver bromide; only then does it enter the toner. That is the sepia toning process Kodak published in 1928 and still publishes, and this product is a packaged instance of it rather than a new chemistry.

Sulphur. The end state is silver sulfide, and Moersch says so of this product himself: a print whose bleached silver bromide has not yet been toned “must therefore either be dissolved by fixation or converted into silver sulphide by toning again”, in his MT5 sodium sulphide bath or in MT3. The sulphur donor is thiourea rather than sodium sulfide, which is what removes the smell — and, on the modern classification, is what makes the exchange a bad bargain rather than a free one.

Odourless. This is the selling point and it is the whole reason the product class exists. A sodium sulfide bath gives off hydrogen sulfide, which stinks, fogs unexposed photographic material and has a workplace exposure limit. Moersch’s own advice for his sulphide toners is to tone outdoors if the darkroom has no ventilation. A thiourea bath does none of that. What it does instead is set out under Safety, and it is not nothing.

And one purpose that is this product’s alone rather than the process’s:

To choose the colour. Every published sulphide toner in this library has one result. Moersch sells the toner and the alkali in separate bottles precisely so that the printer can mix them in different proportions, and prints a table of five settings running from brown-black to bright yellow. The variable is not the thiourea. It is the alkali, and the table is the product.

Recommended uses

Indirect toning of black and white paper, in a dish. That is the whole of the application named anywhere in this product’s literature. No film, no plates, no machine process, no alternative process; the safety data sheets say only “Toner” and “Toner for silverprints”.

Choosing a hue rather than accepting one. The maker’s range is “shades from light yellow to golden ochre to reddish brown”, and the two controls are named: the mixability of toner and activator, and the degree of bleaching. Both are continuous, which is why this product has a table and a formula has a result.

Highlight-only warmth, with a weak bleach. Bleach at 1+20 to 1+50 for a short time and only the highlights carry colour; the higher the dilution, the smoother the transition into the untoned mid-tones. The guide’s own worked example is 40 seconds at 1+30 on Ilford Multigrade IV followed by 30 seconds at setting B.

Split-toned prints, deliberately. Because thiourea reaches only what the bleach converted, a partial bleach produces a print with two image substances in it, and the boundary is a printing decision rather than a fault.

After a pre-tone, when the shadows are to survive. This is the sequence the guide is really built around and it is the one place where three of this maker’s products meet. Tone first in MT1 selenium or in a sodium sulphide bath, then bleach, then tone in MT3. Selenium always starts in the shadows, so the pre-toning time decides how far up the scale the protection extends; the bleach then cannot touch what was already converted, and the thiourea toner works on everything above it. The guide’s worked examples include selenium 1+10 for two and a half minutes, a bleach at 1+20 for one minute, and setting C.

On papers with a high bromide content, if deep brown is what you want. Moersch’s 2007 list of papers that still tone to deep brown — Kentmere Bromide, Adox Nuance, Fomabrom and Fomabrom Variant III, Adox Fine Print VC and all the ILFORD papers — is nearly two decades old and several of those papers are gone. The rule behind the list is not: a chloride-rich emulsion tones yellow whatever the donor.

Not as a rescue, and not on an unwashed print. The single loudest instruction in the whole of this product’s literature is that the print must be completely washed before bleaching. Residual thiosulfate turns the bleach into a reducer, redevelopment becomes impossible, and at least the highlights go irretrievably.

When another formula is preferable

• Almost always, for a home darkroom, and this is the honest headline. The course’s ruling on thiourea is Level C and it applies to the bought product as much as to the raw substance, because the classification survives the dilution. If the question is “should I tone sepia at home”, the answer this course gives is the hypo alum bath T-1a, the only sepia route in the formulary at Level B, which reaches a silver sulfide image without a sulfide reagent or a thiourea bath being handled at all.
• Where the composition matters more than the colour, Kodak T-7a, the nearest open formula and the subject of its own section below. Every quantity published, in two printings seventy-eight years apart, and the disagreement between them printed too.
• Where a simpler published sulphide route is wanted, Kodak Limited’s T-52 — a plain ferricyanide-bromide bleach with no oxalate and no acid, and a sulphide bath at 50 mL of a 200 g/L stock to the litre.
• Where a redder result is wanted than a sulphide bath alone gives, Kodak Limited’s T-56, which puts selenium into the sulphide bath after the bleach. It is Level D and is read rather than made.
• Where the print is to be protected and must not visibly change, no brown toner is the answer. GP-1, Kodak’s gold protective solution, is published in full at Level B; a bought selenium toner such as MT1 or HARMAN’s is the other route, and on neutral papers its intended outcome is that you cannot see it.
• Where the print is not permanent enough and toning is being asked to fix it, nothing here will help. That is a washing and fixing problem, and the answer is ILFORD WASHAID, Kodak’s hypo clearing agent or the open sulfite washing aid followed by a full wash, proved with the residual hypo and silver tests. A bleach met by residual thiosulfate does not tone a print; it eats it.
• Where you want to understand what an odourless toner is, read this page and the thiourea entry and buy nothing. That is a legitimate use of a product page and on this particular product it is the one the course recommends most often.

What the maker publishes

Three bottles, two documents, three safety data sheets, and — for once in this category — a genuinely useful quantity of physical data. What there is not, anywhere, is a composition, a temperature or a capacity.

Three parts, sold as a kit or singly. Part 1 Bleach, Part 2 Toner (thiourea), Part 3 Activator (alkali). Kit 1 holds 100 mL of bleach concentrate making 1 to 4 litres of working solution, plus 100 mL of toner concentrate and 250 mL of activator making 2 litres. Kit 2 holds 250 mL of bleach making 2.5 to 16 litres, plus 250 mL of toner and 1000 mL of activator making 5 litres. At the retrieval date the shop listed the toner concentrate at €15.65, the activator at €23.00, Kit 1 at €25.50 and Kit 2 at €58.20, all including VAT.

And a reason for selling the parts separately, which is also the clearest statement of what the product is. “Different amounts of activator are required depending on the desired image tone. For this reason, all concentrates are also available as single products.” A printer who works at the dark end of the range will run out of toner first; one who works at the yellow end will run out of activator first. That is not a packaging quirk, it is the adjustment table expressed as a price list.

The adjustment table itself, which is the single most useful thing any manufacturer has contributed to this course’s account of brown toning.

⚗The MT3 Vario matching table, as Moersch prints it

The thiourea part is held constant at 50 mL. Only the alkali moves, and the water makes up the difference to a litre.

Setting	A	B	C	D	E
Moersch’s label	brown-black	medium brown	yellowish brown	dark yellow	bright yellow
Toner part	50 mL	50 mL	50 mL	50 mL	50 mL
Controller / Activator	5–30 mL	50–60 mL	90 mL	130 mL	180 mL
Water	930 mL	900 mL	860 mL	820 mL	770 mL

His sentence under it: “The color saturation becomes higher the more alkali solution is added to the toner.”

Read what this table is and is not. It is a maker’s dosing table: five points on a continuum, with a hue attached to each and nothing between them. It is not a composition — the toner part is a concentrate whose only declared substance is thiourea at less than one per cent, and the activator part is a 35 per cent potassium carbonate solution. And it is not a promise: the guide’s own plates show setting E giving a reddish brown with high shadow density on one paper and a bright yellow on another. The paper is in this table as surely as the activator is, and it is the column Moersch could not print.

A bleach dilution range, and one recommendation inside it. 1+10 to 1+200. A dilution of 1+75 “works sufficiently slowly to be able to assess the progress of the bleaching”. The product page’s version is blunter and easier to act on: if the bleach is not to go all the way, dilute at least 1+20, and the bleaching time is then between 20 seconds and three to four minutes.

A washing rule with a visible end point. Bleach at 1+50 or weaker needs only two to five minutes of washing before toning to remove the yellow coloration of the gelatin; strong bleach at 1+10 takes much longer. And then the instruction that replaces a time altogether: “Before toning, water must be added until the yellow colour disappears completely!”

One toning time, and it is short. “The toning of the bleached areas is complete after 20 to 30 seconds.” Almost every plate in the guide is made at 30 seconds.

Keeping, in three statements. The bleach solutions have an almost unlimited shelf life. The concentrates can be kept for years even after opening. The toner can be refreshed with concentrate when the effect wears off.

Thirty pages of plates, each with its recipe. This is where the guide earns its place. A named paper, a named developer, a bleach dilution, a bleach time, a toner setting and a toning time, under a picture of the result: 1+30 for 40 seconds then setting B; 1+20 for 30 seconds then setting A; 1+10 for 30 seconds then setting E; 1+40 for 90 seconds then setting C; MG Warmtone bleached in 1+40 for 30 seconds then setting D. No other manufacturer in this corpus publishes anything like it.

And three safety data sheets whose section 9 is unusually full. Every one of them, dated January 2025:

	Part 1 Bleach	Part 2 Toner	Part 3 Activator
Form and colour	fluid, colourless	fluid, yellow	fluid, colourless
Odour	odourless	odourless	odourless
Density at 20 °C	1.17 g/cm³	1.02 g/cm³	1.4 g/cm³
pH at 20 °C	7–8	6	11.4
Water	more than 80 %	more than 95 %	65 %
Organic solvents, VOC	0 %	0 %	0 %
UFI	N140-Y06P-Y00U-WW19	8H30-X02A-400V-XUHW	Q600-604U-600K-5HTD

Set that beside HARMAN’s selenium sheet, which records every physical property of its liquid except that it is a liquid as Not known, and the difference is striking. Moersch is the most forthcoming manufacturer in this corpus about the physical properties of what he sells, and among the least forthcoming about what is in it. Both facts are on the same five pages.

One of those numbers deserves to be lifted out. The toner concentrate is pH 6. It is not an alkaline bath and it is not a toner until the activator goes in. Everything Moersch writes elsewhere about thiourea baths being “highly alkaline” — up to pH 13.4 — is written about the free Agfa formulas, which use sodium hydroxide. This product’s alkali is a carbonate, its concentrate is pH 11.4, and no working bath at any of the five settings has a published pH at all.

What is not disclosed

The composition of the bleach, beyond an upper bound on two substances. Potassium hexacyanoferrate(III) under 20 per cent w/w and sodium bromide under 6 per cent. Nothing else in that bottle is named, and both figures are ceilings rather than quantities.

The composition of the toner, beyond an upper bound on one substance. Thiourea at less than one per cent w/w, in a liquid the same sheet records as more than 95 per cent water. What the remainder is, the sheet does not say and the guide does not either.

Any pH for any bath the print actually enters. Three concentrates have published pH values. The five settings in the adjustment table have none, and the difference between setting A and setting E is a factor of six in alkali. On a bath whose maker warns elsewhere that highly alkaline thiourea solutions soften gelatin, that is the omission with teeth.

Any temperature, anywhere. Not a working temperature, not a range, not a tolerance, for the bleach, the wash or the toner. Every Kodak and ILFORD toning document in this corpus gives one.

Any capacity. No sheets per litre, no prints per bath, for either the bleach or the toner. What the maker gives instead is a symptom and a remedy: refresh with concentrate when the effect wears off.

Any keeping figure for the mixed working toner. The concentrates keep for years and the bleach working solution keeps almost indefinitely. The bath that has toner and activator in it has no stated life at all.

What the settings do to the chemistry. The table gives volumes and colour names. It does not give a thiourea concentration, an alkali concentration, a pH, or any account of why more alkali should change the hue.

How much of the image is converted. No conversion fraction, no measurement, no accelerated-ageing result. The permanence argument for a sulphide image is Kodak’s and is made about the process; nothing in this product’s literature quantifies it for this product.

And the disagreement the maker never addresses, which has its own callout under The mechanism: the same guide that prints this table says, four pages earlier, that the higher the pH the darker the brown tone.

!Why the bands cannot be added up here either — and why the reason is different

On HARMAN’s selenium sheet the temptation is to total three bands and call the remainder water. Here the arithmetic does not even get started, and it is worth seeing why.

Two of the four figures are one-sided. <20%, <6% and <1% are ceilings. A ceiling has no lower end, so there is no interval to add: the bleach could hold nineteen per cent ferricyanide or two, and both readings satisfy the sheet.

Two of the three sheets name only what forces a classification. The toner sheet names thiourea and nothing else, because thiourea is the only substance in that bottle driving a hazard statement. A composition table lists what classifies, not what is present, and on a mixture that is 95 per cent water the two lists are very different lengths.

And one sheet is the exception that proves the rule. The activator declares potassium carbonate at 35 per cent w/w in section 3 and water at 65 per cent in section 9. Those two figures are both the maker’s, they are printed on the same document, and between them nothing is left over. That is not the course reconstructing a formula; it is the maker disclosing one, and it is the only place in this library where a product page can say so. It is also, unsurprisingly, the least interesting of the three bottles.

Read as hazard documents these three sheets are good evidence. Reassembled into a recipe they would be an invention with a citation stapled to it — and the invention in this case would be a working thiourea toner, which is close to the last thing this course should put into circulation.

Disclosed components

Four substances across three sheets, and no sheet names more than two. Each is discussed here by name, with the figure its own sheet prints and no other.

Potassium ferricyanide, named on the sheet as potassium hexacyanoferrate(III), CAS 13746-66-2, EC 237-323-3, <20%, Eye Irrit. 2 and Aquatic Chronic 2. The oxidant of Part 1 and the substance the whole bench’s safety rules are written around. Moersch’s own guide describes the job of a bleach as transferring the image silver into a silver salt, and says that most bleaches contain potassium ferricyanide and potassium bromide — so the function here is the maker’s, in general terms, even though his sheet assigns none. Two of its properties matter more than its percentage. It is the source of the sheet’s supplemental statement EUH032, contact with acids liberates very toxic gas; and its transport entry names it as the technical name behind UN 3077, which is what puts the bleach into a dangerous-goods class at all. Its ecological figures are what earn the bleach its H411: an algal ErC50 of 1.7 mg/L and a freshwater PNEC of the same number, taken from ECHA. Read the encyclopaedia page before you open the bottle; the hazard is not the ferricyanide ion by itself, it is the ferricyanide ion meeting something acid.

Sodium bromide, CAS 7647-15-6, EC 231-599-9, <6%, not classified. The only line on any of the three sheets that carries a REACH registration number, and the only one the sheet prints without its per-cent sign — the figure reads simply <6 under a column headed % w/w. It carries no classification and no pictogram, and the sheet gives it no function. That it is the halide half of a rehalogenating bleach is the course’s reading, marked as an inference under Rule 7, though it is not a bold one: the whole point of a ferricyanide-bromide bleach is that the oxidised silver is caught in place as a halide rather than dissolved, and a bromide is what catches it. What is genuinely unexplained is the choice of the sodium salt. Every free formula Moersch prints in the same guide — Agfa 500, 501 and 502 — uses potassium bromide, and so does Kodak’s T-7a. He says nothing about why his own product uses the other cation, and this page does not supply a reason.

Thiourea, named on the sheet as Thioharnstoff, CAS 62-56-6, EC 200-543-5, <1%, Acute Tox. 4, Carc. 2, Repr. 2 and Aquatic Chronic 2. The sulphur donor, the reason the product is odourless, and the reason this page is at Level C. Three things about this line are worth noticing.

First, it is in German on an English sheet. Section 3 of the toner sheet is headed in English and prints its identifiers as “CAS-Nr.” and “EG-Nr.” with the substance name untranslated; section 8 spells the same substance “Thiorea” twice. This is a small manufacturer’s document rather than a corporate one, and it is worth saying so plainly, because it is also — unlike the corporate ones — specific about what is in the bottle.

Second, the whole of the mixture’s classification comes from this one line. Harmful if swallowed, suspected of causing cancer, suspected of damaging the unborn child, toxic to aquatic life with long lasting effects: those are thiourea’s harmonised statements under Regulation (EC) No 1272/2008, they are the toner’s, and there is nothing else on the sheet to share them with.

Third, the maker does state its function, in the guide rather than on the sheet, and the statement is the most useful mechanistic sentence in this product’s literature. A thiourea toner “cannot tone the remaining metallic silver, but only the areas where it finds silver salt (in this case silver bromide)”, where a sodium sulphide bath goes beyond the bleached areas. That single sentence explains the split tones, the visible edge, the loss of density on a full bleach, and why pre-toning exists.

Potassium carbonate, CAS 584-08-7, EC 209-529-3, 35 %, Skin Irrit. 2 and Eye Irrit. 2. The activator, and the one component on this page given as a point value rather than a bound. It is the control the product is built around: the toner part stays at 50 mL and the printer chooses the colour by choosing how much of this goes into the litre. Two consequences follow and both matter.

It is a carbonate, not a caustic. Moersch’s free thiourea formulas — Agfa 520 and 525 — are made with 3 g and 15 g of sodium hydroxide per litre, and he measures those baths at up to pH 13.4. This product’s alkali is a 35 per cent potassium carbonate solution at pH 11.4. A reader who transfers the pH 13.4 warning to this bottle has transferred it from a different bath, and although the working pH of a diluted carbonate solution is not published, the concentrate is already two orders of magnitude less alkaline than the figure that warning attaches to. The course notes the difference and does not calculate across it.

And its declaration is complete. 35 per cent potassium carbonate, 65 per cent water, both printed by the maker, nothing left over. Of the four disclosed components on this page it is the only one for which “what is in the bottle” is fully answered — and it is the bottle nobody wanted to know about.

What is in the bottles and not in the tables. Water, which no safety data sheet declares because it drives no classification, and which the sheets themselves put at more than 80 per cent of the bleach and more than 95 per cent of the toner. And whatever sits below the declaration threshold: a wetting agent, a sequestrant, a buffer, a preservative, a bromide in the toner of the kind the Agfa formulas carry at 40 g/L. The sheets’ silence about those is not evidence that there are none.

Behaviour

The bleach decides how much of the print changes; the toner decides what colour it changes to. Those two controls are independent and the maker separates them in every sentence he writes about the product. A weak, short bleach with a dark setting gives warm highlights on a cold print; a full bleach with a yellow setting gives a yellow print. The combinations are a grid, not a line.

Toning is fast and its end is a plateau. Twenty to thirty seconds for the bleached areas, and then nothing more happens, because there is nothing left for the thiourea to reach. This is very different from the polysulphide behaviour of a direct toner that keeps working in the wash, and it is why this product does not need a stopping bath.

A print not fully toned in thirty seconds is a tired bath. That is Moersch’s diagnostic for thiourea toners generally, given in the guide for the free formulas: it is an early sign of exhaustion, and the answer is to restore the bath rather than to extend the time past a minute. For MT3 the product page’s remedy is to refresh with toner concentrate. Note that the two remedies are not the same substance — the guide says regenerate with alkali, the product page says refresh with toner concentrate — and no document explains the difference.

The bath does not die of standing. The bleach working solutions have an almost unlimited shelf life; the concentrates keep for years after opening. What kills a bleach is light and air, which the safety data sheet lists among its conditions to avoid, and what kills a toner is use.

Untoned silver stays untoned, permanently. Because thiourea cannot touch metallic silver, the boundary between the bleached and unbleached parts of the print is a real boundary in the image substance, and it can read as an edge. Longer toning does not cross it. What softens the edge is a weaker bleach with a longer time, or a pre-tone that removes the boundary altogether.

A partial bleach that is never toned leaves the print worse than it started. This is the guide’s own warning and it is easy to miss. Bleached, untoned silver is silver bromide, which is neither stable nor fixed: it will tone itself over time by gas action, uncontrolled. It must either be dissolved by fixing or converted by toning again. Do not stop halfway and dry the print.

The whites yellow if the wash was short. Moersch attributes it to the bleach rather than the toner, and says it happens whichever bleach was used. It is a wash failure with a visible signature and it appears only after toning.

Highly alkaline baths soften gelatin. The guide’s warning belongs to the caustic Agfa formulas and to toning times past a minute, and its remedies are to dry the print between steps or to harden the gelatin beforehand with something like F-5a. Whether it applies to a carbonate activator at any of the five settings is not stated by anybody, and a printer working at setting E has a reason to find out on a test print rather than on a good one.

Image characteristics

The colour belongs to three things, and the toner is only one of them.

The paper, first. Moersch is explicit: the brown you get depends on the form of the silver the bleach removed, which is to say the ratio of silver chloride to silver bromide in the emulsion. A high bromide content promotes deep brown hues. Chloride-rich and mixed emulsions tone yellow, and he adds that this is true “irrespective of the nature of the toner” — thiourea, sodium sulphide or polysulphide alike. Most modern papers carry a mixed emulsion with a high chloride content. If your print goes yellow when you wanted brown, the first suspect is the paper and not the setting.

The setting, second. Light yellow, golden ochre, reddish brown, in the maker’s own words, across five published points. The plates show the range being used in both directions: setting A after a brief 1+20 bleach for a touch of warmth in the highlights, setting E after a hard 1+10 bleach for a fully yellow print.

The bleach, third, and it controls density as much as hue. A full bleach costs contrast and shadow density; stopping at the mid-tones keeps them. Kodak’s independent instruction for this class of toner is the practical form of the same fact: develop fully and print slightly darker than normal, because the toner will take density out.

The exception the guide records and does not explain. On Kentmere Kentona, setting E — the table’s bright yellow — produced “a reddish-brown image tone with high shadow density, even if the image has been completely bleached”. The table is a maker’s guide to his own product on unnamed paper; the plates are the same maker discovering that the paper has a vote.

Pre-toning changes the answer again. After a selenium pre-tone and a bleach, setting C raises colour saturation slightly while maximum black stays where it was — which is a different result from either toner alone, and the reason the guide devotes its last third to sequences rather than to baths.

And the permanence claim is the process’s, not the product’s. Kodak’s is that a silver sulfide image is one of the most stable forms of silver, and that where great permanency is required prints should preferably be toned to it. Nothing in Moersch’s literature quantifies that for MT3, and the Getty Conservation Institute’s atlas adds a complication worth knowing: sulphur toning is the one treatment X-ray fluorescence cannot easily identify afterwards, because the signal hides in the baryta. A sulphide-toned print keeps its permanence and loses its provenance.

The mechanism

Two steps, and the first one is not in dispute. The bleach oxidises the metallic silver of the print, and the bromide catches it in place as silver bromide; the ferricyanide is reduced to ferrocyanide in the process. That is Kodak’s 1928 account and the bleach’s own page carries it with the sources. Nothing leaves the print, which is what makes this a toner’s bleach rather than a reducer.

The second step, in the maker’s own words. Bleached silver bromide is “converted into silver sulphide by toning again”, in his sodium sulphide bath or in MT3. So the end state is silver sulfide and that is a manufacturer’s statement rather than this course’s inference.

What is not printed here is a balanced equation for the thiourea step. The course holds no source that gives one, and writing a plausible one would be the failure Rule 1 exists to prevent. What can be said, because Moersch says it, is the operational boundary: thiourea reaches silver salt and not metallic silver, where sodium sulphide reaches both. Any account of the thiourea mechanism has to explain that asymmetry, and this page does not have one to offer.

Why the colour changes at all is a question about particle size, not about the toner. Kodak’s primer is the source: silver sulfide’s colour varies from light brown to black according to its state of subdivision, and the state of subdivision of the toned image depends on that of the untoned image — which is why the primer’s advice is to develop a print for toning fully but not to over-expose it. The toner does not choose the colour; it inherits it from the silver the bleach converted, and that is the same reason a chloride-rich emulsion goes yellow.

And the role of the alkali, which is this product’s distinguishing feature and the part nobody has explained. Moersch’s system is that the toner part is fixed and the activator is the variable, and the safety data sheet now tells us what the activator is: a 35 per cent potassium carbonate solution at pH 11.4. That the alkali is the control is the maker’s statement. Why more of it should move the hue is not, and the course marks every reading of it as an inference under Rule 7.

⁇The direction of the alkali effect — one document, two answers, and now one new fact

This disagreement is already recorded in Part XX and on the thiourea page. The safety data sheets settle one of the three possibilities raised there and leave the other two open.

The text of the Brown Toning guide says the higher the pH, the darker the brown tone. Its example is a pair of free formulas: Agfa 520 with 3 g of sodium hydroxide per litre gives a delicate yellowish hue, Agfa 525 with 15 g gives a stronger, darker one.

The table in the same guide, for the maker’s own product, runs the other way. Thiourea held at 50 mL, and 5 to 30 mL of activator gives brown-black while 180 mL gives bright yellow. More alkali, yellower.

A third statement, on the page between them, sides with the table. Under a plate of a warm-tone paper toned in Agfa 525 — the more alkaline of the two free baths — Moersch writes that “with Warmtone papers the colour turns yellowish, due to the pH value of this toner”.

What the sheets add. Part XX listed “a different alkali” among the possible explanations. There is one: the free formulas use sodium hydroxide, the product uses potassium carbonate, and the two are not interchangeable in strength or in what they do to a bath. That removes one unknown. It does not resolve the direction, because the guide’s third statement is about a caustic bath and still runs the same way as the carbonate table.

What the course does with this. It reports it. Both statements are the same author’s, in the same document, about the same class of toner. No source in this corpus resolves them, no working pH is published for any of the five settings, and the honest practical conclusion is the one the guide’s own plates keep demonstrating: the direction has to be established on the paper in front of you, with a test strip, before it is trusted on a print that matters.

One inference this page will not draw. It is tempting to read the four disclosed components as a functional scheme — an oxidant, a halide, a sulphur donor and an alkali — and to conclude that any odourless sepia kit is built the same way. Moersch’s guide half invites it: “Odourless toners in shops are thiourea toners. They all contain bleach and toner concentrates. Some of them allow fine tuning of the colours by adjusting the pH-value.” That is a statement about a product class by somebody who competes in it, and it is not evidence about any other manufacturer’s bottle. The one other Moersch sheet the course holds, for MT1 selenium, declares three substances at point values rather than bounds — which shows that even the same maker’s sheets are not written to a single pattern.

The nearest open formula

Kodak T-7a, the sulfide sepia toner Eastman Kodak printed in its 1928 teaching primer and still printed, with one number changed, in 2006.

It is the nearest because it is the same process: bleach in ferricyanide and a bromide until only a faint yellowish brown image remains, wash, and redevelop the silver halide to silver sulfide. Where the two part company is instructive, and the comparison runs in an unfamiliar direction.

	Kodak T-7a	Moersch MT3 Variotoner
Composition	Published in full, twice, seventy-eight years apart	Not published; four substances across three hazard sheets, three of them as upper bounds
Sulphur donor	Sodium sulfide, 22.5 g/L in the working bath	Thiourea, less than 1 % w/w in a concentrate, unquantified in the bath
Smell	Hydrogen sulfide. Moersch’s advice for his own sulphide toners is to work outdoors if there is no ventilation	Odourless, and that is the product’s reason for existing
Bleach	18.75 g/L each of ferricyanide and potassium bromide, plus 48.75 g/L potassium oxalate and 10 mL/L of 28 % acetic acid	Ferricyanide under 20 % and sodium bromide under 6 % in a concentrate, diluted 1+10 to 1+200
Iron protection in the bleach	Potassium oxalate, present and explained: it dissolves the blue iron salt that causes blue spots	Nothing declared. The sheet names two substances and an oxalate is not one of them
Bleach time	Approximately 5 to 8 minutes in 2006; about one minute in 1928	20 seconds to three or four minutes, chosen by the printer
Toning time	Approximately 30 seconds, until no further change	20 to 30 seconds
Temperature	20 °C, stated	Not published anywhere
Colour control	None. One bath, one result	Five published settings from brown-black to bright yellow
Capacity and keeping	Not published	Bleach almost unlimited; concentrates keep for years; working toner not stated
Safety level	C	C
What the course recommends	Read it, and mix it only in a supervised laboratory	Read it, and buy it only if you have one

The last row is the argument and it is unusual twice over. Everywhere else in this library a product page ends by trading a known composition against a documented performance. Here both routes land on the same rung of the rubric, and neither is offered as a home procedure — so the trade is not about safety at all. It is about control. T-7a gives you every gram and one colour. MT3 gives you no grams and a table of colours, plus thirty pages of a maker showing you which bleach dilution goes with which setting on which paper. If what you want is to understand the chemistry, mix the open formula. If what you want is a specific hue on a specific paper, nobody has published an open formula that will get you there, and that gap is what the bought kit is selling into.

Two further things the comparison shows. First, the open formula is in one respect the more careful document: Kodak’s bleach carries potassium oxalate against blue iron spots and acetic acid against blisters, and explains both, where Moersch’s bleach sheet names two substances and no protective additive at all. A published formula can tell you why every line is there; a hazard sheet, by construction, cannot. Second, the odourless option is not the safer option, and this is the sentence to carry away from the page. It removes a gas with a workplace exposure limit and substitutes a suspected carcinogen and reproductive toxin in an open tray. That is a real exchange and it is one a printer should make knowingly rather than by buying the bottle marked odourless.

Safety

Level C, and the reasoning is the point of the page.

The three classifications, as their own sheets give them.

• Part 1, Bleach: Eye Irrit. 2 (H319) and Aquatic Chronic 2 (H411), signal word Warning, pictograms GHS07 and GHS09, precautionary statements P273, P305+P351+P338 and P337+P313 — plus the supplemental statement EUH032, contact with acids liberates very toxic gas.
• Part 2, Toner: Acute Tox. 4 (H302), Carc. 2 (H351), Repr. 2 (H361d) and Aquatic Chronic 2 (H411), signal word Warning, pictograms GHS07, GHS08 and GHS09, precautionary statements P273, P280, P308+P313 and P391. The sheet adds, in its own words, “For professional users only”.
• Part 3, Activator: Skin Irrit. 2 (H315) and Eye Irrit. 2A (H319), signal word Warning, pictogram GHS07, precautionary statements P280, P302+P352, P305+P351+P338, P403+P233 and P501.

Why C and not B. The rubric’s Level C criterion names reagents classified as carcinogenic, as reproductive toxins or as sensitisers at the concentrations used, where a fume cupboard or specialist disposal is the recognised control. The toner as sold is classified as two of those three. Its second criterion — any procedure whose waste cannot lawfully enter a domestic drain — is settled by all three sheets, each of which says the material and its container must be disposed of as hazardous waste. Princeton’s guidance requires local exhaust ventilation for thiourea toning solutions and advises avoiding the substance wherever possible. That is the whole argument, and it is the same one the thiourea page makes.

⚠Buying the bottle does not buy you out of this one

This is the place where the product-page category behaves differently from the way it usually does, and the contrast is worth stating in full.

On HARMAN SELENIUM TONER, the bought bottle is Level B while the solid inside it is Level C. The classifications are not in tension, because the level is assigned to an operation: weighing a powder classified fatal if swallowed and fatal if inhaled is a fume-cupboard operation, and diluting a bottled liquid that already contains it is not. The purchase removed the Level C step.

Here it does not, and the reason is the classification rather than the operation. Thiourea’s carcinogenicity and reproductive-toxicity classifications are not about a powder being weighed. They are about the substance being present, and the mixture as sold carries them: H351 and H361d are printed on the toner’s own safety data sheet, for the liquid in the bottle. There is no step to buy your way out of. The bath in the tray is a suspected carcinogen and a suspected reproductive toxin at whatever the working concentration turns out to be, and the maker’s own sheet says the product is for professional users only.

So this course gives no home procedure for it, and this page is the account of a product rather than an instruction to use one. If you meet it in a supervised laboratory: engineered extraction, splash goggles, chemical-resistant gloves changed the moment they are contaminated, and separate labelled waste for each of the three baths.

✕The bottle may arrive with no warning on it at all

Section 2.2 of the toner’s safety data sheet records that for packages whose contents do not exceed 250 mL, the pictogram, the signal word and the hazard statements are not required. Kit 1’s toner concentrate is 100 mL and Kit 2’s is 250 mL. Both are inside that limit.

So a printer can receive a bottle of a mixture classified suspected of causing cancer and suspected of damaging the unborn child with nothing on the label to say so. That is a labelling provision, not a statement about the contents, and the maker is not hiding anything: the same information is printed on his own shop page under Product safety, with the hazard and precautionary statements in full, and on the safety data sheet the page links.

The practical rule is the one the course gives everywhere: read the safety data sheet for the product in your hands before you open it, and never infer the hazard of a photographic chemical from the size of the bottle it came in.

The rule that governs the whole bench: no acid near the bleach, ever. EUH032 is printed on the bleach’s own sheet, and section 10.3 spells out what the sheet means: violent reaction with strong oxidisers, ammonia, nitrates and nitrites, with release of an acute toxic gas, hydrogen cyanide. Section 5.2 says the same substance is liberated if the bleach burns. A ferricyanide bath and an acid stop bath in the same room is an ordinary darkroom arrangement and a real hazard, and the control is a wash, a separate tray, a separate waste bottle and a separate shelf. The incompatibilities page governs and potassium cyanide’s page carries what the course knows about the gas.

Personal protection, as the three sheets specify it. All three ask for nitrile gloves to EN 374 at 0.11 mm with a breakthrough time of 480 minutes, permeation level 6 — the toner and activator sheets print both figures as minima, the bleach sheet prints them as a minimum thickness and a flat time. That is an unusually specific glove instruction, and it is the same one on all three parts. Glove selection is where that goes. Safety goggles with side protection for the toner and the activator, safety glasses to EN 166 for the bleach, and protective clothing. Wash hands before breaks and after work; keep it away from food, drink and animal feedingstuffs.

Ventilation. The toner sheet asks for the provision of sufficient ventilation and for local and general ventilation under storage; Princeton is stronger and asks for local exhaust ventilation for toning solutions containing thiourea. Run the ventilation check before a session rather than during one. HSE’s EH40 sets no workplace exposure limit for thiourea at all, and states in terms that absence from its list does not indicate that a substance is without risk — so there is no number here to work to, which is an argument for extraction rather than against it.

Sensitisation, which is managed differently from a dose. Neither this product’s sheets nor the harmonised entry classify thiourea as a skin sensitiser, though Japan’s NITE-CMC does and the thiourea page records the disagreement. Where a sensitiser is involved, HSE’s HSG262 principle applies: once a person has reacted, further exposure is prevented rather than managed, and being more careful next time is not a control.

First aid, in the sheets’ own words. Skin: take off contaminated clothing and rinse immediately with water. Eyes: rinse the opened eye for several minutes under running water and consult a doctor if symptoms persist. Swallowing: consult a doctor if symptoms persist — and for the toner, P308+P313, if exposed or concerned, get medical advice. The first-aid page has the course’s fuller procedure and the eyewash SOP has the technique.

Keep thiourea away from oxidisers absolutely. CAMEO records violent decomposition with hydrogen peroxide and nitric acid, and explosion when thiourea is ground with potassium chlorate. The toner’s own sheet says the same more mildly: violent reaction with strong oxidisers and strong acids.

Storage

All three parts at 15 to 25 °C, and each with its own instruction. The sheets agree on the temperature and diverge after it. The toner: store in a dry place, protect from sunlight, avoid heat and cold. The bleach: keep the container tightly closed, and avoid UV radiation, sunlight, and contact with air and oxygen. The activator: keep the container tightly closed, and P403+P233, store in a well-ventilated place.

The concentrates keep for years after opening, and the bleach working solution keeps almost indefinitely. Both statements are the maker’s, on his product page, and they are unusually generous for photographic chemistry. What has no published life at all is the bath with toner and activator in it.

Store the bleach away from anything acid, and not above it. This is the storage instruction the sheets do not print and the incompatibilities page does. A leaking bottle of citric acid stop bath on a shelf above a ferricyanide concentrate is the accident EUH032 is warning about, and shelf order is a control.

Label everything — the part, the setting, the dilution and the date mixed — using the labelling SOP. This product makes labelling harder than most, because the three concentrates are two colourless liquids and one yellow one, all odourless, and a working toner at setting A and one at setting E look identical. An unlabelled or undated container is the entry for what to do when that has already happened, and the unknown-container SOP is the procedure.

Out of reach, and out of a room where photographic materials are stored. The toner sheet’s own labelling is for professional users only; the bleach is a dangerous good for transport. Neither is a kitchen-cupboard article.

Incompatibilities

Acids, and this one governs everything else. Ferricyanide plus acid liberates hydrogen cyanide, and the maker prints EUH032 on his own bleach sheet to say so. No acid stop bath, no acid fixer and no acid rinse follows or precedes the bleach without a thorough wash between; no acid goes into its waste bottle; no acid is stored above it.

Ammonia, nitrates and nitrites, which the bleach’s section 10.3 names alongside strong oxidisers as producing a violent reaction with release of hydrogen cyanide. That is a more specific list than most sheets in this corpus print, and ammonia in particular is worth noting: Moersch’s own Agfa 502 bleach formula, printed in the same guide, contains 10 mL of ammonia per litre. His free formula and his product sheet are not describing compatible chemistry, and a printer who has both on the bench should keep them apart.

Residual fixer on the print, which is an incompatibility even though no sheet calls it one. This is the loudest instruction in the whole of the product’s literature: rinse thoroughly before bleaching, because thiosulfate turns the bleach into a reducer and the highlights go irretrievably. Moersch’s only related statement in the same guide is made about his selenium toner rather than about the bleach — after an alkaline fixer no rinse is needed before toning, after a sour fixer about ten minutes — and he gives no equivalent figure for the step that matters here. Wash until the residual hypo test says you have, not until a clock says so.

Sulphide toners and stop or fixing baths in the same waste container. Kodak’s instruction is explicit — the combination generates hydrogen sulfide gas — and solutions are discarded individually. MT3 itself is not a sulphide toner, but it lives on the same bench as one and shares a bleach with it.

Strong oxidisers, for the thiourea. Hydrogen peroxide, nitric acid, chlorates. CAMEO’s reactivity entry is emphatic and the toner’s own sheet agrees.

Metal trays and tanks, per Kodak’s general toning guidance, which allows only unchipped enamel, hard rubber or plastic. Iron in a ferricyanide bleach also has a specific consequence rather than a general one: it throws Prussian blue spots, which is what Kodak’s potassium oxalate is in the T-7a bleach to prevent and which nothing declared in Moersch’s bleach protects against.

Unexposed photographic materials in the room, on general principle for any toning bench.

Waste

Three baths, three sheets, and all three say the same thing. “This material and its container must be disposed of as hazardous waste… Do not empty into drains.” That instruction is printed identically on the bleach, the toner and the activator, and it is not qualified by dilution.

The hazardous-waste properties each sheet assigns, which is the most precise statement of why:

• Bleach: HP 4 irritant, HP 12 release of an acute toxic gas, HP 14 ecotoxic.
• Toner: HP 6 acute toxicity, HP 7 carcinogenic, HP 10 toxic for reproduction, HP 14 ecotoxic.
• Activator: HP 4 irritant.

Two of the three are dangerous goods in transport. Both the bleach and the toner ship as UN 3077, environmentally hazardous substance, fluid, n.o.s., class 9, packing group III, with the technical name given as potassium hexacyanoferrate(III) on one and thiourea on the other. The activator is not subject to ADR, RID, ADN, IMDG or ICAO-IATA at all. That is a clean summary of where the risk sits.

The aquatic figures, because H411 is the statement that decides the route. Thiourea’s PNECs on the toner sheet are 0.01 mg/L for freshwater, 0.001 mg/L for marine water and 0.38 mg/L for a sewage treatment plant. The bleach’s algal ErC50 is 1.7 mg/L and its freshwater PNEC the same. Those are the numbers behind “do not empty into drains”, and they are small enough that a domestic dilution argument does not survive contact with them.

Never acidified. This is the same rule as the tray rule and the shelf rule, and the waste bottle is where it is most often broken. A spent ferricyanide bleach and a spent stop bath in one container is the reaction EUH032 exists to prevent.

The silver is a complication, not an opportunity. A used bleach carries the silver it took off the print, and a used toner carries silver and bromide. The silver-bearing waste SOP applies alongside the general chemical waste SOP, and whether a refiner will accept a cyanide-complex-bearing or thiourea-bearing stream is a question for the refiner.

What that means for a reader in the United Kingdom. ILFORD’s instruction for domestic users is the practical form: bottle each waste chemical separately, label it appropriately, and take it to the chemical cupboard at a Household Waste and Recycling Centre; for business users, different waste chemicals should not be mixed but kept in separate, appropriately labelled containers. The government’s household hazardous waste guidance is where to start. The disposal caveat governs and local regulation decides.

Troubleshooting

The whites have gone yellow. Almost always the wash between the bleach and the toner. Moersch says it happens whichever bleach was used and that too short a rinse is the cause; his end point is not a time but a colour — wash until the yellow stain in the gelatin has gone completely. A weak bleach at 1+50 or below needs only two to five minutes; a strong one at 1+10 needs considerably more. See also oxidation stain if the yellow is in the image rather than in the base.

The highlights disappeared in the bleach and never came back. Residual fixer in the print. The bleach acted as a reducer instead of a rehalogeniser and the silver was dissolved rather than converted; there is nothing left to redevelop. The fault is upstream and the fix is a longer wash before bleaching, proved with the residual hypo and silver tests and Kodak’s HT-2 rather than assumed.

The print is not fully toned after thirty seconds. Moersch’s own diagnostic: an early sign that the toner is tiring. Refresh the bath with toner concentrate rather than extending the time — and note that his general advice for thiourea baths is to regenerate with alkali instead, which is a different remedy for the same symptom and is not explained.

Nothing happened in the shadows. Expected, and it is the defining behaviour of this product rather than a fault: thiourea reaches only what the bleach converted. If the shadows are to change, either bleach further — at the cost of density and contrast — or pre-tone before bleaching so that the shadows survive as a different image substance.

A hard edge between the toned and untoned parts. Bleach further, or bleach weaker for longer, or tone for longer, in that order of effect. The guide’s rule is that with a partial bleach the edge is more or less pronounced according to the bleach dilution, and that only longer toning times bring a colour change into the shadows and smooth the transition.

It went yellow when I wanted brown. Look at the paper before the setting. A chloride-rich or mixed emulsion tones yellow irrespective of the sulphur donor, and most modern papers are one. A high-bromide paper is what produces deep brown, and the 2007 list in the guide is a starting point rather than a current one.

The surface is dull after drying. The gelatin softened in an alkaline bath. Moersch’s remedies are to keep the toning short, to dry the print between steps, or to harden the gelatin before toning, and he notes that papers differ enormously in how much they tolerate — freshly manufactured paper being the most sensitive. See also cracked emulsion from flattening for the related failure at the other end of the process.

Blue specks in the print. Iron meeting the bleach, forming Prussian blue. Kodak’s answer is potassium oxalate in the bleach and Moersch’s bleach does not declare any; the practical answer is no metal trays, no metal clips and no chipped enamel. Black spots covers the neighbouring defect.

Round purple stains that appear only after toning. Air bubbles trapped between prints during fixing, which Kodak names specifically as a defect visible only after selenium or sulphide toning. Purple spots from fixer air bubbles has it, and the fix is in the fixer.

Mottle in the base that was not there before toning. Kodak attributes it to an exhausted or overconcentrated stop bath, or to insufficient agitation in the first seconds in the stop, and says neither shows until the print is toned. Mottle revealed after toning is the entry.

Yellow stain in the borders and highlights. Exhausted fixer, which leaves insoluble silver compounds that washing cannot remove and that stain when they meet a toner. Residual silver and yellow staining and yellow-brown highlight stain from residual silver have the diagnosis; exhausted fixer has the cause.

Uneven or patchy tone. Uneven toning first, and on resin-coated paper toner edge penetration. Kodak’s instruction that a dry print be soaked for two to three minutes before toning is the prevention most often skipped.

The bleach has stopped working. Light and air are its published enemies — the sheet lists UV radiation, sunlight and contact with air and oxygen among the conditions to avoid — even though the maker says the working solutions keep almost indefinitely. A ferricyanide solution photolyses, and a clear bottle on a windowsill is the usual reason.

I bleached a print, changed my mind, and dried it. That print is now less stable than it was before you started. Bleached, untoned silver is silver bromide, which will tone itself by gas action over time; it must be redeveloped, toned or fixed out. Moersch says so in terms, and silver mirroring is the family of damage this belongs to. Re-wet it and finish the job.

Experiments

Read the level before the list. Every experiment below that puts a print into the toner is a Level C experiment and belongs in a supervised laboratory with extraction, not in a home darkroom. Two of them are not, and they are deliberately first.

Measure what the maker does not publish: the pH of each setting. Make up 250 mL at each of the five settings, calibrate a meter that day with the calibration SOP, and record all five against the activator volume. The concentrate values are published — bleach 7 to 8, toner 6, activator 11.4 — and the five numbers that matter are not published by anybody. This is the single most useful measurement on the page, it takes twenty minutes, and handling the activator alone is a Level B operation rather than a Level C one, because the alkali carries no carcinogenicity classification. Do the activator dilution series first and the ones containing toner concentrate only under the Level C controls.

Plot the alkali against the pH and see whether the curve explains anything. If the five settings turn out to be a narrow pH range, the hue change is not a pH effect and the guide’s disagreement with itself is a disagreement about something else. If they span two units, the direction question becomes a real one and worth a test print. Either result is publishable and neither is currently in print.

Reproduce the matching table on the paper you actually use. Five identical prints, one bleach dilution and time held constant, the five settings, thirty seconds each, dried and compared under one light. Moersch’s labels were written for papers of 2007 and his own plates already contradict them on at least one emulsion. Yours is the only table that describes your darkroom.

Run the bleach as the variable instead. One setting, five bleach dilutions from 1+10 to 1+200 at a fixed time — or one dilution at five times — and watch the tonal boundary move up the scale. This is the control the guide says matters most for density, and it costs nothing but paper.

Test the direction disagreement directly. Two baths, setting A and setting E, one paper, one bleach, matched prints. Photograph them side by side under standard viewing conditions and record the result in the lab notebook with the paper, the developer and the bleach written down. Whatever comes out, it is a datum this course does not have.

Find out how much of the image was really converted. Tone a print, dry it, then bleach a strip of it again: what bleaches is silver, what does not is silver sulfide. Moersch uses exactly this trick to show the extent of selenium toning, and it works the same way here. It also permanently damages the strip, so use a reject.

Compare it with the open formula, in a laboratory that can take both. T-7a at Kodak’s published quantities against MT3 at the setting nearest its colour, on the same paper from the same box. Judge colour, maximum black and the smell — and record the ventilation you needed for each, because that is the comparison the safety argument on this page actually turns on.

Pre-tone and see the shadows survive. MT1 selenium at 1+10 for two and a half minutes, a bleach at 1+20 for one minute, then setting C, against an identical print bleached and toned without the pre-tone. This is the sequence the guide is built around and it is the clearest demonstration in the corpus that toners are steps rather than treatments.

Record all of it. A bought product earns a line in the formula version record as much as a mixed one — the setting, the bleach dilution and time, the wash, the paper, the bottle’s purchase and opening dates, and how many prints the bath had already taken. On a product whose composition is secret, your own bath’s history is the only variable you control and the only one you can prove.