KODAK Rapid Selenium Toner

Kodak Alaris Inc., Rochester, New York (the product originated with Eastman Kodak Company) — sold as liquid concentrate

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 thiosulfatenamed on the sheet as Ammonium thiosulphateCAS 7783-18-8Kodak states no function. It is the largest declared component, it is the working agent of every rapid fixer in this formulary, and reading it here as a silver-halide solvent is the course's inference and not Kodak's statement	25-30 % by weight
Sodium sulfite (anhydrous)named on the sheet as Sodium sulphiteCAS 7757-83-7Kodak states no function, and this page does not choose between the two the chemistry allows. The sheet does record what a sulphite does when the bath meets an acid, which is the reason it matters here	10-15 % by weight
Sodium selenitenamed on the sheet as Selenious acid, disodium saltCAS 10102-18-8The selenium, named by CAS number. The sheet attributes no hazard codes to individual components, but this is the substance that carries the product's occupational exposure limit and every entry on its regulatory list	1-5 % by weight
WaterCAS 7732-18-5Named as an additional component with no percentage against it, which is one more thing than HARMAN's sheet says about the rest of its own bottle	—

Not disclosed. Kodak publishes no composition for KODAK Rapid Selenium Toner, and its two documents do not agree about the one compositional statement it does make. The toning publication says the active ingredient is "a sulfite salt that has a concentration of less than 2 percent" and that working solutions "generally contain less than 1/2 percent selenium sulfite" - a description with no registry number behind it. The safety data sheet names three components with CAS numbers - ammonium thiosulphate at 25-30, sodium sulphite at 10-15 and selenious acid disodium salt at 1-5 in a column headed Weight percent - and adds water in section 16 with no percentage at all. Those bands exist to classify a hazard, not to state a formula, and section 12 records that even the ecological figures are estimated from them. Nothing anywhere gives a function for any component, a selenium content as the element, or the proportion of the silver image a given time and dilution actually converts. And Kodak withholds four practical numbers that HARMAN publishes for the directly competing product: there is no capacity, no working-solution life, no storage temperature and no shelf life for this toner in any Kodak document in this corpus. A reader who wants to know how much selenium is in the tray, how long the bottle keeps, or how many prints it will take, cannot get there from Kodak's literature - and the open formula that would answer the first question is one Kodak Limited published in 1949 and this course carries at Level D.

Nearest open formula. Kodak T-55 — Kodak Limited's T-55 is the only open selenium toner in this library, and it is the one comparison in the formulary where the product and the formula carry the same maker's name. T-55 publishes every quantity - 300 g of crystalline sulphite, 6 g of selenium powder, 190 g of ammonium chloride to the litre - diluted 1 part in 5, ten to fifteen minutes at 18 °C, with a footnote recording that it too was sold ready made. Rapid Selenium Toner publishes no quantities, four dilutions, a completion window of 2 to 8 minutes and a use on film that T-55 never claims. But the usual trade of this page kind is inverted here, because T-55 reaches its bath by boiling elemental selenium powder in an open pan of hot sulphite solution until it dissolves, which is why the course carries it at Level D and gives no procedure for it. So the choice is not a known composition against a known performance: it is a known composition nobody should prepare against an unknown composition anybody can pour. The two are also not the same chemistry. T-55 dissolves the element in a sulphite, which the wider literature reads as a selenosulfate; Kodak Alaris's safety data sheet names selenious acid disodium salt - sodium selenite, selenium(IV) - by registry number. Reading T-55 as a reconstruction of the bottle assumes exactly the thing neither document supports.

Purpose

To convert part of a finished silver image to silver selenide, for protection, for shadow density, or for a change of colour — three jobs that Kodak separates by dilution and states in one sentence each.

At 1:20, to protect the print. Kodak’s own summary of what any of its toners is for begins with permanence: toning converts the black-and-white silver image to an inert compound, which reduces the harmful effects of intense light, ultraviolet radiation, oxidising gases, extremes of temperature and humidity, and fumes. And then the sentence that matters most for this bottle: all Kodak toners will protect the image whether or not they produce a colour shift. The Tones Produced table lists Rapid Selenium once, at 1:20, against the entry No Tone Shift.

At 1:20 or 1:40, to deepen the shadows. “To increase shadow contrast and maximum density with a minimum tone change.” This is the use that made the product famous among printers, and it is the one Kodak backs with an actual curve.

At whatever dilution gives the hue you want, to change the colour. Cool chocolate-brown on warm-tone papers, purplish brown on neutral papers, very little or nothing on cold-tone papers. Kodak’s instruction is to dilute “according to the tone change you want” and it publishes no ratio for any particular hue.

And, alone among the selenium toners in this library, on film. Dilute 1:29, four minutes at 20 °C. No other manufacturer in this corpus claims a film use for its selenium toner.

The selenium-toned silver gelatin print entry sets out the process. This page is about the bottle.

Recommended uses

Display prints and prints wanted for the long term, at 1:20. This is the dilution with the clearest published purpose and the clearest published outcome: protection, with no tone shift.

Prints whose shadows are not carrying, at 1:20 or 1:40. Kodak’s words are “increase shadow contrast and maximum density with a minimum tone change”, and the effect is real enough that the publication tells you to plan for it upstream: Rapid Selenium Toner tends to intensify the image, so you may want to shorten print development slightly — though toning a fully developed print yields an increased tonal scale, which is the better of the two pieces of advice and the one worth taking.

Warm-tone papers, when visible colour is the point. Kodak’s three-way prediction is the same one HARMAN makes for its own product, and it is a statement about papers rather than about toners.

Fibre prints in the combination bath, where the workflow matters as much as the result. Diluting the toner in working-solution Hypo Clearing Agent at 1:20 or 1:40 removes the wash between fixing and toning altogether. Prints go from the fixer straight into the bath — Kodak is explicit that they must not be rinsed first, or they will stain — tone for about three minutes for protection, and then get their full thirty-minute wash. It is the same idea ILFORD reaches from the other end when it tells you to dilute its toner in working-strength WASHAID instead of water.

Negatives, which is this product’s genuinely distinctive claim. 1:29, four minutes at 20 °C with occasional agitation, then a twenty- to thirty-minute wash. Kodak notes a slight increase in contrast at that dilution and says 1:3 or 1:9 will increase it more.

Not for anything Kodak does not name. No metal trays or tanks — the publication forbids them for every toner, in favour of unchipped enamel, hard rubber or plastic. No use as a fixer, despite what is in it. No dilution between 1:3 and 1:29 with a published behaviour attached.

When another formula is preferable

• Where a real brown is wanted on a neutral paper, a sulphide route: Kodak Limited’s T-52 or Kodak’s T-7a, which change the colour of anything, where selenium changes some papers and not others.
• Where a redder result is wanted than selenium alone gives, Kodak Limited’s T-56, which puts selenium into a sulphide bath behind a bleach. It is Level D for the same reason T-55 is.
• Where no selenium is acceptable at all, the hypo-alum bath T-1a — the only sepia route in this formulary at Level B, reaching a silver sulfide image without a sulphide reagent ever being handled.
• Where protection is wanted and the colour must not move at all, GP-1, Kodak’s gold protective solution, which is published in full with its quantities and its ten minutes at 20 °C. It is the open formula for the archival job and it costs what gold costs.
• Where the print is under-washed and toning is being asked to rescue it, nothing here will help. Kodak says so more bluntly than any other document on this page: residual silver salts and traces of hypo cause stains, uneven tones and fading. The answer is Hypo Clearing Agent, the open sulfite washing aid or WASHAID followed by a full wash, proved with the residual hypo and silver tests. A toner that is a quarter ammonium thiosulphate is not a cure for leftover thiosulfate; it is more of it.
• Where you want the maker’s capacity and keeping figures before you commit a session to a bath, buy HARMAN’s toner instead. It is the same three components at overlapping bands with the same selenium species, and its maker publishes a capacity, three working-solution lives and two storage figures. Kodak publishes none of the five.
• When you want to understand a selenium bath rather than buy one, the answer this formulary usually gives — mix the open formula — is the answer this page will not give. Kodak Limited’s T-55 publishes every quantity and is carried at Level D, because its second step is boiling elemental selenium powder in an open pan until it dissolves. Read it for the chemistry. Do not make it.

What the maker publishes

Kodak does not publish a single-product technical sheet for this toner. What it publishes is a place in G-23, Toning Black-and-White Materials, its technical publication for the whole packaged line, dated May 2006 — and dealers serve that publication as this product’s datasheet, which is what it is.

Four dilutions and five jobs. 1:20 for print protection. 1:20 or 1:40 to increase shadow contrast and maximum density with a minimum tone change — two ratios for one purpose, with nothing said about how to choose. 1:20 or 1:40 in working-solution Hypo Clearing Agent for the combination bath. 1:29 for film. 1:3 or 1:9 for film where more contrast is wanted.

One completion window, given as a range across all papers. “Complete toning occurs in 2 to 8 minutes, depending on the paper type and weight”, at 20 °C (68 °F), with agitation. There is no separate time for the protective dilution, which is the number most readers of this page will have come for. The only three-minute figure on the sheet belongs to the combination bath.

A stopping instruction that is really a warning about lag. Remove the print when it has almost the required tone, because toning will continue to some extent in the wash.

Two rewetting rules that are easy to miss and cause stains when missed. A print that has already been dried is rewetted by immersing it in a fixing bath and then rewashing it — not by soaking it in water — or staining may occur. A print that is merely dry, in the toning section’s more general instruction, is soaked in water for two to three minutes.

A page of upstream print processing, which is the most useful part of the document. No hardening fixer for prints you intend to tone, because it makes the emulsion less receptive; two-bath fixing for best results; do not exceed the fixer’s capacity, because the insoluble silver compounds left in the print form a dark yellow stain in borders and highlights when they meet a toner; agitate properly, because air bubbles trapped between prints during fixing later produce round purple stains in selenium- and sulphide-toned prints; do not over-fix, because fixer trapped in an expanded paper base turns toned prints yellow and prolonged fixing can reduce the image; wash fibre prints for an hour with a complete change of water every five minutes, resin-coated prints for four minutes, and do not use Hypo Clearing Agent with resin-coated papers. An overconcentrated stop bath causes mottle in the base of a toned print, and insufficient agitation in the first few seconds in the stop bath causes a mottle that is invisible until you tone.

Handling rules for the tray. No metal trays or tanks — unchipped enamel, hard rubber or plastic only. On resin-coated papers keep toning times to a minimum, and if you must tone them longer than 8 to 10 minutes leave a large border, because toner that penetrates the edges is very difficult to wash out.

A drying note with a real consequence. Drying with heat causes a shift to a cooler tone with some paper/toner combinations, so the dryer goes to its lowest setting and the amount of toning may need adjusting to compensate.

One curve, and it is honest about its own limits. POLYMAX Fine-Art Paper — marked discontinued in the 2006 publication itself — developed in DEKTOL (1:2) at 20 °C for two minutes and toned in Rapid Selenium Toner at 1:40 for four minutes, showing an increase in upper-scale contrast and D-max.

And a compositional statement, which is the only one Kodak’s technical literature makes. “The active ingredient in Rapid Selenium Toner is a sulfite salt that has a concentration of less than 2 percent. Working solutions of the toner generally contain less than ½ percent selenium sulfite. These selenium concentrations are not considered hazardous when you handle the solutions under normal conditions. However, we recommend that you use print tongs and wear clean rubber gloves when you use this toner.”

Separately, a safety data sheet that is one of the most informative in this corpus. Kodak Alaris Inc., product code 1464486, synonym PCD 2667, document Z17000000763 version 4.2, revision date 31 July 2014. It prints a composition table with three CAS numbers, a fourth component in section 16, pH 9, specific gravity 1.32, colour colourless, odour characteristic, mild, boiling point above 100 °C, complete water solubility, occupational exposure limits, acute toxicity data and a full regulatory listing. Set beside HARMAN’s sheet — whose section 9 records colour, odour, pH and density all as Not known — it is a different order of disclosure.

⁇Kodak's two documents do not agree about the selenium

G-23 (Eastman Kodak, 2006): the active ingredient is “a sulfite salt” at less than 2 percent, and working solutions contain less than half a per cent of “selenium sulfite”. Selenium sulfite is not a name with a registry number behind it; it is a description of a selenium species held in a sulfite bath.

The safety data sheet (Kodak Alaris, 2014): Selenious acid, disodium salt, CAS 10102-18-8, at 1-5 in a column headed Weight percent — with sodium sulphite listed separately at 10-15 and ammonium thiosulphate at 25-30. Selenious acid disodium salt is the registry name for sodium selenite, Na₂SeO₃, selenium(IV).

The two statements cannot both be a plain description of the same bottle. If “a sulfite salt” means the selenium species, then less than 2 percent and 1-5 % overlap only in part. If it means the sodium sulphite, it is contradicted outright by 10-15. The course adopts neither reading and does not attempt to reconcile them. Three ordinary explanations are available and none is documented: the eight years between the documents; the change of company from Eastman Kodak to Kodak Alaris; or simply that a 2006 consumer publication was writing loosely about a hazard where a 2014 regulatory document was writing precisely.

The half-per-cent figure needs one further note. It is attached to “working solutions” with no dilution named, across a product sold for use anywhere from 1:3 to 1:40. Read as the sheet writes it, it is a ceiling over the whole range rather than a value for any one dilution, and it is not a measurement of anything you will mix.

Where the page comes down. The safety data sheet is the document that names substances with registry numbers, is written to a regulation that defines what a composition column means, and is the more recent by eight years. It is the source for the components table above and for the Safety section below. G-23 remains the source for everything about use, which is what it is for.

What is not disclosed

The composition, in the sense that matters. Three components with bands and a fourth with none is a hazard classification, not a formula. Nothing states a function for any of them. Nothing gives the selenium as the element rather than as a salt. Nothing gives the proportion of the silver image that a given time and dilution converts.

Anything at all about capacity. Not in sheets, not in square metres, not in litres per print. This is the gap that most affects a working printer, and it is worth stating how unusual it is: the directly competing product publishes at least 25 sheets of 20.3 × 25.4 cm per litre at its standard dilution, and a frank sentence explaining that its bath slows rather than dies. Kodak publishes neither the figure nor the model.

Anything at all about keeping. No shelf life for the sealed concentrate, no expiry, no storage temperature in the technical publication, and no working-solution life at any dilution in a bottle or a tray. The only storage instruction in the whole corpus is the safety data sheet’s, and it is a hazard instruction rather than a keeping figure: original container, tightly closed to prevent the loss of water.

A time for the dilution most readers will use. “2 to 8 minutes” spans every paper and every dilution. The protective 1:20 bath gets no time of its own, and the only three-minute figure on the sheet belongs to the combination bath rather than to plain water.

How to choose between 1:20 and 1:40. Kodak offers both for the same purpose and says nothing about the difference. Its own published curve was made at 1:40.

A pH for anything you will actually put a print into. The concentrate is pH 9. No working dilution has a published pH, and the combination bath — toner in working-solution Hypo Clearing Agent — has no published pH from either product’s literature.

Whether it is still made. No document in this corpus states that the toner has been discontinued, and none states that it has not. The most recent maker publication here that names it is Kodak Alaris’s AJ-3, revised February 2016.

And whatever is present below the declaration threshold. A composition table lists the substances that drive a classification, not the contents. A wetting agent, a sequestrant or a buffer would not necessarily appear on it, and the sheet’s silence is not evidence that there are none.

Disclosed components

Four: three with weight-percent bands in section 3, and a fourth named in section 16 with no figure at all. Each is discussed here with the band the sheet prints and not a quantity.

Ammonium thiosulphate, CAS 7783-18-8, 25-30 % by weight. The largest declared component, and the one that most changes how the bottle should be thought about. At a quarter to a third of the concentrate it is present at a strength that would be unremarkable in a fixer bottle — ammonium thiosulphate is the working agent of every rapid fixer in this formulary, including ILFORD RAPID FIXER and HYPAM — and it carries no hazard classification here, so a reader skimming for danger will skim straight past it. Kodak states no function for it. That a selenium toner is therefore also a weak fixing bath is the course’s reading, marked as an inference under Rule 7, and it has independent support: Moersch’s sheet for its own selenium toner declares 20 % w/w ammonium thiosulfate and HARMAN’s declares 10-30 %. Kodak’s is the highest declared band of the three. The practical consequence is a warning rather than a feature — a print that goes into this bath under-fixed or under-washed is not being rescued by what is in it, and Kodak’s own print-processing page says exactly that.

Sodium sulphite, CAS 7757-83-7, 10-15 % by weight. The second declared component, and the one whose presence the history would predict even if the sheet had not printed it: every historical selenium toner in this course solves the same problem the same way, because the element will not dissolve in water and a sulphite solution is what takes it up. Kodak Limited’s T-55 boils six grams of selenium powder into a sulphite stock for exactly that reason, and the sodium selenosulfate page records what the wider literature calls the product. But that cannot be what the sulphite is doing here, because the selenium in this bottle arrives already soluble as a selenite. Two readings remain and the course adopts neither: sulphite is the standard antioxidant of photographic solutions and would protect a thiosulfate-bearing bath, and sulphite is also a medium in which selenium species are known to interconvert. Kodak states no function. What the sheet does state about it is a hazard rather than a purpose, and it is the one that governs this page: contact with strong acids liberates sulphur dioxide, and some asthmatic or sulfite-sensitive individuals react to it.

Sodium selenite, named on the sheet as Selenious acid, disodium salt, CAS 10102-18-8, 1-5 % by weight. The selenium, and the most valuable line Kodak has contributed to this course’s account of selenium toning. The sheet attributes no GHS codes to individual components — its classification is stated for the mixture as a whole — but this substance is the reason for nearly all of it. It is the only component carrying an occupational exposure limit: ACGIH and OSHA time-weighted averages of 0.2 mg/m³, expressed as Se. It is named alone under CERCLA/SARA 40 CFR 302.4, alone under SARA section 302 as an extremely hazardous substance with a threshold planning quantity, and alone on the California, Minnesota and New Jersey right-to-know lists. Section 11 names it in its general advice and gives the family’s symptoms of overexposure: liver and kidney damage, neurological effects, fatigue, irritability, hair loss, skin lesions, nausea and vomiting, garlic odour of breath and sweat, and a metallic taste. Read its encyclopaedia page before this one.

Water, CAS 7732-18-5, no percentage given. Named in section 16 under Additional Components Include, and again in the Pennsylvania right-to-know list beside the other three. It is worth pointing out because it is one more thing than most sheets say: HARMAN’s names no water at all, and a reader is left to assume the rest of that bottle. Kodak names it and gives it no figure, which is the correct amount of disclosure for a substance that drives no classification — the sheet tells you what the remainder mostly is without telling you how much. This page does not subtract the three bands from a hundred to find out. Those bands exist to classify a hazard, section 12 records that even the ecological figures were estimated from them, and arithmetic on them would turn a hazard document into a formula, which is the one thing a product page must never do.

⁇Four sheets, three selenium species — and Kodak has now named its own

The course’s sodium selenite page records a disagreement between three manufacturers, and states that no source it held named sodium selenite for photography at all. This sheet changes part of that picture.

• Kodak, in G-23 (2006): “a sulfite salt” at under 2 %, working solutions under half a per cent of “selenium sulfite” — a description with no registry number.
• Kodak, in its own safety data sheet (2014): Selenious acid, disodium salt, CAS 10102-18-8 — sodium selenite, selenium(IV).
• HARMAN: sodium selenite, CAS 10102-18-8 — the same substance, the same registry number.
• Moersch: sodium selenate, CAS 13410-01-0 — selenium(VI), a different oxidation state.
• Wall’s 1924 handbook, for the historical baths: sodium selenide, selenium(−II).

What this settles. Two of the three modern manufacturers in this corpus now name the same selenium compound at the same registry number for the same job. Until this sheet, Kodak’s was the vague one, and the sodium selenite page could record that PubChem’s own use listings for the substance name glass, ceramics, bacteriology, seed testing, porcelain, soil and feed supplementation and medicine — and not photography. Two manufacturers now name it for photography on their own hazard sheets.

What it does not settle. It says nothing about Moersch’s bottle, which names a different oxidation state and is entitled to. It says nothing about T-55’s stock, which starts from the element. And it does not make Kodak’s and HARMAN’s products the same product: naming the same active species is not the same as sharing a formulation, and the two sheets’ bands for the other two components are different.

It also tells you something about the earlier vagueness. Kodak’s 2006 wording was a choice about what to disclose in a consumer publication, not a limit of what its documents could say — because its own regulatory document, written to a different audience, says it precisely.

Behaviour

Dilution is the control, and Kodak uses it for three different purposes without ever saying how the three interact. 1:20 protects with no tone shift. 1:20 or 1:40 raises shadow contrast and D-max. Anything you like changes the colour. The same bath does all three at once, in proportions set by time and dilution together, and no document separates them.

The higher densities go first. That is Moersch’s observation and it is the single most useful thing to know about any selenium bath: irrespective of dilution or temperature, the toner always reaches the higher densities first. It is what makes 1:40 for four minutes an intensifier and not a colour change, and it is why Kodak can promise increased shadow density with a minimum tone change without the two claims being in tension.

The conversion is partial, always. Moersch records that after six minutes not all the silver has been transformed to silver selenide. A selenium-toned print is normally a mixture of silver selenide and untoned silver, in proportions the printer chose without measuring — which means protection is proportional to a conversion nobody quantifies, and neither Kodak nor anyone else in this corpus publishes what fraction any of their times and dilutions reaches.

It lags, and Kodak’s instruction is built around the lag. Pull the print when it has almost the required tone, because toning continues to some extent in the wash. Unlike HARMAN, Kodak gives no stop bath and no holding dish for the toner: the wash is the stop, and the wash is also where the last of the toning happens.

It intensifies, and Kodak asks you to plan for it two ways. Shorten print development slightly if you know you will tone; or develop fully and take the increased tonal scale, which is the better advice and the one the publication itself prefers.

Time is a range, not a number. Two to eight minutes covers every paper and every weight. A printer wanting repeatability has to establish their own time on their own paper, and Kodak’s method for that — compare against an untoned print — is not even stated here, though HARMAN’s sheet gives it.

Exhaustion is undescribed. There is no capacity figure and no exhaustion model. HARMAN’s account of the competing product is that the bath does not die but slows, so that a fading rate of tonal change is the symptom rather than a sudden failure. Whether Kodak’s behaves the same way is not documented, and this page does not assume it does merely because the two products declare similar components.

Keeping is undescribed too, which has a practical edge that the missing capacity figure does not: the safety data sheet’s instruction to keep the container tightly closed to prevent the loss of water says that the concentrate can change by evaporation, and nothing tells you what that does to a dilution ratio.

Image characteristics

Three outcomes on three classes of paper, and one of them is “nothing”. Several cool chocolate-brown hues with warm-tone papers, purplish brown tones with neutral-tone papers, very little or no change with cold-tone papers. HARMAN’s independent account of the family gives the same three answers in the same order, which is about as close to corroboration as a subjective colour claim gets.

“No Tone Shift” is a published result, not a failure. It is what Kodak’s own Tones Produced table prints against this toner at 1:20 — the only line in that table whose entry is the absence of an effect. A reader who tones at 1:20, sees nothing, and concludes the bath is dead has misread the product.

Maximum density rises, and there is one curve to show it. POLYMAX Fine-Art Paper in DEKTOL 1:2, toned at 1:40 for four minutes: increased upper-scale contrast and D-max. The paper was already discontinued when the publication was printed, so the direction is transferable and the magnitude is not. No maker in this corpus publishes a figure for a paper you can buy.

Heat drying moves the colour back. Drying with heat causes a shift to a cooler tone with some paper/toner combinations, so the amount of toning may have to be increased to compensate. That is an unusual thing for a manufacturer to admit and it belongs in any test you run: judge the dried print, dried the way you will always dry it.

The signature survives the invisibility. The Getty Conservation Institute’s atlas records that selenium treatment is detectable by X-ray fluorescence long afterwards. A print toned at 1:20 to look untoned is still identifiable as toned in a century — which is the honest summary of what the protective dilution sells: a change you have agreed in advance not to be able to see, on the strength of a maker’s sentence and a conservator’s instrument.

The mechanism

The end state is Kodak’s statement and not this page’s inference. “It converts the silver image to silver selenide.” That sentence is on the packaged-toner page, in the maker’s own words, and it is the one mechanistic claim in the whole document.

What the course cannot do is put a number behind the protection. The silver selenide page records that no source this course holds gives a solubility product, a solubility figure or a formation constant for Ag₂Se. The mechanism is therefore recorded as an observed increase in chemical and environmental stability rather than as a calculation, and no balanced equation for the toning step is printed here, because the course does not hold one and writing a plausible one is the failure Rule 1 exists to prevent.

Why the bath is direct. Selenium works on the metallic silver image itself, with no bleach in front of it, which is why the print goes in fixed and washed and comes out toned — and why it intensifies rather than reduces. Nothing has been converted back to a halide and nothing has been given the opportunity to dissolve. The sulphide toners in this formulary reach a silver sulfide image the other way, through a bleach, and lose density doing it.

⚗Three functional slots, three makers — and the inference is marked as one

Put the three modern composition tables in this corpus side by side:

	KODAK Rapid Selenium Toner	HARMAN Selenium Toner	Moersch MT1 Selentoner
Thiosulfate	Ammonium thiosulphate, 25-30 %	Ammonium thiosulphate, 10-30 %	Ammonium thiosulfate, 20 % w/w
Sulfite	Sodium sulphite, 10-15 %	Sodium sulphite, 10-30 %	Ammonium sulfite, 10 % w/w
Selenium salt	Sodium selenite (Se IV), 1-5 %	Sodium selenite (Se IV), 1-5 %	Sodium selenate (Se VI), 2-3 % w/w
Water declared	Yes, section 16, no figure	Not named	Not named

Three manufacturers on two continents, three hazard sheets written to two different regulatory regimes, and three components each falling into the same three slots.

That a modern packaged selenium toner is built from a thiosulfate, a sulfite and a selenium salt is the course’s reading of three composition tables, and it is an inference under Rule 7, not a statement by any maker. None of the three sheets assigns a function to anything. Three sheets are not a proof of a common formulation; bands and point values are not comparable measurements; and two products naming the same active species may still differ in everything the sheets do not have to declare.

What the comparison establishes without inference is narrower and firmer: the two American and British products name the same selenium compound at the same CAS number, and the German one names a different compound in a different oxidation state. Selenite is selenium(IV); selenate is selenium(VI). Any account of selenium toning that speaks of “the selenium toner” as one substance is wrong about at least one of these three.

Why the bath is also a weak fixer, and why that is a caution rather than a convenience. At 25-30 % this is the highest declared thiosulfate of the three sheets. The reading that the working bath therefore has some silver-halide solvent action is the course’s, marked as an inference, supported by the parallel declarations rather than derived from Kodak. What follows is practical: the toner is not a place to finish an inadequate fix; the print must be properly fixed and thoroughly washed before it goes in; and the waste stream carries thiosulfate as well as selenium and silver. It also explains why the Hypo Clearing Agent combination bath is a sensible piece of engineering rather than a trick — a bath that already carries a thiosulfate is not harmed by being made up in a washing aid.

Why the whole of the handling is about acid, on a product whose only published pH is 9. The concentrate is alkaline, and Kodak’s section 10 is unusually explicit about what changes that: contact with strong acids liberates sulphur dioxide; contact with base liberates ammonia and flammable material; contact with sodium hypochlorite may form chloramine. Its hazardous decomposition products are sulphur oxides, ammonia and chloramine. Separately, the sodium selenite page carries the reasoning the sheet does not: both CAMEO and the international safety card record that a selenite reacts with strong acids to generate a toxic hazard, neither names the gas, and HSE’s EH40 sets dihydrogen selenide at 0.02 ppm over eight hours — among the lowest limits in the whole table. The course has not verified which species an acidified selenite bath releases. It has verified that the family’s volatile hydride is controlled at a level a darkroom has no way of measuring, which is why the rule is absolute rather than proportionate.

And one hazard that belongs to no other toner page in this library. Section 2 records, under other hazards, that dried product residue can act as a reducing agent; section 5 adds that it reacts violently with oxidising materials and may cause spontaneous heating and ignition when absorbed on combustible porous material — rags, paper, sawdust, cotton, clothing. A spill wiped up with a paper towel and left in a bin is the shape of that hazard, and no other selenium-toner document in this corpus mentions it.

The nearest open formula

Kodak T-55, Kodak Limited’s direct selenium toner of 1949 — and this is the only entry in the formulary where the bought product and the open formula carry the same maker’s name on the bottle.

They are not the same company in law. Kodak Limited of London published T-55; Eastman Kodak of Rochester published G-23; Kodak Alaris issued the safety data sheet and sells the toner now. But Kodak Limited’s own footnote to T-55 reads Available as Kodak Selenium Toner — the clearest statement anywhere in this corpus that a published formula and a bottled product can be the same thing, written by the company that did both.

	Kodak T-55 (1949)	KODAK Rapid Selenium Toner
Composition	Published in full: 300 g crystalline sodium sulphite, 6 g selenium powder, 190 g ammonium chloride, water to 1000 c.c.	Not published; three components banded on a hazard sheet, plus water with no figure
Selenium species	The element, dissolved by boiling in sulphite; the wider literature reads the product as a selenosulfate and the course has not verified that	Sodium selenite, CAS 10102-18-8, selenium(IV), named by the maker at 1-5 %
How the selenium gets into solution	By the person making it, at the boil, in an open pan	Already in solution when the bottle is opened
Dilution	1 + 5, and no other	1:20, 1:40, 1:29, 1:9, 1:3, according to purpose and material
Time and temperature	10 to 15 minutes at 18 °C	2 to 8 minutes at 20 °C on paper; 4 minutes at 20 °C on film at 1:29
Material	Paper, and warm-tone paper at that	Paper and film, both with published procedures
Capacity	Not published	Not published
Keeping	Not published	Not published
pH	Not published	9, for the concentrate
Ammonium chloride	190 g/L, function unexplained by Kodak Limited and by this course	Not present, or at least not declared
Safety level	D — historical study, no procedure given	B — a liquid concentrate poured into a dish
What you can change	Everything in principle; nothing in practice, because the course gives no procedure	The dilution, the time, the temperature and the diluent
What the course recommends	Read it	Use it

The last row inverts this page kind’s usual argument. Everywhere else in this library a product page says: here is a bottle with a documented performance and an unknowable composition, here is an open formula with a known composition and an undocumented performance, and here is the bench where you trade one for the other. That argument depends on the open formula being something a reader can make. T-55 is not. Its second step is boiling six grams of elemental selenium powder in hot sulphite solution until it dissolves, and the course carries it at Level D for exactly that reason. So the trade here is a known composition nobody should prepare against an unknown composition anybody can pour, and the honest conclusion is to buy the product.

Two further things the comparison shows, and both cut against reading one page into the other.

Publishing a composition does not mean understanding it. Kodak Limited gives no function for its 190 g/L of ammonium chloride, and neither can this course. T-55 has a published quantity whose purpose is as unknown as Rapid Selenium Toner’s sulphite. Openness and explanation are different things.

They are not the same chemistry. One starts from the element dissolved in a sulphite; the other from a selenite salt already in solution. A reader who treats T-55 as a reconstruction of the modern bottle has assumed precisely what neither document supports — and the fact that both carry the word Kodak makes that assumption easier to make here than anywhere else in the formulary, which is why it is worth saying twice.

Safety

Level B, and the reasoning belongs on the page rather than in a database.

Kodak Alaris classifies the mixture under 29 CFR 1910.1200(d) as Acute toxicity Category 4 (oral), Skin sensitisation Category 1 and Specific target organ toxicity — repeated exposure Category 2, with signal word Warning. Its hazard statements are may cause an allergic skin reaction and may cause damage to organs through prolonged or repeated exposure — central nervous system, kidney, liver. Its HMIS III ratings are Health 2, Flammability 1, Physical Hazard 0; its NFPA ratings are Health 3, Flammability 1, Instability 0.

Why B and not A. The rubric’s Level A ceiling is substances classified at most as irritant, harmful if swallowed, or corrosive at the concentrations actually handled. A sensitiser is above that ceiling and is named explicitly in the first Level B criterion. This mixture is one.

Why B and not C. The Level C criterion that would apply names sensitisers and acutely toxic reagents where a fume cupboard or specialist disposal is the recognised control. The maker’s own recognised control is neither: Kodak’s instruction for this product is print tongs and clean rubber gloves, with adequate ventilation, and it states in as many words that “these selenium concentrations are not considered hazardous when you handle the solutions under normal conditions”. The operation is pouring a liquid concentrate into a dish at room temperature with no weighing of a solid at any point. The process entry reaches the same conclusion for the same object, and so does the HARMAN page for the competing product.

Where that assignment is closest to its limit, and it is the waste. Level C’s fourth criterion is any procedure whose waste cannot lawfully enter a domestic drain and needs a licensed waste contractor. Kodak’s own environmental guidance withholds every drain and refuse route from used Rapid Selenium Toner and directs domestic users to a household hazardous waste collection facility — which is a municipal route rather than a licensed contractor, and is why this stays at B. For a commercial user in the United States it is different, and Kodak says so: used Rapid Selenium Toner is regulated as a hazardous waste under the USEPA Resource Conservation and Recovery Act. A reader operating commercially is in a regime this page’s level does not describe.

⚠The bottle is Level B; the solid inside it is Level C

Sodium selenite is a Level C substance on its own page — classified Danger, fatal if swallowed, fatal or toxic if inhaled, with a workplace limit for selenium of a fifth of a milligram per cubic metre. Nothing here contradicts that, and the two classifications are not in tension: the level is assigned to an operation, not to a substance.

Weighing a hygroscopic powder classified H300 and H330 is a fume-cupboard operation and this course gives no procedure for it. Diluting a bottled liquid in which that powder is already present at 1-5 % is not. The person who buys this bottle has bought their way out of the Level C step, which is the trade this whole page kind exists to describe, and it is the strongest practical argument here for buying rather than mixing.

The exposure limit is the number to hold on to. Kodak’s section 8 gives ACGIH and OSHA time-weighted averages of 0.2 mg/m³ expressed as Se against the selenite — the same figure the selenium and sodium selenite pages carry, and one a domestic room has no way of verifying it meets. Kodak’s engineering answer is process enclosures or local exhaust ventilation; its respiratory answer, if those do not hold the limit, is a full-face positive-pressure air-supplied respirator, or an acid-gas type where decomposition products may have been released. Neither is darkroom equipment. Both are the sheet telling you what the alternative to ventilation is, and the practical instruction is therefore the first one: ventilate properly and do not create the situation the respirator answers.

Personal protection, as the two documents specify it. Impervious gloves and protective clothing — glove selection is where breakthrough time goes; Kodak’s technical publication is blunter and says clean rubber gloves and print tongs. Safety glasses with side shields, or goggles. Wash thoroughly after handling; do not eat, drink or smoke when using the product; contaminated work clothing does not leave the workplace.

Sensitisation is the hazard that changes with repetition, and it is managed differently from the others. H317 is not a dose that gets worse; it is a state that can be acquired. Once a person has reacted, further exposure must be prevented rather than managed. A rash that appears after several toning sessions rather than after one is not a reason to be more careful next time.

And the repeated-exposure line, which HARMAN’s sheet does not carry. May cause damage to organs through prolonged or repeated exposure — central nervous system, kidney, liver. Section 11 fills that in with the selenium family’s own symptom list: liver and kidney damage, neurological effects, fatigue, irritability, hair loss, skin lesions, nausea and vomiting, garlic odour of breath and sweat, metallic taste. This is a chronic hazard on a product used occasionally, and the control is the same as the acute one — gloves, tongs, ventilation, no eating in the room — applied every session rather than when it seems to matter.

First aid, in the sheet’s own words. Inhalation: remove to fresh air, get medical attention. Eyes: flush immediately with plenty of water for at least fifteen minutes, get medical attention, remove contact lenses if easy to do. Skin: flush immediately for at least fifteen minutes while removing contaminated clothing and shoes; wash the clothing before re-use; destroy or thoroughly clean contaminated shoes. Ingestion: do not induce vomiting, and call a physician or poison control centre immediately. The first-aid page has the course’s fuller procedure and the eyewash SOP has the technique.

⚠The bath removes its own warning, twice over

Kodak’s own section 11 lists garlic odour of breath and sweat among the symptoms of selenium overexposure. The selenium family’s salts are also described in the historical literature as having an intense and lasting garlic smell. The smell of the bath and the sign of having absorbed it are the same smell, and a person cannot use their nose to tell the two apart. That is why ventilation here is an engineering control and not a comfort measure.

And the second removal: Kodak records the product’s own odour as characteristic, mild, which is a description of a normal bottle rather than a baseline anyone could use to notice a change.

Keep acid away from this bath entirely — the tray, the bottle, the tongs and the waste jug alike — and rinse thoroughly between the toner and any acidic step in the sequence. Kodak’s own sheet names what an acid gets you here: sulphur dioxide.

Storage

In its original container, tightly closed, and the reason is water. That is the safety data sheet’s whole storage instruction, and the clause matters: keep container tightly closed to prevent the loss of water. A concentrate that evaporates is a concentrate whose dilution ratio has quietly stopped meaning what it meant, on a product with no published shelf life to tell you when to stop trusting it.

Kodak publishes no keeping figures at all, and this is the most practically consequential gap on the page. No shelf life for the sealed concentrate, no storage temperature, no working-solution life in a bottle, no tray life. HARMAN publishes five such numbers for the competing product. Do not borrow them: they belong to a different formulation with different bands, and the whole point of a product page is that undisclosed compositions do not transfer.

Away from incompatible substances, which the sheet does name. Oxidising materials, highly oxygenated or halogenated solvents, and organic compounds containing reducible functional groups. Not the acid shelf. The international safety card for the selenite adds one more worth taking literally on a darkroom shelf: store in an area without drain or sewer access.

Locked, away from food, and out of reach of children, per Kodak’s general safe-handling list — keep chemicals and processing solutions out of the reach of children and pets, and do not store them where food is handled or stored.

Label everything — the product, the dilution, the diluent and the date mixed — with the labelling SOP. A colourless liquid with a mild characteristic odour and no keeping figure is exactly the container that becomes an unlabelled or undated container, and here that is a disposal problem rather than an inconvenience, because what is in the bottle cannot go down a drain. The combination bath needs its own label for the same reason: a tray of Hypo Clearing Agent that has had toner in it is no longer a tray of Hypo Clearing Agent, and Kodak says explicitly that it must not be reused on untoned prints.

Never let dried residue accumulate on porous material. Section 5’s warning that dried product residue can act as a reducing agent, react violently with oxidising materials and cause spontaneous heating when absorbed on rags, paper, sawdust, cotton or clothing is a storage instruction as much as a fire one. Spill cloths are rinsed and disposed of, not dropped in a bin and forgotten.

Incompatibilities

Acids of every kind, and this one governs everything else. Kodak’s own section 10 says contact with strong acids liberates sulphur dioxide; the selenite in the bottle is separately recorded by CAMEO and the international safety card as generating a toxic hazard with strong acids, and the family’s volatile hydride is controlled at 0.02 ppm. No acid stop bath and no acid fixer follows this toner without a thorough wash between. No acid goes into its waste bottle. No acid is stored above it. The incompatibilities page governs.

Sodium hypochlorite — household bleach — which is a hazard specific to this sheet. Contact may form chloramine, a toxic gas, and chloramine is listed among the product’s hazardous decomposition products. A darkroom sink cleaned with bleach while a toning tray is standing in it is the exact shape of this one, and it is not on HARMAN’s sheet.

Strong bases, which the sheet says liberate ammonia and flammable material.

Oxidising materials, halogenated compounds and highly oxygenated solvents, both as an incompatibility and, for the dried residue, as a fire hazard.

Metal trays and tanks, per Kodak’s general toning guidance, which forbids them for every toner in favour of unchipped enamel, hard rubber or plastic.

Hardening fixers, which are an incompatibility of a different kind. Kodak recommends against them for prints intended for toning because they make the emulsion less receptive to the toner — a processing incompatibility rather than a chemical one, and the reason its own advice is a non-hardening fixer for prints you plan to tone.

The waste container, which is where incompatibility usually happens. Spent stop bath and spent toner in the same bottle is the reaction nobody intended. Separate, labelled containers, always.

Developer in either direction, and unexposed photographic materials in the room.

Waste

Three streams in one bottle: selenium, silver and thiosulfate. That is what makes this the most tightly constrained waste of any product page in this library.

Kodak’s own environmental guidance for amateurs gives this product a route by name, and withholds every other. In its table of routes for amateur photographic chemicals, used Rapid Selenium Toner is given no sewer discharge, no discharge to a publicly owned treatment works and no disposal with municipal refuse — every route withheld except household hazardous waste collection. It is one of very few entries in that table treated that way, and the accompanying text is unambiguous: domestic users should not discharge this material to the sewer or discard it in the municipal trash, and should use a household hazardous waste collection facility.

For commercial users in the United States, Kodak states the regulatory position outright: used KODAK Rapid Selenium Toner is regulated as a hazardous waste under the USEPA Resource Conservation and Recovery Act. That is a stronger statement than any other maker in this corpus makes about any photographic solution.

✕G-23's general disposal bullet is not this product's disposal instruction

G-23’s safe-handling list ends with a disposal bullet that tells you to discard solutions individually and flush the drain with plenty of water after each. Read out of context that is a drain instruction on a page about selenium toner.

Read in context it is not: the bullet is about not combining sulphide toners with stop baths or fixing baths, because that combination generates hydrogen sulphide, and the flushing sentence is the tail of that warning. G-23 is a publication covering five toners and its general bullets are general.

The document that addresses this product by name is Kodak’s environmental guidance, and it withholds the drain entirely. Where a general instruction and a specific one differ, the specific one governs, and here the specific one is also the stricter. Nothing from this tray goes down a sink.

Never acidified, and never poured into a jug that has held stop bath or acid fixer. The tray rule and the waste rule are the same rule, and the waste jug is where it is broken, because by then the solutions look equally spent and nobody is thinking about sulphur dioxide.

Why the estimated ecological figures understate it. Section 12 states plainly that its properties are ESTIMATED from the components — fish LC50 greater than 100 mg/l, daphnia EC50 10 to 100 mg/l, readily biodegradable. Those are mixture figures calculated from bands. The international safety card records that selenite bioaccumulates along food chains, particularly in plants and fish, and that is not a property dilution removes. Biodegradability is a statement about the organic burden, not about the selenium, which does not degrade into anything.

Emptied containers retain product residue, which the sheet says explicitly, so the bottle follows the liquid to the same collection point rather than the recycling bin.

The silver in it is a complication, not an opportunity. A used toning bath carries dissolved silver as well as selenium and thiosulfate, so the silver-bearing waste SOP applies alongside the general chemical waste SOP. Whether a silver refiner will accept a selenium-bearing stream is a question for the refiner, and this course does not answer it.

The combination bath is waste twice over. A Hypo Clearing Agent bath used to dilute the toner contains toner, must not be reused on untoned prints, and goes out on the toner’s route rather than the washing aid’s.

The disposal caveat governs and local regulation decides.

Troubleshooting

Nothing visible happened. Ask which dilution first. At 1:20 on a neutral or cold-tone paper, nothing visible is the published result — Kodak’s own table prints No Tone Shift against this toner at that ratio. If it was a stronger dilution on a warm-tone paper and still nothing moved, the next question is the bath, and here Kodak gives you nothing to reason with: no capacity, no working-solution life, no exhaustion model. Time a standard test print instead, and keep the times.

The shadows did not deepen either. Check the fixer before the toner. A hardening fixer makes the emulsion less receptive, and Kodak recommends a non-hardening fixer for any print you intend to tone.

Uneven tone, patchiness or mottle. Start at uneven toning and mottle revealed after toning. Kodak’s two causes are both upstream and both easy to miss: an overconcentrated stop bath — from evaporation in a tray left more than three days or a tank left more than a month — causes mottle in the base of a toned print; and insufficient agitation in the first few seconds in the stop bath causes a mottle that is invisible until you tone.

Round purple stains that appear only after toning. Air bubbles trapped between or under prints during fixing, which Kodak names specifically as a defect that shows up only after selenium or sulphide toning. Purple spots from fixer air bubbles is the entry, and the fix is in the fixer, not the toner.

A dark yellow stain in the borders and highlights. Insoluble silver compounds left by an exhausted fixing bath, which washing will not remove and which stain when they meet a toner. Residual silver and yellow staining and yellow-brown highlight stain from residual silver have the diagnosis; the residual hypo and silver tests will tell you before you tone rather than after.

The whole print went yellow. Prolonged fixing, which expands the paper base and traps fixer in it — Kodak’s own limits are approximately ten minutes for fibre-base and two for resin-coated. Residual thiosulfate is the entry.

Staining on a print that had already been dried before toning. It was rewetted the wrong way. Kodak’s instruction is to immerse a dried print in a fixing bath and then rewash it, not simply to soak it.

A dark line creeping in from the edges of a resin-coated print. Toner edge penetration on RC, which Kodak anticipates: keep RC toning times to a minimum, and leave a large border if you must go beyond 8 to 10 minutes.

The tone kept moving after the print left the bath. Expected, and Kodak says so: toning continues to some extent in the wash, so pull the print when it has almost the tone you want.

The print came out cooler than it looked wet. Heat drying, which Kodak records as causing a shift to a cooler tone with some paper/toner combinations. Drop the dryer to its lowest setting or accept the shift and tone a little further to compensate — but judge the dried print, always.

A sharp garlic-like smell. Leave the room and ventilate it. Do not investigate the tray first, and do not treat the smell as reassurance that you would notice a problem: it is also a symptom of overexposure.

A rash or irritation that appears after several sessions rather than after one. Treat it as sensitisation, not as an accident: stop using the product, get medical advice, and read the H317 paragraph in Safety again. This is the one failure on this page that does not improve with technique.

A bottle on the shelf, half full, undated. An unlabelled or undated container is the entry. With no published shelf life for this product there is no rule that will tell you whether it is still good, and no drain to pour it down if it is not.

Experiments

Establish the time Kodak does not give you. “2 to 8 minutes” is a range across every paper. Take your paper, your developer and your fixer, tone identical prints at 1:20 for 1, 2, 4 and 8 minutes, dry them the way you always dry them, and read them side by side against an untoned control. What you are producing is the number the sheet withheld, for the only paper you actually use. Record it in the formula version record.

Measure the capacity Kodak does not publish. Tone one standard test print to a fixed visible change, timing it, at the start of a litre’s life and after every fifth sheet through it, then plot time against cumulative sheets. HARMAN’s model for the competing product is that the bath slows rather than dies; a smooth rising curve supports that model for this one, and a sharp knee means Kodak’s bath behaves differently. Either result is worth having, because no document in this corpus states which it is.

Settle 1:20 against 1:40. Kodak offers both for the same purpose and says nothing about the difference. A step wedge on your paper, processed identically, toned four minutes in each, read on a densitometer. Kodak’s own published curve was made at 1:40, so this also tells you how far your paper sits from the one paper Kodak measured.

Measure the intensification the maker claims and does not quantify for any current paper. The same step wedge, half toned and half not, read as two curves. Kodak’s claim is increased upper-scale contrast and D-max; this is that claim on a paper you can still buy.

Find where the partial conversion sits. Prints pulled at 1, 2, 4 and 8 minutes, all at one dilution. Moersch’s observation is that a selenium bath has not converted all the silver even at six minutes; the consequence is that every selenium-toned print is a mixture, and the printer sets the proportions without measuring them.

Three papers in one tray. Warm-tone, neutral and cold-tone, toned together for the same time at the same dilution. Kodak’s three predicted outcomes — cool chocolate, purplish brown, nothing discernible — are the clearest demonstration in this formulary that a toner’s colour belongs to the paper.

Run the combination bath against the plain one. Two matched fibre prints: one toned at 1:20 in water after a full wash, one taken straight from the fixer, unrinsed, into 1:20 made up in working-solution Hypo Clearing Agent, both then washed thirty minutes. Judge the colour, read the D-max, and run a residual hypo and silver test on each — because the whole argument for the shortcut is that it does not cost you permanence, and that is a testable claim rather than a promise.

Test the film use nobody else claims. A clip of film at 1:29 for four minutes at 20 °C against an untoned clip from the same roll, read on a densitometer. Kodak says a slight increase in contrast; 1:3 and 1:9 are said to increase it further with no figure at all. This is the only selenium toner in the library with a published film procedure, and it is the least tested claim on the page.

Measure the working pH Kodak does not publish. The concentrate is 9. Mix a litre at 1:20 and a litre at 1:40, calibrate a meter that day with the calibration SOP, and record both — and then measure the combination bath, which no document in this corpus gives a pH for at all. Knowing whether your tray sits well on the alkaline side is the single most safety-relevant measurement on this page.

Find out whether the toner really is a weak fixer. The inference above is the course’s and it is testable. A clip of unexposed, undeveloped film in a small volume of working-strength toner, timed to clear, against an identical clip in working-strength RAPID FIXER, using the clearing time test. At 25-30 % declared thiosulfate this is the sheet in the corpus most likely to give a clearing time. No clearing at all is an equally publishable result.

This against the other bottle, and against the open protective formula. HARMAN’s toner declares the same selenium species at the same CAS number with different bands for the other two components; GP-1 is gold, published in full, at Level B, for the same archival purpose. Matched prints, judged for colour shift and read for D-max. The three-way comparison is the one this formulary is actually for.

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