Moersch MT1 Selentoner

A bought product gets a page of its own kind in this library, because the alternative is a formula page with the formula missing. What follows is what Moersch publishes, which is a great deal about behaviour and almost nothing about quantities; what his safety data sheet discloses, which is three substances and a page of physical properties his competitors leave blank; what the two together still do not say; and the open formula the course teaches that comes nearest.

This one is worth reading even if you never buy the bottle. The maker’s own instructions are the best account of selenium toning in this corpus, they were written by somebody standing at a tray rather than by a technical department, and they begin by telling you that the usual reason for buying the product is the wrong one.

Moersch Photochemie — 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 sulfiteCAS 10196-04-0No function is stated by the maker. The course does not choose between the two the chemistry allows, and says so under Disclosed components	10%	Eye Irrit. 2, STOT SE 3, H319, H335
Ammonium thiosulfateCAS 7783-18-8The largest declared component. The sheet leaves its classification cell empty and states no function; the maker's Brown Toning guide states separately that selenium toners contain thiosulphate and gives a rinse rule that follows from it	20%
Sodium selenateCAS 13410-01-0The selenium — selenium(VI), and the only component the sheet gives a REACH registration number, 01-2120772103-63-xxxx. The sheet prints hazard classes for it rather than hazard statement codes, and this row reproduces what is printed	2-3 %	Acute Tox. 2, STOT RE 2, Aquatic Acute 1, Aquatic Chronic 1

Not disclosed. Moersch publishes no composition for MT1 Selentoner. The safety data sheet names three components — ammonium sulfite at 10%, ammonium thiosulfate at 20% and sodium selenate at 2-3 % — and those figures are a hazard classification's inputs, not an assay of the bottle: nothing on the sheet states that the list is complete, a composition table names the substances that drive a classification rather than the contents, and anything below the disclosure threshold does not appear at all. No function is given for any of the three. Beyond composition, the maker publishes no capacity at any dilution, no working-solution life, no keeping figure for the concentrate either sealed or opened, no toning temperature (the guide declines to give one on the ground that the effect is the same irrespective of temperature), no toning time as an instruction rather than as a caption to a particular plate on a particular paper, no selenium content expressed as the element, no figure for how much of the silver image any given time and dilution converts, and no occupational exposure limit — section 8.1 records that the information is not available. A reader who wants to know how many grams of selenium are in their tray, or how many prints a litre will take before it slows, cannot get there from Moersch's literature, and the open formula that would answer the first question is one this course publishes at Level D and asks nobody to make.

Nearest open formula. Kodak T-55 — Both are direct selenium toners for paper, worked in a tray at room temperature, and both leave a print that is part silver selenide and part untoned silver. After that they diverge further than any other product-and-formula pair in this library. Kodak Limited's T-55 publishes every quantity — 300 g of crystalline sulphite, 6 g of selenium powder, 190 g of ammonium chloride to the litre — and reaches them by boiling elemental selenium in an open pan until it dissolves, which is why the course carries it at Level D and gives no procedure for it. Moersch publishes no quantities and starts from a selenate that is soluble before the bottle is opened. T-55 has exactly one working dilution, 1+5, and one instruction, 10 to 15 minutes at 18 °C; MT1 is worked anywhere from 1+5 to 1+400, and which end you choose decides whether you are intensifying shadows or moving the image colour. And the two selenium species are at opposite ends of the element's range — T-55 dissolves the element in sulfite and the wider literature reads the product as a selenosulfate, while Moersch declares selenium(VI). So the trade here is not the formulary's usual one of a known composition against a known performance. It is a known composition nobody should prepare against an unknown composition anybody can buy, plus a guide that teaches the bath's behaviour better than either datasheet teaches its own.

Purpose

To convert part of a finished silver print to silver selenide — and, in this maker’s framing, to do it for the shadows first and for permanence second.

That ordering is Moersch’s own and he states it in the opening lines of his guide. “Recent discussions about image silver stabilisation by means of selenium toning appear pointless to me. There are more effective ways to achieve archival permanence like toning in gold, sulphur or sistan. But even weak selenium toning is better in terms of archival permanence than no toning at all. A fine printer has other reasons for using selenium, though. Selenium toner allows us to increase the densities of the shadows exclusively.”

So the three purposes, in the order their maker puts them:

To raise shadow density and separate the deep tones. A distinctive increase in dmax, deep shadows that read as more differentiated, and a higher contrast range. This is the effect the product is sold for, and it is available at strong dilutions in under a minute.

To move the image colour cooler and less green. The size of the shift belongs to the paper emulsion and to the developer rather than to the toner. It is reached at high dilutions, and the greenish cast most printers dislike can, in Moersch’s words, be shifted to more pleasant hues in a very dilute bath.

To protect the image — which he concedes is real and ranks third behind gold, sulphur and Sistan. A page about a selenium toner whose maker says selenium is not the best protective toner is unusual enough to be worth stating plainly rather than burying: it is the strongest evidence in this corpus that the archival argument for selenium is a weaker argument than the trade makes it.

And one purpose the other selenium products in this library do not document at all:

To pre-tone before a bleach. In the companion Brown Toning guide, MT1 goes on first, to protect the shadows from a rehalogenating bleach, so that a subsequent sulphur or thiourea toner can reach the highlights and mid-tones without stripping the shadows away. Toning time decides how far up the scale the protection extends. The selenium toned silver gelatin print entry carries the process; this page is about the bottle.

Recommended uses

Shadow intensification, strong and short. 1+5 to 1+20 for 20 to 60 seconds. This is the use the guide is built around, and the one with a published time attached.

A colour shift, dilute and long. 1+100 to 1+400, chosen because in a stronger bath the shadows start losing density before the highlights have been reached.

Warm-tone papers, if you want to see it happen. Warmtone paper tones quickly and with a clear change in image colour. It is also the paper on which the progress of toning is easiest to judge, which matters on a bath whose maker publishes no times.

Cold-tone and neutral papers, if you want protection without a visible change. With coldtone paper the alteration is often barely visible even in a strong solution held a long time, and Moersch names Ilford Multigrade IV developed in a neutral-tone developer as a paper on which selenium toning is hardly visible at all. That is a use, not a failure — but see Troubleshooting before concluding that nothing happened.

As a pre-toner at 1+10 before a bleach, in split and brown toning sequences. Selenium always starts in the shadows, so the toning time decides whether only the shadows or also the mid-tones survive the bleach.

As an over-toner after a sulphur toner. Moersch’s own example is 1+10 for 5 minutes after sulphur, where the slightly toned greenish shadows take a selenium tone and, unusually for selenium, the highlights receive a reddish hue as well.

Straight out of an alkaline fixer, with no rinse between. This is a maker’s statement and it is worth having, because it removes a step: if you fix in something like TF-2, the print goes from fixer to toner. After a sour fixer, rinse for around ten minutes first.

Not for film, and not for anything the maker does not name. Section 1.2 of the safety data sheet gives the application as a toner for silver gelatine prints, and section 7.3 as a toner for silver prints after fixing. No film, no plates, no machine process, no alternative process.

When another formula is preferable

• Where permanence is the whole point, the maker’s own answer is gold, sulphur or Sistan rather than selenium. The open formula for the first is GP-1, Kodak’s gold protective solution, published in full with its ten minutes at 20 °C and carried at Level B. It costs what gold costs, and it is the formula this page would point at first if protection were the only question.
• Where a sulphur route is acceptable, Moersch’s own comparison plate is the argument: on Ilford Multigrade IV his MT5 sulphur toner at 1+10 for 3 minutes raised shadow density more than MT1 at 1+50 for 5 minutes, and he judges the protective effect “considerably higher” for a similar dilution and duration, with selenium not reaching the upper mid-tones at all. The open sulphide formulas are T-7a and Kodak Limited’s T-52.
• Where sepia is wanted and no sulphide reagent may be handled, the hypo-alum bath T-1a, which is the only sepia route in this formulary at Level B.
• Where a maker’s procedural numbers matter more than a maker’s understanding, HARMAN SELENIUM TONER is the better-documented bottle. It publishes a capacity, three keeping figures for the working solution, two keeping figures for the concentrate, a working temperature with a tolerance and a time at one of its two dilutions. Moersch publishes none of those. What HARMAN does not publish is any account of what the bath actually does to a print, and Moersch’s guide is worth more than all of HARMAN’s numbers to a printer trying to learn the process.
• Where the print is not properly fixed or washed, nothing on this page helps. That is a fixing and washing problem, and the answers are ILFORD WASHAID, the open sulfite washing aid or Kodak’s hypo clearing agent followed by a full wash, with the residual hypo and silver tests to prove it. A toner that contains 20 per cent ammonium thiosulfate is not a rescue for an under-washed print.
• Where you want to understand a selenium bath rather than buy one, the usual answer this formulary gives is the one it cannot give here. Kodak Limited’s T-55 publishes every quantity and is carried at Level D, because its second step is boiling six grams of elemental selenium powder in an open pan of hot sulfite solution until it dissolves. Read it for the chemistry. Do not make it.

What the maker publishes

Three documents and a fourth that mentions the product in passing, and none of them is a technical datasheet in the sense the rest of this formulary’s product pages are used to.

The guide, Selenium Toning. Six pages, written in the first person, illustrated with named photographers’ prints and captioned with the dilution and the time each one took. It is the primary source for this page. What it publishes:

• The governing rule. “Irrespective of the dilution or temperature, the toner always reaches the higher densities first.”
• Two dilution regimes with two purposes. 1+5 to 1+20 for 20 to 60 seconds if only the shadows are to intensify; 1+100 to 1+400 if the toner is to reach the highlights before shadow density begins to fall.
• How to stop it. Short strong toning “has to be stopped abruptly”, and — the sentence that earns its exclamation mark — “Clearing agents are no stop baths for selenium toners!” The stop is rapid dilution of the toner still held in emulsion and paper base under running water, with both surfaces gently wiped with cotton wool.
• What each class of paper does. All papers are accessible to selenium toning; warmtone tones quickly and visibly, coldtone often barely at all.
• The diagnostic. How far toning has really progressed “is only visible if you bleach”. A red brown image with tonality still in the highlights means the goal is reached; worn-out highlights mean toning was too short for maximum protection. And after the bleach, fixing removes the untoned silver and lightens the print, while reverse development with any developer restores it instead.
• A name for the invisible part. Even where the highlights look untoned, “a small membrane will have been created around the silver grain. This is called hidden selenium toning.”
• A rule that ties the toner to the developer. “The warmer the print was developed, the higher should the toner be diluted to prevent excessive cooling of the image tone.”
• Eight worked dilutions and times, in the captions rather than in a table — 1+6 for 4 minutes, 1+10 for 40 seconds, 1+10 for 1 minute 30, 1+10 for 2 minutes, 1+10 for 5 minutes, 1+20 for 2 minutes, 1+50 for 3 minutes, 1+100 for 2 minutes, each on a named paper in a named developer.

The safety data sheet, version 3, printing date and revision 16 February 2025, written to REACH (EC) No 1907/2006. Composition, classification, first aid, glove data, disposal — and section 9, which is where this sheet becomes the most informative selenium document in the corpus on the physical side. Colourless fluid; odour ammonia like; vapour pressure 23 hPa at 20 °C; density 1.20 g/cm³ at 20 °C; fully miscible with water; pH 9.53 at 20 °C; organic solvents 0 per cent; water more than 67 per cent; VOC 0 per cent; solid content less than 33 per cent.

The product page, which carries three things found nowhere else: the dilution range “1+10 to 1+400”; the pack sizes, 250 ml and 1 litre; and the maker’s regulatory statement quoted in full under The mechanism below, in which he names his selenium salt in running prose and says which salt it is not.

The Brown Toning guide, which is about thiourea and sulphur toning and uses MT1 as a step in those sequences. It is the source of the pre-toning times, of the split-tone observation, of the statement that after six minutes not all the silver has been converted, and of the one sentence about composition that any manufacturer in this corpus has volunteered outside a hazard table.

!The numbers Moersch prints that HARMAN records as Not known

Two European manufacturers sell a selenium toner for paper. Both write a safety data sheet to the same regulation. Set section 9 of each beside the other and the difference is not a difference of chemistry, it is a difference of how much a maker chose to fill in.

Section 9 property	Moersch MT1	HARMAN Selenium Toner
Appearance	fluid, colourless	Liquid
Odour	ammonia like	Not known
pH	9.53 at 20 °C	Not known
Density	1.20 g/cm³ at 20 °C	Not known
Water solubility	fully miscible	Not known
Vapour pressure	23 hPa at 20 °C	Not known
Water content	more than 67 %	not stated
Solid content	less than 33 %	not stated
Incompatible materials (section 10.5)	release of toxic materials with acids	Not known

The pH is the one that matters most. Every handling rule on a selenium page comes back to no acid, ever, and a reader who wants to know how much margin the bath has before an accidental carry-over of stop bath becomes a problem needs a starting pH. Moersch gives it: 9.53, comfortably alkaline. HARMAN’s sheet records it as Not known, which is a legitimate answer to a regulatory question and useless to a printer.

Nothing here says Moersch’s product is safer, better made or better understood. It says his sheet is more completely filled in, and that a reader comparing two products should compare what each maker was willing to write down.

What is not disclosed

The composition as a formula. Three components, two of them printed as single percentages and one as a two-point band, with no function stated for any of them, no order of addition, no water specification, no pH adjustment, no preservative statement and no manufacturing route. A safety data sheet lists the substances that drive a classification. It is not a contents list, and nothing on this one says the list is complete.

Any capacity, anywhere. No sheets per litre, no square metres per litre, no statement of how a working bath changes as it is used. HARMAN at least publishes a floor and a model of exhaustion; Moersch publishes neither. On a bath whose whole control is dilution and time, not knowing whether your third session is working in the same solution as your first is a real gap.

Any keeping figure. Nothing for the concentrate sealed, nothing for the concentrate once opened, nothing for a working solution in a bottle or in a tray. The safety data sheet gives storage conditions — tightly closed, dry, 10 to 25 °C, away from foodstuffs, under lock and key — and those are not the same thing as a shelf life.

A temperature. Declined rather than omitted, which is a different and more interesting silence: the guide’s governing rule is stated to hold irrespective of temperature. That tells you temperature is not the control. It does not tell you whether a cold darkroom slows the bath down.

A toning time as an instruction. Every time on the page is a caption to a plate — this paper, in this developer, at this dilution, for this long, giving this result. That is more honest than a generic table and less usable at a tray, and it is why the bleach diagnostic matters so much here.

How much of the silver any given treatment converts. The only figure in either guide is a negative one: after six minutes at 1+10, not all of it.

A selenium content as the element, in the concentrate or in any working bath.

An occupational exposure limit. Section 8.1 reads “This information is not available”, which is a statement about the mixture and not about selenium; the limits on the selenium page are milligram-per-cubic-metre figures for the element and its compounds.

And a coherent account of its own toxicity. The safety data sheet’s section 2.1 and its section 2.2 do not agree, and its section 11 disagrees with both. That is set out under Safety, because it changes what a reader should do rather than merely what they should know.

!Why 10 % plus 20 % plus 2–3 % is still not a recipe

Moersch’s composition table is more specific than HARMAN’s — two point values against two bands three-fold wide — and the temptation to treat it as a formula is correspondingly stronger. Three reasons it is not, in the order they bite.

It is not stated to be complete. A composition table under section 3 names the substances that drive the mixture’s classification. A wetting agent, a sequestrant, a buffer or a preservative present below its own disclosure threshold drives no classification and appears nowhere. The sheet’s silence about a fourth ingredient is not evidence that there is not one.

The percentages are w/w and the dilutions are volumetric. The sheet gives a density, 1.20 g/cm³, which means a reader could multiply and arrive at grams per litre. This page does not do that arithmetic and asks you not to either. A concentration on a hazard sheet is an input to a classification, not an assay; multiplying it by a density does not turn it into one; and a number produced that way, printed with a citation beside it, is exactly the kind of fabrication that citation makes harder to spot. Under Rule 1 the course does not publish a composition it cannot source, and a computed composition is not a sourced one.

Even if it were complete and even if it were an assay, it would not be a procedure. T-55 is published complete, in grams, by Kodak Limited — and Kodak Limited gives no function for 190 grams per litre of ammonium chloride, and neither can this course. A list of quantities is not an understanding of a bath. That is the argument this whole formulary rests on, and it cuts both ways.

What the table is good for is set out in the next section, and it is not nothing: it identifies the selenium species, it says which of the three components dominates, and it tells a reader which of the sheet’s hazards belong to which substance.

Disclosed components

Three, in the order the safety data sheet prints them, each with the concentration exactly as the sheet gives it. One thing about the table before the components: the sheet does not use the same kind of hazard label for all three, and the rows above reproduce whatever is printed rather than converting one into the other. Ammonium sulfite gets both hazard classes and hazard statement codes. Sodium selenate gets hazard classes only, with no H-numbers. Ammonium thiosulfate gets an empty cell. Converting selenate’s “Acute Tox. 2” into an H-code would mean choosing between H300 and H330 on the reader’s behalf, and the sheet does not make that choice.

Ammonium sulfite, CAS 10196-04-0, EC 233-484-9, 10%. Classified on the sheet Eye Irrit. 2 and STOT SE 3, H319 and H335. It is a sulfite, and every selenium toner in this course’s corpus contains one — Kodak describes the active ingredient of its own product as “a sulfite salt”, HARMAN declares sodium sulphite at 10-30 %, and Kodak Limited’s T-55 is built on 300 grams of it per litre. But the reason T-55 needs sulfite cannot be the reason this bottle contains it. T-55’s sulfite exists to dissolve elemental selenium, which will not dissolve in water; Moersch’s selenium arrives as a selenate, already soluble, and nothing needs dissolving. Two other readings are available — sulfite is the standard antioxidant of photographic solutions and would protect a thiosulfate-bearing bath, and sulfite is a medium in which selenium species are known to interconvert — and the course adopts neither. Moersch states no function, no other document in the corpus discusses this product’s sulfite, and choosing between the two would be reconstructing a formulation by inference. Note also what kind of sulfite it is: an ammonium salt where HARMAN’s is a sodium salt.

Ammonium thiosulfate, CAS 7783-18-8, EC 231-982-0, 20%. The largest declared component of the bottle, at twice the sulfite and between about seven and ten times the selenium, and the one the sheet leaves entirely unclassified — no hazard class, no H-code, no pictogram. A reader skimming the table can miss that a toner contains, as its biggest named ingredient, the working agent of every rapid fixer in this formulary, including ILFORD RAPID FIXER and HYPAM.

And here this page can do something the HARMAN page cannot. There, the observation that a selenium toner is also a weak fixing bath had to be marked as the course’s inference from a composition table. Here it is the maker’s own statement, in the Brown Toning guide, in his own words: “the selenium toners of all manufacturers that I know of contain thiosulphate, so that you have to rinse thoroughly before bleaching. If you use an alkaline fixer, you don’t need to rinse between fixer and selenium toner. After using a sour fixer you should rinse for around 10 minutes.” That is a manufacturer telling you that his toner carries a fixing agent, and telling you what to do about it in both directions — the rinse you can skip after an alkaline fixer, and the ten minutes you cannot skip after a sour one. He still does not say what the thiosulfate is for, and this page does not guess.

Sodium selenate, CAS 13410-01-0, EC 236-501-8, 2-3 %. The selenium, and the only component carrying a REACH registration number on the sheet, 01-2120772103-63-xxxx. Its hazard classes are Acute Tox. 2, STOT RE 2, Aquatic Acute 1 and Aquatic Chronic 1 — acutely toxic, damaging to organs on repeated exposure, and very toxic to aquatic life both acutely and chronically. Every serious hazard the mixture carries traces back to this line, and at 2 to 3 per cent it is the smallest of the three by a factor of between three and five.

It is a selenate, selenium(VI), which matters more than it looks. The sodium selenite page records that this corpus now holds four manufacturers’ statements naming four different selenium species across three oxidation states, and Moersch’s is the highest of them. It is not HARMAN’s selenite, it is not the selenosulfate the wider literature reads into a sulfite-dissolved bath, and it is not the selenide of the nineteenth- and early twentieth-century formulas.

⁇The maker says which salt it is — and, uniquely, which salt it is not

Moersch’s product page carries a compositional statement in running prose rather than in a hazard table, and it exists because a regulation changed:

The legal regulations have changed: Selenium toner based on sodium selenite may now only be marketed in vol % <1. This leads to questions about changing the dilution ratios of this product. Answer: This product does not contain sodium selenite but sodium selenate, the preparation did not have to be changed. All information on dilution to working solution in instructions and under picture examples is up to date as before.

Three things follow, and only the first two are the maker’s.

His. The salt is a selenate and is not a selenite; the formulation was not changed; and every dilution in his guides and plate captions still applies. That last clause is worth having, because a reader who found an older guide and a newer bottle would otherwise have to wonder.

His. A selenite-based selenium toner now faces a marketing restriction his does not. He does not say which instrument imposes it, and the course has not traced it; the page reports the maker’s statement as a statement rather than as a finding about European chemicals law.

Not his, and marked as inference under Rule 7. It is tempting to read this as Moersch having chosen a selenate because of the regulation. His words say the opposite — the preparation “did not have to be changed”, so the selenate predates the change — and nothing on any of his documents says why the salt was chosen in the first place. The course records that it is a selenate and that the maker says so. Why, nobody outside Hürth knows.

And what is in the bottle and not in the table. Water, which no safety data sheet declares because it drives no classification, and which section 9 puts at more than 67 per cent. Whatever else sits below the disclosure threshold. And, on the evidence of section 9’s own odour line — ammonia like — free ammonia, since two of the three declared components are ammonium salts and the solution sits at pH 9.53. That last sentence is the course’s reading and not the maker’s statement: he reports the odour and never explains it, and the ammonium hydroxide page is where the chemistry of an alkaline ammonium salt solution belongs. It is a reading with a practical edge, which is why it is here at all — the smell over the tray is probably ammonia and probably not selenium, and Troubleshooting returns to why that matters.

Behaviour

The higher densities go first, always. “Irrespective of the dilution or temperature, the toner always reaches the higher densities first.” Everything else on this page is a consequence of that one sentence. It means selenium toning is not a uniform treatment that you apply for longer to get more of; it is a front that moves down the tonal scale from the shadows, and dilution and time decide how far it gets.

So the two regimes are not two strengths of the same thing. A strong bath used briefly stops the front in the shadows: dmax rises, the deep tones separate, nothing else moves. A very dilute bath used long lets the front reach the mid-tones and highlights — which is the only way to shift image colour across the whole print — at the cost that if you overrun it, shadow density starts coming back down. Choosing 1+10 and waiting is not a slower route to the 1+400 result. It is a different result.

Temperature is not a control, and the maker says so. The rule holds irrespective of it. That is a genuinely unusual claim in this formulary, where almost every bath is specified to a degree or two, and it means a printer has one fewer variable and one more reason to trust the clock and the dilution.

It does not stop when you take the print out, and a clearing agent will not stop it. Moersch is emphatic: “Clearing agents are no stop baths for selenium toners!” The toner is still in the emulsion and in the paper base when the print leaves the tray, and the only stop he gives is physical — quick dilution under running water with both surfaces gently wiped with cotton wool. On a 20-second bath at 1+6 the difference between stopping properly and putting the print in a washing aid is the difference between the result you judged and a result you did not.

Every paper tones; not every paper shows it. Warmtone paper tones quickly and with a clear change in image colour. Coldtone paper often shows an alteration that is barely visible even in a strong solution held a long time — “amazingly little is going on”, as he puts it — and Ilford Multigrade IV developed in a neutral-tone developer is his named example of a paper on which selenium is hardly visible at all. If the print was toned for protection, that is not a problem. It only becomes one if you conclude from the appearance that nothing happened, which is exactly what the bleach test exists to settle.

The developer you printed in changes the dilution you should tone at. “The warmer the print was developed, the higher should the toner be diluted to prevent excessive cooling of the image tone.” No other toner document this page draws on ties the toner’s dilution to the developer, and it is the kind of instruction that only comes from somebody who has run out of ways to explain a bad result to a customer.

In a strong bath the print splits before it converts. After about three minutes at 1+10, the shadows appear red and the densities that have not yet been fully toned separate clearly in a cooler colour. The highlights, he notes, start blue and only survive a subsequent bleach once they have changed to the red of the neighbouring densities. That is a visible progress indicator on a bath with no published times, and it works only in the strong regime.

Conversion is partial, and it is partial for longer than you would guess. After six minutes at 1+10 — an aggressive treatment by any measure — not all the silver has been transformed to silver selenide, and the remainder can be re-halogenated and toned in thiourea afterwards. So a selenium-toned print is normally a mixture of silver selenide and untoned silver in proportions the printer chose without measuring. Protection is proportional to a conversion nobody measures, which is the same conclusion the process page reaches from Kodak’s and HARMAN’s sides.

It carries a fixing agent into the tray. Twenty per cent ammonium thiosulfate in the concentrate, on the maker’s own sheet, and the maker’s own instruction that a print must be rinsed thoroughly before any bleach that follows. In the other direction the same fact buys you a step: no rinse is needed between an alkaline fixer and the toner.

Exhaustion is undocumented. No capacity, no exhaustion model, no statement that the bath slows. That is not a claim that it lasts forever; it is an absence, and the only honest way to work around it is to time a standard test print at intervals and keep the number.

Image characteristics

A distinctive rise in dmax, and deep shadows that separate. Moersch’s own summary is that apart from the increase in maximum density, “the deep shadows appear more differentiated”, and that a higher contrast range together with the colour shift makes toned prints “look more brilliant”. No figure is published for any of it, by him or by anyone else in this corpus, for any current paper.

A shift towards cooler and less green tints, whose size is the paper’s and the developer’s. He says so explicitly: the shift “is dependent on the composition of the paper emulsion and on the developer”. This is the same conclusion HARMAN reaches from the other end — that the colour outcome belongs to the paper — but Moersch adds the developer, which HARMAN does not.

The green goes, if you dilute enough. “The greenish cast of the image silver, which most photographers do not appreciate, can be shifted to more pleasant hues in highly diluted working solutions.” That is a use case, and it is one a strong short bath will not deliver, because the front never reaches the tones where a green cast is most visible.

Three classes of paper, three outcomes. Warmtone, quick and clearly coloured. Neutral, intermediate. Coldtone, often barely visible. The Getty Conservation Institute’s atlas describes the same thing from the conservator’s side — when selenium toning is done for permanence rather than for colour it causes no major colour shift, only a slight increase in image contrast and brilliance.

Under a bleach, the toned and untoned parts of the same print read differently. Toned silver survives as a red-brown image; untoned silver bleaches to a salt and, if fixed away, simply lightens the print. That is what makes the bleach a measurement rather than a mistake, and it is the only way this course knows of to see how far a selenium bath actually got.

Against a sulphur toner on the same paper, selenium is the weaker intensifier. Moersch’s plate puts MT1 at 1+50 for 5 minutes beside his MT5 sulphur toner at 1+10 for 3 minutes on Ilford Multigrade IV, and records that the sulphur toner raised shadow density more and protected considerably better, and that selenium would not have reached the upper mid-tones. A manufacturer publishing a comparison in which his own product comes second is rare enough to be worth citing on its own account.

As an over-toner it behaves unusually. Following a sulphur toner at 1+10 for 5 minutes, “not only the shadow densities got affected as usual with Selenium, but also the highlights received a reddish hue” — the one documented case in either guide where selenium reaches the highlights without a very high dilution.

The signature outlasts everybody. Selenium treatment can be detected by X-ray fluorescence long afterwards. A print toned at 1+400 to look almost untoned is still identifiable as toned in a century.

The mechanism

The end state is not in doubt and is not this page’s inference. Kodak states outright that a selenium toner converts the silver image to silver selenide, and Moersch uses the same term for what a bleach leaves behind. What the course cannot do is put a number behind the protection: no source it holds gives a solubility product, a solubility figure or a formation constant for Ag₂Se, so the mechanism is recorded as an observed increase in chemical and environmental stability and not as a calculation. No balanced equation for the toning step is printed on this page, because the course does not hold one and writing a plausible one would be the failure Rule 1 exists to prevent.

What this product adds to the mechanism is a starting oxidation state, and it is the highest one in the corpus. Selenate is selenium(VI). Silver selenide is selenium(−II). Getting from one to the other is a reduction of eight oxidation-state units, in a bath that also contains a sulfite and a thiosulfate and sits at pH 9.53, on a print made of metallic silver. That arithmetic is the course’s and is offered as a statement of the size of the question, not as an answer to it. No source this course holds describes the pathway, names an intermediate or says which of the bath’s components does the reducing — and a page that supplied one would be inventing chemistry to fill a gap it had just finished pointing at.

⚗Four makers, four selenium species, and what each will tell you

The composition tables are only half of what a maker discloses. Set out what each of the four selenium sources in this corpus actually publishes and the picture is less about chemistry than about disclosure policy.

	Selenium species named	Concentration given as	pH published	Acid incompatibility stated	Capacity published
Moersch MT1	Sodium selenate, CAS 13410-01-0 — Se(VI)	2-3 % w/w	Yes, 9.53	Yes, in two sections	No
HARMAN Selenium Toner	Sodium selenite, CAS 10102-18-8 — Se(IV)	1-5 %, a band	No, Not known	No, none known	Yes
Kodak Rapid Selenium Toner	“a sulfite salt”; “selenium sulfite” — no CAS	less than 2 %	No	Not in the toning publication	Yes
Kodak Ltd T-55 (1949, open formula)	Elemental selenium, boiled into sulfite	6 g/L, published	No	No	No

Three oxidation states among the three modern products, and a fourth route in the historical formula. The two European sheets are written to the same regulation, disclose the same number of components, and name different compounds. Any account of selenium toning that speaks of “the selenium toner” as one substance is wrong about at least two of these.

That the three modern products share a common architecture — a selenium salt, a sulfite and, where declared, a thiosulfate — is the course’s reading of two composition tables and one manufacturer’s sentence. It is an inference under Rule 7, not a statement by any of the makers. None of the three sheets assigns a function to anything, and Kodak names no compound at all.

Why the bath is also a weak fixer — and here it is not an inference. Twenty per cent ammonium thiosulfate is a fixer-bottle concentration, and the maker states in the Brown Toning guide that selenium toners contain thiosulphate and that the print must be rinsed thoroughly before bleaching because of it. What follows is practical rather than theoretical: the toner is not a place to finish an inadequate fix; the print goes in properly fixed and, after a sour fixer, properly rinsed; and the spent bath carries thiosulfate into the waste bottle alongside selenium and dissolved silver.

Why every handling rule comes back to acid — and here the maker helps, where HARMAN does not. Section 10.3 of Moersch’s sheet states a violent reaction with strong acids, and section 10.5 states the release of toxic materials with acids. Neither line names the gas. What the course can supply is the reason the rule is absolute rather than proportionate: HSE’s EH40 sets dihydrogen selenide at 0.02 ppm over eight hours and 0.05 ppm over fifteen minutes, among the lowest limits in the whole table. The course has not verified which species an acidified selenate bath releases, and says so; it has verified that the family’s volatile hydride is controlled at a level no darkroom can measure. That is enough to make the rule “no acid, ever” rather than “keep the acid down”.

Why the bleach test is a mechanism test. A rehalogenating bleach converts metallic silver back to a silver halide and leaves silver selenide alone. So bleaching a toned print separates what was converted from what was not, visibly, and Moersch’s diagnostic is exactly that experiment run for information: a red brown image with tonality still in the highlights means the conversion reached the whole scale; worn-out highlights mean it did not. This is the only method in the corpus for observing the extent of selenium conversion without an instrument, and it is destructive unless the bleached print is redeveloped rather than fixed — which the guide says works, with any developer.

And “hidden selenium toning” is the maker’s name for the part the test cannot see. Even in highlights that look untoned, he says, “a small membrane will have been created around the silver grain”. The course records the term and the claim as his. No source it holds measures such a membrane, gives it a thickness, or shows what protection it confers, and this page does not treat the phrase as more than a description.

The nearest open formula

Kodak T-55, Kodak Limited’s direct selenium toner of 1949 — the only selenium toner in this formulary published as a formula rather than sold as a product, and therefore the only possible comparison. It is also, uniquely in this library, a formula the course asks nobody to make.

	Kodak T-55 (1949)	Moersch MT1 Selentoner
Composition	Published complete — 300 g crystalline sodium sulphite, 6 g selenium powder, 190 g ammonium chloride, water to 1000 c.c.	Not published; three components on a hazard sheet, at 10%, 20% and 2-3 %
Selenium species	The element, dissolved by boiling in sulfite; the wider literature reads the product as a selenosulfate and the course has not verified that	Sodium selenate, Se(VI), named by CAS, EC and REACH registration number
Getting the selenium into solution	By the person making it, in an open pan, at the boil	Already done, in a sealed bottle
Working dilution	1+5, and no other	1+5 to 1+400, and which end you pick changes the result in kind
Time	10 to 15 minutes	20 seconds to 6 minutes, depending on the end of the range
Temperature	18 °C, specified	Not specified, and explicitly said not to govern
pH	Not published	9.53 for the concentrate
Capacity	Not published	Not published
Keeping	Not published	Storage conditions only; no shelf life
What the maker teaches you about the process	Nothing — it is a table of quantities and a two-line instruction	Six pages, with plates, on how the bath moves down the tonal scale
Safety level	D — historical study, no procedure given	B — a liquid concentrate poured into a dish
What the course recommends	Read it	Use it

The usual product-page argument in this library is that the bottle buys you documented performance and the open formula buys you a known composition, and that a reader can choose. Here neither half of that is quite true. T-55’s composition is known and its performance is documented in two lines; MT1’s composition is secret and its performance is documented better than any other toner in this formulary. What you are actually choosing between is a bath you must not prepare and a bath you cannot analyse — and, unusually, the one you cannot analyse is the one whose behaviour you will understand.

Three further things the comparison shows.

The published composition does not deliver understanding. Kodak Limited prints 190 grams per litre of ammonium chloride and gives no reason for it, and neither can this course. T-55 has a published quantity whose purpose is exactly as unknown as MT1’s ammonium sulfite. Publishing the numbers and explaining the bath are different achievements, and only one maker here has managed either.

The dilution ratios are not comparable and it is a trap to compare them. T-55 at 1+5 and MT1 at 1+5 are the same arithmetic performed on two entirely different stocks, one of which carries 6 g/L of selenium as the element and the other of which nobody outside Hürth can quantify. A reader who reasons that “1+5 is 1+5” has assumed the equivalence this page exists to deny.

And the two baths are not the same chemistry. One starts from the element dissolved in sulfite, at selenium(0) heading somewhere the literature reads as a selenosulfate; the other starts from selenium(VI). Treating T-55 as a reconstruction of the bottle would be an error in both directions at once.

Safety

Level B, and on this product the reasoning has to be written out, because the maker’s own sheet gives two different answers to the question the level depends on.

What the sheet classifies. Section 2.1 classifies the mixture Acute Tox. 2 (H300), STOT RE 2 (H373), Eye Dam. 1 (H318) and Skin Sens. 1 (H317). Section 2.2 gives the label as signal word Danger with pictograms GHS07, GHS08 and GHS09, and then prints only two hazard statements — H302, harmful if swallowed and H335, may cause respiratory irritation — with precautionary statements P102, P280, P301+P312, P302+P352, P305+P351+P338 and P333.

Why B and not A. The rubric’s Level A ceiling is a substance whose classification, at the concentration actually handled, is at most irritant or harmful. A sensitiser is named explicitly in the first Level B criterion, and one half of this sheet says the mixture is one. So does its own symptom list, which records under If on skin a risk of absorption via the skin — a line the equivalent HARMAN sheet does not carry. The concentrate also holds a component the sheet itself classifies Acute Tox. 2, and the maker asks for it to be stored under lock and key.

Why B and not C. The Level C criterion that would apply names reagents where a fume cupboard or specialist disposal is the recognised control. No solid is weighed at any point: the operation is pouring a bottled liquid into a measuring cylinder and diluting it, at room temperature, at ratios from 1+5 to 1+400. The maker’s own controls are ventilation, nitrile gloves and eye protection, not containment; section 5.2 records the mixture as non-combustible; and the working bath a print actually meets is between a sixth and a four-hundredth of the concentrate. Specialist disposal is required, which the Waste section takes seriously, but disposal alone does not set the level.

The declared raised step. The first pour of the undiluted concentrate is the part of this that earns the letter, and it carries its controls with it: gloves on before the cap comes off, eye protection on, the bottle over a tray rather than over a sink, and the measuring cylinder rinsed into the working bath rather than into the drain.

⚠The sheet disagrees with itself about how poisonous this is, and the milder half is the one on the shop page

This is not a quibble about wording. Section 2.1 and section 2.2 of the same document, one page apart, classify the same mixture differently, and section 11 sides with the milder of the two.

	Section 2.1, classification	Section 2.2, label	Section 11, toxicological information
Swallowing	Acute Tox. 2 — H300, fatal if swallowed	H302, harmful if swallowed	“Harmful if swallowed”, with oral LD50 7 mg/kg in the rat, attributed to ECHA
Eyes	Eye Dam. 1 — H318	not listed	“Shall not be classified as seriously damaging to the eye or eye irritant”
Skin	Skin Sens. 1 — H317	not listed	“Shall not be classified as a respiratory or skin sensitiser”
Organs, repeated exposure	STOT RE 2 — H373	not listed as a statement; GHS08 is on the pictogram list	“May cause damage to organs through prolonged or repeated exposure”
Breathing	not listed	H335, may cause respiratory irritation	not classified for single-exposure organ toxicity

Section 16’s list of relevant H-phrases gives H302 and H335 only, and the maker’s shop page carries the consumer label in the same mild form — signal word Caution, one statement, harmful if swallowed. Even section 2.2 is split against itself: its signal word is Danger, which belongs with the severe half, while its statements belong with the mild half, and GHS06, the skull, is absent from a label whose own classification table says Acute Tox. 2. Its GHS09 has no aquatic classification in section 2.1 to hang on, though section 12.1 does say the mixture is toxic to aquatic organisms with long-lasting effects.

Three observations, all the course’s and all marked as such. First, the sheet does not say whether its LD50 of 7 mg/kg is a measurement on the mixture or a figure carried across from a component’s registration dossier, and those are very different claims. Second, this course’s own GHS reference records H302 as the category 4 statement, at the bottom of the oral acute-toxicity scale, and H300 at the top; the sheet prints both, for the same product, on facing pages. Third, nothing here suggests bad faith — a small manufacturer’s sheet built from component data can end up with a classification table and a label generated on different bases — but the effect on a reader is the same either way.

What to do about it: take the more severe reading. A document that contradicts itself gives no basis for choosing its milder half, and the milder half is also the commercially convenient one. So this page’s handling assumes H300, H318, H317 and H373 — treat it as fatal if swallowed, capable of serious eye damage, capable of sensitising, and harmful on repeated exposure — and the Level B controls follow from that rather than from the label.

Personal protection, and here the sheet is better than most. Section 8.2 specifies nitrile rubber gloves, minimum layer thickness 0.11 mm, breakthrough time 480 minutes, on a named tested material, KCL 741 Dermatril L — a specific glove with a specific EN 374 figure, which is exactly what the glove selection page asks for and rarely gets. Eye protection is given as safety glasses to EN 166 or an equivalent NIOSH standard; the course’s Level B assumes splash goggles, and where the two differ the stronger governs, particularly given that half of this sheet classifies the mixture Eye Dam. 1. Protective clothing, and the PPE donning and removal SOP for the order.

Ventilation. Sections 6.1 and 7.1 both ask for adequate ventilation, the label carries H335, and the liquid’s own odour is described as ammonia-like. Run the ventilation check before a session at the strong end of the range, where you will be leaning over the tray watching a twenty-second change.

No exposure limit is available, section 8.1 says so, and that is a statement about the mixture. The selenium page carries the limits that do exist for the element and its compounds, and a domestic room has no way of knowing whether it meets them. This is a reason for ventilation as an engineering control rather than as a comfort.

First aid, in the sheet’s own words. Inhalation, fresh air. Skin, take off immediately all contaminated clothing and rinse the skin with water. Eyes, rinse out with plenty of water, call an ophthalmologist, remove contact lenses. Swallowed, rinse the mouth, drink plenty of water, call a doctor. Symptoms listed are diarrhoea, vomiting and gastrointestinal complaints if swallowed; cough and dyspnoea if inhaled; and risk of absorption through the skin. The first aid quick reference and the eyewash SOP carry the course’s procedure.

In a fire the mixture is non-combustible, and section 5.3 asks for self-contained breathing apparatus.

Sensitisation is managed by prevention, not by care. On the severe reading the mixture is a skin sensitiser, and a sensitisation is a state that can be acquired rather than a dose that gets worse. A rash appearing after several toning sessions rather than after one is not a reason to be more careful next time.

And record the sheet you actually read. Version 3, 16 February 2025. Use the recording a safety data sheet SOP: on a product whose maker revises a two-page composition table between versions, the version you assessed is part of the assessment.

Storage

What the maker specifies, and it is conditions rather than a clock. Tightly closed. Dry. Stored away from foodstuffs. Under lock and key and out of the reach of children. Recommended storage temperature 10 to 25 °C. That is the whole of section 7.2, and it is the whole of what Moersch publishes about keeping this product.

What he does not publish is the part a darkroom actually needs. No shelf life for a sealed bottle. No clock once it is opened. No working-solution life in a bottle or in a tray. Set that against HARMAN’s five published figures — two years sealed, six months once opened, six months full at working strength, one month half full, seven days in a tray — and the gap is stark. It is an absence, not a claim of indefinite keeping, and the working assumption a printer should make is that a diluted selenium bath is no more stable than any other alkaline thiosulfate-bearing solution in an open tray.

So make your own clock. Write the purchase date and the opening date on the concentrate, and the dilution and mixing date on every working bottle, using the labelling SOP. Then record what the bath did against how old it was, in the formula version record. On a product with no published capacity and no published keeping figure, your own log is not supplementary data; it is the only data there is.

Buy the size your darkroom will actually use. The two pack sizes are 250 ml and 1 litre. The smaller one is not small: at the dilute end of the maker’s own range, 250 ml of concentrate makes a hundred litres of working bath, and even at 1+10 it makes nearly three. With no opened-bottle figure to work to, a bottle you will finish is worth more than a bottle you will store.

It looks like water and smells like household cleaner. Colourless, fully miscible, ammonia-like. There is no colour, no indicator and no distinctive photographic smell to identify it by, so an unlabelled or undated container of this is worse than an unlabelled container of almost anything else on the shelf — it is a selenium-bearing liquid that nobody can name and that must not go down a drain.

On its own shelf, and not above or below anything acidic. The incompatibilities page governs, and the reason is in the next section.

Incompatibilities

Acids, in every form, and this one governs everything else. Section 10.3 of the maker’s sheet states a violent reaction with strong acids; section 10.5 states the release of toxic materials with acids. Neither line names the gas, and the course has not verified which species an acidified selenate bath gives off. What is verified is that the selenium family’s volatile hydride is controlled at 0.02 ppm over eight hours, which is a level no darkroom can measure. That is why the rule is no acid, ever rather than “keep the acid low”: there is no margin to manage.

It is worth pausing on how much better this is than the alternative. The equivalent HARMAN sheet records incompatible materials as none known in section 7.2 and Not known in section 10.5. Both sheets describe a bottled selenium salt in a room whose next tray down is very often an acid stop bath, and only one of them says so. When two sheets disagree about whether a hazard exists, the one that names it is the one to work to.

Acid stop baths and sour fixers, as the case a darkroom actually meets. The toner goes in after the fixer, so the risk is carry-over — on the print, on tongs, on fingers. The maker gives the rule for the print: after a sour fixer, rinse for around ten minutes before the toner; after an alkaline fixer, no rinse is needed at all. He gives it in the Brown Toning guide, in the context of bleaching, and it applies here for the stronger reason.

Clearing agents and washing aids — not an incompatibility, a misuse. “Clearing agents are no stop baths for selenium toners!” A print moved from a strong short toning bath into WASHAID, hypo clearing agent or the open sulfite washing aid is a print still toning. Those baths belong later in the sequence, after the toner has been rinsed out.

Bleaches, and rinse thoroughly first. A rehalogenating bleach after a selenium pre-tone is a standard step in this maker’s own sequences, and his instruction is explicit that the thiosulfate the toner carries must be rinsed out before the print reaches the bleach.

Metal trays and tanks, per Kodak’s general toning guidance, which forbids them for every toner.

Food, drink and animal feed, in the sheet’s own words, and the household drain, which is the subject of the next section.

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

The waste container, which is where the incompatibility actually happens. Spent stop bath and spent toner in the same bottle is the reaction nobody intended and the one most easily arranged at the end of a long session. Separate, labelled containers, every time.

Waste

Three streams in one bottle: selenium, silver and thiosulfate. The maker’s own instruction is the shortest and strictest on any sheet in this corpus. Section 13.1: “This material and its container must be disposed of as hazardous waste.” Section 6.2 and section 8.2 both say the same thing twice over — do not allow it to enter sewers, surface water or ground water; do not let the product enter drains. Section 13.2 records the hazardous properties as HP5, specific target organ toxicity and aspiration toxicity, HP6, acute toxicity, and HP14, ecotoxic.

Contaminated packaging is treated as the substance. Section 13.1 says so; completely emptied packages may be recycled. In practice that means the concentrate bottle goes to the hazardous waste collection with whatever is left in it rather than being rinsed out at the sink, because rinsing it out at the sink is the discharge the sheet forbids.

A spill is absorbed, not washed away. Section 6.3 asks for absorption with a liquid-binding material — sand, diatomite, acid binders, universal binders, sawdust — with adequate ventilation. Note that section 6.2 also says “dilute with plenty of water”, which sits oddly beside “do not allow to enter sewers”, and the resolution is the obvious one: dilution is for the surface and the person, containment is for the liquid. The spill response SOP governs.

The ecological figures, quoted as printed. Section 12.1 states that the mixture is toxic to aquatic organisms with long lasting effects, and gives LC50 2060 mg/l for fish at 96 h, ErC50 45.000 mg/l for algae at 96 h, EC50 greater than 3200 mg/l for microorganisms at 3 h, and NOEC values of 330 mg/l for fish at 60 d, 100 mg/l for aquatic invertebrates at 24 d and 1.030 mg/l for algae at 10 d, all attributed to ECHA. Two of those numbers use a full stop where the rest of the sheet uses it as a decimal point — the same document writes 1.20 g/cm³, 9.53 and 0.11 mm — so “45.000” and “1.030” are ambiguous between a European thousands separator and a decimal. This page reproduces them as printed and converts nothing. The sheet also does not say whether the figures are for the mixture or for one of its components, and the declared sodium selenate carries Aquatic Acute 1 and Aquatic Chronic 1 in its own right. The classification is what governs disposal, not the numbers.

The silver 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 refiner will take a selenium-bearing stream is a question for the refiner, and this course does not answer it.

Never acidified, and never combined with an acid stream, which is the tray rule restated at the sink, where it is broken more often.

The independent guidance points the same way. In Kodak’s table of disposal routes for amateur photographic chemicals, a used selenium toner is given no sewer discharge, no discharge to a treatment works and no disposal with refuse — every route withheld except household hazardous waste collection. It is one of very few entries in that table treated that way.

And a very dilute bath is still a selenium stream. A litre of 1+400 working solution holds about a four-hundredth of the selenium of a litre of concentrate, and exactly the same number of drains it may not go down. Dilution is a printing control on this page, not a disposal method. The disposal caveat governs and local regulation decides.

Troubleshooting

Nothing visible happened. Ask three questions in order, because on this product the answer is usually the paper. Which paper — coldtone paper often shows almost nothing even in a strong bath held a long time, and Ilford Multigrade IV in a neutral-tone developer is the maker’s named example of a paper on which selenium toning is hardly visible. Which developer — the warmer the print was developed, the more the toner shows. Which dilution — at 1+400 an invisible result is the intended one. If the print was toned for protection, invisibility is not a fault. If you need to know whether anything happened, the answer is the bleach test below and not a longer bath.

The shadows went dense and the highlights never moved. That is the strong regime working correctly. Selenium reaches the higher densities first whatever you do; to reach the highlights you have to go to 1+100 or beyond and accept a longer bath.

The highlights finally came and the shadows went flat. That is the strong regime overrun. The maker’s warning is exactly this — in a bath stronger than about 1+100, the shadows start losing density before the highlights have been reached. Dilute further and start again on a fresh print.

The tone came out too cool, or too blue. Look at the developer, not the toner. The rule is that the warmer the print was developed, the more the toner should be diluted to prevent excessive cooling of the image tone.

It went on toning after I took it out. Then it was not stopped. A clearing agent will not do it; neither will dropping the print into a holding tray. Rinse under running water immediately and wipe both surfaces with cotton wool, which is the maker’s own method and the only one he gives.

I cannot tell how far it got. Bleach a test print. A red brown image with tonality still in the highlights means the conversion reached the whole scale; worn-out highlights mean it did not. Then either fix — which removes the untoned silver and lightens the print permanently — or redevelop in any developer, which the guide says restores the original condition. Do this on a work print, not on the print.

Yellowish highlights after a selenium pre-tone, a bleach and a sulphur toner. The selenium did not reach far enough up the scale before the bleach. Longer in the selenium, or stronger, and judge it by the split-tone signal — the highlights go from blue to the red of the neighbouring densities as they take.

Uneven tone, patchiness or mottle. Uneven toning and mottle revealed after toning. A twenty-second bath punishes slow immersion more than a four-minute one does.

A dark line creeping in from the edges of a resin-coated print. Toner edge penetration on RC.

Round purple stains that appear only after toning. Air bubbles trapped between prints during fixing, which Kodak names as a defect that shows up only after selenium or sulfide toning. Purple spots from fixer air bubbles is the entry, and the fix is upstream in the fixer.

Yellow staining, uneven tone and later fading together. Residual silver salts and traces of hypo, which is a fixing and washing failure and not a toning one. Residual thiosulfate and residual silver and yellow staining have the diagnosis; the residual hypo and silver tests will tell you before you tone rather than after.

The bath seems slower than it used to be. Nobody can tell you whether it is, because no capacity and no working-solution life are published. Time a standard test print to a fixed visible change at the start of a bath’s life and again every few sessions, and keep the numbers. That is the only instrument you have.

A smell over the tray. Read this one carefully, because the two candidate smells mean opposite things. The maker’s sheet describes the product’s own odour as ammonia-like, which is consistent with a solution of ammonium salts at pH 9.53 and is what you should expect over an open tray. The selenium page records something else entirely — that selenium salts have an intense and lasting garlic odour, and that garlic breath is a listed symptom of selenium exposure. The course cannot tell you which smell a leaking bottle of this product gives, and it will not guess. The rule that follows works either way: if you smell garlic rather than ammonia, leave the room and ventilate it, and do not investigate the tray first.

A rash or irritation appearing after several sessions rather than after one. Treat it as sensitisation. Stop using the product and get medical advice, and note that this is precisely the hazard on which the maker’s own sheet contradicts itself — section 2.1 classifies the mixture Skin Sens. 1, section 11 says it should not be so classified. The severe reading governs.

Two colourless bottles and no labels. An unlabelled or undated container, and on this shelf it is a disposal problem rather than an inconvenience, because neither bottle may go down a drain and neither can be identified by looking at it.

A dilution you are no longer sure of. Dilution ratio misread. With a working range running from 1+5 to 1+400, a misread ratio here does not give a slightly wrong result; it gives the other result entirely.

Experiments

Check the pH the maker publishes, and measure the ones he does not. Calibrate that day with the meter calibration SOP, read the concentrate — the sheet says 9.53 at 20 °C, so this is a check on your meter as much as on the bottle — then read 1+10, 1+50 and 1+400. Nobody publishes a working-bath pH for any selenium toner in this corpus, and it is the most safety-relevant number on the page.

Test the claim that a clearing agent will not stop it. Four identical prints at 1+10 for 40 seconds. Stop one under running water with both surfaces wiped, one in a washing aid, one in plain standing water, one in a holding tray for two minutes before washing. Dry them all and read the shadow densities against each other. The maker’s exclamation mark is a testable claim, and the differences should be visible without a densitometer.

Turn the bleach diagnostic into a conversion curve. A step wedge printed on one paper, toned at 1+10 for 20 s, 40 s, 90 s, 2 min, 4 min and 6 min, then bleached and fixed. What survives the bleach is what was converted, so the set is a map of how far down the scale the selenium front reached at each time. This is the maker’s own method used as a measurement, and it produces the number nobody publishes.

Then run the recovery he claims. The guide says that redeveloping the bleached print in any developer, instead of fixing it, restores the original condition. Prove it on one sheet of the set above, and you have a non-destructive version of the same test.

Dilution against tone, on one paper, in one session. 1+10, 1+50, 1+100 and 1+400, all for the same time on the same paper from the same negative. The prediction is that the first changes only the shadows and the last changes the whole scale slightly, and seeing it in four prints is worth more than reading it here.

The developer rule as a matrix. Two developers, one warm-working and one neutral, four prints each, toned at 1+10 and at 1+100. Moersch’s rule says the warm-developed prints need the higher dilution to avoid excessive cooling. It is the only claim this page has met that ties a toner’s dilution to a developer, and it deserves to be tested rather than repeated.

Measure how much of a fixer it is. The maker says selenium toners contain thiosulphate and his sheet says 20 per cent. A clip of unexposed, undeveloped film in working-strength toner, timed to clear against an identical clip in RAPID FIXER, using the clearing time test. A very long clearing time is a result; no clearing at all is an equally publishable one.

Test the rinse rule in both directions. Fix two prints in an alkaline fixer and two in an acid fixer; tone one of each straight from the fixer and one of each after a ten-minute rinse; then run the residual hypo and silver tests on all four after the full archival sequence. The maker says the rinse is unnecessary after an alkaline fixer and essential after a sour one. This is what that costs or saves.

Test his own ranking of the protective toners. He puts gold, sulphur and Sistan above selenium. Matched prints in MT1 at 1+20, in GP-1 and in T-7a, each bleached afterwards to show how much of the image survives. A manufacturer who ranks his own product third has given you an unusually clean hypothesis.

Find where the bath stops being the bath you calibrated. With no capacity published, time a standard test print to a fixed visible change at the start of a litre’s life and after every fifth sheet through it, and plot time against cumulative area. Whatever curve you get is more than any maker publishes for this product.

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