Kodak T-55

The only direct selenium toner in this corpus whose composition is published. Every other one the course has a source for is a bottle whose maker does not say what is in it — which is a perfectly legitimate way to sell a toner and a fatal one for a formulary. Kodak Limited printed this in London in 1949 with a mixing procedure, a dilution, a time and a temperature, and noted in a footnote that the same thing was on the shelf as Kodak Selenium Toner.

⚠Level D: this page is not a procedure

Selenium is classified for historical study only, and its page gives the two reasons against the rubric: a safer modern route exists and is taught instead — a bought, dilute liquid toner that never asks anyone to handle the element — and the character of the original method, which is a fusion with caustic soda or a boil with sodium sulfide or sulfite of a substance classified toxic by two routes, carried out beside photographic materials.

The second of those describes the first step of this formula exactly. So this entry does what a Level D page does: it gives the chemistry, the workflow in outline, the image characteristics and the hazards, and states explicitly that it is not a procedure. There is no protective equipment list that makes boiling six grams of selenium powder acceptable at home and none is offered.

Handling a bought selenium toner is a different question with a different answer, and it is on the selenium page, which says to follow the sheet for the product in your hand rather than either page.

Ingredient	Quantity	Form the source specifies
Sodium sulfite (anhydrous)	300 g or 150 g (anhydrous)	crystalline
Selenium	6 g	powder
Ammonium chloride	190 g
Water	to make 1000 mL	at 70 °C; About 700 c.c. of hot water to start - Kodak Limited gives no figure for "hot" and the 70 °C recorded here is the course's reading of an instruction to boil in it, stated as such - then cold water to make 1000 c.c. at the end.

Purpose

To convert a silver image to a selenide, for a warmer colour and a more stable print. Kodak Limited’s own header is “Selenium toner for ‘Bromesko’ and warm-tone lantern slides” — it names the materials and not the colour, which is characteristic of selenium: what it does to the image tone depends far more on the paper than on the bath.

Kodak’s modern sheet fills in what the 1949 handbook leaves out. A selenium toner converts the silver image to silver selenide; it gives cool chocolate-brown hues with warm-tone papers, purplish brown with neutral-tone papers and very little or no change with cold-tone papers; it tends to intensify the image rather than weaken it; and it protects the print whether or not it produces a colour shift.

Recommended uses

Warm-tone papers, which is what Kodak Limited names, and which is where the colour change is largest. The modern sheets agree: warm-tone papers usually produce the most visible effect.

Lantern slides, which the 1949 header names alongside the paper — this bath was used on plates as well as prints.

Where the print is to be protected rather than recoloured. That is the modern use of selenium and it is worth knowing that it is modern: the Getty Conservation Institute’s atlas, quoted on the silver selenide page, dates the change of purpose, from a toner used for a dark brown-orange tone to a step in archival processing. Kodak Limited in 1949 sold this as a toner for warm-tone papers, not as a protective treatment.

Not for cold-tone papers, if colour is the point. They barely move.

When another formula is preferable

• In every practical case, a bought selenium toner. That is not a hedge: it is the reasoning behind the selenium page’s Level D classification, and this page exists to explain a formula, not to displace that conclusion.
• Where warm brown is wanted on a neutral paper, a sulfide route — T-52 or T-7a — which changes the colour of anything.
• Where a redder, warmer result is wanted than selenium alone gives, Kodak Limited’s own T-56, which puts selenium into a sulfide bath and bleaches the print first. It is on this page’s facing page in the handbook and it is also Level D.
• Where no sulfide and no selenium are acceptable at all, the hypo-alum bath T-1a, which is the only sepia route in this formulary at Level B.

Mixing

Kodak Limited’s four sentences, recorded because they are the formula and not because the course is asking for them to be followed.

1. Dissolve the sulfite in about 700 c.c. of hot water.
2. Add the selenium powder and boil until it is completely dissolved.
3. Allow the solution to cool; then add the ammonium chloride and stir until it is dissolved.
4. Make up to the required bulk with cold water.

Two details in that sequence carry the whole of the chemistry. The selenium goes in hot, because it will not dissolve otherwise; the ammonium chloride goes in cold, after the solution has cooled, and Kodak Limited is explicit about the order without saying why. Wall’s 1924 handbook makes the same kind of remark about a different selenium bath — that better sepia tones are obtained by adding the selenium solution when cold — which suggests the period knew that hot selenium solutions and other reagents do not mix well, without anyone in this corpus writing down the reason.

🧮What one part in six gives

The stock carries 6 g of selenium to the litre. Diluted 1 + 5:

6 g/L ÷ 6 = 1.0 g per litre

Selenium in the working bath

300 g/L ÷ 6 = 50 g per litre

Sodium sulfite, crystalline

190 g/L ÷ 6 = 31.7 g per litre

Ammonium chloride

One gram of selenium per litre of working bath, which is 0.1 per cent, and worth holding against the only modern figure in the corpus: Kodak describes the working solutions of its Rapid Selenium Toner as containing less than half a per cent of what it calls “selenium sulfite”. Those two numbers are not comparable — one is the element, the other an unnamed compound — and this page does not compare them. It records both so that a reader can see that they are the same order of magnitude and can also see why they cannot simply be set equal.

The crystalline sulfite is the heptahydrate at 252.15 g/mol against the anhydrous salt’s 126.04, which is why Kodak Limited’s alternative form is exactly half the weight.

Behaviour

Ten to fifteen minutes at 18 °C, which is a cool bath by the standards of this section — and much longer than the modern packaged toners, which Kodak works at 20 °C for 2 to 8 minutes at its own dilutions.

The print is fixed and well washed first, and well washed afterwards. Kodak Limited’s whole working instruction is one sentence and half of it is about washing.

It intensifies rather than weakens. This is the property that separates selenium from every sepia toner on these pages, and Kodak’s modern advice follows from it: shorten print development slightly if a print is to be selenium toned, where a sepia toner asks you to lengthen it.

Toning continues in the wash. Kodak’s modern sheet says so of its own product — remove the print when it has almost the required tone, because toning will continue to some extent in the wash — and it is the kind of behaviour that belongs to the chemistry rather than to a brand.

The conversion is not complete, and a maker says so. Moersch’s account, quoted on the silver selenide page, records that after six minutes in a selenium bath not all the silver has been transformed. A selenium-toned print is normally a mixture of silver selenide and untoned silver in proportions the printer chose by time and dilution.

Image characteristics

The colour belongs to the paper. Kodak Limited names two materials and no colour. The modern sheets name three outcomes for three classes of paper and the third of them is no change.

Maximum density rises. Kodak’s modern sheet carries a curve for a fine-art paper toned at 1+40 for four minutes showing increased upper-scale contrast and D-max. That is a property of selenium toning generally, at a dilution that is not this formula’s, on a paper that no longer exists — take it as the direction of the effect and not as a number for this bath.

It leaves a signature that survives. The Getty atlas records that selenium treatment can be detected by X-ray fluorescence long afterwards, which is the opposite of sulfur toning, whose signal hides inside the baryta layer. If you want a toned print that can be identified as toned in a century, this is the route.

Partial toning is the normal state, not a failure. See Behaviour.

The mechanism

⁇What boiling selenium in a sulfite solution gives, and what the course will not conclude from it

Kodak Limited’s preparation is: dissolve sodium sulfite, add selenium powder, boil until dissolved. The sodium selenosulfate page records what the wider chemical literature calls that product — selenium dissolved in sulfite is a selenosulfate — and Wall’s 1929 emulsion monograph establishes that sodium selenosulfate is a real compound with a real photographic use and gives its formula.

Na₂SO₃ + Se → Na₂SeSO₃

The preparation, as the wider chemical literature reads it

What this page will not do is close the question that page leaves open. The open question there is whether Kodak’s Rapid Selenium Toner, whose maker describes its active ingredient only as “a sulfite salt”, contains this compound. T-55 is a third document and it does not settle that: it is a different toner, made by a different Kodak company, fifty-seven years earlier, and Kodak Limited names no compound for its own stock either. What T-55 does add is that a Kodak selenium toner whose composition is published is made by dissolving the element in a sulfite — which makes the reading more plausible and still does not make it a fact. The sodium selenite page compares three manufacturers’ statements and finds three different oxidation states of selenium among them; that comparison is the state of the evidence and this formula does not change it.

Note also what T-55 is not. Wall’s 1924 selenium baths dissolve the element in sodium sulfide, or fuse it with caustic soda, and what those give is a selenide. Kodak Limited’s own T-56 is the sulfide route. T-55 is the sulfite route, and the difference between them is the difference between two oxidation states of selenium and two entirely different baths.

What happens to the print is stated here as the manufacturers and the conservators state it, and not as a reaction. Kodak says a selenium toner converts the silver image to silver selenide. The silver selenide page then says, in as many words, that no source this course holds gives a solubility product, a solubility figure or a formation constant for Ag₂Se, and that the mechanism of selenium’s protection is therefore recorded as an observed increase in chemical and environmental stability rather than 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.

Why this bath is direct and the sulfide toners are not. 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. That is also why it intensifies: nothing has been converted to a halide and nothing has been given the chance to dissolve.

Function of every ingredient

Sodium sulfite, 300 g crystalline or 150 g anhydrous to the litre of stock. The solvent for the element, and the reason there is a bath at all: selenium is an insoluble solid and a hot sulfite solution is what takes it up. It is present at fifty times the weight of the selenium, so it is not a trace reagent but the bulk of the formula. Kodak Limited prints it twice, as it prints every sulfite and carbonate twice, and the crystalline form at 252.15 g/mol is exactly double the anhydrous at 126.04, which is why the alternative weight is exactly half. More would dissolve the selenium faster and no source says what else it would do; less, past a point, leaves selenium undissolved on the bottom of the pan, which is where Kodak Limited’s instruction to boil until it is completely dissolved comes from.

Selenium, 6 g to the litre of stock, 1 g to the litre of working bath. The toning element, and the whole reason this page is Level D. Read its page before anything else on this one: it carries the classification, the exposure limits — which are among the lowest any darkroom substance carries — and the reasoning that puts the historical preparation out of reach of a home laboratory. More selenium is not a control any source read here publishes; less tones more slowly. The form matters and Kodak Limited specifies it: powder, which is the form that will dissolve on boiling and also the form whose dust is a hazard in its own right.

Ammonium chloride, 190 g to the litre of stock. The ingredient this page cannot explain, and it is better to say so than to guess. Kodak Limited gives no function for it and no other source in the corpus discusses a selenium toner containing it. What can be stated is factual: it is added cold, after the selenium has dissolved and the solution has cooled, which means it is not part of the dissolving step; and at 190 g/L it is nearly two-thirds the weight of the sulfite, so it is a major constituent rather than a trace. Two readings are available and the course adopts neither: a chloride at 3.6 mol/L is a strong silver-halide solvent, which would make it a fixing agent in the bath, and an ammonium salt with a sulfite is a buffer. Neither is sourced. Under Rule 6 this formula is therefore published with one ingredient whose function is described rather than explained, and that limitation is stated here rather than papered over.

Water, hot then cold. About 700 c.c. hot to dissolve the sulfite and boil the selenium into it, then cold water to make 1000 c.c. Kodak Limited does not say how hot “hot” is; the instruction to boil the mixture is the only temperature the formula really fixes.

Interactions

With acid, and this is the one that matters. The silver selenide page carries it with its source: Princeton’s guidance for photographic studios states that treating selenium salts with acid may release highly toxic hydrogen selenide gas, and EH40 sets that gas at 0.02 ppm — one of the lowest limits in the table. No acid bath and no acid stop follows a selenium toner without a wash between, and no acid goes into its waste.

With a fixing bath, before toning. Kodak Limited’s instruction is a fixed and well-washed print. Kodak’s modern guidance is more specific about why: residual silver salts and traces of hypo cause stains, uneven tones and fading, and prints that were dried before toning should be rewetted through a fixing bath and rewashed rather than simply soaked.

With the wash after it, which is not a rinse but part of the toning: the reaction continues there.

With trapped air in the fixer, which Kodak names as the cause of round purple stains that appear only after selenium or sulfide toning.

With metal trays, which Kodak’s general toning guidance forbids for every toner.

Variants

Kodak T-56, the sulfide-selenium toner, on the facing page of the same handbook: 250 g of sodium sulfide and 5.7 g of selenium powder to the litre of stock, used after a ferricyanide-bromide bleach at 50 c.c. of stock to the litre. Almost the same weight of selenium by a completely different route, giving a selenide rather than a selenosulfate and requiring the print to be bleached first. Its own page sets out the difference.

Wall’s 1924 selenium baths, which dissolve the element in sodium sulfide or fuse it with caustic soda. These are the preparations the selenium page names when it explains the Level D classification, and they are recorded here as the reason for that classification rather than as formulas.

The packaged toners. Kodak’s Rapid Selenium Toner, Harman’s and Moersch’s are all sold without a published composition, so the formulary cannot carry them as formulas at all — the course teaches a proprietary product as behaviour and disclosed components only, never as a reconstruction. What each maker does publish is a dilution, a time, a temperature and a hazard statement, and those are the numbers to work to if you have one of those bottles.

No course variant is offered, and no dilution is invented. Kodak Limited publishes 1 + 5 and nothing else. The modern products’ 1+20 and 1+40 dilutions belong to different, undisclosed concentrates and cannot be transferred to this stock.

Safety

Level D, from selenium, and the classification is the element’s rather than the bath’s. Read that page; this one does not restate its exposure limits, its classification or its first aid, and does not soften them.

This page gives no procedure and the course asks nobody to perform it. The specific step that puts it out of reach is the second one: boiling elemental selenium powder in an open pan of sulfite solution until it dissolves. That is not a step a home laboratory has the controls for, and the Level D policy is what governs the page rather than a longer equipment list.

Two hazards are worth naming even though nobody here will meet them, because they explain the classification rather than mitigate it. The first is the dust of the powder before it goes in. The second is acid afterwards: selenium salts and acid give hydrogen selenide, whose exposure limit is 0.02 ppm.

If you are using a bought selenium toner instead — which is what the course expects — the product’s own sheet is the authority. Harman calls its toner a toxic chemical, states that it is toxic if swallowed and may cause sensitisation by skin contact, and requires rubber gloves in all use and disposal, eye or face protection, and work in a well-ventilated area, preferably with some form of air extraction. Kodak, for its more dilute product, recommends print tongs and clean rubber gloves and immediate washing of any splash.

Storage

Kodak Limited publishes no keeping figure for the stock and none is invented here. What it does publish is that the bath is made as a stock and diluted for use, which is the shape of a solution meant to be kept.

Stoppered, labelled, dated, and nowhere near an acid. The acid rule is the same one that governs the tray and the waste bottle.

Not in a room with photographic materials, as a general rule for a toner shelf.

A bought toner is stored to its own sheet, and this page’s instructions do not apply to it.

Incompatibilities

Acids of every kind. Hydrogen selenide. This is the incompatibility that governs selenium chemistry from the stock bottle to the waste container.

Stop baths and acid fixers, as a particular case of the above, in the tray and in the sink.

Metal trays and tanks, per Kodak’s general toning guidance.

Unexposed photographic materials, in the room.

Developer, in either direction.

Waste

A selenium-bearing stream, and one of the most clearly regulated in photography. The selenium page carries the detail with its source: Kodak’s environmental guidelines for amateur photographers give Rapid Selenium Toner every route withheld except household hazardous waste collection — no sewer discharge, no discharge to a treatment works, no disposal with refuse.

Never acidified, and never combined with any acid stream.

Collect it, label it as selenium-bearing, and take it to a hazardous waste collection. Follow the general chemical waste SOP, the silver-bearing waste SOP where the bath has toned prints, and the disposal ruling. Local regulation decides, and this course cannot tell you what it says where you are.

Troubleshooting

Recorded from the sources for the sake of understanding the formula, not as instructions for running it.

Selenium still on the bottom of the pan. Kodak Limited’s own criterion is unambiguous: boil until it is completely dissolved. An undissolved element is a stock of unknown strength.

Nothing happens to the print. Cold-tone paper, most likely, on which Kodak’s modern sheets say there is very little or no change by design. Otherwise a bath that has been used past its useful life, for which no published capacity figure exists.

Yellow stain, uneven tone, or fading. Kodak names the cause and it is upstream: residual silver salts and traces of hypo from an exhausted fixer or an incomplete wash.

Round purple stains. Air bubbles trapped between prints during fixing. Kodak names this specifically as a defect that shows up only after selenium or sulfide toning.

The tone kept going after the print left the bath. Expected: toning continues in the wash, so the print is pulled slightly early.

A sharp garlic-like smell. Leave and ventilate. Selenium compounds and acid give hydrogen selenide, and its exposure limit is two hundredths of a part per million.

Experiments

These are experiments for a supervised laboratory that already has a selenium toner, not reasons to make one.

Measure the intensification. A step wedge toned in a bought selenium toner at the maker’s protective dilution, read before and after. Kodak’s claim is increased upper-scale contrast and maximum density with minimal colour change; this is that claim as a pair of curves on your paper.

Find where partial toning sits. Identical prints pulled at 1, 2, 4 and 8 minutes. Moersch’s observation is that a selenium bath does not convert all the silver even at six minutes; the visible consequence is that a selenium-toned print is a mixture, and the mixture is the printer’s choice.

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

Read the dilution as the control. The same paper at the maker’s two published dilutions, timed to the same visible change. What differs is not only speed: the colour path is different, which is why the sheets give different dilutions for protection and for tone.