Kodak T-56

T-52 with two changes to one bottle: fifty grams more sodium sulfide per litre of stock, and 5.7 g of selenium powder dissolved into it. Everything else — the bleach, the dilution, the sequence, the instruction, even the wording of the instruction — is the same. It is the clearest demonstration in this formulary that a maker’s formula family is a set of variations on one bottle.

⚠Level D: this page is not a procedure

Selenium is classified for historical study only, and its page names, as one of the two reasons, a boil with sodium sulfide of a substance classified toxic by two routes, carried out beside photographic materials. That is what making this formula’s Solution B requires — and Kodak Limited, unlike its own T-55, prints no procedure for doing it.

So this entry gives the chemistry, the workflow in outline, the image characteristics and the hazards, and states explicitly that it is not a procedure. The Level D policy governs it. The sulfide half would put it at Level C on its own; the selenium takes it further.

Bleaching Solution — the rehalogenating bleach

Ingredient	Quantity	Form the source specifies
Potassium ferricyanide	50 g
Potassium bromide	50 g
Water	to make 1000 mL
Identical, salt for salt, to T-52's Solution A, and to the formulary's standalone entry for this bleach. Kodak Limited prints it twice at the same quantities.

Stock Sulphide-Selenium Solution — the redeveloper, as a keeping stock

Ingredient	Quantity	Form the source specifies
Sodium sulfide	250 g	pure
Selenium	5.7 g	powder
Water	to make 1000 mL
Fifty grams per litre more sulfide than T-52's stock, plus the selenium. Kodak Limited gives no mixing procedure for this solution and none is invented here; the comparable step in T-55 is a boil.

Toning Solution — the working redeveloper

Ingredient	Quantity	Form the source specifies
Stock Sulphide-Selenium Solution	50 mL
Water	to make 1000 mL
Thrown away after use, exactly as T-52's Solution C is.

Used in this order — toning a bromide, Bromesko or Kodura print

1. Bleaching Solution — until the image is bleached — No time is published. The end point is the disappearance of the black.
2. Water — until the yellow stain is removed — A criterion rather than a time, and the step that keeps the bleach out of the toner.
3. Toning Solution — until the tone is complete
4. Water — brief wash in running water

Bleach in Solution A, wash until the yellow stain is removed and tone in Solution C. Complete with brief wash in running water. Throw away Solution C after use.

Word for word the same instruction Kodak Limited prints for T-52, with "the" added before "yellow stain". The two formulas are worked identically; only the stock differs.

Purpose

To reach a warmer, redder brown than a plain sulfide toner gives, by putting selenium into the redeveloper. Kodak Limited’s header is “Sulphide-selenium toner for bromide, ‘Bromesko’ and ‘Kodura’ prints” — three named paper families and no stated colour, which is the handbook’s habit throughout the toner section.

The formula’s real interest is structural. Selenium can be brought to a print two ways, and Kodak Limited printed both on the same page: dissolved in sulfite and used directly on the silver image (T-55), or dissolved in sulfide and used on a bleached one (this formula). Those are two different selenium chemistries and two different processes that happen to share an element.

Recommended uses

Bromide, Bromesko and Kodura prints, which is what the handbook names.

Where a plain sulfide sepia is too yellow. The selenium is what moves the result towards red.

Where the bleach-and-redevelop workflow is already in use. The bleach is the same solution; only the second bottle changes. A darkroom set up for T-52 is set up for this.

When another formula is preferable

• T-52, if the colour is acceptable, because it is the same process one hazard class lower: the same bleach, the same dilution, the same instructions, no selenium.
• T-55, if selenium is the point and a bleach is not. It works directly on the silver image, intensifies rather than weakens, and is the route the modern packaged toners descend from.
• A bought selenium toner, in every practical case, for the reasons the selenium page gives.
• T-1a, the hypo-alum bath, if the requirement is a brown print from a formula the course classifies at Level B.

Mixing

Three solutions, and Kodak Limited tells you how to make one of them.

1. Solution A, the bleach: 50 g of potassium ferricyanide, then 50 g of potassium bromide, water to 1000 mL. This is the formulary’s standalone bleach and everything on that page applies.
2. Solution B, the sulfide-selenium stock: 250 g of pure sodium sulfide and 5.7 g of selenium powder, water to 1000 mL. No procedure is published. The handbook gives T-55 four sentences on how to get selenium into solution — dissolve the sulfite hot, add the powder, boil until it is completely dissolved, cool — and gives this solution nothing at all. Wall’s 1924 handbook describes the same class of preparation as dissolving the element in sodium sulfide, and adds that better sepia tones are obtained by adding the selenium solution when cold. That is the state of the published record and this page does not extend it.
3. Solution C, the working toner: 50 mL of B, water to 1000 mL. Made when wanted, discarded afterwards.

🧮How much selenium is actually in the bath, and how little

The stock is 250 g/L of sodium sulfide and 5.7 g/L of selenium. Diluted one part in twenty:

250 g/L × 50/1000 = 12.5 g per litre

Sodium sulfide in the working bath

5.7 g/L × 50/1000 = 0.285 g per litre

Selenium in the working bath

Against T-52’s 10 g/L, the sulfide here is 25 per cent stronger. The selenium is the interesting number. In moles, at 78.05 g/mol for the sulfide and 78.97 for the element, the stock carries about 3.20 mol/L of sulfide against 0.072 mol/L of selenium — forty-four to one.

So this is a sulfide toner with a few per cent of selenium in it, not a selenium toner with sulfide added. The image it makes is predominantly silver sulfide with some silver selenide among it, and the colour shift the formula exists for is bought with a very small molar addition — which is worth noticing, because it is the same order of dilution at which selenium works in the modern protective toners.

Note also the weight against T-55: 6.0 g/L of selenium in the stock there, 5.7 g/L here. Kodak Limited put almost exactly the same weight of selenium in both stocks and then diluted them by wildly different amounts — 1 + 5 for T-55, one part in twenty for T-56 — so the working baths differ by a factor of about three and a half in selenium. The routes are not comparable dose for dose and the handbook makes no attempt to compare them.

Behaviour

Worked exactly like T-52, and the handbook’s instruction for the two is the same sentence. Bleach, wash to a criterion, tone, wash briefly, discard the toner.

No times and no temperatures are published, for any of the three baths. End points only.

The bleached print between the baths is light-sensitive, being silver bromide in gelatin, and the effect is small.

The print loses density, as every bleach-and-redevelop toner’s does.

The stock is a keeping solution and the working bath is not. Kodak Limited’s only keeping statement about this formula is that Solution C is thrown away after use.

Image characteristics

Warmer and redder than a plain sulfide print, which is the whole reason for the formula and the only claim Kodak Limited implicitly makes by printing both.

The colour is still inherited. The 1928 primer’s rule governs every sulfide route: silver sulfide runs from light brown to black according to its state of subdivision, and the subdivision comes from the image that was bleached. Selenium moves where in that range the print lands; it does not take the choice away from the paper.

The image is a mixture and always was. See the arithmetic above: at forty-four to one, the sulfide is doing most of the converting.

Permanence. The claim belongs to the two product substances rather than to this bath, and both their pages carry it — with the important asymmetry that silver sulfide has a solubility product behind its claim and silver selenide does not, because no source the course holds gives one.

The mechanism

The bleach and the sulfide half are the same chemistry as T-52’s, and they are set out there.

⚗The two steps this formula shares with every indirect sulfide toner

Ag + [Fe(CN)₆]³⁻ + Br⁻ → AgBr + [Fe(CN)₆]⁴⁻

Solution A: the image becomes a halide again

2 AgBr + S²⁻ → Ag₂S + 2 Br⁻

Solution C, the sulfide half: the halide becomes the toned image

What the selenium does is not written as an equation here, and that is deliberate. The silver selenide page states 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 contribution is therefore recorded as manufacturers and conservators state it rather than as a calculation. The same limit applies to the exchange reaction inside this bath. What can be said without going beyond the sources is structural: a bath containing sulfide and selenide ions together, meeting silver bromide, can form either product, and the proportions will follow the concentrations and the relative insolubilities — of which the course knows one and not the other.

What is in the bottle is not settled either. The selenium page records that Wall’s 1924 baths dissolve the element in sodium sulfide or fuse it with caustic soda, and that what those give is selenide, selenium(−II). This stock is made the same way. That is a different species from the one T-55 makes by boiling the element in a sulfite, and the sodium selenosulfate page is explicit that confusing the two makes the historical formulas look milder than they were. This page keeps them apart and closes neither question.

Why more sulfide than T-52. Kodak Limited does not say. What is observable is that the extra 50 g/L arrives in the same bottle as the selenium and that the element has to be got into solution somehow; a stronger sulfide is a better solvent for it. That is a reading, not a source, and it is offered as one.

Function of every ingredient

Potassium ferricyanide, 50 g to the litre of Solution A. The oxidiser, one electron per silver atom, and the ingredient that sets how much silver the bleach can convert before it is spent. More is faster and less even; less is slower and more controllable. Its own page carries the hazard, which is what it does with acid rather than what it does with silver, and the bleach’s own entry carries the rest.

Potassium bromide, 50 g to the litre of Solution A. The halide that catches the oxidised silver as silver bromide in place, which is what makes this a toner’s bleach rather than a reducer. At nearly threefold molar excess over the ferricyanide it keeps the precipitation ahead of the oxidation.

Sodium sulfide, 250 g to the litre of Solution B. Two jobs, and the second is what distinguishes this formula from T-52. It is the sulfide source, converting the bleached silver bromide into silver sulfide; and it is the solvent for the selenium, because the element does not dissolve in water and a strong sulfide solution is one of the two preparations the period used. That second job is the most likely reason there is fifty grams per litre more of it here than in T-52’s stock — a reading the handbook does not confirm. More tones faster and buys nothing published; less would also carry less selenium into solution. Its own page carries the classification and the incompatibilities.

Selenium, 5.7 g to the litre of Solution B, 0.285 g to the litre of the working bath. The element that shifts the colour towards red, and the reason this page is Level D rather than Level C. It is present at about one part in forty-four by moles against the sulfide, which is a dopant rather than a co-equal reagent. Kodak Limited specifies the powder, which is the form that will dissolve, and gives no procedure for dissolving it. More selenium is not a control any source read here publishes. Read its page before anything else: it carries exposure limits among the lowest of any darkroom substance, and the reasoning that puts the preparation out of a home laboratory’s reach.

Solution B, 50 mL of it in every litre of Solution C. Kodak Limited’s own ingredient line for the working toner is a volume of its own stock. It is recorded that way because that is how the bath is made and because writing out the sulfide and the selenium separately here would put the course’s arithmetic where the handbook’s instruction was — and would hide the fact that both are diluted together, by the same factor, from one bottle.

Water, to make each of the three solutions to its litre. Kodak Limited gives no temperature for any of them, which is itself worth noticing next to T-55, where the water temperature is the formula’s most important instruction.

Interactions

With acid, twice over and for two different gases. Sulfide and acid give hydrogen sulfide; selenium compounds and acid give hydrogen selenide, whose exposure limit is 0.02 ppm. Both rules are on the chemical pages with their sources. The practical consequence is one rule: no acid anywhere in this sequence, in the trays, on the bench or in the waste.

With the bleach that precedes it, through the wash. Kodak Limited’s criterion — wash until the yellow stain is removed — is the control, and this bleach has the advantage of containing no acid of its own.

With iron, in the bleach. This bleach carries no potassium oxalate, so a trace of iron from a tray or a clip throws blue spots of Prussian blue. Plastic or glass trays.

With hypo, forming inside an ageing sulfide stock, which eventually makes the toner a fixing bath.

With unexposed photographic materials. The 1928 primer’s rule: none in a room where sulfides are kept or sulfide toning is done.

Variants

Kodak T-52, on the facing page: the same bleach, the same dilution, the same instruction, a sulfide stock at 200 g/L and no selenium. It is the formula this one is built on and it is a hazard class lower. See its page.

Kodak T-55, on the same page: 6.0 g/L of selenium dissolved in sulfite instead of sulfide, used directly on the silver image with no bleach, diluted 1 + 5, ten to fifteen minutes at 18 °C. Nearly the same weight of the element by a completely different route. See its page.

Kodak T-7a, the American indirect sulfide toner, whose bleach carries potassium oxalate and acetic acid and whose sulfide strength Kodak changed between printings. See its page.

Wall’s 1924 selenium-sulfide baths, which are the general form of this stock and the ones the selenium page cites when it explains the Level D classification.

No course variant is offered. There is nothing to reformulate: the selenium is the point of the formula and removing it gives T-52, which already exists and is already published.

Safety

Level D, from selenium. Level C would be the floor, from sodium sulfide alone. Read both pages; neither is restated here and neither is softened.

The course gives no procedure for this formula and asks nobody to perform it. The step that settles it is getting 5.7 g of selenium powder into a strong sodium sulfide solution — the preparation the selenium page names as one of its two reasons for the classification, and the one Kodak Limited declines to describe.

⚠Two gases, one rule

The reason this formula’s hazard is not simply the sum of its parts is that both of its active substances answer to acid, and they answer with different gases.

Sulfide plus acid gives hydrogen sulfide, which deadens the sense of smell that would warn you. Selenium compounds plus acid give hydrogen selenide, which EH40 sets at 0.02 ppm, one of the lowest limits in the table.

One rule covers both and it is absolute: no acid in the sequence, in the trays, on the bench, or in the waste container. That includes the reflex of neutralising an alkaline waste before disposal, which is the forbidden move for both halves of this bath at once.

Storage

Solution A in a dark or yellow bottle, because a ferricyanide solution photolyses.

Solution B sealed, labelled, dated, and nowhere near an acid. Kodak Limited publishes no keeping figure and none is invented here. What can be said from the other sources is that a dissolved sodium sulfide keeps unreliably and decomposes towards hypo — Wall’s account is on the T-52 page — and that this stock has a selenium load as well, so what fails is not only the toning but the disposal classification of what is left.

Solution C is not stored. Kodak Limited’s own direction is to throw it away after use.

Not in a room with photographic materials.

Label it as selenium-bearing as well as sulfide-bearing, because the waste route depends on the first of those and the tray rules on the second.

Incompatibilities

Acids of every kind, for both of the reasons above.

Stop baths and acid fixers, in the tray and in the sink.

Oxidisers, with the sulfide.

Iron and steel, in the bleach.

Hypo, into the bleach and inside an ageing stock.

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

Unexposed film and paper, in the room.

Developer, in either direction.

Waste

Two hazardous streams and they never meet each other or an acid.

The spent bleach carries ferricyanide, ferrocyanide and bromide, in its own labelled container.

The spent toner is strongly alkaline and carries sulfide and selenium, which makes it the more tightly regulated of the two. Kodak’s own instruction for the sulfide half is a prohibition: sulfide-type toners are never discarded with stop baths or fixing baths, because the combination generates hydrogen sulfide gas. The selenium half is the reason the selenium page records every disposal route withheld except hazardous waste collection.

Never neutralised. Collect, label as selenium-bearing, and follow the general chemical waste SOP, the silver-bearing waste SOP 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.

The selenium will not dissolve in the sulfide. Kodak Limited publishes no procedure for this step. T-55’s comparable instruction is to boil until the element is completely dissolved, and Wall’s is to add the selenium solution cold. Neither is an instruction for this formula and neither is offered as one.

The bleached print will not tone. The sulfide stock has decomposed; the three stages of that failure are described on the T-52 page from Wall’s 1912 account.

Blue spots. Iron in the bleach. This bleach has no oxalate to protect against it.

The colour is no redder than a plain sulfide print. The selenium is a forty-fourth of the sulfide by moles; if it did not dissolve, or the stock is old, there is very little there to make a difference.

Yellow stain in the highlights. Fixing and washing before the toner, not the toner.

Any smell at all over the trays. Leave and ventilate, then find the acid. Two of the possible gases here have exposure limits in the parts-per-million and parts-per-hundred-million range.

Experiments

For a supervised laboratory that already has the reagents, not a reason to acquire them.

Put the three 1949 toners side by side. T-52, T-55 and T-56 on identical prints from one negative, on one paper. Kodak Limited printed all three on two facing pages and never compared them; nothing in this corpus shows the comparison, and it is the whole argument for why a maker sold three.

Vary the selenium and hold everything else. Stocks at the published 5.7 g/L and at half and double it, all diluted the same way, all after the same bleach. The formula’s claim is that the element is what makes the result redder; this is the dose-response curve behind that claim, and no source read for this course publishes one.

Read the density loss against T-52. Same bleach, same dilution, same times, two stocks. Whether the extra 50 g/L of sulfide changes anything but the selenium’s solubility is a question the handbook leaves open.

Look for the signature. The Getty atlas records that selenium can be detected in a print by X-ray fluorescence long afterwards while sulfur toning hides inside the baryta. A print from this bath should show both — a selenium signal and a sulfur signal that cannot be separated from the paper’s own.