Lab: Bleaching and Redeveloping a Sepia Print

Kodak tell you to make a print slightly darker than normal because a sulfide toner will reduce its density. They do not say how much darker, and no source read for this course puts a number on the loss for a developing-out paper. That gap is why this session exists: by the end of it the adjective in the manufacturer’s sheet will be a figure in your notebook, measured on your paper at five marked patches.

You will also have a print that is part silver and part silver sulfide, made by stopping the bleach a third of the way and converting whatever it reached. That print is why the indirect route survives beside the direct ones: all the control lives in the first bath, because the second is over before you can intervene in it.

Purpose

To run Kodak’s T-7a exactly as its 2006 printing gives it, on three identically printed resin-coated sheets — one bleached to Kodak’s endpoint and fully redeveloped, one bleached for a third of that time and fully redeveloped, one taken through the same soak, rinses, wash and drying with no bleach and no toner — and to measure the same five marked patches on each before and after, so the changes are attributable to the toning rather than the handling.

Three things leave the bench: before-and-after readings with your own repeatability figure beside them; a print exposure correction in stops for sepia toning on that paper; and two toned prints, one fully converted and one split.

Learning objectives

By the end of this session you will be able to:

• Mix a two-solution published toner from its stocks, and say which of the four bleach ingredients acts on the image and which three answer defects that have nothing to do with silver.
• State, in your own paper’s numbers, what a sulfide conversion costs in density and where on the scale.
• Explain why the rinse between bleach and toner is a step of the formula rather than a courtesy, and name the two things it prevents.
• Judge a bleach by its endpoint, and say why a published bleach time is the least transferable number on the sheet.
• Produce a deliberately partial conversion, and state the obligation it carries and how you discharged it.
• Design the untoned control so that it measures handling rather than nothing.
• Add up a resin-coated print’s wet time and compare it with what its own maker advises.
• Route four waste streams into three containers without putting an acid next to a sulfide.

Prerequisites

• Sulfide and sepia toning, which is the chemistry this page executes. The two routes to silver sulfide, what each bleach ingredient answers, the solubility argument behind instantaneous redevelopment and the rule governing every sulfide bath are established there and not repeated here.
• Laboratory safety and PPE and chemical waste and silver waste, which own the controls and the containers.
• Washing, drying, flattening and mounting, which owns the wash and the drying this page holds constant across three prints.
• The archival processing sequence and fixer capacity and exhaustion, for the fixing and washing the prints must already have had. Kodak’s own finding is that improper fixing is probably the major cause of stains in toned prints, so a print that failed it cannot be rescued tonight.
• Concentration and dilution and weighing a solid.

Safety classification

Level B, an advanced home laboratory, with one operation declared at Level C and deliberately placed outside the session — the weighing of sodium sulfide. The classification is argued rather than asserted, because this is where the course’s rule that the operation sets the level, not the substance does its work.

Which Level B criteria apply. Three of the rubric’s four: fine powders that must not be inhaled, forty-eight grams of oxalate and nineteen each of ferricyanide and bromide; a concentrated alkali, the sulfide bath being alkaline by hydrolysis whether or not alkali was added; and a corrosive-splash failure mode, because sodium sulfide carries H314 in every ECHA notification on record.

Why the session is not Level C, tested against three of that level’s criteria. Acutely toxic reagents at the concentrations used, where a fume cupboard is the recognised control: the working toner is Kodak’s own dilution, 22.5 g/L or 2.25 per cent w/v, in an open tray at room temperature with no acid near it, and the hazardous substance is the solid, which is not in the room. Waste needing a licensed contractor: everything is collected, but a household’s route to a collected photochemical stream is a household waste and recycling centre, which is what the government’s guidance and ILFORD’s advice to domestic users both name — see the disposal ruling. Chromium(VI), formaldehyde and the like: none is present, and this page uses no hardener.

Where the Level C operation went. Making Stock Solution B means weighing 22.5 g of a deliquescent solid classified H314, H311 and H301. That stays Level C, and happens once, on a different day, outside this session, under the controls the sodium sulfide page states. A reader who cannot meet them does not do the weighing; the Alternative route is written for them.

⚠What is not a hazard here, and the conditions that would change that

Hydrogen cyanide. Potassium ferricyanide is a cyanide complex, and the international chemical safety card states that it decomposes on heating and on contact with acids, producing toxic gases including hydrogen cyanide; Princeton add that it is released if the substance is heated, if hot acid is added, or under strong ultraviolet such as a carbon arc, and that cases of poisoning have occurred through treating Farmer’s reducer with acid. None of those three conditions occurs here. Nothing is heated. No acid is added beyond the 10 mL of 28 per cent acetic acid Kodak put in two litres of stock, which leaves the working bleach near the pH of 5.8 to 6.2 Foma’s data sheet independently records for the same chemistry. There is no ultraviolet source in the room. What would change this is tipping the bleach into an acid stop bath, warming it, or adding a strong acid — which is why the waste rules below exist.

The gas over the toner. Hydrogen sulfide is not a product of toning but the hydrolysis equilibrium of the sulfide ion running in air, present the whole time the bath exists and no more so when a print is in it. Hence a control of dilution, ventilation and time rather than a hood over the tray, and a bath mixed at the start of the session and discarded at the end.

No heated bath — the direct hypo-alum route holds a half-strength fixing bath at 49 °C and this one does not — and no mains work.

Hazards

Hazard	Where it arises	Control
Severe skin burns and eye damage, sodium sulfide	The stock bottle; a splash of working toner	Splash goggles and gloves from the moment the stock is opened; pour into a graduate standing in a tray
Hydrogen sulfide from acidifying a sulfide	The rinse discipline, the waste bottles, any acid in the room	Two-minute rinse between bleach and toner; three separate waste containers; the stop bath out of the room
Hydrogen cyanide from acidifying or heating a ferricyanide	Waste handling above all, not the tray	Ferricyanide waste in its own container, never meeting acid or sulfide; nothing heated
Inhalation of fine powder	Weighing the three bleach solids	A tray, still air, one jar open at a time, particulate mask, by the weighing procedure
Eye irritation, ferricyanide and bromide	Weighing; a splash at the tray	Eye protection with side shields from the first jar to the last rinse
Aquatic toxicity	Every stream tonight	Collect all of it; see Disposal
Fogging of unexposed material	Any paper or film left in the room	Sealed and carried out before the sulfide stock is opened; the room aired before it returns
Blue staining from stray iron	A chipped enamel tray, a steel clip, a rusted spring	Plastic or unchipped enamel only; the oxalate is only a second line
Working with liquids in dim light	Only the printing session before this one	Trays laid out with the lights on; toning is a room-light job

Required PPE

Chemical splash goggles, not spectacles, whenever the sulfide stock bottle is open or being poured — the one upgrade over a standard printing session, because H314 is a statement about eyes as well as skin. Spectacles with side shields are adequate once the working toner is in the tray. Nitrile gloves, single-use, of the 0.2 mm thickness the HSE printing guidance specifies for manual processing, changed the moment one is contaminated inside; read glove selection first. A particulate mask for weighing the three bleach solids. An apron: a ferricyanide splash on a shirt is permanent.

Ventilation

What the specialist guidance asks for. Princeton’s photography guidance says toning solutions must be used with local exhaust ventilation — capture at source, which a home darkroom almost never has. HSE’s guidance on airborne contaminants describes the usual arrangement as local exhaust for the main sources and general ventilation for minor ones, which says how the two relate rather than letting you substitute one for the other.

What a home darkroom can achieve. HSE’s COSHH essentials sheet for manual film and plate development specifies general ventilation greater than five air changes per hour, with a through draught, from powered wall- or window-mounted fans, with easy-to-clean lipped surfaces and shallow trays for spillage. That is the control this page requires; run the ventilation check before the session, not during it.

Why the gap matters. Hydrogen sulfide has an approved workplace exposure limit of 5 ppm as an eight-hour average and 10 ppm over fifteen minutes; NIOSH sets a ceiling of 10 ppm and an IDLH of 100 ppm. You cannot measure any of those, and NIOSH’s own note is that the sense of smell becomes rapidly fatigued and can not be relied upon to warn of the gas. General ventilation is therefore the achievable control rather than a measurement-backed one, made adequate by three other things: the bath is dilute, it exists for under an hour, and no acid reaches it. Where even the through draught is missing, Moersch’s fallback is to tone outdoors.

Materials

Item	Quantity	Note
Variable-contrast resin-coated paper, 5 × 7 in	5 sheets	Three for the sequence, one cut into strips for the endpoint trial, one spare. Resin-coated so the session can end with three dry prints
A negative you have already printed	1	Full scale, with a real black, a real white and detail in both: Kodak’s rule is that toning cannot disguise poor print quality
Card, 5 × 7 in, for the patch template	1	Five 10 mm holes and a corner notch registering against the print’s corner: this is what lets you read the same spots twice
Distilled or deionised water	1 L	For the two stocks, so the bath and not the tap is what you study
Tap water	6 L	Soak, rinses, wash
Storage bottles, 500 mL and 250 mL, opaque, tight closure	2	A ferricyanide solution photolyses to Prussian blue in the light
Waste containers, 1 L, labelled, screw-capped	3	Ferricyanide, sulfide, silver-bearing; see Waste streams

Chemicals

The quantities below are a quarter of Kodak’s bleach stock and half of Kodak’s toner stock; the working solutions are Kodak’s own, unscaled. The full formula, both printings, their disagreement and the function of every ingredient are on the T-7a page.

Bleach — Stock Solution A, a quarter batch:

Chemical	Quantity	Form
Potassium ferricyanide	18.75 g	Anhydrous. The only ingredient that acts on the image
Potassium bromide	18.75 g	Anhydrous. Decides that this is a bleach and not a reducer
Potassium oxalate	48.75 g	Kodak print “potassium oxalate” without a hydrate; the course reads that as the monohydrate
Acetic acid, 28 per cent	10 mL	Kodak’s footnote makes 28 per cent from 3 parts glacial acid to 8 parts water
Water at 20 °C	500 mL	Kodak give water as an amount added, not a volume to make up to, so the stock’s final volume is unpublished — measure yours

Toner — Stock Solution B, a half batch:

Chemical	Quantity	Form
Sodium sulfide	22.5 g	Anhydrous. Weighed on a different day, outside this session, under Level C controls, or bought as a made-up stock
Water at 20 °C	250 mL	90 g/L, Kodak’s own stock strength in both printings

The two working baths, exactly as Kodak print them:

Bath	Made from	Strength
Bleach working solution, 500 mL	250 mL of Stock A plus 250 mL of water	18.75 g/L each of ferricyanide and bromide, 48.75 g/L oxalate, 10 mL/L of 28 per cent acetic acid
Toner working solution, 500 mL	125 mL of Stock B plus 375 mL of water	22.5 g/L sodium sulfide, or 2.25 per cent w/v

And on the printing bench, in the session that precedes this one:

Chemical	Quantity	Form
Paper developer concentrate	50 mL	1+9 to make 500 mL; 1 minute at 20 °C for this paper
Citric acid stop bath concentrate	25 mL	1+19 to make 500 mL; 10 seconds at 18 to 24 °C
Ammonium thiosulfate rapid fixer concentrate	200 mL	1+4 as two baths of 500 mL, 30 seconds each. Non-hardening, on Kodak’s instruction for prints to be toned

!Why the toner strength here is Kodak's larger figure

Kodak printed T-7a’s toner working solution twice and did not print the same thing twice: 22.5 g/L in 2006, 10.4 g/L in 1928, same stock, same formula number, no explanation. This page follows the later statement, which also sits inside the range other sources support — Moersch gives 0.5 to 2 per cent, Bullock found 3 per cent best, Kodak Limited’s T-52 works at 10 g/L.

The spread tells you this is not a precision setting. Both baths go to completion; what changes is how fast, and how many prints the bath will do before it fails. Kodak Limited cover the second in one line: throw the toning solution away after use.

Equipment

Balance reading to 0.01 g, checked by the balance and thermometer check. Weighing boats, a spatula, a tray for the balance. A 500 mL and a 250 mL graduate, a 1 L beaker, a stirring rod, a funnel, a thermometer.

Five processing dishes of 8 × 10 in — soak, bleach, rinse, toner, wash — in plastic or unchipped enamel. Kodak’s instruction is a formulation problem as much as a corrosion one: do not use metal trays or tanks for toning solutions. The 1928 primer says what a chipped enamel tray does — a trace of iron in the bleach throws blue spots of ferric ferrocyanide onto the print — and the oxalate in T-7a exists to make that trace soluble rather than to make the tray acceptable.

Two pairs of print tongs, kept apart and never swapped: one for the bleach and rinses, one for the toner. A tong that has been in the acid bleach and goes into the sulfide is the same mistake as a print that has, and easier to make.

A timer, a pencil, and — if you built one — the reflection head of your densitometer.

Estimated cost

Band ££. The capital is already yours. What this session adds to the shelf is a jar each of three chemicals no other part of the course has asked for — ferricyanide, oxalate and sodium sulfide — and the sulfide is the one to think hardest about, because it deliquesces. The planner holds the dated figures and the gaps.

Estimated consumables cost

Every price with a number is the planner’s own dated UK figure and every quantity is from the Materials and Chemicals tables. Three rows carry no number, which is the important part of the table rather than a blemish on it.

Consumed	This session	Sourced price	Cost this session
RC paper, 5 × 7 in	5 sheets	£16.06 for 25 sheets to £44.71 for 100	£2.24 to £3.21
Paper developer concentrate	50 mL	£10.52 per 500 mL to £20.03 per 1 L	£1.00 to £1.05
Stop bath concentrate	25 mL	£10.66 to £12.18 per 500 mL	£0.53 to £0.61
Rapid fixer concentrate	200 mL, as two baths	£21.05 to £25.98 per 1 L	£4.21 to £5.20
Potassium bromide	18.75 g into the stock; about half used tonight	£23.00 per 250 g	£1.73 to make the stock, of which about £0.86 leaves with tonight’s tray
Potassium ferricyanide	18.75 g	£17.99 per 230 g, checked 7 September 2026, or about £0.08 a gram	£1.47
Potassium oxalate	48.75 g	The price file could not price it. It is among the clearing-bath and sensitiser solids the file names as one gap	—
Acetic acid, 28 per cent	10 mL	Not priced at this strength. The file prices acetic acid at 80 per cent, £11.89 a litre, and names the glacial acid as a gap; neither is the 28 per cent this bath wants, and a strength conversion is arithmetic rather than a price	—
Sodium sulfide, anhydrous	22.5 g	The price file could not price it. Sodium sulfide is a gap it names, and sulfide toning is one of the uses recorded against it	—

The priced rows come to about £11 to £13 for one run, and that is a floor rather than a total: three of the nine consumables have no sourced price, and all three are peculiar to this page.

Outside the table, because the price file does not hold it, is one observation from a British retailer on 6 September 2026, given as a magnitude rather than as planner data: the packaged sepia kit at £23.99 for two 250 mL bottles. The ferricyanide has crossed that line the other way. The 230 g pack the same retailer listed is now a dated record in the file, which is why its row above carries a number.

Equipment is deliberately absent: a dish, a pair of tongs and a balance are not consumed, and counting them would stop the number measuring what the consumables calculator needs.

Waste streams

Four streams, three containers, one pairing that must never share a bottle.

• Ferricyanide — 500 mL of spent bleach with hexacyanoferrate(II) and (III), bromide, oxalate and acetic acid, in its own labelled container. Princeton’s guidance lists ferricyanide solutions among the photographic solutions to treat as hazardous waste.
• Sulfide — 500 mL of spent toner, and the first rinse after it, which is where Moersch says the smell gets worse and therefore where the carried sulfide is.
• Silver-bearing — the spent second fixer bath, under the silver-bearing waste procedure.
• The remaining rinse and wash waters, dilute and still collected, because the disposal ruling has no measurement that would justify otherwise.

⚠The one thing on this page that could actually hurt you is a waste bottle

Kodak’s instruction in G-23 is one sentence about a bottle rather than a tray: do not discard sulfide-type toners with stop baths or fixing baths, because the combination will generate hydrogen sulfide gas. The Environment Agency’s waste guidance writes the same chemistry out and gives sodium sulfide the supplemental statement for liberating a toxic gas on contact with acids.

S²⁻ + 2 H⁺ → H₂S

Why the sulfide bottle and the acid bottle are never the same bottle

The bleach is mildly acid by design; so is a stop bath and an acid fixer. Two things a tidy worker gets wrong. A funnel is not neutral: one used for the bleach and then the toner has carried acid into a sulfide, in a narrow neck, over a bottle. And do not top up a part-used bottle from another session without reading its label — the unlabelled container procedure exists because this is how it goes wrong.

Alternative route

Four readers cannot follow the page as written, and they need four different answers.

Without a through draught, tone outdoors. Moersch’s own recommendation and the most complete of the four: a darkroom with no ventilation and little fresh air should not be used for sulfur solutions, and the risk can be ruled out by toning outdoors and watering the print twice before returning indoors. Take the baths out on a board, run the sequence on an outdoor bench, and bring the print back only after two changes of water. No number on this page changes.

Without a densitometer, measure in steps. Make a dried reference strip in the printing session: one 5 × 7 sheet exposed in eight bands from clear to maximum black, processed and dried with the others. Every judgement is then “which band does this patch match”, made side by side in even light with both pieces dry. Part XVIII’s maximum-black experiment sets the route out with its limits: the resolution is the spacing of your bands, and the near-white end is where the eye is weakest — unfortunate, because the highlights are where a sepia toner does its most visible damage. What survives is the direction and the ranking.

Without a darkroom, bring the prints. Toning needs no darkness: Kodak note that the bleach converts image silver to light-sensitive silver bromide and that you may prefer a safelight, but add that the effect is extremely small and may not be noticeable. Only the printing needs a room, and it can be somebody else’s. What cannot be delegated is the design — the five sheets must come from one printing session at one exposure — so give whoever makes them this page’s Preparation section.

Where the sulfide route cannot be run at all, the packaged kit is what the market sells — and here is what its own data sheet says it is. Foma’s Fomatoner Sepia, two 250 mL bottles, at £23.99 from a British retailer on 6 September 2026. The course fetched both halves of its safety data sheet.

• Part A is a ferricyanide-bromide bleach, the chemistry above: Foma classify the mixture Eye Irrit. 2 H319 and nothing else, name a ferricyanide and a bromide each at less than 15 per cent, and give a pH of 5.8 to 6.2. The bought bleach is mildly acid too, so the rinse rule applies unchanged.
• Part B is a thiourea toner. Its composition names a carbonate at less than 40 per cent, disodium EDTA at less than 5, a bromide at less than 3, and index number 612-082-00-0, CAS 62-56-6, at less than 1 — thiourea, carrying Carc. 2 H351, Repr. 2 H361d, Acute Tox. 4 H302 and Aquatic Chronic 2 H411 as a substance. The bath’s pH is about 11.5.

That is not the safety improvement the word “odourless” implies, and the course will not sell it as one. The sheet does show a real difference of degree: Foma classify the mixture as Eye Irrit. 2, Skin Irrit. 2 and STOT SE 3, with no carcinogenicity or reproductive-toxicity classification, because the thiourea sits below the concentration at which those carry over. A dilute, professionally formulated bought bath is a different proposition from an open home-mixed tray at pH 13, and a reader may weigh that. What they may not do is believe they have avoided the substance. The course’s own position, argued on the thiourea page, is that its practical work stays on the sulfide route with the sulfide route’s controls, and that outdoors is the accessibility answer rather than a change of reagent.

And where none of the four is possible. The manifest promised, as a last resort, a data set of the course’s own to work the analysis from. That data set does not exist: the course has not run this session and publishes no measurements from it, and inventing a table of densities to keep the promise is exactly what Rule 1 forbids. What is offered instead is under Analysis — the arithmetic worked on figures constructed to demonstrate the method, labelled as constructed. If you run the session, your table is the one thing this page most needs.

Preparation

Before the day: the two stocks

1. Weigh the sodium sulfide and make Stock Solution B on a different day, outside this session, under the sodium sulfide page’s Level C controls: 22.5 g into 250 mL of water. Label it by the labelling procedure with substance, strength, date and initials, and keep it capped, cool and away from anything acid. Or buy a made-up sulfide stock and skip the step, which is the ruling’s own second option.
2. Make Stock Solution A, which is Level B work. Dissolve in Kodak’s order — ferricyanide, bromide, oxalate, then the acetic acid — into 500 mL of water at 20 °C. Measure the finished volume and write it on the label, because Kodak do not publish it and your working dilution depends on knowing it. Into an opaque bottle: a ferricyanide solution photolyses to Prussian blue in the light, and a bottle of that is pigment rather than bleach.

The printing session, where this lab is won or lost

3. Print five identical 5 × 7 sheets at one exposure, with a border of about 15 to 20 mm — the course’s own figure, sized so an edge-penetrated strip can be trimmed with the measured patches well inside it. Kodak say to develop fully and make the print slightly darker than normal because the toners reduce density; they do not say how much darker, and the modification depends on the paper emulsion type and grade. Start about a third of a stop darker than your best straight print — the course’s own starting point, not Kodak’s — and record it, because tonight replaces it with a measured figure.
4. Develop every sheet for the same time, at the paper maker’s figure, and do not pull one early because it looks right: the 1928 primer’s rule is that a print for sulfide toning should be fully developed but not over-exposed, because the toned image inherits the untoned one’s state of subdivision.
5. Two-bath fixing, in a non-hardening fixer, at the paper maker’s time for each bath. Kodak recommend two-bath fixing for prints to be toned and advise against a hardening fixer because it makes the emulsion less receptive; ILFORD advise against one independently because it reduces washing efficiency. Do not extend the fixing — Kodak’s ceiling is about two minutes for resin-coated papers, and prolonged fixing drives fixer into the base, where no wash retrieves it and where it turns a toned print yellow.
6. Wash thoroughly, then dry by the method you will use again tonight. Moersch’s warning governs steps 5 and 6 together: residual thiosulfate makes the bleach act as a reducer, redevelopment becomes impossible and at least the highlights vanish irretrievably. If in doubt, run ST-1 and HT-2 on the spare sheet first.

The written plan, before the first tray is filled

7. Write the session out on one sheet and put it on the wall. It has a step that takes thirty seconds, a step whose length you will not know until you are in it, and a pairing of liquids that must not meet. The plan names every bath and its volume; every time, and whether it is a clock time or an endpoint; the temperature band; the ventilation arrangement; where the waste containers stand and which tong belongs to which tray; and where the session stops, which is the end of the wash.
8. Set up for separation. Paper boxes and negatives are sealed and carried out of the room before the sulfide stock is opened: the 1928 primer’s rule is that no photographic materials should be stored where sulfides are kept or sulfide toning is done, because a very small quantity of hydrogen sulfide converts enough silver halide to sulfide to produce severe fog. The acid stop bath goes out with them. Trays are dedicated and never metal; tongs are dedicated and never swapped.
9. Mark the patches. Lay the template on each print, corner notch to corner, and mark the five hole centres on the back with a soft pencil. Choose five that span the scale: a highlight with detail, an upper mid-tone, a mid-tone, a lower mid-tone and the deepest shadow that still holds separation.
10. Read and record all five patches on all three prints, dry, before anything is wetted. There is no second chance at the “before” half of the measurement.
11. Check the balance and thermometer, and bring every bath to 18 to 21 °C.

!An instruction the source does not extend, and neither does this page

Kodak’s general Toning section says a print already dry is soaked in water for 2 to 3 minutes before toning, and that is what steps 6, 10 and 16 do. Two pages later, under Rapid Selenium Toner only, Kodak say something stronger: dried prints should be rewetted by immersion in a fixing bath and rewashed, or staining may occur. G-23 does not repeat that for either sulfide toner and gives no reason, so the course reports the asymmetry rather than resolving it. The staining mechanism Kodak describe elsewhere is one they attribute to selenium and sulfide toners alike, which argues the instruction ought to carry across; but an argument is not a published instruction. A reader who takes the cautious route is borrowing a step from a different toner, and should record that they did.

📓A temperature Kodak did not print, and how this page fills the gap

T-7a gives 20 °C for the water its stocks are made with and no working temperature for either bath. That is a real gap in the formula, not an oversight this page can quietly patch. What the same sheet publishes two pages earlier is a working band for Kodak’s packaged Sepia Toner — a bleach-and-redevelop kit doing the same conversion by the same route: bleach at 18 to 21 °C, tone at 18 to 21 °C. This page works in that band and says plainly that it is borrowing it from the nearest published statement for the same process by the same maker. Record your actual temperatures; if you ever compare your bleach time with somebody else’s, temperature is the first thing to check.

Procedure

Five stages, about 150 minutes if the printing session happened on another day. The clock is dominated by the bleach, whose length you do not yet know, and by the drying.

The session in five stages

1. 1Stage 1 — bench, baths and separation (about 25 minutes)Paper and negatives out of the room, five dishes filled in room light, three waste containers labelled and open, working bleach and working toner mixed last
2. 2Stage 2 — the endpoint trial on a test strip (about 15 minutes)Find how long the bleach takes to reach Kodak’s endpoint on your paper. This number sets the third stage
3. 3Stage 3 — print B, the partial bleach, then print A, the full bleach (about 35 minutes)Each: soak, bleach, two-minute rinse, toner, rinse, wash. B first, because its bleach is timed and A’s is judged
4. 4Stage 4 — the control, and the drying that must be identical (about 30 minutes)Print C through the same soak, rinses and wash with no bleach and no toner; all three air-dried together, no heat
5. 5Stage 5 — read, record, clean up and route the waste (about 45 minutes)The same five patches, the same template, the same light; then the bottles

Times are the course's own estimates for a first run on 5 x 7 in resin-coated paper. The only bath with a published time you can rely on is the two-minute rinse.

Stage 1 — the bench, and the one thing that goes on it last

The bench, laid out for a sequence in which two liquids must not meet

1. 1Acid zone: soak and bleach — the bleach carries 10 mL of 28 per cent acetic acid per litre of working solution
2. 2The rinse, straddling the boundary — two minutes in cold running water; the only step on this page whose time is not negotiable
3. 3Alkaline zone: toner — its own tongs, its own funnel, its own bottle
4. 4Three waste containers, spaced apart — ferricyanide, sulfide, silver-bearing; the first two never share a vessel or a funnel
5. 5Out of the room before the sulfide is opened — paper, negatives, and the acid stop bath from the printing session

Drawn to show the separation rather than the plumbing. The layout is the course's own; the rules it encodes are Kodak's, Princeton's and Moersch's.

1. Carry the paper, negatives and stop bath out of the room. Open a window and run the fan.
2. Fill the soak, rinse and wash dishes with water at 18 to 21 °C.
3. Label and open the three waste containers, apart from one another.
4. Mix the working bleach: 250 mL of Stock A into 250 mL of water. Cap the stock.
5. Mix the working toner last: 125 mL of Stock B into 375 mL of water, goggles on. Cap the stock and take it off the bench. The bath now exists, and so does the hydrolysis equilibrium that makes the room smell, so from here the session is on a clock of its own.

Stage 2 — the endpoint trial, which is the number Kodak cannot give you

6. Cut the fourth sheet into four strips and soak one for 2 to 3 minutes, as Kodak direct for a print that is already dry.
7. Into the bleach, timer started, agitating continuously, and watch what disappears first. Kodak’s 2006 wording for T-7a is until only a faint yellowish brown image remains, expected at approximately 5 to 8 minutes; the 1928 printing of the identical bath expects about one minute and a slightly further endpoint.
8. Whatever you measure is your number. Call it t. Do not average Kodak’s two printings: they disagree by a factor of six, and the disagreement sits on the formula page as evidence rather than a range.
9. Rinse the strip two minutes, tone it, rinse it and wash it — the whole sequence once, on a piece you do not mind losing.

Stage 3 — print B, then print A

10. Print B, the partial bleach. Soak 2 to 3 minutes. Into the bleach for one third of t, timed to the second, agitating exactly as for the strip. That fraction is the course’s own choice: no source publishes a partial-bleach time, because the point of a partial bleach is that it is yours. Record it as a fraction of t rather than as minutes, so it survives a change of bath.
11. Rinse two minutes in cold running water. A step of the formula, doing two jobs: keeping the acid of the bleach out of an alkaline sulfide bath, which is the rule Princeton states in exactly those terms, and taking the spent ferricyanide out of the gelatin so the toner meets bleached halide rather than a working oxidant.
12. Into the toner, agitating, until no further change occurs in the tone — approximately 30 seconds on Kodak’s T-7a instruction, approximately 60 on the same sheet’s packaged Sepia procedure. Watch the print rather than the clock, and record how long it took.
13. Rinse. Kodak’s T-7a instruction is immediately rinse the print with water, with no time; the packaged Sepia procedure gives 30 seconds. This page rinses two minutes and says why: the acid-and-sulfide rule of step 11 runs in this direction too, and a print carrying sulfide into any acid is the carrier the rule is about. The two minutes is the course’s own control, derived from the rule rather than copied from the sheet. First rinse water to the sulfide container.
14. Wash 4 minutes in running water, Kodak’s figure for a resin-coated print after T-7a. Do not shorten it. An untoned print holds residual thiosulfate, a slow permanence problem; a toned print holds residual sulfide, an active one — it goes on converting the image after you have chosen the colour, and it is a source of the gas that fogs unexposed paper and attacks silver images near the drying rack.
15. Print A, the full bleach. The same sequence, except that the bleach runs to the endpoint by eye. Record its time; it will likely exceed t, because the bath has done two pieces of work and a bleach judged by its endpoint absorbs that fatigue where one judged by a clock does not. That is why A goes second.

!What print B now owes you, and how to discharge it

Moersch’s warning lands exactly here: a print in which not-yet-toned metallic silver has been bleached to silver bromide is no longer archival, because that bromide would tone uncontrolled over time by gas action; it must be dissolved by fixation or converted to silver sulfide by toning again.

Read what that does and does not say about print B. The silver the bleach converted is now silver sulfide; the silver it never reached is still metallic silver. Both are stable, and the print is a legitimate split-toned object. The obligation is that the redevelopment be complete, not that the bleaching be, so the check is on the toner: hold print B under a strong light while it is wet and look for any area still the pale creamy yellow of bleached halide. If you find one, back into the toner; if the toner will not shift it, mix a fresh bath.

Stage 4 — the control, and the drying

16. Print C goes through the same water as the others and nothing else: soak 2 to 3 minutes, two minutes in the rinse dish, a second rinse, four minutes in the wash. A control that stays dry in a drawer measures nothing, because the difference you attribute to toning would then contain every effect of wetting, swelling and drying a sheet of paper.
17. Dry all three by the same method, at the same time, in the same place: surface water removed the same way, then air-dried at room temperature, 10 to 20 minutes for this paper. No heat — Kodak note that heat drying shifts to a cooler tone with some paper and toner combinations, and a drying method that changes the hue is a second variable inside an experiment trying to measure the first.
18. While they dry, add up the wet time.

🧮The wet-time budget, and the manufacturer's limit it runs into

Arithmetic worth doing before you print rather than after, because it decides your borders.

t_wet = t_soak + t_bleach + t_rinse + t_tone + t_rinse2 + t_wash

Total wet time for one toned print

Kodak’s published figures, with this page’s two-minute second rinse: 2 to 3 minutes of soak, 5 to 8 of bleach, 2 of rinse, 0.5 to 1 of toner, 2 of rinse and 4 of wash — 15.5 to 20 minutes in water.

Beside that, what the paper’s own maker says. ILFORD state that prolonged immersion causes edge penetration and print curl with resin-coated papers, and that wet times longer than 15 minutes should be avoided. Kodak arrive at the same place from their side: keep toning times for resin-coated papers to a minimum, and if you tone one for longer than 8 to 10 minutes leave a large border to trim.

Two makers, one conclusion: a sepia-toned resin-coated print is at or past the paper’s own limit before you have done anything wrong. The border is part of the method, edge penetration is expected rather than a fault, and this is the strongest argument for fibre base.

Stage 5 — read and record

19. Read the same five patches on all three dry prints, same template, same instrument or reference strip, same light. Read the control first: the difference between its readings is your noise floor.
20. Record the hue against the untoned control, side by side under a named light, and say what the light is. This is a ranked verbal comparison, not a colour measurement.
21. Route the waste, clean up, and write the session log before leaving the room.

Expected observations

In the bleach. The image goes first in the shadows and last in the highlights, and to a pale creamy yellow rather than to nothing — that yellow is silver bromide in gelatin, which is what Kodak mean by only a faint yellowish brown image remains. A print pale all over in under a minute says the bath is stronger or warmer than you thought; one dark at ten minutes says the opposite.

In the rinse. Yellow comes out of the sheet into the water; Kodak Limited’s instruction for the same process is to wash until the stain is gone, a usefully concrete endpoint.

In the toner. The image comes back fast enough to startle you: Kodak’s thirty seconds is roughly how long a sulfide ion takes to diffuse through the emulsion. The colour is mostly the paper’s — silver sulfide runs from light brown to black according to its state of subdivision, which the toned image inherits, so a mixed modern emulsion tends yellower and a bromide-rich one browner whatever you do in the tray.

On print B. The shadows bleached first, so they are the silver sulfide while the highlights are still metallic silver. A reader expecting the opposite is thinking of a direct toner.

On the dry prints. The density is lower, clearest in the mid-tones and shadows, and smaller than the wet print suggested — a wet print always looks darker, which is dry-down.

At the edges. A darker or differently coloured band a few millimetres in from the trimmed edge is toner in the paper core, arriving through the cut edge. That justifies the border.

What is happening chemically

Two reactions carry the whole sequence, and the lesson argues them in full. The bleach is a redox reaction between a solid and a dissolved oxidant, running at the rate the ferricyanide reaches the silver:

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

The bleach: minutes, and dependent on concentration, temperature and agitation

The redevelopment is not a reduction at all — the silver is Ag⁺ before the toner touches it and Ag⁺ afterwards — and it goes because silver sulfide is thirty-six orders of magnitude less soluble than silver bromide:

2 AgBr + S²⁻ → Ag₂S + 2 Br⁻

The redevelopment: seconds, and limited only by diffusion into the gelatin

Which is why every setting you can choose lives in the first bath, and why Kodak’s instruction for the toner is not a time but a condition. Three things the bench adds to that.

The bleach is one oxidation with two possible endings, and the bath decides which. What becomes of the Ag⁺ depends on the anion available. Loaded with bromide, it comes down as silver bromide on the site of the grain it came from and nothing leaves the print — a bleach. Loaded with thiosulfate, it forms a soluble complex and walks out — Farmer’s reducer. That is the mechanism behind Moersch’s warning about carrying fixer into the bleach: thiosulfate in the gelatin turns the bleach into a reducer locally, in the highlights first, where there is least silver to lose and where losing it shows most.

A bleach exhausts by making its own product, converting hexacyanoferrate(III) to (II) and consuming bromide with every silver atom. Kodak publish no capacity for T-7a, and the absence is honest: an endpoint judged by eye means an exhausting bath shows itself as a longer time rather than a worse print, so a reader who records times has the figure Kodak did not.

The toner exhausts worse: it does not slow down, it becomes something else. CAMEO records that aqueous sodium sulfide converts in air to sodium hydroxide and sodium thiosulfate — and thiosulfate is hypo, which dissolves silver bromide, so an old sulfide bath is a fixing bath wearing a toner’s label. Wall’s 1912 dictionary gives three stages: a yellow-brown result, an apparent failure to act, then the bleached image gradually disappearing. Hence Kodak Limited’s instruction to throw the bath away after use.

🔬Why the density falls, and the one published number that exists

Silver sulfide is a weaker pigment not because it is browner but because it covers less area per atom of silver. Mike Ware quantifies the covering power of the two substances photometrically: complete conversion of nanoparticle silver to silver sulfide drops optical density by a factor of about 30.

That number does not transfer to your print, and Ware says why: in modern papers the higher concentration of silver and its larger particle size make the loss far less apparent, a gelatin print carrying roughly ten times the silver of a salt print and carrying it as micron-scale filaments rather than 10 nm spheres. How much less is a question no source read for this course answers with a figure for a developing-out paper. That is the hole this session fills — so be clear that your number is a figure for your paper, developer, exposure and bleach endpoint, not a constant of sulfide toning.

Data to record

Two records. The session log is one line; the measurement table is one row per patch per print.

The session log

Date and room temperature. Paper: maker, product, surface, weight, size, box code. Developer, dilution, temperature and time. Stop and fixer, which baths and their running totals. Wash route and drying method by name. Printing exposure in stops, including the amount added for the toning, with the enlarger settings from the printing map. Then, for tonight: the bleach stock’s measured volume; both baths’ temperatures; t; B’s bleach time as a fraction of t; A’s bleach time; both toning times; every rinse and wash time; the wet time per print; the light the prints were judged under; and which waste went where.

The measurement table

Column	What goes in it
Print	A (full), B (partial), C (control)
Patch	1 to 5, highlight to shadow
Density before	Reflection density of the dry print before any bath, or the matched band number
Density after	The same patch, dry, after the sequence
Change	After minus before, signed
Hue, after	Words, against the untoned control, under the named light
Notes	Edge penetration, mottle, staining, anything you would not want to have to remember

The one number that is not in the table

Your noise floor, from print C: the largest of its five before-and-after differences is the smallest change this session can detect. Write it at the top of the analysis rather than the bottom, because it constrains what follows rather than commenting on it.

Analysis

First, fix what you may claim. Print C should have moved very little; whatever it did move by is the combined effect of soaking, washing, drying and your reading repeatability, and no smaller difference is a result. If C moved more than either toned print, the session measured its own noise, and the fix is a second run rather than a smaller claim.

Second, read the loss patch by patch. Not how much density the toner cost but where: a loss concentrated in the shadows says something different from a flat one.

Third, convert the loss into stops. Where the paper’s curve is roughly straight through the mid-tones, the correction is the density loss divided by the density change per stop at the same part of the scale, and you measured the second in Part XVIII.

🧮The arithmetic, worked on constructed figures

Every number in this box is invented to demonstrate the method. None is a measurement, none is a source, and none should be copied into your notebook. The course has not run this session; see the Alternative route.

Suppose the mid-tone patch reads 0.94 before and 0.71 after, and the control moved by 0.02 at worst. The loss is 0.23, comfortably above the noise floor, so it is a result. Suppose your own test strip shows the mid-tones moving about 0.30 in reflection density per stop. Then:

ΔE = ΔD_toning / (ΔD / stop)

Exposure correction for the density a toner removes

ΔE = 0.23 / 0.30 = 0.77 stops, about three quarters of a stop darker for the next sepia print on this paper. Two things follow. The third of a stop this page told you to start with would have been less than half of what the measurement asks for, which is the ordinary outcome of replacing a guess with a measurement. And the arithmetic assumes the density change per stop is constant over the range measured, which it is not near the toe or shoulder — so divide at a mid-tone patch.

Fourth, compare A with B. If B’s shadows match A’s and B’s highlights match C’s, the split is clean. If B’s highlights sit between A’s and C’s, the bleach had begun on them when you pulled it and your fraction of t was larger than you thought — a statement about your bath and agitation, not about the formula.

Fifth, be careful about colour. Three dry prints, one light source, no instrument: what you can write honestly is a ranked statement with C as the reference, not a magnitude. Four sources agree the hue comes from the paper rather than the toner — the 1928 primer’s state-of-subdivision mechanism, Moersch on chloride-rich emulsions toning yellow whatever the toner, Bullock on faster emulsions running purpler, and Kodak on image colour varying with paper emulsion type and grade.

Sixth, every finding rests on one print per condition; name the two you would most want to repeat.

Troubleshooting

What you see	Where it came from	What to do
The bleach barely touches the print in ten minutes	A cold bath, a tired stock, or a stock diluted against an assumed volume	Check the temperature, then the stock’s volume against its label; mix a fresh bath before blaming the formula
The bleach eats the highlights and the print will not redevelop	Fixer carried into the bleach: residual thiosulfate makes it act as a reducer	Nothing recovers that sheet; the fault is the printing session’s washing. Run HT-2 next time
Areas that stay pale creamy yellow after toning	Bleached silver bromide the toner did not reach, or a bath beginning to fail	Back into the toner; if it will not shift, mix a fresh one: uneven toning
Dark yellow stain, worst in borders and highlights	An exhausted fixing bath leaving insoluble silver compounds washing cannot remove	Residual silver staining: the toner revealed it, the fixer caused it
General yellowing of the whole sheet	Prolonged fixing: the base absorbed fixer no wash retrieves	Shorten the fix to the paper maker’s figure; Kodak’s RC ceiling is about two minutes
Mottle in the base, absent before toning	An overconcentrated stop bath, or too little agitation in its first seconds	Mottle revealed after toning: replace the stop bath, agitate from the first second
Round purple spots	Air bubbles trapped between or under prints during fixing	Purple spots from fixer air bubbles: separate the prints, keep them moving
A darker band inside the trimmed edge	Toner in the paper core, entering through the cut edge over a long wet time	Toner edge penetration on RC: trim to the border, and next time leave more
Blue specks	A trace of iron meeting the ferrocyanide the bleach has just made	The oxalate is a second line of defence. Find the iron
A print that will not lie flat	Print curl from a long wet time, which ILFORD warn of alongside edge penetration	Dry under light even pressure: drying and flattening

Clean-up

Trays, tongs and graduates washed in a fixed order — bleach side first, toner side second, wash last — so nothing travels from an acid vessel into an alkaline one. Two funnels, or one rinsed thoroughly between the bottles. Both stock bottles capped and returned to storage, separated from each other and from every acid on the shelf: the incompatible pair is a shelf problem as much as a tray problem. Room aired before the paper and negatives come back; bench wiped with the gloves still on, gloves off last. Run lab closing.

Storage

The stocks keep; the working baths do not. Kodak Limited’s instruction applies to T-7a’s bath too: throw the toning solution away after use. Do not keep the unused bleach either — it is a diluted, part-oxidised bath whose remaining capacity you cannot know, and the point of a stock is that a known bath can be mixed from it in a minute.

Stock A goes back into its opaque bottle, as full as it will go, labelled with the substance, the strength, the measured volume and the date. Stock B goes back capped tight, in the dark, away from acids and from photographic materials. Kodak publish no shelf life for either and this course does not invent one; what it can tell you is what failure looks like. For the bleach, a blue tinge or precipitate as the ferricyanide photolyses. For the sulfide, Wall’s three stages — and the reason the bottle is kept full and closed is the air oxidation that produces them.

The prints go into the record with their measurement table. Label print B a split-toned sheet rather than a sepia print: in five years the difference will not be obvious from looking at it.

Disposal considerations

Three things are true at once, and a page that gives only the first is not being straight with you.

The chemistry. Spent bleach is hexacyanoferrate(III) and (II) with bromide, oxalate and acetic acid; spent toner is an alkaline sulfide part-converted to hydroxide and thiosulfate. Neither may meet the other or an acid, for the reasons under Waste streams. Both are harmful to aquatic life — sulfide H400 in every ECHA notification, ferricyanide H411 in about 45 per cent.

The general practice. Collect each stream separately, labelled and closed, and take it to a facility that accepts it. Kodak’s environmental guidance for amateurs puts sepia toner among the products for which household hazardous waste collection is an option, and notes that most communities have such a facility for domestic items that should not go through the trash, the septic system or the sewer. Foma’s data sheets give the waste codes 09 01 01*, 20 01 17* and 15 01 10* and the plain instruction not to flush the product into the sewer. ILFORD’s advice to United Kingdom domestic users names a household waste and recycling centre.

The jurisdiction. What a household may lawfully do with these streams differs by country and by council, and none of this is legal advice. Read the disposal caveat before deciding anything here, and check your local regulations. The reason the course collects everything rather than computing a threshold is set out there: an absolute hazardous entry in the List of Waste applies even where the waste displays no hazardous property, so dilution does not reclassify a stream.

Questions

1. Kodak print T-7a’s toner working solution at 22.5 g/L in 2006 and at 10.4 g/L in 1928, with the same stock and the same formula number. Explain why both baths nevertheless convert the whole of a bleached image, and name what the difference in strength does change.
2. Print B is bleached for one third of t and then redeveloped. A reader objects that it is therefore only one third toned and cannot be archival. Answer precisely, and say what would make the objection correct.
3. Your untoned control moved by 0.05 in reflection density between its readings, and print A’s mid-tone moved by 0.11. Write, in one sentence, what you may report.
4. This page rinses for two minutes where Kodak’s sheet says “immediately”. Give the argument, and say which part of it is Kodak’s and which the course’s.
5. Add up the wet time for one toned resin-coated print from the published figures, compare it with what the paper’s own maker advises, and state the two consequences for how you print the sheet.
6. You are offered the packaged kit as “the odourless option”. Using its maker’s own data sheet, say what is in the toner half, what the mixture is and is not classified as, and what you would want to know before deciding.

Further experiments

Run it on fibre base and pay in hours. A fibre print has no plastic layers for a toner to creep between and no fifteen-minute wet-time limit; what it has instead is a thirty-minute wash after the toner, the hardening step T-7a specifies for fibre prints and this page skipped, and a drying time that puts the measurement into the next day. The hardening bath — 2 parts F-5a to 16 parts water — is acid, so the two-minute rinse argued in step 13 becomes load-bearing rather than prudent.

Bleach a series and plot the conversion. Six strips from an extra sheet of the same printing, bleached for one sixth, two sixths and so on of t, redeveloped identically, the same patch measured on each. That curve is the transfer function of a split tone, and nobody in this corpus has published one.

Change the bleach and hold everything else. Kodak Limited’s T-52 bleach is plain ferricyanide and bromide with no acid and no oxalate. Bullock found the ratio of the salts has little effect on the result while strength affects speed and colour; nobody in this corpus has tested that on a modern emulsion.

Test the bath you were told to throw away. Keep tonight’s working toner stoppered and in a week tone a strip in it beside one in a fresh bath. Wall’s taxonomy predicts a yellow-brown result first and a failure to act later; a date on the first stage would be a real contribution.

Measure what a hot dryer does to the hue. Kodak state that heat drying shifts to a cooler tone with some paper and toner combinations and do not say which. Two identical toned prints, one air-dried and one dried warm, settle it for your paper.

Recap

• The measurement is the point. Kodak tell you to print darker and no source puts a number on the loss for a developing-out paper. Five patches, three prints, before and after, and the adjective becomes stops.
• All the control lives in the bleach. Redevelopment is a precipitation driven by thirty-six orders of magnitude of solubility, so a split tone is made by stopping the first bath.
• Judge the bleach by its endpoint. Kodak’s two printings of the identical bath disagree by a factor of six. Bleach the timed print first and the judged print second, so the bath’s fatigue lands harmlessly.
• The two-minute rinse is a step of the formula, keeping an acid bleach out of an alkaline sulfide bath and taking the working oxidant out of the gelatin. The rinse on the far side of the toner is the same rule the other way round, and this page lengthens it and says so.
• The control goes through the water, or what you attribute to toning contains every effect of wetting and drying paper.
• Add up the wet time. Two makers put a sepia-toned RC print at or past the paper’s own fifteen-minute limit, so the wide border is part of the method.
• Three bottles, and the funnel counts. The only genuinely dangerous moment in two hours is somebody tidying an acid and a sulfide into the same container.
• A partly bleached print owes a complete redevelopment, not a complete bleach. Check for pale yellow while it is still wet.

Check your understanding

Question 1. Why does this page bleach the partially bleached print (B) before the fully bleached print (A), rather than the other way round?

• Because a partial bleach uses less of the bath, so more is left for the second print
• Because B’s bleach is timed as a fraction of a measured endpoint while A’s is judged by eye, so bath fatigue would corrupt B’s result and merely lengthens A’s
• Because the shadows of a partially bleached print are more sensitive to a fresh bath
• Because Kodak specify that order in the T-7a working instructions

Show the answer and why

Answer: Because B’s bleach is timed as a fraction of a measured endpoint while A’s is judged by eye, so bath fatigue would corrupt B’s result and merely lengthens A’s

A ferricyanide bleach exhausts as it works: every silver atom oxidised converts hexacyanoferrate(III) to hexacyanoferrate(II) and consumes a bromide ion. A print bleached to a visual endpoint absorbs that by taking longer and still arriving at the same place. A print bleached for a fixed number of seconds does not: the same clock time in a tireder bath is a smaller fraction of the conversion. So the time-based arm goes first. Kodak give no order at all, because Kodak do not describe a partial bleach.

Question 2. The untoned control is soaked, rinsed twice and washed exactly like the toned prints, with no bleach and no toner. What does that buy, and what would a dry control have cost you?

• Nothing in particular; it is a courtesy so that all three prints look consistent
• It makes the control measure handling — wetting, swelling, washing and drying — so that the difference attributed to toning is toning alone; a dry control would have folded every wet-and-dry effect into the toning result
• It ensures the control fixes properly
• It allows the control to be toned later if the result is disappointing

Show the answer and why

Answer: It makes the control measure handling — wetting, swelling, washing and drying — so that the difference attributed to toning is toning alone; a dry control would have folded every wet-and-dry effect into the toning result

A control exists to hold everything constant except the one variable. Here the variable is the toning chemistry and everything else in the sequence is water. A print that stayed in a drawer would differ from the toned prints by the toning and by four immersions and a second drying, with no way to separate the two. The control also supplies the noise floor: the largest of its own before-and-after differences is the smallest change the session can honestly detect.

Question 3. A reader mixes T-7a exactly, tones a resin-coated print and finds a dark band a few millimetres inside the edge that no washing removes. What has happened, and which two published statements predicted it?

• The bleach was too strong; Kodak and ILFORD both warn against overconcentrated bleaches
• Toner entered the paper core through the cut edge during a long wet time: Kodak direct that resin-coated prints toned for more than 8 to 10 minutes carry a large border to be trimmed, and ILFORD advise avoiding wet times longer than 15 minutes because of edge penetration and curl
• The fixer was exhausted, which always shows first at the edges
• The print was dried with heat, which drives toner outwards to the edges

Show the answer and why

Answer: Toner entered the paper core through the cut edge during a long wet time: Kodak direct that resin-coated prints toned for more than 8 to 10 minutes carry a large border to be trimmed, and ILFORD advise avoiding wet times longer than 15 minutes because of edge penetration and curl

A resin-coated sheet is a paper core sealed between two polyethylene layers, so liquid reaches the core only through the cut edge — and then cannot easily be washed back out. The published sepia sequence adds up to roughly 15.5 to 20 minutes of wet time before anything goes wrong, which is at or past the limit ILFORD give for their own paper. The border is part of the method rather than a matter of taste, and edge penetration is an expected observation on this page rather than a fault.

Question 4. Kodak’s T-7a step 4 says only "immediately rinse the print with water". This page rinses for two minutes instead. What is the argument, and how should the page describe the change?

• It is a correction to an error in Kodak’s sheet and should be presented as the right procedure
• A print leaving a sulfide bath carries sulfide into whatever comes next, and the acid-and-sulfide rule applies in that direction too; the page keeps Kodak’s step and labels the two minutes as the course’s own control derived from that rule
• Two minutes is Kodak’s figure elsewhere in the same sheet, so no labelling is needed
• The longer rinse is needed to remove residual bromide, which would otherwise stain

Show the answer and why

Answer: A print leaving a sulfide bath carries sulfide into whatever comes next, and the acid-and-sulfide rule applies in that direction too; the page keeps Kodak’s step and labels the two minutes as the course’s own control derived from that rule

The rule that acid and sulfide must not meet is symmetrical, and the print is the carrier in both directions. It matters most where an acid hardening bath follows the toner, which is Kodak’s own step 5 for fibre-base prints. Rule 7 governs how this is written: Kodak’s instruction is Kodak’s, the two-minute figure is the course’s own derivation from a rule Princeton states, and the page must say which is which rather than presenting a modified formula as the published one.

Question 5. A packaged sepia kit is sold as odourless. Its maker’s safety data sheet names, in the toner half, index number 612-082-00-0, CAS 62-56-6, at less than 1 per cent, and classifies the mixture only as Eye Irrit. 2, Skin Irrit. 2 and STOT SE 3. What is the honest reading?

• The kit is the safer option and should be recommended as the accessible route
• That substance is thiourea, which carries Carc. 2 and Repr. 2 as a substance; the mixture is not so classified because the concentration is below the carry-over threshold, so the buyer is choosing a dilute bought thiourea bath rather than avoiding thiourea
• The CAS number identifies sodium sulfide in a stabilised form
• The absence of a carcinogenicity classification on the mixture means the component is not a carcinogen

Show the answer and why

Answer: That substance is thiourea, which carries Carc. 2 and Repr. 2 as a substance; the mixture is not so classified because the concentration is below the carry-over threshold, so the buyer is choosing a dilute bought thiourea bath rather than avoiding thiourea

CAS 62-56-6 is thiourea and index 612-082-00-0 is its harmonised CLP entry. A mixture is classified from its components and their concentrations, so a component below the relevant generic concentration limit does not carry its class into the mixture — a statement about labelling thresholds, not about the substance. The difference of degree is real and a reader may reasonably weigh it. What is not available is the belief that "odourless" means the substance is absent, and the course’s own route to accessibility here is working outdoors on the sulfide bath rather than changing reagent.

Question 6. Your sulfide bath tones the first print brown, gives the second a yellow-brown image, and by the third appears to do nothing at all. What is happening, and what is the source of the fault?

• The bath is being diluted by carry-over from the rinse and simply needs topping up
• The sulfide is converting in air to hydroxide and thiosulfate, so the bath is progressively becoming a fixing bath; the answer is a fresh bath, and the instruction is to discard a working toner after use
• The prints were under-bleached, and the bath is correct
• The bath has absorbed bromide from the prints, which restrains the toning reaction

Show the answer and why

Answer: The sulfide is converting in air to hydroxide and thiosulfate, so the bath is progressively becoming a fixing bath; the answer is a fresh bath, and the instruction is to discard a working toner after use

CAMEO records that aqueous sodium sulfide solutions gradually convert to sodium hydroxide and sodium thiosulfate on exposure to air. Thiosulfate is hypo, and hypo dissolves silver bromide, so a decayed sulfide bath removes the bleached image rather than converting it. Wall’s 1912 dictionary gives exactly this progression in three stages — a yellow-brown image, then an apparent failure to act, then the bleached image gradually disappearing — and Kodak’s 1928 primer notes the same fault arriving from the other end, in a jar of old sodium sulfide that already contains hypo. Kodak Limited’s one-line instruction for the working bath is to throw it away after use.

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