Lab: Mixing and Comparing Print Developers

Three trays, three developers, one negative, and a single rule that decides whether the evening produced knowledge or an anecdote: nothing changes between the trays except the developer. Not the paper, not the exposure, not the time, not the temperature, not the agitation, not the light you judge under. Everything a printer normally adjusts by instinct is nailed down for one session, so that the difference you measure at the end has only one place it can have come from.

Two of the three developers you will have mixed yourself, from five jars and a balance. The third is a bought concentrate whose composition its maker does not publish. That contrast is deliberate: by the end you will know what you can say about a developer you built and what you can only say about a developer you bought.

Purpose

To mix two 500 mL batches of Kodak D-72 stock from raw chemicals — one exactly as Kodak published it, one with the bromide doubled and versioned as the course’s own revision — and to compare both against a proprietary paper developer under a design tight enough that the measured differences are attributable.

Three products leave the bench: two labelled, dated bottles; a set of prints and contact-printed step wedges with numbers written against them; and a printing map for every sheet, which is the record that makes the rest of the course’s printing possible.

Learning objectives

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

• Scale a published formula to the volume you actually need and state each weight to the precision your balance supports rather than to the precision the arithmetic offers.
• Give the two distinct reasons Kodak state for the dissolving order in a metol formula, and say what goes wrong if you ignore each.
• Prepare and dose a percentage stock solution, and explain why a source that offers “1.9 g or 19 mL of a 10 per cent solution” is offering an accuracy improvement rather than a convenience.
• Assign a formula version to a deliberate change, and record the changed variable, the reason and the prediction before the result exists.
• Design a three-arm comparison in which exactly one thing varies, and name the four things you had to hold to achieve that.
• Read maximum black, base white and the first separated step from a contact-printed wedge, and say what each number does and does not settle.
• State the repeatability of your own process and refuse to claim any difference smaller than it.
• Write a printing map complete enough that somebody else could reproduce one of tonight’s sheets.

Prerequisites

• Print developer chemistry and the developer-paper pair, which is the whole of the theory this session tests. The alkali, the restrainer, development to completion, capacity and aerial oxidation are assumed and not repeated.
• Lab: mixing D-23 and D-76 from raw chemicals, which taught the weighing, the dissolving order and the bottle label. This session is the same craft at a higher pH.
• Concentration and dilution, for per cent w/v and for the difference between a stock solution and a working solution.
• Commissioning your laboratory, for the balance and its check.
• Commissioning the enlarger, for a head whose uniformity you have measured and a safe working time you have tested.

Safety classification

Level A: a standard home darkroom, with one step declared at Level B controls — the weighing of the developing agents — stated here so you meet it before the procedure rather than inside it. That is the rubric’s rule for a raised step: the operation sets the level, not the substance, and the controls are written where the step is.

• The solutions. Two alkaline developers at roughly a tenth of a mole of carbonate per litre, a dilute citric acid stop and a non-hardening fixer, all at room temperature, handled with tongs by the litre. This is the same handling as the tray sequence in Part XVI.
• The weighing, which is not. Metol is classified with signal word Warning and carries H317, may cause an allergic skin reaction, alongside H302, H319 and H373; hydroquinone is classified Danger and carries H317 with H318, H341 and H351. Both are handled as loose powders, and the Level B criterion the rubric names is fine powders that must not be inhaled. The controls for that step, in full: weigh in a tray, in still air, one jar open at a time, with nitrile gloves, eye protection and a particulate mask; do not pour from a height; no paper open in the room; wipe the bench down and wash your hands before touching anything else. Work through the weighing procedure, which exists for this.
• Sodium sulfite is the surprise on the list. It is classified Danger with H314 — causes severe skin burns and eye damage — and it is the largest single weight in the formula. Its dust is not a nuisance dust and the tray is not optional.
• Sodium carbonate carries H319 and potassium bromide carries H315, H319 and H335. Both are eye hazards in a room where your hands are wet and the lights are off.
• Temperature. Kodak’s directions call for water at about 52 °C, which is the top of the Level A band rather than beyond it. Nothing here is heated on a hob; the water comes from a tap and is checked with the thermometer you print by.
• Mains. The enlarger and its timer are mains equipment, commissioned in Parts XVI and XVII, and nothing is opened or wired tonight.

What is not a hazard here, and why. There is no sulfur dioxide risk, although forty-five grams of sulfite pass through your hands. Sulfite releases the gas when it meets an acid, and every vessel it enters tonight is alkaline from the first gram onwards — the acid on the bench is in a different tray, on the other side of a boundary the procedure draws for exactly this reason. There is no solvent vapour, because there is no solvent: the entire session is aqueous. There is no silver hazard in the developer; Kodak’s own environmental guidance puts developer solutions at negligible silver, and the silver in this session is all downstream, in the fixer. And the finished developers are alkaline rather than caustic — a carbonate bath is not a hydroxide bath, and the difference is two orders of magnitude in hydroxide ion, which is why the control is gloves and tongs rather than a face shield.

Hazards

Hazard	Where it arises	Control
Skin sensitisation, metol and hydroquinone	Weighing; splashes from the developer trays	Nitrile gloves throughout; tongs rather than fingers; a sensitisation is permanent once acquired
Serious eye damage, sodium sulfite	Weighing 45 g of a fine powder, twice	Eye protection from the moment the first jar is opened; tray weighing; still air
Eye irritation, carbonate and bromide	Weighing; alkaline splash	Eye protection; rinse a splash immediately at the tap and keep rinsing
Inhalation of fine powder	The dry side of the bench	Particulate mask; one jar open at a time; no pouring from a height
Alkaline solution on skin	Three trays of developer at pH near 10.5	Gloves; tongs; a print is never lifted with fingers
Aquatic toxicity	Every one of tonight’s waste streams	Collect; never a drain; see Disposal considerations
Working in near darkness with liquids	The whole printing half	Bench laid out and trays filled with the lights on; a fixed tray order that does not change; the floor cleared before the lights go off

Required PPE

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. Eye protection with side shields from the first jar to the last rinse. A particulate mask for the weighing step only, which is the one control that distinguishes it from the rest of the session. An apron or overall, because a carbonate developer stains and a fixer splash on a shirt finds its way onto the next print.

Read glove selection before you assume a box of gloves is a box of gloves; it says what the published permeation data cover and what they do not.

Ventilation

An openable window or an extractor giving a through draught, which is the general ventilation the HSE printing sheet specifies for manual development — more than five air changes an hour, achieved by cross-flow rather than by a fan pointing at the trays. Nothing tonight generates a vapour that needs capture at source: there is no ammonia, no acid stronger than dilute citric, no heat. What the ventilation is actually for is the weighing, where the airborne hazard is a settling powder rather than a gas, and the answer there is still air at the balance and a through draught in the room, which are not the same requirement and are met by different means. Run the ventilation check before the session, not during it.

Materials

Item	Quantity	Note
Variable-contrast resin-coated paper, 8 × 10 in, glossy	10 sheets	The session’s paper. RC because it fixes in 30 seconds, washes in 2 minutes and dries in 10 to 20 minutes at room temperature, which is the only reason a comparison of dry prints fits inside one evening
A negative you know	1	Middling contrast, with a real black, a real white and a face or a texture in the mid-tones. Not a difficult negative: tonight is about the developer
21-step transmission step wedge	1	Contact-printed beside each image. Its increment is nominal, as Part IX established, and nothing here treats it as certified
Distilled or deionised water	1.5 L	For the two stocks and the bromide solution, so that the only variable between them is the one you introduced
Tap water, drawn and stood	3 L	For the working dilutions, the stop and the fixer. ILFORD instruct drawing it off and letting it stand, because mains water is highly aerated
Storage bottles, 500 mL, tight closure	2	Brown glass or HDPE. Filled to the shoulder
Bottle, 100 mL	1	For the 10 per cent potassium bromide solution

Chemicals

Weights are for 500 mL of stock, which is half of Kodak’s published litre. The full formula, its provenance, its dilutions and the two Kodak printings that disagree about what it is for are on the D-72 page and are not restated here.

Chemical	Quantity per 500 mL of stock	Form
Metol	1.55 g	Powder. Kodak call it Elon
Sodium sulfite	22.5 g	Anhydrous
Hydroquinone	6.10 g	Powder
Sodium carbonate	33.75 g	Anhydrous
Potassium bromide	0.95 g, dosed as 9.5 mL of a 10 % w/v solution	Batch 001. Batch 002 takes 19.0 mL, which is 1.90 g
Water	to 500 mL	250 mL of it at about 52 °C to start

And on the wet bench, common to all three arms:

Chemical	Quantity	Form
Citric acid stop bath concentrate	50 mL	Diluted 1+19 to make 1 L, 10 seconds at 18 to 24 °C
Ammonium thiosulfate rapid fixer concentrate	200 mL	Diluted 1+4 to make 1 L, 30 seconds for RC paper
Proprietary paper developer concentrate	75 mL	Diluted 1+9 to make 750 mL

!What the third developer is, and what the course may say about it

The bought concentrate is a product, not a formula. Its maker publishes that it is a dimezone-s and hydroquinone liquid concentrate, publishes its dilutions, its times, its capacities and a pH band for the fresh working solution, and does not publish what is in it. Under the course’s rule on proprietary formulations, a product is taught as behaviour and disclosed components only, and nothing on this page reconstructs a recipe from a safety data sheet.

That is precisely why it is in the comparison. You will end the evening able to say what it did, in numbers, beside two developers you can also say what is in. Notice which of the two kinds of knowledge lets you change something on purpose.

Equipment

Balance reading to 0.01 g, checked against its mass before the first weighing by the balance and thermometer check. Weighing boats or papers, a spatula, and a tray for the balance to stand in. Two 600 mL beakers, one 250 mL and one 100 mL graduated cylinder, a 10 mL graduated syringe for the bromide solution, a stirring rod, a funnel. Thermometer. Six processing dishes of 10 × 12 in — three developer, one stop, one fixer, one wash — which is what the bench diagram draws. Four will do if you take the stop, the fixer and the wash in turn in one dish rinsed between, and the cost is time and a contamination risk the design would rather not carry. Three pairs of print tongs, one pair per developer, and one further pair for the stop and fixer. Enlarger, timer, easel, safelight at its tested distance. A contact printing frame or a sheet of 3 mm glass. A wash tray. A drying rack. The reflection head of your densitometer if you built one; the Alternative route below is written for you if you did not.

Estimated cost

Band ££. The capital is already yours: balance, dishes, tongs, enlarger, timer. What this session adds to the shelf is a jar each of five chemicals, and four of the five are jars Part VIII already bought. The planner holds the dated figures and the gaps; the band here is the recurring cost of running the session again, not the cost of being able to run it once.

Estimated consumables cost

Every price below is the planner’s own dated UK figure, and every quantity is from the Materials and Chemicals tables above. The ranges are the spread between the suppliers the price file read on the same day.

Consumed	This session	Sourced price	Cost this session
RC paper, 8 × 10 in	10 sheets	£33.50 for 25 sheets to £96.18 for 100	£9.60 to £13.40
Metol	3.10 g	£16.20 per 50 g	£1.00
Hydroquinone	12.20 g	£11.89 per 50 g	£2.90
Sodium sulfite, anhydrous	45.0 g	£13.68 to £19.98 per kg	£0.62 to £0.90
Sodium carbonate, anhydrous	67.5 g	£7.20 per 500 g	£0.97
Potassium bromide	2.85 g used of the 10.0 g made up	£23.00 per 250 g	£0.26 used; £0.92 to make the 100 mL stock, which keeps
Paper developer concentrate	75 mL	£10.52 per 500 mL to £20.03 per 1 L	£1.50 to £1.58
Stop bath concentrate	50 mL	£10.66 to £12.18 per 500 mL	£1.07 to £1.22
Rapid fixer concentrate	200 mL	£21.05 to £25.98 per 1 L	£4.21 to £5.20
21-step transmission step wedge	0 — it is not consumed	The price file could not price one. It is named in the file’s own gap list: the largest UK photographic retailer searched returned no result	—

Adding the rows that carry numbers gives about £22 to £27 for one run. Two things about that figure. The paper is half of it, which is the shape of every printing session in this course and the reason the arithmetic in Analysis is worth doing before you expose rather than after. And the subtotal is a floor rather than a total: the step wedge has no sourced price, and a fibre-base sheet has none either, so a reader who swaps the paper is outside the figure entirely.

Equipment is deliberately absent from the table. A balance is not consumed, a dish is not consumed and neither is a pair of tongs; counting them would make the number larger and stop it measuring what the consumables calculator needs, which is what one run uses up.

Waste streams

Four, kept apart, and the first two must never share a container.

• Alkaline developer — about 2.3 L of it by the end, from three trays. Its silver content is negligible on Kodak’s own table; its hazard is its pH and its aquatic classification. One labelled container, by the general chemical waste procedure.
• Acid stop — 1 L of dilute citric acid. A separate container. An acid meeting a sulfite-bearing alkaline developer in a closed bottle is the one genuinely avoidable incident of the evening, and the incompatibility page has the reaction.
• Silver-bearing — the spent fixer and the first wash, into the labelled silver container under the silver-bearing waste procedure.
• Solids — gloves, weighing papers, wipes and any print you are not keeping. A processed sheet carries silver in hardened gelatin and is not household paper.

All four sit under the disposal caveat, and its jurisdictional sentence is not a formality: what a household may lawfully do with a photochemical stream is a question of local rules and local collection. Check your local regulations.

Alternative route

Without a densitometer, the whole session works and you lose magnitude rather than direction. Read the wedges by eye against each other, laid side by side in even light, and record step numbers instead of densities: the first step that is distinguishable from paper white, and the first step that is indistinguishable from its neighbour at the black end. Those two integers per print are a real measurement — they are what Hurter and Driffield’s own definition of a paper’s range is built from — and the arithmetic in Analysis works on them unchanged. What you cannot do is compare your numbers with anybody else’s, or detect a difference smaller than one step, which for a nominal 0.15 wedge is about half a stop. Say so in the record rather than implying a precision you did not have.

Without a balance reading to 0.01 g, do not attempt the sub-gram weights. Take the whole formula to a litre instead of 500 mL, which doubles every weight and halves the relative error, and accept that you will make more developer than you need — or buy the two agents as a packed developer and run the comparison with the bromide variation only, which is one arm rather than three.

Without a darkroom there is no route to this page, and it would be dishonest to pretend otherwise. An enlarging paper is a developing-out material with an equivalent film speed of about 3 to 6 on its maker’s own comparison and it fogs in ordinary room light. What a reader without a room can do is the mixing half — which is a bench session in daylight, produces the two bottles and the version record, and can be finished in a friend’s darkroom or a shared facility later.

Preparation

1. Read the D-72 page first. Tonight reproduces Kodak’s quantities without modification, and the one modification the session does make is declared, versioned and confined to a single ingredient.
2. Choose and clean the negative, and print nothing with it beforehand. A negative you have already printed tonight is a negative whose exposure you will unconsciously chase.
3. Make up the 10 per cent potassium bromide solution in daylight, before anything else: weigh 10.00 g into a 100 mL cylinder, dissolve, make to 100 mL, and label it with the substance, the strength, the date and your initials by the labelling procedure. This is the one preparation that must be right, because both bromide doses come out of it.
4. Write the two version records now, before you mix, by the versioning procedure, which issues the code before anything is weighed: D72-EB-001, D-72 exactly as the 1928 printing gives it; D72-EB-002, the same formula with potassium bromide raised from 1.9 to 3.8 g/L of stock and nothing else altered. Write the prediction for 002 in the notebook before you mix it. A prediction written afterwards is not a prediction.
5. Check the balance against its mass, and the thermometer against a second thermometer.
6. Lay out the dry side and the wet side of the bench with a gap between them, and do not carry a wet hand across it.
7. Fill the trays and set the tray order with the room lights on. Once they are off, nothing moves, and every sheet comes out of the packet by the dim-light handling procedure.

📓What D72-EB-002 is, and what the course is not claiming about it

Doubling the bromide is a change the course is making, not a formula anybody published. What can be said honestly is where it sits in the family. Across Kodak’s own paper developers the bromide runs from 0.9 g/L in D-158, through 1.9 in D-72 and 2.8 in D-163, to 6.3 in D-156 and 12.5 in D-166, the last two filed by Kodak as warm-tone developers with their carbonate reduced as their bromide rises.

So 3.8 g/L is inside the published span of the family, between D-163 and D-156. It is not inside any published formula: nobody has printed D-72 at 3.8 g/L, and at D-72’s own alkali and agent doses the outcome is unknown. That is the point of the arm. Predict it from the mechanism the previous lesson gave you — bromide restrains hydroquinone considerably more than it restrains metol — and then find out whether you were right.

Procedure

Five stages, about 150 minutes. The clock is dominated by the mixing, which cannot be rushed, and by the drying, which can be done while you read.

The session in five stages

1. 1Stage 1 — the bromide stock and the two D-72 batches (about 45 minutes)Dry side, lights on, Level B controls at the balance
2. 2Stage 2 — the bench, the baths and the repeatability control (about 20 minutes)Three developer trays, one shared stop, one shared fixer, one wash
3. 3Stage 3 — the base exposure, found once and used three times (about 20 minutes)
4. 4Stage 4 — arm 1, identical exposure; arm 2, matched black (about 45 minutes)Six sheets, each carrying its image and its contact wedge
5. 5Stage 5 — dry, read, record, bottle and label (about 20 minutes)

Stage 1 — mixing, on the dry side, with the lights on

Both batches follow Kodak’s own dissolving order, and the order is chemistry rather than custom. Kodak Limited give two reasons for it: metol goes in first because it is only slightly soluble in a sulfite solution that has no alkali in it, so a metol added after the sulfite may simply refuse to dissolve; and the sequence as a whole limits the time an agent spends in solution meeting air before the preservative arrives. They also note that potassium bromide may be added at any stage, which is why tonight’s one deliberate change can be made last, to a batch that is otherwise identical.

8. Measure 250 mL of distilled water at about 52 °C into a 600 mL beaker and stand the thermometer in it. Work the whole of this stage with the mask on and one jar open at a time.
9. Dissolve the metol, 1.55 g, completely, before anything else goes in. Stir until the solution is clear. It will look like nothing has happened; that is correct.
10. Add the sodium sulfite, 22.5 g, and stir until dissolved. The solution stays water-clear.
11. Add the hydroquinone, 6.10 g. This is the one that takes patience.
12. Add the sodium carbonate, 33.75 g. It dissolves readily and the beaker warms slightly.
13. Add the bromide as solution: draw 9.5 mL of the 10 per cent stock with the syringe and deliver it under the surface. Stir.
14. Make up to 500 mL with cold distilled water, stir thoroughly, and let it come to room temperature. Bottle it, fill to the shoulder, and label it D72-EB-001 with the date and the formula reference by the labelling procedure.
15. Repeat steps 8 to 14 exactly for the second batch, changing one number: 19.0 mL of the bromide stock instead of 9.5 mL. Label it D72-EB-002. Do not tell yourself you will remember which bottle is which.

✕The three ways this stage goes wrong, in order of how often

Adding the sulfite before the metol. The metol then dissolves slowly or not at all, you stir for ten minutes, and you finish with a developer of unknown metol concentration because some of it is still on the bottom of the beaker. Kodak state the rule; this is what it is protecting.

Weighing the carbonate as the crystals when the formula says anhydrous. The decahydrate is about two and a half times the weight for the same carbonate, so 33.75 g of crystals is roughly 13 g of anhydrous equivalent — a bath at a third of the intended alkalinity, which will look like an under-exposure fault all evening. The hydrate entry in the atlas is this mistake.

Making up to 500 mL by adding 500 mL. Solids occupy volume. Make up to the mark, never add the nominal volume to the solids — the atlas entry exists because this one is universal and invisible.

Stage 2 — the bench, the baths, and the boundary between them

16. Dilute each developer to its working strength, immediately before use, which is the maker’s own instruction for the concentrate and is good practice for the other two: 150 mL of D72-EB-001 to 750 mL with water at 20 °C — that is 1+4, one part of stock to four of water, which is the dilution Kodak print as 1:4 for bromide enlarging papers and the course writes in its own notation throughout; the same for D72-EB-002; and 75 mL of the concentrate to 750 mL, which is 1+9.
17. Make 1 L of stop at 1+19 and 1 L of fixer at 1+4.
18. Set the trays in a fixed order and put one pair of tongs in each developer and leave it there. The fourth pair lives in the stop and carries prints from the stop into the fixer. No pair of tongs ever enters a developer it did not start in, and no developer tongs ever touch the stop.
19. Bring every bath to 20 °C ± 1 °C, the wash water included, and write the four readings down.
20. Label a corner of the bench for the repeatability control: the last sheet of the evening will be a repeat of the first, in the same bath, and its job is to measure your process rather than your developers.

The bench, and the contamination boundary the design depends on

1. 1Balance in a tray, jars closed — the only place a powder is open
2. 2The boundary — no wet hand crosses it, no jar crosses it
3. 3Three developer dishes, three pairs of tongs — a pair never leaves its dish
4. 4Stop and fixer, one shared pair — travels only downstream
5. 5Wash, then the rack — the first wash is silver-bearing

Stage 3 — one base exposure, found once

The comparison needs a single exposure that all three developers receive. Find it in the reference bath, D72-EB-001, and then do not change it.

21. Put the negative in the carrier, set the head height and focus, and stop the lens to its working aperture. Write both down: a printing map that omits the head height is a map of nowhere.
22. Set filter 2, or the equivalent dial-in, and leave it there all evening. Contrast is not a variable tonight.
23. Expose a test strip in the usual cumulative way — 2 s, then 2 s more, then 4 s more, then 8 s more, which is the maker’s own first-print sequence and gives 2, 4, 8 and 16 seconds across the strip.
24. Develop it in D72-EB-001 for the session’s common time of 2 minutes at 20 °C, with the same agitation you will use all evening, then stop, fix, wash and dry it.
25. Choose the base exposure from the dry strip, not the wet one, and write down the light you chose it under.

⚗Why all three developers get two minutes, and what that assumption rests on

Fixing a common time is the whole design, and it needs a defence rather than an assertion.

What the sources publish. For this paper the maker gives its own concentrate at 1+9 one minute on resin-coated stock, and gives two of its other developers two minutes on the same stock. For D-72 at 1+4, Kodak’s 1928 printing gives one and a half minutes on bromide enlarging papers. Two minutes is therefore at or above every published minimum on the bench.

What justifies going past a published time. Paper is developed to completion. The same maker states that on correctly exposed fibre prints, development may be extended to six minutes without any noticeable change in contrast or fog — which is a published statement that the plateau is wide.

What the course is inferring, and marks as an inference. That six-minute statement is made for fibre prints in the maker’s own developers. Applying it to a resin-coated sheet, and to a ninety-eight-year-old Kodak formula, is the course’s reasoning and not the maker’s. It is a reasonable inference and it is testable, which is why the base-density column of your controls matters: if two minutes had lifted the fog, the unexposed control sheets would show it. If yours do, say so, and rerun the comparison at each developer’s own published time instead.

Stage 4 — the two arms

Every sheet in this stage carries two things: the projected image on most of the sheet, and the 21-step wedge contact-printed in a masked strip along one edge, given the same exposure through the enlarger with the lens capped for the projection and uncapped for the contact, or — simpler and what this page recommends — the wedge laid in the easel margin under the same beam for the same time.

26. Arm 1, identical exposure. Three sheets, one per developer, all at the base exposure from step 25, all developed 2 minutes at 20 °C with identical agitation: slide the sheet in smoothly, emulsion up, no bubbles, rock the dish continuously, lift ten seconds before the time and let it drain, as the maker’s own instruction has it. Ten seconds in the stop, thirty seconds in the fixer, two minutes in the wash.
27. Three control sheets. Half a sheet per developer, unexposed, straight into the developer, same time, same everything. These are the base-white and developer-fog readings and they are not optional: without them you cannot tell a developer that fogs from a paper that is fogged.
28. Read the arm 1 wedges wet enough to plan — the step at which each first separates from paper white — and compute the exposure change that would bring the two slower baths to the same first separated step as the fastest. One step of a nominal 0.15 wedge is half a stop, so the correction is in halves of a stop and comes straight off the timer.
29. Arm 2, matched black. Three more sheets at the corrected exposures. Now the developers are compared at the same place on their own curves, which is the only way to see what is left when speed has been taken out of the comparison.
30. The repeatability control. One last sheet: a repeat of the arm 1 print in D72-EB-001, at the same exposure, at the end of the session. Nothing about it is meant to be different. Whatever difference it shows is the noise floor of your process, and it is the number that decides which of tonight’s findings you are entitled to report.

Stage 5 — dry, read, record

31. Dry every sheet by one method, stated and recorded: air on a rack at room temperature, face up, for the 10 to 20 minutes the maker gives for this paper. Do not glaze or ferrotype a resin-coated sheet — the polythene sticks to the plate.
32. Read every wedge and every control dry, and read them all in one sitting.
33. Judge image colour with the dry prints side by side under one stated light source, and write the source down. A tone judgement made under a tungsten bulb and one made under daylight are two different judgements and neither travels.
34. Fill the printing map for every sheet. Then bottle, top up, cap and shelve the two stocks.

Expected observations

In the beaker. The metol solution stays clear; the hydroquinone takes the longest to dissolve of the five; the carbonate makes the beaker perceptibly warm. Both finished stocks are water-clear to faintly straw. A stock that is amber before you have used it has oxidised in the making — usually because the dissolving order slipped — and the honest response is to discard it rather than to print with an unknown.

In the tray. The image appears. Write down when: emergence time is the cheapest diagnostic in printing and it is the number you will want in three weeks when a bath is dying. This paper’s maker publishes about 10 seconds for a correctly exposed print in their concentrate at 1+9; D-72 at 1 in 4 is a different bath and no published emergence time exists for it on a modern paper, so yours is the measurement, and it belongs in the record with the rest.

Between the arms. Expect the differences to be smaller than you hoped and larger than nothing. The prediction the mechanism supports — more bromide restrains hydroquinone more than metol, so the bromide-heavy bath should be slower, cleaner in the whites and possibly warmer in tone — is a prediction and not a result. The bought concentrate is a modern dimezone-s formulation designed for this paper family and may well be the fastest of the three.

In the controls. All three unexposed sheets should be close to the paper’s own base. A control that is grey is telling you something about the developer, not about the print, and developer fog on paper is where that goes.

What is happening chemically

Nothing tonight is new chemistry, and that is worth saying plainly: the whole session is Part VIII applied to a different material at a different pH. What the bench adds is the ability to move one term at a time.

The reduction is the same one:

AgBr(s) + e⁻ → Ag(s) + Br⁻

Every developed grain, and every bromide ion it releases into the bath

and the electron is paid for by the agent, written for the alkaline bath it works in:

C₆H₆O₂ + 2 OH⁻ → C₆H₄O₂ + 2 H₂O + 2 e⁻

Hydroquinone oxidised — and the reason a carbonate bath is not an optional refinement

Three consequences of those two lines govern the evening.

The bromide you add and the bromide development makes are the same ion. A restrainer works by raising the bromide concentration at the crystal surface before development starts, and development then raises it further with every grain reduced. That is why D72-EB-002 is not merely “the same developer, slower”: it starts where D72-EB-001 finishes, and a bath’s whole history is written in that one concentration. It is also why the capacity of a tray falls as it works, and why an exhausted bath cannot be rescued by adding fresh concentrate — you would be adding agent to a bath whose bromide you no longer know.

Restraint is not even-handed. Kodak’s 1928 primer states it directly: a small quantity of bromide affects hydroquinone considerably, and does not affect metol nearly so much. A metol–hydroquinone developer is therefore not one developer with a rate but two agents with different sensitivities to the same knob, and turning the bromide up shifts the balance between them as well as slowing the whole. The visible consequences the course expects — cleaner whites, a slower bath, a possible shift in image colour — all follow from that asymmetry, and the tone shift in particular is the course’s own reading rather than a statement any of these sources makes.

The tray is a reactor with an enormous free surface. A 10 × 12 in dish presents roughly 0.08 m² of air–liquid interface, and at pH 10.5 hydroquinone oxidises quickly in air. That is why the maker instructs mixing the working solution directly before use and why Kodak’s own 1949 table gives D-72 24 hours standing in a dish against three months in a full stoppered bottle. Nothing you do tonight changes that; the design merely holds it equal across the three trays by mixing all three at the same moment.

🧮Scaling a formula, and the precision your balance actually gives you

The arithmetic is trivial and the discipline is not.

m = m₁ × (V / V₁)

Scaling a published formula

m is the mass you weigh, m₁ the mass the source gives, V the volume you are making and V₁ the volume the source makes. For hydroquinone at 500 mL: 12.2 × (500 / 1000) = 6.10 g.

The discipline is the second step. Your balance reads to 0.01 g, so 6.10 g carries a relative uncertainty of about 0.16 per cent and the smallest weight, the 0.95 g of bromide, carries about 1.05 per cent — which is why this page doses the bromide from a 10 per cent solution instead. Kodak printed that alternative themselves, and it is not a convenience: weighing 10.00 g once to make the stock is a 0.1 per cent error, and every dose drawn from it inherits that rather than the 1 per cent you would incur weighing under a gram five times.

Do not write 6.100 g in the notebook. Three decimal places on a two-decimal balance is a claim you did not make, and the whole point of the version record is that a reader in three years can tell what you actually knew.

Data to record

This is the section the rest of the course leans on, and it has two halves that people routinely collapse into one. The session log is one line per batch. The printing map is one sheet per print. They answer different questions and neither substitutes for the other.

The session log

One line, written at the bench: date; the two version numbers and their mixing times; the balance’s check result; every bath’s measured temperature; the paper, its surface and its box code; the developers’ emergence times; the number of sheets through each bath against its published capacity; the fixer’s running total; the wash route; the drying method; the light the prints were judged under; and the waste routed. The print-processing archival sequence specifies what that line has to carry for a print you intend to keep, and this page does not repeat it.

The printing map

📓What a printing map is, and why a print without one cannot be repeated

A printing map is the written record of everything done to make one print, kept with the negative rather than in a general log, so that the print can be made again. It is the single most important habit in this half of the course, and Parts XIX to XXV all assume you have it.

What goes on it, in the order the work happens:

1. The negative — its identifier, and its measured density range if you have one.
2. The geometry — head height, lens, working aperture, easel size and the borders. Change any of these and every time on the sheet is wrong.
3. The contrast — the filter or the dial-in, and which paper the range figure came from.
4. The base exposure, in stops rather than only in seconds. Part XVII’s arithmetic is what makes this travel: seconds belong to one head height and stops belong to the print.
5. Every dodge and every burn as its own line, with the area named and the amount in stops. Never netted off. A face dodged a third and a sky burned two thirds are two instructions.
6. The paper — maker, product, surface, weight, size, box code, and which side you printed on.
7. The chemistry — developer id and version, dilution, temperature, time, agitation scheme; stop; fixer, which bath and its running total; wash route; and the drying method by name.
8. The dry-down correction applied, and where it came from — which is the number the next page measures.
9. The judgement conditions — the light you assessed the dry print under.
10. The date, and the sheet’s own number in the session.

Why a print without one cannot be repeated. Look at that list: it is about fifteen independent settings, and human memory reliably retains two of them. A print is not a single act but the intersection of all fifteen, and the intersection is not recoverable by inspection — you cannot look at a dry print and read its head height off it. So a printer without a map is not revising in the second session, they are searching again, from a slightly different starting point, having lost whatever was good about the first attempt.

There is a sharper reason for tonight in particular. The differences this lab is trying to measure are smaller than the drift between two unrecorded sessions. If your developer comparison and your process noise are the same size, the comparison has no content, and the only thing standing between you and that outcome is the map.

The map is also what makes a print’s authorship checkable. Everything a fine print owes to the darkroom is on it, which is what lets a printer say honestly what was done to a photograph.

The comparison grid

One table, three rows, filled from the dry sheets:

Per developer	What to enter
Version or product, and dilution	D72-EB-001 at 1+4, D72-EB-002 at 1+4, the concentrate at 1+9
Emergence time, seconds	Measured, at the base exposure
Maximum black	Reflection density of the darkest wedge step, or the step number at which the wedge stops darkening
Base white	Reflection density of the unexposed processed control, not of the raw paper
First separated step	The first wedge step distinguishable from paper white
Image colour	In words, with the light source named
Arm 2 exposure correction	In stops, relative to arm 1
Repeatability	The difference between the two D72-EB-001 prints, in the same units

Analysis

First, work out what you are allowed to claim. Take the repeatability control from step 30 and compare it with its twin from arm 1. Whatever separates those two sheets — a hundredth or two of reflection density if you measured, a step or nothing if you judged — is your noise floor. Any difference between developers smaller than it is not a result. Write the floor at the top of the analysis, before the findings, so it constrains them.

Second, separate speed from everything else. Arm 1 answers how much density did each bath produce from the same light. Arm 2 answers what is different once they are all at the same black. Those are different questions and the usual muddle in developer comparisons is reporting the first as though it answered the second. If your bromide-heavy bath needed half a stop more exposure and then matched D72-EB-001 at every step, the honest finding is “the bromide cost half a stop of paper speed and changed nothing else that this method can see” — which is a real result, and a more useful one than a vague claim about deeper blacks.

Third, read the two ends separately. Maximum black is a ceiling set mostly by the paper and the surface: the maker publishes 2.15 for the current version of this paper against 2.05 for the one it replaced, on the same base. If your three developers all reach the same maximum black, that is the expected outcome and not a failure of the experiment — the developer’s leverage is at the other end, in the base white and the first few steps, where the restrainer works.

Fourth, be careful with colour. Image colour is the least measurable and most reported quantity in printing. You have three dry prints, one light source and no instrument. What you can honestly write is a ranked statement — “002 read warmer than 001 side by side under the stated lamp; the concentrate sat between them” — and not a magnitude. Rank comparisons made side by side under one light are reliable; remembered comparisons across sessions are not.

Fifth, ask what a second run would settle. Almost every finding tonight rests on one sheet per cell. Name the two findings you would most want to repeat, and say what the repeat would need: another evening, another paper batch, or the same evening with the tray order reversed to see whether position in the sequence mattered.

Troubleshooting

What you see	Where to look
Prints flat and grey in one bath only, whites clean	That bath. Exhausted developer is unlikely on a fresh mix; suspect the dilution or a missed ingredient
Whites grey on every print including the controls	Not the developer comparison. Developer fog on paper if the controls are grey, paper storage fog if a fresh packet is clean, and Part XVI’s page if neither
A print mottled and weak, with the pattern of the first flow of developer	Muddy print from snatched development — the sheet came out early, or the agitation stalled in the first thirty seconds
A bath amber before it was used	Oxidised developer. The dissolving order or an old jar of sulfite
Milky patches in the clear areas after fixing	Under-fixing, and the shared fixer affects all three arms at once
Yellowing in the borders as the prints dry	Residual silver and yellow staining — a fixer question, not a developer question
Parallel drag marks down a print	Squeegee lines on prints, which is a drying fault and will corrupt a density reading
The two D-72 baths behave identically	Check the syringe volumes in the notebook. This is the most likely single failure of the session, and it is silent

Clean-up

Tongs, dishes and cylinders washed in the order developer, stop, fixer and rinsed between, so that nothing travels upstream. The bromide syringe rinsed three times and dried. The balance brushed, its tray wiped, and the five jars capped and returned to storage — the sulfite in particular, which is the shortest-lived thing on the shelf once opened. Bench wiped down with the gloves still on, gloves off last. Run lab closing.

Storage

The two stocks go into full, tightly closed bottles, filled to the shoulder and labelled with the version, the date and the maker of every ingredient. Kodak’s own keeping figures for D-72 are on the formula page and are the numbers to plan against: three months in a full stoppered bottle, one month in a half-full one, and twenty-four hours standing in a dish. The bought concentrate keeps unopened for two years at 5 to 20 °C on its maker’s statement and six months once opened; its working solution, like both of yours, should not be kept beyond one working day in an open dish.

The keeping test, which is the point of writing the date on the label. In four weeks, mix a fresh working bath from the kept D72-EB-001, print the wedge again at tonight’s exposure and time, and compare two numbers against tonight’s record: the first separated step and the maximum black. If they have moved, you have measured your own storage rather than repeating somebody’s shelf-life claim. If they have not, you have earned the right to trust the bottle for another month.

Disposal considerations

Spent paper developer is an alkaline solution of an aminophenol and a dihydroxybenzene, both classified as very toxic to aquatic life; it carries negligible silver on Kodak’s own table, so its problem is toxicity and pH rather than metal. Spent stop is a dilute weak acid, and its only real hazard is what happens if it meets the sulfite in the developer container. Spent fixer and the first wash are silver-bearing and are the stream that matters most: they hold dissolved silver complexes, and the chemistry and the recovery routes belong to Part XII.

The general practice is to collect each stream separately, keep it labelled and closed, and take it to a facility that accepts it. In the United Kingdom, ILFORD’s own advice to domestic users is a household waste and recycling centre rather than a drain, and the government’s hazardous-waste service is where you find the nearest one. Local regulation governs, and what a household may lawfully do with any of these streams differs by jurisdiction and sometimes by street. Check your local regulations, and read the disposal caveat before you decide anything from this paragraph.

Questions

1. You mix D72-EB-002 and find it needs two thirds of a stop more exposure than D72-EB-001 to reach the same first separated step, but reaches an identical maximum black. What has the extra bromide done, and what has it demonstrably not done?
2. Your repeatability control differs from its twin by more than the difference between two of your developers. Write, in one sentence, what you may report from tonight.
3. The formula offers potassium bromide as “1.9 g or 19 mL of a 10 per cent solution”. Show that these are the same dose, and give the reason a careful worker prefers the second.
4. All three of tonight’s baths reached the same maximum black. A printer concludes that print developers do not affect maximum black. What is wrong with the inference, and what experiment would test the claim properly?
5. You develop for two minutes where the paper’s maker publishes one. Name the published statement that makes this defensible, name the part of the argument that is the course’s own inference, and name the observation on tonight’s sheets that would falsify it.
6. A friend asks which of the three developers is best. Answer in two sentences, one of which must name a quantity you measured and one of which must name something you cannot say about the concentrate that you can say about the other two.

Further experiments

Move the alkali instead of the restrainer. Mix a third batch at D-72’s bromide with the carbonate reduced by a third, versioned as D72-EB-003, and print it against 001. The previous lesson’s design table predicts a slower, cleaner, warmer bath; this measures how much of that comes from the alkali alone.

Run the dilution series the source published. D-72 has three published dilutions, one per paper family, and the 1928 primer notes that one paper developed at another’s dilution goes colder. Print the same negative at 1+1, 1+2 and 1+4 with the time adjusted to keep every arm inside its plateau, and find out whether a modern variable-contrast paper still shows that shift.

Measure the capacity you were given. The concentrate’s maker publishes 100 resin-coated 8 × 10 prints per litre at 1+9. Print a wedge strip after every tenth sheet through one litre and plot the first separated step against sheet count. Where the curve turns is your capacity, and comparing it with the published figure is a measurement of your agitation, your tray and your session length as much as of the developer.

Take one bath overnight and print from it in the morning. Kodak’s dish life for D-72 is twenty-four hours; the concentrate’s maker gives one working day. Leave a covered tray and an uncovered tray side by side, print the same wedge from both, and put a number on the difference a floating lid makes.

Recap

• The session’s discipline is one sentence: only the developer changes. Paper, exposure, filter, time, temperature, agitation, drying and viewing light are all held, and the design is worth more than the chemistry it measures.
• The dissolving order is chemistry. Metol first because it is barely soluble in a sulfite solution without alkali; the sequence as a whole to limit an agent’s time in air. Bromide may go in at any stage, which is what makes a single-variable change possible.
• Dose a small quantity as a solution. 19 mL of a 10 per cent stock is 1.9 g at a tenth of the weighing error, and Kodak printed the alternative themselves.
• A deliberate change gets a version number and a written prediction. D72-EB-002 is inside the published bromide span of the Kodak paper family and inside no published formula, and the page says which of those two things it is.
• Two arms, because speed and everything else are different questions. Identical exposure measures the speed difference; matched black measures what survives once speed is removed.
• The repeatability control decides what you may claim. A difference smaller than your own noise floor is not a finding.
• The printing map is one sheet per print and the session log is one line per batch. Fifteen settings intersect in a print and memory keeps two of them; without the map the second session is a fresh search rather than a revision.
• Bottle, label, date — and then test the keeping rather than quoting it.

Check your understanding

Question 1. You are making 500 mL of D-72 stock and your balance reads to 0.01 g. Which single weight in the formula most limits the accuracy of the batch, and what does the source itself offer as the fix?

• The sodium carbonate at 33.75 g, because it is the largest weight and therefore the largest absolute error
• The potassium bromide at 0.95 g, because a ±0.01 g uncertainty is about 1 per cent of it — and the source offers the same dose as 9.5 mL of a 10 per cent solution instead
• The hydroquinone at 6.10 g, because it is the contrast agent
• None of them: a 0.01 g balance is adequate for every weight in the formula

Show the answer and why

Answer: The potassium bromide at 0.95 g, because a ±0.01 g uncertainty is about 1 per cent of it — and the source offers the same dose as 9.5 mL of a 10 per cent solution instead

Accuracy is relative, not absolute. A ±0.01 g uncertainty on 33.75 g is three hundredths of a per cent and on 0.95 g it is about 1.05 per cent, so the smallest weight is always the weakest link in a scaled formula. Kodak print the alternative in the same table — 1.9 g or 19 mL of a 10 per cent solution per litre — and it is an accuracy improvement rather than a convenience, because weighing 10.00 g once to make the stock is a 0.1 per cent error that every subsequent dose inherits.

Question 2. You develop the same negative in three baths at the same exposure. The bromide-boosted bath gives a visibly lighter print. A printer concludes the extra bromide has lowered the paper’s maximum black. What is wrong with that, and what settles it?

• Nothing is wrong: a lighter print means a lower maximum black
• The lighter print shows a speed difference, not a ceiling difference — the arm-2 print, re-exposed to reach the same first separated step, is what shows whether maximum black actually moved
• The conclusion is right but the mechanism is wrong: bromide dissolves developed silver
• Maximum black cannot be affected by a developer under any circumstances

Show the answer and why

Answer: The lighter print shows a speed difference, not a ceiling difference — the arm-2 print, re-exposed to reach the same first separated step, is what shows whether maximum black actually moved

A restrainer raises the exposure needed to reach any given density, which makes the whole print lighter at a fixed exposure. That is a shift along the exposure axis and says nothing about where the curve tops out. Maximum black is a ceiling set mostly by the paper and its surface — the maker publishes 2.15 for this paper and 2.05 for its predecessor on the same base — and the only way to test whether a developer moved it is to give each bath the exposure it needs to reach its own top and then read the top. That is exactly why the session has two arms.

Question 3. Your repeatability control differs from its twin, printed in the same bath at the same exposure earlier in the session, by more than any difference you measured between the three developers. What may you report?

• The developer differences, since they were measured first and the control drifted afterwards
• That the process noise exceeded the effect, so no difference between the developers is established by this session — and that is itself a finding worth writing down
• The average of the three developers, which cancels the noise
• Nothing at all; the session is wasted and the data should be discarded

Show the answer and why

Answer: That the process noise exceeded the effect, so no difference between the developers is established by this session — and that is itself a finding worth writing down

A comparison can only resolve differences larger than its own repeatability, and the control exists to measure that floor rather than to be a spare print. Reporting an effect smaller than the noise is the commonest failure in darkroom testing, and it is what makes so much printing advice irreproducible. The session is not wasted: you have measured your own process stability, which tells you what a second run needs — more sheets per cell, tighter temperature control, or a larger deliberate change — and the data stay in the notebook as the baseline that second run is compared with.

Question 4. Two prints from tonight look identical in the tray and different when dry. Which record makes that observation usable a month from now?

• The session log, because it holds the developer versions
• The printing map for each sheet, because it holds the geometry, the exposure in stops, the paper and box code, the chemistry with its version, the drying method and the light each print was judged under
• The bottle labels, since they carry the mixing dates
• A note in the margin saying which print was better

Show the answer and why

Answer: The printing map for each sheet, because it holds the geometry, the exposure in stops, the paper and box code, the chemistry with its version, the drying method and the light each print was judged under

The session log is one line per batch and answers what was on the bench; the map is one sheet per print and answers what was done to this sheet. Only the map carries the fifteen or so settings whose intersection a print is, including the two that decide whether a wet-versus-dry observation means anything at all: the drying method and the viewing light. Without them the observation is an anecdote, because you cannot tell later whether the difference belonged to the developer, the drying or the lamp.

Question 5. Why does this page develop every arm for two minutes when the paper’s own maker publishes one minute for the concentrate at 1+9?

• Because longer development always gives deeper blacks on paper
• Because a common time is required by the design, two minutes is at or above every published minimum on the bench, and the maker publishes that development may be extended to six minutes without noticeable change in contrast or fog — with the transfer of that fibre-paper statement to this material marked as the course’s inference and tested by the control sheets
• Because D-72 is an old formula and old formulas need longer
• Because two minutes is the standard development time for all photographic papers

Show the answer and why

Answer: Because a common time is required by the design, two minutes is at or above every published minimum on the bench, and the maker publishes that development may be extended to six minutes without noticeable change in contrast or fog — with the transfer of that fibre-paper statement to this material marked as the course’s inference and tested by the control sheets

Holding the time constant is what makes the developer the only variable, so the question becomes whether a single time can be inside every bath’s plateau at once. Two minutes clears every published minimum here, and the six-minute ceiling published for fibre prints in the maker’s own developers is the evidence that the plateau is wide. But that statement was made for a different support and different developers, so applying it to this material and to a Kodak formula from 1928 is reasoning the course is doing, not a claim the maker made — which is why the page says so and why the unexposed control sheets are the falsification test: if two minutes had lifted the fog, they would show it.

Question 6. You have spent fixer, spent alkaline developer and spent stop bath at the end of the session. Which pairing is the one the procedure is specifically designed to prevent, and why?

• Fixer and developer, because the mixture fogs paper
• Stop bath and developer, because an acid meeting a sulfite-bearing alkaline solution in a closed container is the avoidable incident of the evening
• Fixer and stop, because both are acidic
• Developer and wash water, because of the pH change

Show the answer and why

Answer: Stop bath and developer, because an acid meeting a sulfite-bearing alkaline solution in a closed container is the avoidable incident of the evening

Sulfite releases sulfur dioxide when it meets an acid, and a paper developer carries 45 g of sulfite per litre of stock. That is why the session keeps the whole mixing half alkaline from the first gram, why the stop bath lives on the other side of a stated boundary with its own tongs, and why the waste containers are separate and labelled rather than merely different. The developer-into-fixer direction is a real problem too — it is what shortens a fixer’s life and why the stop exists at all — but it is a quality fault rather than a gas.

Check my answersClear