Print Developer Chemistry and the Developer-Paper Pair

Set a film developer and a paper developer side by side and the difference is not subtle. Kodak’s D-76 carries two grams of borax per litre and no bromide at all. Kodak’s D-72, the archetype paper developer, carries sixty-seven and a half grams of sodium carbonate and 1.9 grams of potassium bromide. Both contain metol and hydroquinone. Both develop silver. They are built to answer different questions.

Everything on this page is Part VIII’s chemistry applied to a new material — agents, alkalis, preservatives, restrainers, superadditivity and kinetics are all assumed here and none of them is re-derived. What is new is the brief.

The design brief of a paper developer

What the developer has to do, and what each requirement forces

1. 1Develop a very thin, very fine-grained emulsionless silver, smaller crystals, and no need for the solvent action that keeps a film’s grain down
2. 2To completion, in one to three minutesso the reaction must be fast, which means a high pH
3. 3At room temperature20 °C, in an open tray, with no thermostat — so speed cannot be bought with heat
4. 4Leaving a clean white baseno fog at all, on a material whose whites are the reference for everything — so heavy restraint
5. 5In an open dish, for a sessiona large free surface, so oxidation is designed for rather than avoided

Contrast that with a film developer’s brief and the differences fall out. A film is developed to a chosen contrast and pulled out at a time that sets it, in a closed tank, at a controlled temperature, where grain matters and base fog is measured but small. A print is developed until nothing more happens, in a dish, in front of you, and the whiteness of its base is the thing the whole print is judged against.

Two agents, and the modern substitution

Print developers are almost all two-agent developers, and they come in two families.

MQ — metol and hydroquinone — is the classical pair, and every Kodak formula in this course’s paper library is one. PQ — Phenidone and hydroquinone — replaces the metol with a pyrazolidone at a tenth of the dose, and is what most modern products are. Part VIII’s superadditivity page explains why either pair develops faster than the sum of its parts: the fast agent does the reducing at the grain and the hydroquinone regenerates it from solution, so the fast agent is a catalyst that is continuously restored rather than a reagent that is consumed.

Nothing about that is different on paper. What is different is which pair the makers use now, and they tell you.

⚗Dimezone S — the substance on the packet that nobody explains

ILFORD describe MULTIGRADE developer and PQ UNIVERSAL as “dimezone-s/hydroquinone” developers and BROMOPHEN as a “phenidone/hydroquinone” one. Three of the four ILFORD paper developers in the corpus therefore run on Dimezone S rather than on Phenidone.

Dimezone S is 4-hydroxymethyl-4-methyl-1-phenyl-3-pyrazolidinone: Phenidone with a methyl and a hydroxymethyl group added at the 4-position of the ring. The chemistry of the superadditive pair is unchanged — it is a pyrazolidone doing a pyrazolidone’s job — and what the substitution buys is solution stability, which is why it appears in liquid concentrates and Phenidone appears in BROMOPHEN’s powder. That reading is the course’s inference from where each substance is used, and not an ILFORD statement; ILFORD name the substances and explain nothing.

For a home worker the practical point is different and worth saying plainly: you will never weigh Dimezone S. It is not sold in gram quantities to individuals in the way metol and hydroquinone are. It is a substance to recognise on a datasheet, so that you know a bought concentrate is a PQ-type developer and behaves like one.

Foma give the third variation. FOMATOL LQN is phenidone–hydroquinone; FOMATOL P is phenidone–isoascorbate, a powder developer with no hydroquinone in it at all, using the ascorbate chemistry Part VIII met as the regenerating partner instead.

The alkali, and why paper runs two pH units hotter

Here is the number that defines the whole subject, and ILFORD publish it:

Solution	Published pH at 20 °C
ILFORD MULTIGRADE developer, 1+9	10.45 – 10.55
ILFORD PQ UNIVERSAL, 1+9	10.48 – 10.58
ILFORD BROMOPHEN stock	10.30 – 10.50
ILFORD ID-11 film developer, stock	8.60 – 8.70

Part VIII worked out what that gap means and the answer is not “a bit more alkaline”: the hydroxide-ion concentrations differ by about five orders of magnitude. A developing agent works as its anion, the fraction ionised is set by pH against the agent’s pK_a, and at 10.5 hydroquinone is substantially ionised where at 8.65 it is barely started.

🧮Why the brief forces the pH, in one argument

The paper has to be developed to completion in about ninety seconds at 20 °C. Completion means every developable crystal reduced, not a chosen fraction of them. There are only three ways to make a reaction go faster: raise the temperature, raise the concentration, or change the equilibrium that governs how much of the reagent is in its active form.

Temperature is fixed at room temperature by the brief — an open dish has no thermostat and ILFORD warn that high temperatures cut solution life sharply and give times too short to agitate evenly. Concentration of the agents is limited by solubility and by cost. That leaves pH, and pH is enormously effective because it acts on the fraction ionised rather than on the amount present.

So the carbonate load follows from the ninety seconds. Kodak’s 1928 primer says the same thing from the other end, and names the price: more alkali means more energy, and also more chemical fog and more softening of the gelatin. A paper developer is a bath deliberately run near the edge of fogging, which is exactly why the next section exists.

The buffer’s job is the one Part X and Part VIII already established, and it is doing more work in a tray than in a tank: prints come out of the developer carrying alkali and go into acid, and the tongs and fingers that come back carry a little acid the other way. A carbonate bath holds its pH against that while a borate one would not, which is why paper developers are carbonate developers and why ILFORD can publish a capacity in prints rather than a life in minutes.

The restrainer, and the design space it opens

Now the Kodak paper library, all from one 1949 handbook and one 1928 primer, arranged so that the design space is visible. Every figure is per litre of stock.

Formula	Metol	Sulfite	Hydroquinone	Carbonate	Bromide	Stated purpose
D-76 (film)	2.0	100	5.0	borax 2.0	0	fine grain on film
D-158	3.2	50	13.3	69	0.9	Velox, blue-black tone
D-72	3.1	45	12.2	67.5	1.9	the archetype paper developer
D-49	3.1	45	11.5	45	2.1	portrait bromide papers
D-163	2.3	75	17.0	65	2.8	universal, normal to high contrast
D-52	1.5	22.5	6.3	15	added at the tray	four bromide doses, one per paper
D-156	1.7	22	6.8	16	6.3	warm tone
D-166	1.15	25	8.5	25	12.5	extra warm tone

Read the last two columns together and the whole family resolves into one movement. As the carbonate falls, the bromide rises, and the image goes warm. D-72 is 67.5 g of carbonate against 1.9 g of bromide; D-166 is 25 against 12.5. The blue-black Velox developer D-158 sits at the other extreme with the most alkali in the library and the least bromide.

Why does paper need so much more restraint than film? Three reasons, and they compound.

The pH is higher, so the bath is nearer chemical fog, and Kodak’s primer names alkali quantity as a cause of it directly.

The white matters absolutely. A film’s base fog is subtracted out when the print is exposed. A print’s base fog is the highlight, and there is nothing downstream to remove it.

Bromide is the by-product, so restraint by mass action is free chemistry rather than an additive foreign to the reaction. Development releases bromide ion:

AgBr + e⁻ → Ag + Br⁻

What development puts into the bath, and what a restrainer supplies in advance

⚗Why the restrainer moves the tone as well as the fog

Kodak’s 1928 primer makes the observation that turns bromide from a fog control into a tone control: a small quantity of bromide “affects hydroquinone and does not affect Elon nearly so much”, and the higher an agent’s reduction potential the more bromide is needed for a given effect.

The two agents are therefore restrained unequally. Add bromide and the hydroquinone half of the pair is slowed more than the metol half, so the balance of the superadditive pair shifts and the image is built at a different rate and in a different form. Since image colour is developed particle size, a change in the rate of deposition is a change in the colour. That is the mechanism behind the whole right-hand column of the table above.

Rule 7 note. The unequal restraint is Kodak’s published statement. The step from it to image colour is the course’s own reading, consistent with Getty’s account of warm tone as restricted particle growth and with the fact that Kodak filed D-156 and D-166 under warm tone and put five and ten times the bromide in them. No source in the corpus states the chain in those words.

Organic antifoggants are the other route, and the difference is one of scale. Benzotriazole and 6-nitrobenzimidazole are dosed in fractions of a gram where a bromide is dosed in grams, because they act by forming an extremely insoluble silver salt on the crystal surface rather than by mass action on an equilibrium. Part VIII owns that distinction and the course keeps the words apart: a restrainer works by mass action, an antifoggant is the organic compound. Neither Kodak’s paper formulas nor ILFORD’s published descriptions state a benzotriazole concentration for a paper developer, so no figure is given here; what the course can say is the ratio of scales and the mechanism.

Development to completion

This is the single largest difference between developing film and developing paper, and getting it wrong is the most common fault in a beginner’s darkroom.

ILFORD state the plateau: with MULTIGRADE developer at 1+9 the recommended time for a fibre paper is 1½ to 3 minutes, and development can be extended up to 6 minutes “without any noticeable change in contrast or fog”. Kodak’s paper-chemicals sheet gives DEKTOL at ¾ to 3 minutes for RC papers and ¾ to 4 minutes for fibre. Those are ranges within a plateau, not a scale of contrast.

What extends and what does not, as development goes on

• Maximum black — rises to a limit
• Base density — rises without one

Show the numbers behind this plot

Two curves against development time. The maximum black rises steeply for the first minute, reaches a plateau at about ninety seconds and is flat from there to six minutes and beyond. The base density starts near zero, stays low through the recommended range, and then begins to climb slowly and does not stop. The useful window is the region where the first curve has flattened and the second has not yet lifted.

Series	Development time, minutes	Reflection density
Maximum black — rises to a limit	0.00	0.00
Maximum black — rises to a limit	0.25	0.15
Maximum black — rises to a limit	0.50	0.70
Maximum black — rises to a limit	0.75	1.35
Maximum black — rises to a limit	1.00	1.80
Maximum black — rises to a limit	1.25	2.00
Maximum black — rises to a limit	1.50	2.10
Maximum black — rises to a limit	2.00	2.14
Maximum black — rises to a limit	3.00	2.15
Maximum black — rises to a limit	4.00	2.15
Maximum black — rises to a limit	6.00	2.15
Maximum black — rises to a limit	8.00	2.15
Base density — rises without one	0.00	0.04
Base density — rises without one	0.50	0.04
Base density — rises without one	1.00	0.04
Base density — rises without one	1.50	0.05
Base density — rises without one	2.00	0.06
Base density — rises without one	3.00	0.07
Base density — rises without one	4.00	0.09
Base density — rises without one	6.00	0.15
Base density — rises without one	8.00	0.23

Drawn, not measured. The shape is the argument: one quantity saturates and the other does not. The experiment in this part measures the real pair for one paper and one developer, and the numbers it returns are yours. The curve is drawn to show the shape, not measured from a real material. Your own materials will differ, and measuring them is what the sensitometry part of the course is for.

Two things change when development is extended, and they change differently. The maximum black rises to a limit — there are only so many developable crystals, and once they are all reduced no further time can add density. Base fog rises without a limit, because unexposed crystals go on turning over slowly for as long as the sheet is in the bath. The useful window is where the first has flattened and the second has not yet lifted, and it is wide: ILFORD’s six minutes against a recommended ninety seconds.

✕Snatching a print is not the same as printing it lighter

The habit is universal and it is wrong: the print looks too dark in the tray, so it comes out early.

What that gives is not a lighter print. It is an incompletely developed one. ILFORD’s own words on the RC sheet: “Prints developed for shorter times may be underdeveloped and lacking in contrast and density.” The blacks never reached their limit, so they are weak and often slightly warm — silver caught mid-deposition is finer than silver fully deposited — and because agitation is never perfectly even for the first thirty seconds, the shortfall is uneven: mottled, with the pattern of the way the developer first flowed across the sheet.

The atlas has the entry: muddy print from snatched development.

What to do instead is trivial and is the whole discipline of printing: leave the print in for its full time, and give it less exposure next time. Time is not the exposure control. The enlarger is.

One more published number belongs here, because it is the one you actually watch. Emergence time — when the image first appears — is a manufacturer-published property of a correctly exposed print, and it is the most useful diagnostic in the tray. ILFORD: approximately 10 seconds for RC and 20 to 35 seconds for fibre with MULTIGRADE 1+9. Kodak’s D-166 states about 50 seconds at its published dilution and time. An image that appears in three seconds is over-exposed; one that has not appeared in a minute is under-exposed or the developer is dying.

Capacity and exhaustion, which are not the same thing

The course keeps these words apart deliberately. Capacity is how much work a bath can do before its performance falls outside what you will accept. Exhaustion is the state of having done it. One is a published quantity; the other is a condition you diagnose.

The published capacities are worth having in one place:

Developer	Dilution	8 × 10 prints per litre, RC	per litre, FB
ILFORD MULTIGRADE	1+9	100	50
ILFORD MULTIGRADE	1+14	70	40
ILFORD PQ UNIVERSAL	1+9	70	45
ILFORD BROMOPHEN	1+3	70	45
Kodak DEKTOL	1:2	32 (120 per US gallon)	32
Kodak D-163	1:3	—	~6.6 (30 per 4.55 L)
Kodak D-163	1:1	—	~7.9 (36 per 4.55 L)

Two columns of that table need a word of caution about what the sources actually say. Kodak publish one figure, not two: E-103CP gives DEKTOL a useful capacity of 120 8 × 10 sheets per US gallon without separating RC from fibre, and the same figure is entered in both columns here. The 1949 figures are per 160 imperial fluid ounces, which is 4.55 litres, and they are fibre figures by default because resin-coated paper did not exist in 1949. Only ILFORD publish the two supports apart.

Two things jump out. A fibre print costs about twice a resin-coated one, because it carries far more developer away in its base. And the older formulas are far less economical than the modern concentrates — D-163 at about seven 8 × 10 prints per litre against MULTIGRADE’s fifty. Kodak also publish a time limit alongside the count: DEKTOL and POLYMAX T working solutions last one working day in a tray, whatever their remaining capacity.

📓The symptoms of an exhausting bath, in the order they arrive

Learn the order, because the first two are easy to mistake for an exposure error.

1. Longer emergence. The image takes noticeably longer to appear than the maker’s published figure. This is the earliest sign and the cheapest to check, which is why the emergence time is worth writing down when the bath is fresh.
2. Weaker blacks. The maximum black falls short at the full development time. The print looks flat rather than light.
3. A warmer tone. Kodak’s 1949 table says it in as many words for the warm-tone developer D-156, where the useful-life column reads: “exhaustion affects colour of image; life depends on quality required.” That is a maker declining to publish a number because the endpoint is a judgement about colour.
4. Staining. Oxidised developer products in a dying bath stain the base, and the stain does not wash out.

The atlas entries are exhausted developer, grey highlights from developer exhaustion and developer fog on paper.

An exhausted tray is discarded, not extended. There is no replenishment scheme for a tray of print developer in any source in this corpus, and topping up a spent bath with fresh concentrate gives you a bath of unknown bromide concentration and unknown pH, which is a bath whose behaviour you no longer know.

Aerial oxidation, which is why a print developer dies faster than a film developer

A tray has an enormous free surface and a filled tank has almost none. Part VIII’s aerial oxidation experiment established the chemistry and measured it; the point here is the geometry, and it is arithmetic you can do yourself. A 12 × 16 inch dish is 305 × 406 mm, so a litre of developer in it presents about 0.12 m² of air-liquid interface. The same litre in a daylight tank filled to its neck presents the area of the neck and nothing else. Put that surface at pH 10.5, where hydroquinone oxidises fastest, and the tray is a device for exposing developer to air.

The published shelf lives track this exactly, and they are the strongest evidence for the mechanism in the corpus. From Kodak’s 1949 handbook, all for baths standing in a dish:

Developer	Life in a dish	Why
D-72	24 hours	45 g of sulfite per litre
D-166	8 hours	25 g of sulfite, and half the metol of D-72
D-156	6 hours	22 g of sulfite
D-170, amidol	30 minutes	amidol in sulfite, with no alkali to stabilise it

The sulfite column is most of the explanation, and Part VIII owns the mechanism: sulfite is the preservative that intercepts the quinone oxidation products before they build up.

Read the correlation carefully, though, because it is not a proportionality. Halving the sulfite from 45 to 22 g/L takes the dish life from 24 hours to six, which is a quarter and not a half — and the warm-tone formulas differ from D-72 in their agent doses and their alkali as well as in their sulfite, so no single-variable law can be read off four rows of a table. What the column supports is the direction and the mechanism, not an exponent.

What is worth doing about it, and roughly what each is worth: mix the working solution immediately before use, which ILFORD instruct directly; use the smallest tray the print will fit in, because the loss goes with area; float a lid or a sheet of plastic on a bath that is standing; and draw off mains water and let it stand for a few minutes before mixing, which is also ILFORD’s instruction, because pressurised mains water is highly aerated. The atlas entry for the result is oxidised developer.

Temperature and dilution, which are not economy measures

Both are published controls, and both change more than one thing at once.

Temperature. 20 °C ± 1 °C is ILFORD’s recommendation, with the note that slightly lower needs slightly longer and slightly higher needs slightly shorter — and the warning that high temperatures “will reduce the effective solution life considerably and may give very short development times that can lead to uneven processing”. That last clause is the real limit: below about a minute you cannot get the developer over the sheet evenly before the reaction has done most of its work.

Dilution. ILFORD offer MULTIGRADE at 1+9 or 1+14 and describe the second as being for “greater control during development, and for economy”. Read the tables and the trade is visible: 1+14 costs 30 per cent of the capacity (70 RC prints per litre against 100) and buys a longer development time — 1 minute 30 against 1 minute on RC — which is what “greater control” means.

✦The manufacturer's dilutions are different developers

The habit to break is thinking of a dilution as the same developer with more water in it. It is a bath at a different agent concentration, a different bromide concentration and a different rate, which reaches the same plateau by a different route and in a different time.

Kodak’s D-72 makes this explicit and is the clearest teaching case in the formulary: one stock, three published dilutions, one per paper family. 1:1 for Velox and other chloride contact papers at 45 seconds; 1:2 for Azo at 45 seconds; 1:4 for bromide enlarging papers at 1½ minutes. And the note that gives the game away — Azo developed at the Velox dilution goes colder. Same stock, same paper, different dilution, different colour.

Foma go further in the warm direction and publish the arithmetic: dilute FOMATOL PW 1+1 and double the development time; dilute 1+3 and take about four times as long; each step gives a warmer image tone on the Fomatone papers.

Warm-tone print developers, and how they actually work

Everything above assembles into one recipe. A warm-tone developer slows the rate of deposition so that the silver is laid down in a finer form, and every published warm-tone formula does it by the same three moves.

1. More bromide. D-156 has 6.3 g/L and D-166 has 12.5 g/L against D-72’s 1.9. It restrains the hydroquinone half of the pair disproportionately and slows the whole deposition.
2. Less alkali. D-156 has 16 g of carbonate against D-72’s 67.5, and D-166 has 25. Lower pH means less of each agent ionised, which means a slower reaction throughout.
3. Less of everything else. D-166 carries about a third of D-72’s metol. The bath is weaker in every direction, and takes 2 minutes at 1:3 to do what D-72 does in 1½ at 1:4.

The sulfite falls with the rest — D-156 at 22 g/L against D-72’s 45 — and that is a genuine cost rather than a design feature: it is why the dish life drops from 24 hours to six.

Three further agents belong in this section, and the course’s position on each differs.

Chlorohydroquinone and glycin both have encyclopaedia entries and both appear in the warm-tone literature. No formula using either is published in this course’s formulary, because no source in the corpus prints one with the provenance Rule 6 requires. Ansco 130, the glycin paper developer most often named, is a case in point: the course has not found a publication by its originator or by its manufacturer, only secondary accounts, and under the course’s own rule a formula known through somebody who did not devise it stays behaviour-only. So this page names the agents, describes what they are said to do, and prints no quantities.

p-Aminophenol is the exception that is fully sourced, and for a different reason. Kodak published D-173 in 1949 as a metol-free paper developer, expressly so that people with metol dermatitis could keep printing. That is a formula with a stated purpose, printed by its maker, and it is in the formulary.

Amidol, treated separately

Amidol — 2,4-diaminophenol dihydrochloride — earns its own section because it breaks the rule the rest of the page is built on.

It develops without an alkali. Kodak’s 1928 primer states the rule and the exception in one sentence: most developing agents cannot develop at all by themselves, and “with the exception of Acrol” — Kodak’s name for amidol — they must be in an alkaline solution. Both Kodak amidol formulas in the formulary are alkali-free: D-51 is amidol and sulfite; D-170 is amidol, sulfite and a gram of bromide.

It is unstable. D-170’s published dish life is thirty minutes. Nothing else in the paper library is close.

Its reputation for maximum black is practitioner interpretation. It is widely reported to give a deeper black than an MQ developer on the same paper. No Tier 1 or Tier 2 source in the corpus measures it, so the course records it as a claim to test rather than a fact, and the experiment in this part gives the method that would settle it for one paper.

⚠Why the lab in this part does not use amidol

Amidol’s ECHA aggregated classification carries the signal word Danger with three pictograms — GHS06 (acute toxicity), GHS07 and GHS08 (serious health hazard) — where metol and hydroquinone carry Warning or Danger with a narrower set. Its encyclopaedia entry classifies it Level B and details the controls.

Under the course’s ruling that the operation sets the level, weighing amidol as a powder is a Level B weighing that could be done outside a session. But there is a second consideration and it decides the matter for a teaching lab: a developer with a thirty-minute working life cannot support a comparison in which three baths are used over two hours. Amidol is taught here as chemistry, and the lab uses D-72 and its variants.

Two-bath and water-bath development

Both are compensating techniques: soak the print in developer, then move it to a second bath — plain water, or a weaker or differently balanced developer — where the developer already in the emulsion continues to work and exhausts itself locally. Where the image is dense the local developer is used up quickly and development stops; where it is thin, development continues. The result is compression of the highlights without a loss of shadow separation.

⁇What the course can and cannot say about these

The mechanism is sound and is not in dispute: local exhaustion in a still bath is the same physics as the adjacency effects Part VIII established for film, applied at the scale of a whole tonal region rather than an edge.

No Tier 1 or Tier 2 source in this course’s corpus documents either technique for prints. No manufacturer sheet mentions them; no conservation publication describes them. What exists is practitioner convention, widely and consistently reported.

So the course teaches them as practice with the evidence labelled. They are described here as mechanism, they are not given as a procedure with times, and if the course publishes times for them they will be its own measurements made under the experiment framework and labelled as such. That is the same treatment Part XIII gave dry-down and that the course’s ruling on thin-evidence practices requires.

The developer-paper pair as a design decision

Nothing on this page is a property of a developer alone. Every number is a property of a developer-and-paper pair, and the makers write it that way: ILFORD recommend BROMOPHEN specifically for MULTIGRADE Warmtone papers “to get the warmest image tone”; Foma formulated FOMATOL PW specifically for the Fomatone papers; Kodak describe DEKTOL as producing “neutral or cold tones with cold-tone papers and warm tones with warm-tone papers”, which is a statement that the developer’s contribution depends on what it is developing.

So the choice in front of a printer is not “which is the best print developer”. It is:

If you want	Move	What it costs
A colder, harder image	more alkali, less bromide — D-158’s direction	more risk of fog; the bath is nearer the edge
A warmer image	more bromide, less alkali — D-156, D-166	speed, dish life and capacity
Longer to see what is happening	a weaker dilution	about a third of the capacity
A bath that survives the session	more sulfite, a smaller tray, a lid	nothing, and it is the cheapest improvement here
The deepest black a paper can give	to be determined by measurement	a session, and it is what the experiment is for

🧪The comparison that settles it for your own darkroom

One negative. One paper. Three developers — say D-72 at the enlarging-paper dilution, D-72 with the bromide raised, and a bought concentrate — each at the paper’s own recommended time and temperature. Print to the same maximum black, not to the same exposure, so that the comparison is of what the developers do rather than of how fast they are.

That is the lab, and its one methodological demand is worth stating before you get there: decide before you start what difference would be large enough to matter, because three prints will always look slightly different and most of that difference is the repeatability of your own process rather than the chemistry.

Recap

• A paper developer’s brief is completion in one to three minutes, at room temperature, in an open tray, with a clean white base. Every other difference from a film developer follows from it.
• The pH is the answer to the ninety seconds. ILFORD publish 10.45 to 10.55 for MULTIGRADE 1+9 against 8.60 to 8.70 for their film developer — five orders of magnitude in hydroxide ion. The price Kodak name is chemical fog and softened gelatin.
• The restrainer pays that price back, and does more: bromide restrains hydroquinone more than metol, so it moves the tone as well as the fog. The Kodak library runs from D-158 at 0.9 g/L and blue-black to D-166 at 12.5 g/L and extra-warm, with the carbonate falling as the bromide rises.
• Paper is developed to completion. Maximum black rises to a limit; base fog rises without one; the window between is wide. Snatching a print gives a mottled, weak, incompletely developed print and not a lighter one — reduce the exposure instead.
• Capacity is published, exhaustion is diagnosed. 100 RC or 50 FB 8 × 10 prints per litre for MULTIGRADE 1+9; a fibre print costs about twice a resin-coated one; symptoms arrive in the order slow emergence, weak blacks, warm tone, stain.
• A tray is mostly surface, so a print developer dies of air. The dish lives in Kodak’s own table track the sulfite: 24 hours for D-72, 6 for D-156, 30 minutes for amidol D-170.
• Dilutions are different developers. D-72’s three published dilutions are one per paper family, and Azo at the Velox dilution goes colder.
• Amidol is the alkali-free exception, is classified Danger with three pictograms, keeps for half an hour, and its maximum-black reputation is a claim to measure rather than a fact to repeat.
• Every figure belongs to a developer-and-paper pair. Change either and re-measure.

Check your understanding

Question 1. A print developer is mixed with sodium bicarbonate in place of the sodium carbonate the formula calls for. What happens, and why?

• Nothing — both are alkalis and the developer is buffered either way
• The bath sits near pH 8.3 instead of 10.5, so very little of the hydroquinone is ionised; prints come up slowly, never reach maximum black in the published time, and look thin
• The bath fogs, because bicarbonate is a weaker restrainer
• The developer works normally but has a shorter dish life

Show the answer and why

Answer: The bath sits near pH 8.3 instead of 10.5, so very little of the hydroquinone is ionised; prints come up slowly, never reach maximum black in the published time, and look thin

Part VIII did this arithmetic: a bicarbonate solution sits near pH 8.3 and a carbonate paper bath near 10.5, which is more than two orders of magnitude in hydroxide ion. A developing agent works as its anion, and the fraction ionised is set by pH against the agent’s pKa, so the reaction rate collapses. The visible result is exactly what an under-developed print looks like — weak, flat, and not reaching its black — which is why the fault is so often blamed on exposure.

Question 2. A printer doubles the development time from 1½ to 3 minutes on a fibre paper in MULTIGRADE 1+9. What changes?

• The contrast rises, as it would on film
• Essentially nothing — ILFORD state that development can be extended to six minutes without noticeable change in contrast or fog, so both times are inside the plateau
• The maximum black doubles
• The base fog doubles and the print is ruined

Show the answer and why

Answer: Essentially nothing — ILFORD state that development can be extended to six minutes without noticeable change in contrast or fog, so both times are inside the plateau

This is the difference between developing to a chosen contrast and developing to completion. A print’s maximum black saturates once every developable crystal is reduced, and base fog rises so slowly that ILFORD can publish a six-minute ceiling for a ninety-second recommendation. Development time is therefore not a contrast control on paper — which is exactly why the exposure and the filter are, and why snatching a print early is a fault rather than a lighter print.

Question 3. Kodak’s D-156 carries 6.3 g of potassium bromide per litre and 16 g of carbonate; D-72 carries 1.9 g and 67.5 g. Kodak file D-156 under warm tone. What is the mechanism, and which part of it is the course’s own inference?

• The bromide converts some developed silver to silver bromide, which is brown; this is fully established
• More bromide and less alkali both slow the deposition of silver, and finer developed particles read warmer — established that bromide restrains hydroquinone more than metol, inferred that this is what moves the colour
• The bromide reacts with the carbonate to form a warm-toning complex; this is established
• Nothing is established; the filing under warm tone is a marketing decision

Show the answer and why

Answer: More bromide and less alkali both slow the deposition of silver, and finer developed particles read warmer — established that bromide restrains hydroquinone more than metol, inferred that this is what moves the colour

Two published facts and one course inference. Kodak state that a small quantity of bromide affects hydroquinone much more than it affects metol; Getty state that warm tone in modern papers comes from restricted growth of silver particles during development. Joining them — unequal restraint changes the rate and form of deposition, and therefore the colour — is the course’s reading, marked as such on the page. No single source states the chain in those words, and a page that presented it as established would be over-claiming.

Question 4. Two litres of the same developer are used for a session: one in a 12 × 16 inch tray, one in a covered bottle. The tray bath fails first. What is the dominant mechanism, and which single ingredient of the formula most affects how long it survives?

• Carry-over of stop bath; the carbonate
• Aerial oxidation of the developing agents at the large free surface; the sulfite
• Bromide accumulation from development; the potassium bromide
• Evaporation; the water

Show the answer and why

Answer: Aerial oxidation of the developing agents at the large free surface; the sulfite

A tray is mostly surface and a bottle is almost none, and at pH 10.5 hydroquinone oxidises quickly in air. Sulfite is the preservative that intercepts the oxidation products, so the dish lives in Kodak’s own 1949 table track it almost exactly: D-72 with 45 g of sulfite per litre keeps 24 hours in a dish, D-156 with 22 g keeps six, and the amidol developer D-170 with no alkali to stabilise it keeps thirty minutes. Bromide accumulation is real and is what the capacity figure counts, but it does not explain why an unused tray dies overnight.

Question 5. A printer wants to publish a warm-tone glycin developer formula on a course page. What does the course’s provenance rule require?

• Nothing special — glycin is a well-known developing agent with an encyclopaedia entry
• A publication by the person or company who devised the formula; secondary accounts leave it behaviour-only, so the agent may be named and described but no quantities printed
• Only that the safety data be verified
• That it be tested by the course before publication

Show the answer and why

Answer: A publication by the person or company who devised the formula; secondary accounts leave it behaviour-only, so the agent may be named and described but no quantities printed

Rule 6 asks for provenance, and the course owner’s ruling adds that a formula published by the person who devised it is primary evidence for that formula, while one known only through somebody who did not devise it stays behaviour-only until the original is found. Ansco 130 is the case in point: widely circulated, and not traceable in this corpus to its originator or its manufacturer. So glycin gets a chemical page and a description of what it is said to do, and no quantities. Kodak’s D-173 shows the contrast — a metol-free paper developer printed by its maker with a stated purpose, which is why it is in the formulary.

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