Kodak D-9

The far end of the developer range, and the reason the formulary needed a schema that could hold two solutions. D-9 is one agent, one alkali and an enormous quantity of restrainer: hydroquinone and caustic soda, which together develop a process plate in three minutes, kept in separate bottles because in one bottle they would not survive the week.

!The caustic stock is the hazard on this page

Kodak’s own warning, printed under the formula: cold water always, because dissolving sodium hydroxide evolves considerable heat, and with hot water the solution will boil with explosive violence and may cause serious burns if the hot alkali spatters on the hands or face. Read the sodium hydroxide page before you open the tub, and see Safety below.

Stock Solution A — the developing agent, kept acid so that it keeps

Ingredient	Quantity	Form the source specifies
Sodium bisulfite	22.5 g
Hydroquinone	22.5 g
Potassium bromide	22.5 g
Water	to make 1000 mL	at 52 °C; The primer starts with 500 c.c. at about 52 degrees C, dissolves the three solids in it in the order given, and makes up to 1.0 litre with cold water. The 52 degrees C belongs to the first 500 mL only.
The preservative goes in first, which is the primer's general rule for every formula that does not contain Elon. Bromide is last and it does not matter where it goes: the primer states that bromide has no action on the developing agents and that it is immaterial at what stage it is added.

Stock Solution B — the alkali, and nothing else

Ingredient	Quantity	Form the source specifies
Sodium hydroxide	52.5 g	caustic soda
Water	1000 mL, added	"Cold water 1.0 liter", with the caustic added to it and no make-up line - and the primer states its own convention, that "cold water to make" is reserved for the line that fixes a final volume. Cold is not a preference: the primer warns that with hot water the solution will boil with explosive violence and may burn the hands or face.
One solid in water. The whole of the mixing instruction for this stock is a safety instruction.

Mixed in the ratio — the working developer, mixed at the moment of use

1 part Stock Solution A + 1 part Stock Solution B

Use equal parts of A and B and develop about three minutes at 65 °F (18 °C). Solution A should be stirred thoroughly when the caustic alkali is added to it; otherwise the heavy caustic solution will sink to the bottom.

The order is stated even though the ratio is one to one: the caustic goes into A and A is stirred while it does. A 52.5 g/L caustic solution is appreciably denser than the stock it is poured into, and an unstirred tray is two layers rather than a developer.

Purpose

To develop process materials in a tray, quickly. Kodak’s header is “Process Tray Developer (Hydroquinone-Caustic)” and that is all the statement of purpose there is; the primer prints no description, no contrast claim, no capacity and no keeping figure.

Process is the load-bearing word and the primer uses it consistently on these pages: D-11, the formula overleaf, is recommended for use with Process and Process Panchromatic Films or Plates, and Kodak Limited’s later D-8 — the same two chemicals in one bottle — is headed for maximum contrast on process materials. Process materials are the high-contrast films and plates of photomechanical reproduction, and a developer for them is judged by how black the blacks are and how clean the whites, not by gradation.

Read positively, this is the formula that shows what alkali does. It is the only developer in this formulary whose alkali is hydroxide alone, and the alkalis, buffers and pH lesson uses it as the extreme term of the comparison: half a mole of free hydroxide per litre in the working bath against 4.5 millionths of a mole in a borax developer, five orders of magnitude apart.

Recommended uses

Process films and plates, which is what Kodak names.

Where three minutes is the requirement. Very few published developers work this fast at 18 °C, and the alkali is the reason.

As a teaching formula. D-9 makes four arguments visible that a normal developer hides: what a caustic alkali does that a carbonate does not, why a two-solution developer exists at all, why bisulfite rather than sulfite is the preservative in one, and what quantity of bromide it takes to hold an energetic bath in check. It is the formula the restrainers and antifoggants lesson and the classical developing agents lesson both reach for when they want an extreme.

Where a bath must be mixed fresh for each session anyway. There is no keeping penalty in a formula that was never going to be kept.

When another formula is preferable

• For ordinary negatives, almost anything else. D-76 for fine grain, D-19 for a high-contrast bath that is still a general-purpose one, D-23 for softness. A caustic hydroquinone bath is not a compromise between these; it is a different job.
• When one bottle is wanted rather than two, Kodak Limited’s D-8, which is the same chemistry as a single solution carrying 90 g/L of sulfite, keeps two months in a full bottle and is set out under Variants.
• When contrast has to be adjustable, D-11 on the facing page of the primer, which Kodak says gives very good contrast in five minutes and which it tells you to dilute with an equal volume of water when less contrast is wanted. D-9 is published with no dilution at all.
• When the darkroom is warm. The primer warns that alkalis soften gelatin and that too alkaline a developer over-swells the coating and gives frilling or blisters in warm weather. Nothing in this formulary is more alkaline than this.
• When caustic soda should not be in the room. That is a legitimate reason, and it is why the course publishes D-32 — which uses 4.2 g/L of caustic as a trim on a carbonate alkali — as well as this one.

Mixing

Two bottles, and the second one is the dangerous one.

1. Stock Solution A. Into 500 mL of water at about 52 °C dissolve, in the order given, 22.5 g of sodium bisulfite, then 22.5 g of hydroquinone, then 22.5 g of potassium bromide. Make up to 1,000 mL with cold water. Preservative first is the primer’s general rule for every formula without Elon in it; the bromide’s position is immaterial, because bromide has no action on the developing agents.
2. Stock Solution B. Into 1,000 mL of cold water, and with the vessel open and room to rise, add 52.5 g of sodium hydroxide a little at a time, stirring. Never the other way about, never warm water, never a closed vessel.
3. The working developer, and only when the tray is wanted. Equal parts of A and B, with B poured into A while A is stirred. The primer says why: the heavy caustic solution will otherwise sink to the bottom.

On that last instruction. A one-to-one ratio does not usually need an order of addition, and Kodak gives one anyway. A 52.5 g/L caustic solution is denser than stock A; poured in unstirred it forms a layer, and what is in the tray is then two solutions rather than one developer. It is the cheapest mistake on the page to make and the easiest to avoid.

🧮What equal parts actually put in the tray

Halving both stocks:

22.5 g/L ÷ 2 = 11.25 g per litre = 0.102 mol/L

Hydroquinone

22.5 g/L ÷ 2 = 11.25 g per litre = 0.095 mol/L

Potassium bromide

22.5 g/L ÷ 2 = 11.25 g per litre = 0.108 mol/L

Sodium bisulfite

52.5 g/L ÷ 2 = 26.25 g per litre = 0.656 mol/L

Sodium hydroxide

Two things fall out of that, and both are the course’s arithmetic on Kodak’s published weights.

There is very nearly one bromide ion per hydroquinone molecule — 0.095 against 0.102 mol/L. No other developer in this formulary comes within an order of magnitude of that ratio.

The bisulfite spends part of the caustic. The primer states the reaction for the carbonate case: the bisulfite is converted to sulfite by the alkali, neutralising an equivalent quantity of it and so exerting an apparent restraining action. Here that is 0.108 mol of the 0.656:

0.656 − 0.108 = 0.548 mol/L, or about 21.9 g/L of NaOH

Free hydroxide after the bisulfite is served

Still more than five hydroxides per hydroquinone, and about half a mole per litre of free alkali — which is the figure the alkalis and pH lesson sets against a borax developer’s 4.5 × 10⁻⁶ mol/L.

Behaviour

It is fast, and it is fast because nothing is holding the alkali back. The primer’s account of why carbonate is normally used is the clearest statement of what D-9 gives up: a carbonate is a reservoir, releasing hydroxide as it is used and keeping the concentration nearly constant, whereas a proportional quantity of caustic alkali would present all of its alkali at once and would soon be exhausted. D-9 takes the second option deliberately. It develops in three minutes and it has no reserve at all.

It is a one-shot bath in practice, and the sources say nothing either way. No capacity and no keeping figure is published for D-9 in any printing the course has read. What is published is the reason to expect both to be poor: a solution with no buffer loses activity as its alkali is consumed, and an alkaline hydroquinone solution oxidises fast — the primer says that adding alkali to hydroquinone increases the rate of oxidation so much that the solution rapidly turns dark brown and a plate developed in it is stained and fogged.

The two stocks, on the other hand, should both keep well — and that is the whole point of the arrangement. Solution A is acid, and the primer states the principle in terms: bisulfite is preferable as a preservative in a two-solution developer because oxidation progresses less readily in acid than in alkaline solution. Solution B is a caustic solution with nothing in it to oxidise. Kodak publishes no figure for either, so neither is stated here.

It softens gelatin. The primer warns that alkalis soften the emulsion and that an over-alkaline developer over-swells the coating and gives frilling or blisters in warm weather. This bath is the corpus maximum for alkalinity; treat 18 °C as a ceiling as well as a working temperature.

It carries a restrainer load that is not a contrast control. Eleven grams per litre is roughly three times what D-19b uses and more than twenty times DK-50’s. It is not there to shape a curve. It is there because a bath this alkaline would otherwise reduce unexposed grains as readily as exposed ones.

Image characteristics

The honest answer is that the sources do not describe them. Kodak prints this formula with a header, two stocks, a ratio and a time, and nothing else. It publishes no contrast claim, no speed statement, no account of grain and no tone description for D-9 in either printing, and this page does not supply any of them.

What can be said, and where it comes from. Hydroquinone is the agent whose dose raises contrast and maximum density and lengthens the time before anything appears — that is established on the hydroquinone page from Kodak’s own account of the agents. Kodak Limited’s D-8 is hydroquinone and caustic soda in one bottle and is headed maximum contrast. Kodak’s own D-11, a process developer of milder construction, is described as giving very good contrast in five minutes. The inference that D-9 is a short-scale, high-contrast developer is a strong one and it is still an inference.

One published consequence does belong here, from the general chapter rather than from the formula: too much alkali produces chemical fog. D-9’s answer to that is its bromide, and the two are in balance only as long as neither is altered.

The mechanism

Development is the reduction of exposed silver halide to silver, and hydroquinone is the reductant.

AgBr + e⁻ → Ag + Br⁻

What the developing agent has to accomplish, one grain at a time

⚗Why hydroquinone, of all the agents, is the one used with caustic

The primer ranks the developing agents by reduction potential - by how much bromide is needed to hold each back - and puts hydroquinone lowest, then pyro, then Elon highest. Its consequence is stated in one sentence: the developers of higher reduction potential require less alkali, and so hydroquinone is often used with caustic alkalis, while the other developing agents require only the weaker carbonated alkali.

The ionisation constants line up with that. The IUPAC dataset gives benzene-1,4-diol a pKa₁ near 9.9 and a pKa₂ near 11.4; a carbonate developer works between the two, and a caustic developer at pH 13-odd is past both.

C₆H₆O₂ → C₆H₅O₂⁻ + H⁺

First ionisation, pKa about 9.9 — the step a carbonate developer straddles

C₆H₅O₂⁻ → C₆H₄O₂²⁻ + H⁺

Second ionisation, pKa about 11.4 — the step a caustic bath passes and a carbonate one does not

That the doubly ionised species is the active reducer is the obvious reading and the course has not sourced it - the hydroquinone page records the same caution. What is established is the alkali dependence Kodak describes and the constants that sit on the same scale.

And the oxidation product is the reason for two bottles. Hydroquinone oxidises to quinone, and the primer says the rate in alkali is so great that the solution rapidly turns dark brown and the plate developed in it is stained and fogged.

2 C₆H₆O₂ + O₂ → 2 C₆H₄O₂ + 2 H₂O

What an alkaline hydroquinone solution does to itself in air

Stock A keeps because it is acid; the primer’s own rule is that oxidation progresses less readily in acid than in alkaline solution, which is why the preservative here is the bisulfite and not the sulfite.

Function of every ingredient

Sodium bisulfite, 22.5 g/L in Stock A. The preservative, and specifically the acid preservative. Sodium sulfite is an alkaline salt; bisulfite is its acid partner, and the primer states the design rule directly — bisulfite is preferable as a preservative in a two-solution developer, since oxidation progresses less readily in acid than in alkaline solution. So it does two things at once: it takes up the quinone that forms, as any sulfite does, and it holds stock A on the acid side where hydroquinone keeps. More of it would keep the stock better still and spend more of the caustic when the two meet — 0.108 mol/L of it already consumes about a sixth of the alkali. Less would give a stock that browns. Commercial dry sodium bisulfite is chiefly metabisulphite that converts on dissolving, and the primer notes that it is difficult to prepare free from iron, which matters if the same tub has been near a pyro developer.

Hydroquinone, 22.5 g/L in Stock A, 11.25 g/L in the tray. The developing agent, and the only one — there is no metol here to do the shadows first. It is the agent Kodak’s ranking puts at the low-potential end, which is exactly why it is the one paired with a caustic alkali: it needs the most alkali to work, and it tolerates the most bromide. More hydroquinone raises contrast and maximum density and lengthens the time before anything appears; less gives a flatter result at the same shadow speed. Compare D-76’s 5 g/L, buffered with borax, against this 11.25 — the same molecule, at opposite ends of its range. In the bottle it keeps well dry and dark; wet and alkaline it oxidises very rapidly, which is the whole architecture of this page.

Potassium bromide, 22.5 g/L in Stock A, 11.25 g/L in the tray. The restrainer, at an equal weight to the hydroquinone and — because their molar masses are 119 and 110 — very nearly an equal number of ions. The primer’s account of what bromide is for is that it compensates for chemical fog produced by the developer or inherent in the emulsion, and its account of what produces chemical fog is too much alkali. Those two statements meet in this formula: the bromide is the price of the caustic. Less of it and a bath holding half a mole of hydroxide per litre begins to reduce unexposed grains. More and the development slows badly, because the primer also records that bromide restrains hydroquinone hard and metol far less — a hydroquinone-only developer is the most bromide-sensitive construction there is. It can be added at any stage of mixing, having no action on the agent.

Sodium hydroxide, 52.5 g/L, the whole of Stock B. The alkali, the energy and the hazard. It is free hydroxide with no reservoir behind it: the primer contrasts it with a carbonate, which dissociates as it is used and holds a small concentration nearly constant, and says that a proportional quantity of caustic alkali would soon be exhausted. That is the trade D-9 makes — three minutes now, and no reserve. More would produce chemical fog, which the bromide is already fighting, and would soften the gelatin further; less would slow the bath, and the primer’s rule is that the energy depends on the amount of alkali present. Two practical properties belong to the solid rather than to the formula and both are on its own page: it is deliquescent and takes up carbon dioxide from the air, so an old tub has gained water and lost strength, and its dissolution is strongly exothermic, which is the subject of Kodak’s own warning above.

Water, and the two temperatures it comes at. 500 mL at about 52 °C to dissolve stock A’s three solids, made up cold to a litre; and a full litre of cold water for stock B, into which the caustic goes. The cold in stock B is not about the chemistry of development at all — it is the only thing standing between the reader and a boiling alkali. Note also what stock B’s line does not say: it is “cold water 1.0 liter”, not “cold water to make”, so 52.5 g of solid is added to a litre and the finished volume is a little more than that. Kodak’s own convention, stated in the same book, reserves “to make” for the line that fixes a final volume.

Interactions

With the acid stops and fixers that follow it. A film coming out of a bath holding half a mole of hydroxide per litre carries a great deal of alkali into the next tray. An acid rinse before the fixer matters more here than after any other developer in this formulary, and the capacity figures on F-1’s page show what it is worth.

With warm weather, badly. Alkali softens gelatin; this is the most alkaline bath in the corpus.

With air, once mixed. The mixed developer is an alkaline hydroquinone solution, which is the combination the primer says turns dark brown rapidly.

With carbon dioxide, in stock B, slowly: caustic soda in an open or often-opened bottle converts itself to carbonate, and a stock that has done so is weaker than its label. Kodak’s own remedy is a waxed cork rather than a glass stopper, which cements itself fast with the carbonate that forms.

With glass, also in stock B: the caustic slowly dissolves it and frosts the inside of the bottle.

Variants

Kodak Limited’s D-8, the same chemistry in one bottle. 90 g/L of anhydrous sulfite, 45 g/L of hydroquinone, 37.5 g/L of caustic soda and 30 g/L of potassium bromide, made to a litre, used two parts stock to one part water, developing in 2 to 5 minutes at 21 °C. Worked out, the D-8 tray holds 25 g/L of caustic soda against D-9’s 26.25 — nearly the same alkali — with 30 g/L of hydroquinone against 11.25 and 20 g/L of bromide against 11.25. It is the richer bath, and Kodak heads it maximum contrast.

And it settles a question this page would otherwise have got wrong. It is tempting to say that a caustic hydroquinone developer must be kept in two solutions. D-8 shows that it need not: with 90 g/L of sulfite in it, Kodak’s table gives that single bottle two months full and one month half full. What D-9 does is take the other route — a very small preservative load, kept acid, with the alkali in its own bottle — and Kodak’s general note on storage says why either is available: developers particularly susceptible to aerial oxidation are often divided into two or three solutions with the developing agent kept separate from the alkali. D-8 is not written up in this formulary; it is recorded here because it is the control that keeps this page honest.

D-11, the primer’s other process developer, on the facing page: Elon and hydroquinone with potassium carbonate, five minutes at 18 °C, and diluted with an equal volume of water when less contrast is wanted. The comparison worth holding on to is that D-11 offers a contrast control and D-9 does not.

D-32, where caustic soda appears as 4.2 g/L alongside 30 g/L of carbonate — the same ion used as a trim rather than as the engine, and the mildest thing this course publishes with caustic soda in it.

The 1924 printing, identical in composition and in its three minutes at 65 °F, without the 52 °C and without the word “about”. Corroboration rather than a variant.

No course variant is offered. Weakening the caustic without weakening the bromide would give a slow bath; weakening both would give a different formula that Kodak has already published under other numbers. The safe version of this developer is D-11, and it is Kodak’s.

Safety

Level B, and the level is set by Stock B on the bench rather than by the tray.

Dissolving sodium hydroxide is the hazardous operation. Kodak’s own warning is printed under the formula and is worth repeating exactly: cold water always, because considerable heat is evolved, and if hot water is used the solution will boil with explosive violence and may cause serious burns if the hot alkali spatters on the hands or face. CAMEO’s datasheet, quoted on the chemical page, adds that dissolution can liberate enough heat to cause steaming and spattering and to ignite adjacent combustible material.

The controls follow from that. Add the solid to the water, never water to the solid. A little at a time. An open vessel with room to rise, never a closed one, which the heat can pressurise. Goggles rather than glasses, gloves, and the alkali spill procedure known before you start rather than looked up afterwards. An alkali splash in the eye is the injury this page exists to prevent, and it does not hurt at first.

52.5 g/L is a strong solution and it stays hazardous after it is cold. So does the working developer at 26 g/L. Treat the tray as corrosive, not merely as a developer.

Hydroquinone is the most heavily classified substance in an ordinary developer and this bath carries more of it than most. Read its page; the controls are gloves, no dust, and no skin contact with the working solution.

Keep every acid out of the room’s caustic operations. Neutralising a caustic spill with acid is not the procedure; the alkali spill SOP is.

Storage

Two bottles, and neither of them keeps according to any published figure. Kodak gives no shelf life for D-9 in either printing, and it does not appear in Kodak Limited’s keeping table at all. What the sources establish is the reason for the arrangement rather than its result: an acid stock oxidises less readily than an alkaline one, and a developer susceptible to aerial oxidation is divided so that the agent and the alkali are apart.

Stock A in a full, tightly stoppered bottle, dark and cool. It should keep well and no number is put on that here.

Stock B in a plastic bottle, or in glass with a waxed cork rather than a ground-glass stopper — Kodak’s 1928 warning is that a glass stopper cements itself fast with the sodium carbonate that forms, and that the caustic frosts the inside of the glass by dissolving it. Keep it closed against carbon dioxide; an old bottle is a weaker alkali than its label says.

The mixed developer is not stored. Mix what the tray needs and discard it. An alkaline hydroquinone solution browns quickly, and a bath with no alkali reserve is losing energy from the moment it is poured.

Label both bottles with the formula, the letter, the strength and the date, per the labelling SOP, and label Stock B as corrosive in words a person who has never read this page would understand. Two colourless solutions on a shelf are indistinguishable, and mistaking the caustic for the developer stock is the accident this formula makes possible.

Incompatibilities

Acids of every kind, with Stock B and with the working bath. Neutralisation is violently exothermic and is not a spill procedure.

Aluminium, zinc and tin, which caustic soda attacks with the evolution of hydrogen. No metal trays, no metal funnels, no metal measures for Stock B.

Glass stoppers and, over time, glass itself, per Kodak’s own note.

Fixer, in either direction — one pair of tongs per tray, and the more so with a developer this alkaline.

Anything the incompatibilities page lists against a strong alkali, which is the page to read rather than this paragraph.

Waste

Alkaline and corrosive, and not a silver stream. Spent D-9 carries hydroquinone, its oxidation products, bromide and a great deal of sodium hydroxide. It is the developer waste stream, not the fixer one.

It is the strongest alkali this course asks anyone to dispose of, and dilution is not neutralisation. Never pour it into an acid waste container: the reaction is exothermic and the container may not be vented.

Collect it, label it as corrosive, keep it separate from the acid and silver-bearing streams, and follow the general chemical waste SOP and the disposal ruling. Local regulation decides what may go anywhere else, and this course cannot tell you what it says where you are.

Troubleshooting

The caustic solution got hot, or spat. Stop. The primer’s warning is the diagnosis: hot water was used, or the solid went in too fast, or the vessel was too small. Let it cool before going near it, and read the alkali spill SOP before the next attempt.

Development is uneven, or one part of the tray works faster than another. The caustic was not stirred into stock A. Kodak names this failure explicitly: the heavy caustic solution sinks to the bottom. Stir when combining, and stir the tray.

The mixed developer went brown in the tray. Expected of an alkaline hydroquinone solution, and rapidly. Mix for the session and discard.

Fog across the whole frame. Too much alkali relative to bromide. Check that stock A was made with all three solids and that stock B was not made stronger than 52.5 g/L; an over-concentrated caustic stock is the likeliest cause, and a bath this alkaline has no margin.

Nothing is developing, or everything is very slow. The opposite error: too much bromide, or a caustic stock that has taken up carbon dioxide and lost strength. Kodak’s own note is that caustic soda absorbs water and carbon dioxide from the air.

The negative frilled or blistered. Alkali softens gelatin and this is the most alkaline bath in the formulary. Work at 18 °C, harden in the fixer, and consider whether a chrome alum bath between developer and fixer is warranted.

The stock A bottle has gone brown. The bisulfite has been used up or was under-weighed. An acid hydroquinone stock should not brown; if it has, the acid half of the design has failed.

The stock B bottle will not open. Kodak’s own observation: a glass stopper cements itself fast with the carbonate that forms. Do not force it over a sink; warm the neck and expect it to be weak alkali inside.

Experiments

Plot the alkali against everything else. Make Stock B at 52.5, 26 and 13 g/L, mix each one-to-one with the same Stock A, and develop identical step wedges for the same three minutes. The primer says the energy of a developer depends on the quantity of alkali and that too much gives chemical fog. That is two claims and one strip of film settles both.

Find where the bromide is buying its keep. Hold the alkali constant and make Stock A at 22.5, 11 and 0 g/L of potassium bromide. The unexposed density should climb as the bromide falls, and the restrainers lesson predicts it will climb faster than the image density falls.

Test the two-solution argument directly. Mix a litre of working developer and bottle it, and bottle a litre each of A and B, then make a fresh tray from the stocks at one day, one week and one month and develop identical strips against the kept working solution. Kodak publishes no keeping figure for any of the three; this experiment produces all of them.

Compare it with D-8’s single bottle. Mix D-8 to Kodak Limited’s formula and D-9 to this one, and develop the same material in each to the same time. The trays hold nearly the same caustic soda; almost everything else differs. Kodak publishes no comparison of the two anywhere the course has read.

Watch what a carbonate reservoir is worth. Develop sheet after sheet in a fixed volume of D-9 and of D-72 diluted to a similar development time, measuring pH and density as you go. The primer’s claim is that the carbonate holds its concentration nearly constant while the caustic is soon exhausted. That is a graph nobody in this corpus has drawn.