Kodak D-34

Kodak’s 1928 primer prints two lantern slide developers on facing pages, heads one Blue Black Tones and the other Warm Black Tones, and offers not a word of explanation for either name. This is the first of the pair: an ordinary metol-hydroquinone developer with unusually little sulfite in it, split into an agent stock and an alkali stock in exactly the way the primer’s own chapter says a two-solution developer is split.

Stock Solution A — the developing agents and their preservative

Ingredient	Quantity	Form the source specifies
Metol	4.2 g	Kodak calls it Elon
Sodium sulfite (anhydrous)	15 g	desiccated
Hydroquinone	15 g	1924 spells it Hydrochinon
Water	to make 1000 mL	at 52 °C; 500 c.c. at about 52 degrees C to dissolve the three solids in the order given, then cold water to make 1.0 litre. The 52 degrees C belongs to the first 500 mL alone.
Elon first, which is Kodak's exception to its own preservative-first rule: Elon is readily soluble in warm water and only slightly soluble in a sulphite solution without alkali, so a sulphite dissolved first throws a white precipitate of the Elon base.

Stock Solution B — the alkali and the restrainer

Ingredient	Quantity	Form the source specifies
Sodium carbonate (anhydrous)	15 g	anhydrous, which is what Kodak's "Sodium Carbonate (E. K. Co.)" means; the primer prints no crystalline alternative for this formula and none is computed into the table
Potassium bromide	2.1 g
Water	1000 mL, added	"Water 1.0 liter", with the two solids added to it and no closing make-up line; the primer reserves "cold water to make" for the line that fixes a final volume. No temperature is given for this stock in either printing.
The primer states that bromide has no action on the developing agents and that it is immaterial at what stage it is added, so the order within this stock is Kodak's printing order rather than a chemical requirement.

Mixed in the ratio — the working developer, normal tones

1 part Stock Solution A + 1 part Stock Solution B

For use, take equal parts of A and B. Develop 1½ to 3 minutes at 70 °F (21 °C).

The working bath holds 2.1 g/L of metol, 7.5 g/L each of sulfite, hydroquinone and anhydrous carbonate, and 1.05 g/L of potassium bromide.

Mixed in the ratio — softer tones

1 part Stock Solution A + 1 part Stock Solution B + 2 parts water

For softer tones, dilute with an equal amount of water.

Kodak's own words are "dilute with an equal amount of water", which is the mixed developer plus its own volume again - so one part A, one part B and two parts water, halving every strength. The 1924 printing calls the result "softer results" rather than "softer tones", and neither printing publishes a time for the diluted bath.

Purpose

To develop lantern slide plates to a blue-black image. The heading is the purpose, and it is the only statement of purpose the source makes.

A lantern slide is a positive on glass, made to be projected. Two things follow that a negative developer does not have to care about, and both are visible in this formula. The image is looked through at magnification, so its colour is part of the picture rather than a curiosity — a blue-black slide and a warm-black slide of the same negative are two different pictures. And the clear glass is the paper white of the medium, so fog anywhere is fog everywhere.

The second published direction is as much a part of the formula as the first. For softer tones, dilute the mixed developer with an equal amount of water. Kodak gives this formula a contrast control and does not give one to D-9.

Recommended uses

Lantern slides, for a cold image. The paired formula D-32 is the warm one.

Any transparency where the projected colour matters. The plates D-34 was written for are gone; the question of what colour a developed silver image is has not gone anywhere.

As the readable example of a two-solution developer. The primer’s own definition is that a two-solution developer is a one-solution developer split into two parts, one containing the carbonate and bromide, the other containing the developing agent and preservative, so that it oxidises less readily and keeps well. D-34 is that sentence made into a formula, ingredient for ingredient — which is worth noticing beside D-9, which puts its bromide in the agent stock and therefore does not fit the definition.

As the low-sulfite end of the metol-hydroquinone family. Fifteen grams per litre of stock and 7.5 in the tray, against D-72’s 45 and D-76’s 100. Reading those three together is the cheapest lesson in what sulfite is doing in a developer.

When another formula is preferable

• For warm blacks on the same plate, D-32, which is the primer’s answer on the facing page and a completely different construction.
• For a warm tone on paper, D-156 or D-166, which Kodak Limited describes in those terms. A lantern slide developer is not a paper developer and the materials are not interchangeable.
• For negatives, D-76 or D-72 according to the job. D-34’s very low sulfite is a deliberate choice for a plate that is projected, not a general one.
• For maximum contrast, D-9 or the process developers. D-34 is a normal-scale developer with a softening control, not a hard one.
• Where two bottles are inconvenient, almost any single-solution developer in this formulary. The split here buys keeping, and it is only worth having if the stocks are actually going to be kept.

Mixing

Two bottles. Neither of them is hazardous in the way D-9’s second bottle is.

1. Stock Solution A. Into 500 mL of water at about 52 °C dissolve the Elon first, then the sodium sulfite, then the hydroquinone, and make up to 1,000 mL with cold water.
2. Stock Solution B. Into 1,000 mL of water dissolve 15 g of anhydrous sodium carbonate and 2.1 g of potassium bromide.
3. The working developer. Equal parts of A and B.
4. For softer tones, dilute that mixture with an equal amount of water.

Why Elon goes in first, and it is the one mixing rule on this page that matters. Kodak’s general instruction is preservative first, and it prints an explicit exception for formulas containing Elon: Elon is readily soluble in warm water and only slightly soluble in sulphite solutions without alkali, so if the sulfite goes in first a white precipitate of the Elon base often appears — the salt is an insoluble base made soluble by an acid, and a weak alkali such as sulfite neutralises the acid and puts the base out of solution. The primer adds the reassurance: the precipitate is soluble in excess water and in carbonate solution, so it usually redissolves when the alkali arrives and no harm has been done. Better not to make it.

The bromide’s position is immaterial. The primer says so in terms: bromide has no action on the developing agents and it does not matter at what stage it is added.

🧮What equal parts put in the tray, and what dilution does to it

Halving both stocks:

4.2 g/L ÷ 2 = 2.1 g per litre

Metol

15 g/L ÷ 2 = 7.5 g per litre

Sodium sulfite

15 g/L ÷ 2 = 7.5 g per litre

Hydroquinone

15 g/L ÷ 2 = 7.5 g per litre

Sodium carbonate, anhydrous

2.1 g/L ÷ 2 = 1.05 g per litre

Potassium bromide

Kodak’s softening direction halves all five again — 1.05 g/L of metol, 3.75 g/L each of sulfite, hydroquinone and carbonate, 0.53 g/L of bromide.

That is the interesting thing about the control. It does not change the ratio of anything to anything. Restrainer, alkali and agents all fall together, and the primer’s account of dilution as a contrast control (given for D-11, on another page) is the same: dilute with an equal volume of water when less contrast is wanted. Compare D-32, where the control is a ratio between the two stocks and therefore changes the alkali alone. Two lantern slide developers, printed on facing pages, with two different kinds of knob on them.

Behaviour

The stocks keep and the mixture does not. That is the primer’s stated reason for a two-solution developer — split so that the developer oxidises less readily and therefore keeps well — and it is the only keeping statement the source makes about D-34. No shelf life and no capacity is published for this formula in either printing, and D-34 does not appear in Kodak Limited’s keeping table because that handbook does not carry the formula. None is invented here.

It works in one and a half to three minutes at 21 °C, which is a wide bracket for a formula with a published time, and the width is the point: a lantern slide is developed to a density you can judge by looking through it.

Its alkali has a reserve. Carbonate dissociates as it is used and keeps the hydroxide concentration nearly constant, which is exactly what D-9’s caustic soda cannot do. Seven and a half grams per litre in the tray is a third of what a print developer such as D-72 carries at its usual dilution.

Its sulfite is doing one job, not two. At 7.5 g/L in the working bath there is no silver solvent action to speak of — that is D-76’s hundred grams per litre, and the solvent action and grain lesson is where the distinction is drawn. Here the sulfite is a preservative and nothing more. Whether that has anything to do with the blue-black heading is not something the sources say, and this page does not guess.

Image characteristics

Blue-black, on Kodak’s word and no more than that. The heading is the claim, and the primer prints no account of how the formula makes it — no comparison with the warm-tone formula on the next page, no mention of grain size, no measurement.

What the course can legitimately add is where the colour comes from in general, which Part IV establishes: finely divided silver is coloured and filamentary silver is neutral black, so an image tone is a particle-size reading. Kodak’s own primer uses that mechanism elsewhere, for dichroic fog. What nobody in this corpus establishes is which part of D-34 puts the silver into the form that reads blue. The candidates are visible — a low sulfite load, a moderate carbonate alkali, a metol-hydroquinone pair rather than hydroquinone alone — and they are candidates rather than an explanation.

Contrast is controllable and the control is dilution. Softer tones, in Kodak’s 1928 wording; softer results, in 1924’s. It is worth noticing that Kodak changed the word in a formula whose title is about tone, and worth not reading anything into it.

Fog shows in the highlights of a projected slide more than anywhere else, which is what the 1.05 g/L of bromide in the working bath is for.

The mechanism

Two agents, one alkali, one restrainer — the ordinary construction, described in full on how development works and superadditivity.

AgBr + e⁻ → Ag + Br⁻

What both agents are doing, grain by grain

⚗Why the carbonate is in the other bottle

An alkaline developing-agent solution oxidises fast. The primer’s account is unambiguous: hydroquinone in water turns brown on standing, and on adding an alkali such as sodium carbonate the rate of oxidation is increased to such an extent that the solution very rapidly turns dark brown, and a plate developed in it is stained and fogged.

2 C₆H₆O₂ + O₂ → 2 C₆H₄O₂ + 2 H₂O

Hydroquinone to quinone, the reaction the sulfite and the second bottle both exist to slow

Keeping the carbonate apart removes the accelerator from the bottle, and the sulfite that stays with the agents mops up what oxidises anyway. The primer’s definition of a two-solution developer is exactly this division - carbonate and bromide in one part, developing agent and preservative in the other.

And the bromide travels with the carbonate for a reason that is not chemical. It has no action on the agents, so it can go in either bottle; putting it in the alkali stock means the agent stock is the simplest possible thing to keep, and it means a worker who wants to alter the restrainer is altering the bottle that is not the delicate one. That last sentence is a reading and not something Kodak says.

Function of every ingredient

Metol, 4.2 g/L in Stock A, 2.1 g/L in the tray. The agent that starts the image. Kodak’s own ranking puts Elon at the high-potential end — it needs the least alkali and tolerates the most bromide — so it works early and it works in the shadows, and the density it builds is what the hydroquinone then extends. More of it gives a faster, softer, flatter image; less gives a longer time to first appearance and a harder result. It is the one ingredient with a mixing rule attached: dissolve it first, in warm water, before the sulfite, or it precipitates as its insoluble base. Note also that the two agents are not simply additive — the superadditivity lesson sets out what a metol-hydroquinone pair does that neither does alone.

Sodium sulfite, 15 g/L in Stock A, 7.5 g/L in the tray. The preservative, and here only the preservative. It takes up the quinone that hydroquinone’s oxidation produces and it keeps the stock from browning. What makes this dose worth remarking on is how small it is: a third of D-72’s and a seventh of D-76’s, which is well below the concentration at which sulfite starts to act as a silver bromide solvent and soften the grain. More of it would keep the stock longer and begin to dissolve silver; less would give a stock that browns and an image liable to stain. The desiccated salt is meant — Kodak’s tested sulphite — and the heptahydrate crystals would need about twice the weight.

Hydroquinone, 15 g/L in Stock A, 7.5 g/L in the tray, three and a half times the metol by weight. The contrast agent and the density builder. It is slow to start and it does not stop, which is what puts a projectable black into a slide. More raises contrast and maximum density and lengthens the time before anything appears; less gives a softer, flatter slide at the same shadow speed. It is also the agent that bromide restrains hardest, which is why 1 g/L of bromide does real work in this bath. Compare the same molecule at 5 g/L in D-76 and at 11.25 g/L in a caustic bath in D-9.

Sodium carbonate, 15 g/L in Stock B, 7.5 g/L in the tray. The alkali, and a reservoir rather than a dose: the primer explains that a carbonate is only partly dissociated at any moment, so it keeps a small hydroxide concentration nearly constant as development proceeds, where a proportional quantity of caustic alkali would present everything at once and be exhausted. The energy of the developer depends on how much of it there is — more gives a faster bath and, past a point, chemical fog and a softened, over-swollen gelatin; less gives a slow one. The form is the anhydrous salt, which is what Kodak’s own “Sodium Carbonate (E. K. Co.)” means: its 1949 handbook prints the same formulas with anhydrous figures identical to the primer’s and crystalline figures about two and two-thirds larger, which settles the question. Using the decahydrate crystals weight for weight would give a bath a third as alkaline as intended.

Potassium bromide, 2.1 g/L in Stock B, 1.05 g/L in the tray. The restrainer, holding down chemical fog and keeping the clear glass of a projected slide clear. More slows development and cleans the highlights further, at the cost of shadow speed and — as Hurter and Driffield measured, and the restrainers lesson reproduces — at the cost of the image colour itself, which turns fawn at extreme doses. Less fogs. One gram per litre is an ordinary working dose, an order of magnitude below D-9’s eleven. It sits in the alkali stock, which is where the primer’s definition of a two-solution developer puts it, and it could sit anywhere: bromide has no action on the developing agents.

Water, at two temperatures and in two roles. 500 mL at about 52 °C to dissolve Stock A’s three solids, made up cold to a litre; and a plain litre for Stock B, printed as an addition rather than a make-up, so that stock is a little over a litre when the two solids are in it. Then water again as the third ingredient of the softening dilution — the only contrast control this formula has, and Kodak prints it as part of the formula rather than as advice.

Interactions

With the plate rather than with a film. A lantern plate clears in 30 seconds to a minute in a fixing bath, per the primer, and washes in 2 to 3 minutes — both far shorter than a negative material — so the whole sequence after this developer is quicker than the habits of film processing suggest.

With an acid stop or acid fixer, in the ordinary way. Carbonate carried into a fixing bath is what exhausts it, and the capacity figures on F-1’s page show what a rinse is worth.

With air, once mixed. An alkaline metol-hydroquinone solution oxidises; the two-bottle arrangement exists precisely so that this only happens in the tray.

With warmth. The published temperature is 21 °C and the primer’s general warning is that alkalis soften gelatin and that an over-alkaline developer over-swells the coating. This bath is mild by that standard, but 21 °C is warmer than most of the primer’s other formulas run.

With the sulfite tub’s age. A small sulfite dose is more sensitive to a stale tub than a large one: sulfite oxidises to sulfate on standing and sulfate is not a preservative.

Variants

D-32, Warm Black Tones, printed on the facing page and the reason this one says blue. It is a different formula rather than a version of this one: no metol, hydroquinone alone, citric acid in the agent stock and caustic soda beside the carbonate in the alkali stock, with the ratio of the two stocks as its control instead of a dilution.

Kodak’s own softening dilution, which is printed as part of the formula and is recorded above as a second combination rather than as a variant, because it is the maker’s own.

Wall’s Seed lantern plate developers, 1924. Wall’s handbook prints a developer for Seed Lantern Black Tone Transparency Plates of exactly this architecture — Solution A of Elon, hydroquinone and dry sodium sulfite, Solution B of potassium bromide and dry sodium carbonate, mixed in equal volumes and used at about 70 °F — and beside it a Seed Hydroquinone Developer for Warm Tones whose A carries hydroquinone, sulfite, bromide and citric acid and whose B carries carbonate and caustic soda, with the instruction that for still warmer tones use more B. That is an independent maker arriving at both of Kodak’s constructions and both of Kodak’s controls. The course does not print Wall’s quantities: the two columns of that table are not reliably aligned in the copy it has read, and a transcribed number that might be off by a column is worse than no number. What is corroborated here is the architecture, not the strengths.

The 1924 printing of D-34 itself, identical in composition, without a time or a temperature and with “softer results” for “softer tones”. Corroboration rather than a variant.

No course variant is offered. The formula already carries its own softening control, and the tone the heading promises is a property of the composition as printed.

Safety

Level B, and it is the two developing agents that set it rather than anything unusual in the formula.

Metol is the sensitiser. Metol dermatitis is the classic darkroom occupational complaint and it is why Kodak Limited printed an Elon-free paper developer, D-173. Gloves, no skin contact with the working bath, and no dust while weighing.

Hydroquinone is the most heavily classified substance in an ordinary developer. Read its page before opening the jar; the controls are gloves, dust discipline and no skin contact.

Sodium carbonate is an alkali and an irritant as a dust, but this is a moderate solution and not a caustic one. There is nothing on this page comparable to D-9’s caustic stock.

Weigh the small quantities properly. 2.1 g of bromide and 4.2 g of metol are near the bottom of what a kitchen scale can do honestly; the weighing SOP and the balance check are the procedures, and Kodak Limited’s own rule is that quantities under 0.7 g should be made up as a percentage solution and measured by volume instead.

Ventilation as for any darkroom. Nothing here evolves a gas.

Storage

Two bottles, and Kodak publishes no figure for either. The primer’s statement is qualitative — a two-solution developer keeps well because it oxidises less readily — and that is all the source gives. D-34 is absent from Kodak Limited’s keeping table, so there is nothing to borrow.

Stock A full, tightly stoppered, cool and dark. It is the perishable half: a metol-hydroquinone solution with only 15 g/L of sulfite protecting it. Small bottles rather than one large one, because the air space in a large bottle grows every time it is opened.

Stock B is a carbonate and bromide solution and should be untroubled by anything but evaporation and dust.

The mixed developer is not stored. Mix what the session needs. An alkaline agent solution browns, and a browning developer stains.

Label both bottles with the formula, the letter, the strength and the date, per the labelling SOP, and record the batch on the formula version record. Two colourless solutions on a shelf are indistinguishable, and this formula’s two stocks are used in equal parts, so a swap is not self-correcting.

Incompatibilities

Fixer and stop bath, in either direction, as for every developer. One pair of tongs per tray.

Acids, which neutralise the carbonate and stop the bath — that is what a stop bath is for, and it is not wanted in the developer bottle.

Oxidising agents of any kind, which destroy both developing agents.

Iron, in the water or from a container: the primer’s general advice for developer solutions is clean water and clean vessels, and iron is the contaminant its chemical notes single out.

Anything the incompatibilities page lists against an alkali or against a reducing agent, which is the page to read rather than this paragraph.

Waste

Developer waste, not silver waste. Spent D-34 carries metol, hydroquinone, their oxidation products, carbonate, sulfite and bromide, and a little dissolved silver from the plate.

It is alkaline, and it must not go into an acid waste container. Keep the developer stream and the fixer stream apart; that separation is the whole basis of the general chemical waste SOP.

Hydroquinone is the constituent that makes this more than soapy water, and it is the reason developer waste is collected rather than poured away. Follow the disposal ruling. Local regulation decides, and this course cannot tell you what it says where you are.

Troubleshooting

A white precipitate appeared while mixing Stock A. The sulfite went in before the Elon. The primer says it is the insoluble Elon base and that it usually redissolves in excess water or on adding carbonate — but in this formula the carbonate is in the other bottle, so the excess water is the only remedy available. Re-make the stock rather than hoping.

Stock A has gone brown. Oxidation, and with only 15 g/L of sulfite there is not much margin. Check the age of the sulfite tub before blaming the bottle.

The slide is fogged or the clear glass is not clear. Too little bromide, an alkali error, or an old plate. Check the arithmetic on Stock B first: the bromide and the carbonate are both in it, and getting that bottle wrong moves two things at once.

The slide is thin and flat. Under-development, or the softening dilution was used when it was not wanted. Kodak’s bracket is one and a half to three minutes at 21 °C; take the top of it before changing the formula.

The slide is too contrasty for projection. Kodak’s own control: dilute the mixed developer with an equal amount of water.

The tone is not what the heading promises. The honest answer is that neither Kodak nor this course can tell you why. The heading is a claim about the formula as printed; a variation in plate, exposure, development time or temperature will move an image colour, and none of those relationships is established in this corpus.

The image is stained. An oxidised stock, or development continued in air rather than under the surface.

Experiments

Photograph the difference the headings claim. Develop identical plates or films in D-34 and in D-32 to the same maximum density, then look at both by transmitted light against a neutral source and photograph them side by side. Kodak names two colours and shows nothing. This is the missing figure of the pair.

Take the sulfite series. D-34’s 7.5 g/L in the tray, D-72’s 15 at 1+2, and D-76’s 100, on the same material to the same density. The solvent action and grain lesson predicts what should change; a lantern slide developer at the bottom of the range is the control that lesson lacks.

Test whether the dilution really is a tone control. Kodak calls the diluted bath “softer tones” in 1928 and “softer results” in 1924. Develop three plates — mixed, diluted, and mixed but developed for a shorter time to the same contrast — and see whether the dilution changes anything the shorter time does not. If it does not, 1924’s wording was the better one.

Find out where the bromide belongs. Make Stock A with the bromide in it and Stock B without, mix one-to-one, and develop against the formula as printed. The primer says bromide has no action on the developing agents, so the two trays should behave identically — and the two stocks should keep differently. The second half of that is the interesting half and nobody has measured it.

Test the keeping the primer claims and does not quantify. Bottle A, bottle B, and a litre of the mixed developer, and develop identical plates from each at one day, one week and one month. Three numbers Kodak never printed.