Kodak D-49

This formula sits three inches below D-72 on the same page of Kodak’s 1928 primer, and it is D-72 with one substantial change and two small ones. That makes it the most useful formula in this library for learning what a single ingredient does, because the control was published alongside it by the same company in the same year.

Ingredient	D-49	D-72, for comparison
Metol	3.1 g	3.1 g
Sodium sulfite	45.0 g	45.0 g
Hydroquinone	11.5 g	12.2 g
Sodium carbonate	45.0 g	67.5 g
Potassium bromide	2.1 g	1.9 g
Water to make	1000 mL	1000 mL

Purpose

To develop a bromide enlarging paper to a softer print than the general-purpose formula gives, over a longer development. Kodak titles it the Portrait Bromide Paper Developer, and “portrait” on a 1928 formula sheet means a print in which the light tones separate gently and the contrast does not fight the subject.

Recommended uses

Bromide enlarging paper at 1:1, not less than one and three quarter minutes at 21 °C. That is the whole of what the primer publishes.

Read the time as Kodak wrote it. Not less than is not a hedge; it is the correct way to state a print development time, because a print is developed to completion and the time only has to be long enough for completion to happen. Pulling a print at a minute gives an under-developed print with mottled, unresolved low tones rather than a lighter version of the same image.

When another formula is preferable

• For general printing at normal contrast, D-72 at 1:4 on the same paper, which is the formula this one was published as an alternative to.
• For normal to high contrast, D-163.
• For a warm image tone rather than a soft one, D-156, which cuts the alkali much further and raises the bromide threefold. Comparing D-49 with D-156 shows how far you can take one lever before the result stops being “softer” and starts being “warmer”.
• For a developer that lets you set the restrainer per paper, D-52 leaves the bromide out of the stock entirely.

Mixing

Dissolve in the order given, starting with 500 mL of water at about 52 °C and making up to a litre with cold water afterwards. Kodak Limited’s later handbook states the rule the 1928 order follows: the Elon goes first because it is readily soluble in warm water but only slightly soluble in a sulfite solution with no alkali in it; the preservative next; the second agent after that; the alkali last; and the bromide wherever you like, since it has no action on the agents.

1. Metol, dissolved completely in the warm half-litre.
2. Sodium sulfite.
3. Hydroquinone.
4. Sodium carbonate.
5. Potassium bromide.
6. Cold water to 1000 mL.

⚗Which carbonate the 1928 primer means

The primer writes “Sodium Carbonate (E. K. Co.)” — Kodak’s own tested grade — and does not name a hydrate. The course reads it as the anhydrous salt, on the arithmetic rather than on assumption: the same book gives D-72 67.5 g of that carbonate, and Kodak Limited’s 1949 handbook prints D-72’s carbonate as 67.5 g anhydrous against 180 g crystalline. The anhydrous column matches exactly and the crystalline one does not.

If you have the crystals rather than the anhydrous salt, the 1949 handbook’s own printed columns work out at a factor of about 2.67 to 2.69, and the molar ratio of the decahydrate to the anhydrous salt is 2.70. Its prose offers two and a half as a rule of thumb, which is a rounding that costs you seven per cent of your alkali — and in this formula, whose whole identity is a reduced alkali, seven per cent is worth caring about.

Behaviour

It is slower than D-72 and that is the product. One and three quarter minutes against D-72’s ninety seconds on the same class of paper, from a bath at two thirds of the alkalinity. A slower development at a lower pH gives a print in which the highlight densities build less steeply, which is what a portrait paper wants.

Nothing about its life is published. Kodak’s 1928 primer prints no keeping-properties table for developers and gives no sheet count for this formula, so this page carries no capacity and no shelf life. That is an absence in the source, not an omission here. If you need those figures, measure them and put your own in the lab notebook; the sensible starting assumption is that a bath like D-72’s keeps like D-72’s, and the sensible practice is to treat that as an assumption.

It carries slightly more bromide than D-72, which is the second small change and works with the first: a longer development in an open dish is a longer opportunity for fog, and 2.1 g/L against 1.9 g/L pays for it.

Image characteristics

Contrast. Softer than D-72 on the same paper. Tonality. Long and gentle. Colour. Not stated by the primer, and the course does not guess — the two levers that move image colour, alkali and bromide, have both moved here in the warm direction, but only a little, and Kodak’s own warm-tone formulas move them very much further before claiming a colour. Staining. None. Grain, acutance and speed are not meaningful properties of a paper developer.

The mechanism

45.0 g/L ÷ 105.99 g/mol = 0.425 mol/L

Sodium carbonate

67.5 g/L ÷ 105.99 g/mol = 0.637 mol/L

The same in D-72

11.5 g/L ÷ 110.11 g/mol = 0.104 mol/L

Hydroquinone

2.1 g/L ÷ 119.00 g/mol = 0.0176 mol/L

Potassium bromide

One third of the alkali, removed on purpose. The 1928 primer gives the rule this formula applies: the quantity of alkali governs the energy of a developer; too much tends to produce chemical fog and too little makes it slow; and alkalis soften the gelatin, so an over-alkaline bath frills in warm weather. Kodak has moved deliberately towards the slow end of that trade.

What lowering the alkali does to the two agents is not symmetrical. Metol works well across a wide pH range and has the highest reduction potential of the agents Kodak ranked; hydroquinone, with the lowest, is the agent whose activity falls away fastest as the pH comes down. So dropping the carbonate by a third takes a disproportionate amount out of the agent that builds density steadily and rapidly, and leaves the agent that starts the image nearly alone. Less density-building means less contrast, which is exactly what a portrait developer is for.

The trimmed hydroquinone reinforces it, barely. 11.5 g against 12.2 g is a six per cent reduction and is the smallest change on the sheet. It points the same way as the alkali change and is inside the weighing error of a domestic balance, which is a useful reminder that not every difference between two published formulas is a difference the maker expected you to be able to detect.

And the extra bromide is a consequence, not a purpose. Bromide acts far more strongly on hydroquinone than on metol. In a bath that has already lost some of its hydroquinone activity to a lower pH, a further two hundred milligrams per litre of bromide is a small, targeted addition — enough to hold fog through a development twice as long, without taking much more from an agent that is already restrained by the alkali. Part VIII covers restrainers.

Function of every ingredient

Metol, 3.1 g. The starting agent, at exactly the dose of the general-purpose formula. It has the highest reduction potential of the agents Kodak ranked, so it begins development in the lightly exposed regions and brings the image up everywhere at once; it is barely affected by the bromide and comparatively insensitive to temperature. Kodak left it alone here, which tells you that the softness was not to be bought by weakening the image’s start. More metol would raise shadow density and speed the appearance; less would make the print slow across the whole scale rather than softer. It is a skin sensitiser and it is why this page is Level B.

Sodium sulfite, 45.0 g. The preservative and the acid reserve, at the same dose as the general-purpose formula. It scavenges dissolved oxygen and intercepts the oxidised agents before they form coloured products; it also carries most of what a stop bath has to neutralise out of a carried-over print. More sulfite keeps better and eventually begins to dissolve silver, which on paper only costs density; less and an open dish browns within the session.

Hydroquinone, 11.5 g. The contrast agent, trimmed by six per cent. It gains density steadily and rapidly once the image is up, decides how black the blacks are, and is the temperature-sensitive half of the pair. In this formula it is doubly restrained — by a lower pH and by slightly more bromide — which is where the softness comes from. More hydroquinone raises contrast and maximum black; less and a portrait print becomes a flat one.

Sodium carbonate, anhydrous, 45.0 g. The alkali, and the change that defines the formula. It sets the pH region in which hydroquinone is active and supplies a carbonate–bicarbonate buffer to hold it as the agents release acid. At two thirds of D-72’s dose the bath is slower, softer and less liable to fog, and its gelatin swells less — the primer names all four of those consequences in one paragraph. More carbonate turns this formula back into D-72; less and the development time stretches past what an open dish will tolerate.

Potassium bromide, 2.1 g. The restrainer. It suppresses development of grains carrying no latent image, keeping the whites of a print white through a development long enough for fog to matter. Because it acts far more strongly on hydroquinone than on metol, its effect lands on the agent already held back by the pH. More bromide cleans the whites further, warms the tone and eventually costs shadow separation; less fogs, and fogs sooner here than in a faster formula because the paper is in the bath for longer.

Water to 1000 mL. Not inert, and half of it goes in warm. Iron is the classic contaminant; a stock that has crystallised in the cold is warmed and redissolved rather than decanted.

Interactions

Alkali and agent, taken one step. The single most transferable lesson in this library: lowering the alkali softens a print because it restrains the density-building agent more than the image-starting one. The same lever taken much further, together with a large bromide increase, gives D-156 and a change of colour rather than of contrast.

Alkali and restrainer. They act on the same agent, which is why Kodak could move both a little rather than either a lot. Doubling the bromide alone would have slowed the bath without softening it as cleanly; halving the alkali alone would have made the times impractical.

Agent and agent. Superadditivity, discussed in Part VIII. The usual explanation, that the second agent regenerates the oxidised first, is not stated by any source this course holds and is not asserted here.

Formula and paper. “Portrait bromide paper” was a product class of the period with its own emulsion characteristics. On a modern variable-contrast paper the same softening is available from the filtration, over a wider range and with better control, and that is the honest recommendation. The reason to mix this formula now is to see a single ingredient’s effect isolated by a manufacturer.

Variants

D-72 is the control, printed by the same company on the same page in the same year, and the pair is as close to a published controlled experiment as this part of the literature offers.

D-52 is the third paper developer on that page and takes a different approach to the same flexibility, leaving the bromide out of the stock so that the printer doses it per paper.

The course’s own variants belong in the formula version record. This formula and D-72 already define an axis; a version at 55 g/L of carbonate sits between them and is a legitimate thing to mix, provided it is recorded as yours and not as Kodak’s.

Safety

Level B, on the two substances that put every metol–hydroquinone formula there. Metol is a skin sensitiser and sensitisation is permanent. Hydroquinone carries a Danger classification with suspected carcinogenicity and mutagenicity and causes serious eye damage. Sodium carbonate at 45 g/L is an eye hazard in the stock, though less of one than in the formulas carrying 65 g/L and more.

A longer development is a longer exposure for you as well as for the paper. Nearly two minutes per print, in an open tray, is time in which hands reach in. Print tongs, one pair per tray, never interchanged; nitrile gloves if you handle prints at all. The classification rubric sets what Level B assumes and the gloves page covers the choice.

Weighing is the other exposure. Five powders, two of them fine and hazardous. Extraction running or an enclosure, never a draught, splash goggles on.

Storage

No keeping figures are published for this formula. The library’s general practice applies: stock in a tightly closed bottle filled as full as it will go, several small bottles rather than one large one, and working solution mixed for the session. Label with the formula, the dilution and the date, per the labelling SOP — and this one especially, because at 1:1 it looks identical in the bottle to several others here.

Treat a brown or amber stock as suspect and test it against a control print before using it on anything that matters.

Incompatibilities

Acid, deliberately, in the next tray. A splash of stop bath into a bath already at reduced alkalinity has proportionally more effect than the same splash into D-72. Tongs never travel backwards along the sequence.

Fixer, in either direction. Thiosulfate carried back fogs and stains; developer carried forward raises the fixer’s pH, and the 1928 primer records the result — a white sludge, an alkaline bath and prints likely to stain brown.

Oxidising agents — ferricyanide, permanganate, persulfate — never meet a developing agent in a bottle or a drain. See chemical incompatibilities.

Waste

A dilute alkaline solution carrying two developing agents with aquatic-toxicity classifications, and essentially no silver. Its own labelled container, never the fixer bottle. The disposal caveat governs and the general chemical waste SOP gives the procedure. Local regulation decides.

Troubleshooting

Prints that look flat. The formula working as published. If you wanted normal contrast you wanted D-72, and extending the time will add density without adding separation.

Prints that never finish. Check the temperature: at 21 °C published, a bath at 16 °C in a cold darkroom is asking a restrained hydroquinone to work in the conditions it likes least.

Mottled, uneven low tones. The signature of a print pulled before development was complete. The primer’s “not less than” is doing real work.

Grey whites through a long session. Fog. A near-two-minute development gives a safelight twice as long to do damage as a Velox print does; test the safelight before adjusting the bromide.

A print that comes out looking like D-72’s. Check the carbonate. If the crystals were weighed against the anhydrous figure, or the anhydrous salt against the crystalline one, the alkali is wrong by a factor of two and a half in one direction or the other, and this formula is nothing but its alkali.

Experiments

The published controlled pair. Print one negative on one paper in this formula at 1:1 and in D-72 at 1:4, both to completion, matching print density by exposure. The only meaningful difference between the two working baths is the alkali. Measure the contrast difference, and you have measured what a third of the carbonate is worth. Record it against the developer laboratory report.

Walk the alkali axis. Mix this formula at 45, 55 and 67.5 g/L of carbonate and print the same negative in all three. You are filling in the gap between two published Kodak formulas, which is a good way to find out whether the axis is linear.

Separate the two small changes. Mix D-49 with D-72’s hydroquinone and bromide but D-49’s carbonate. If the print matches the real D-49, the two small changes were cosmetic and the alkali is the whole formula — which is the hypothesis this page argues for and has not tested.

Measure the completion time. Develop identical prints for 60, 105, 150 and 240 seconds at 21 °C and read the maximum black. Where the curve flattens is the completion time for your paper in this bath, and it is the number Kodak’s “not less than” was pointing at.