Kodak D-19

D-76 and D-19 came out of the same laboratory a few years apart and share three ingredients out of four. Read them side by side and you can watch a manufacturer turn one design into its opposite by changing quantities alone.

Ingredient	Quantity	Form the source specifies
Metol	2.5 g	Kodak calls it Elon
Sodium sulfite	105.0 g	Kodak’s own desiccated salt
Hydroquinone	9.8 g
Sodium carbonate	52.5 g	Kodak’s own dry salt
Potassium bromide	6.3 g
Water to make	1000 mL	starting from 500 mL at about 52 °C

!Which D-19, and which salt

Two Kodak formulas carry this number and they are not the same. This page is the D-19 of Kodak’s 1928 Elementary Photographic Chemistry. Kodak Limited’s 1949 handbook prints a revised formula designated D-19b, whose quantities differ in every line. Both are published here. The rest of the course cites D-19b, because it is the later Kodak revision and the one whose figures Parts VIII and IX were written against.

And the figures circulating today under the bare name “D-19” match neither, which is exactly the situation Rule 6 exists for. The course prints what its sources print.

The salt question is settled by arithmetic, not by assumption. The 1928 tables say only “Sodium Sulphite (E. K. Co.)” and “Sodium Carbonate (E. K. Co.)”, and both substances were sold in more than one form. Two pieces of evidence fix it. The primer states in its own chemistry chapter that Eastman Tested Sulphite is the desiccated salt. And the primer’s D-72 prints 45.0 g of sulfite and 67.5 g of carbonate per litre, which are exactly the figures Kodak Limited’s 1949 handbook gives in its anhydrous parentheses for the same formula. So the 1928 quantities are anhydrous quantities. That is a reading of two sources rather than a statement from one, and it is labelled as such.

Purpose

High contrast. The 1928 primer heads it “X-ray Developer Formula”, and the job is to take a subject of very short exposure range and give it a very steep gradient in five minutes.

Recommended uses

Anything where the negative is a record rather than a picture: line copy, document work, high contrast negatives for alternative-process printing, and the radiographic and scientific record work the formula was written for.

As a teaching object. It is the far end of the line whose other end is D-23, and mixing both makes the argument of Part VIII concrete: the same four classes of ingredient, in different proportions, give a soft developer and a hard one.

When another formula is preferable

• For any continuous-tone negative, D-76 or DK-50. This formula will crush a normal subject.
• For the later Kodak revision of this same design, D-19b — less of everything, and a published replenisher.
• For moderate contrast increase rather than high contrast, take Kodak’s own advice under DK-50 and raise the alkali there instead. The step from DK-50 to D-19 is not a small adjustment; it is a sixfold change in alkalinity.

Mixing

Metol, sulfite, hydroquinone, carbonate, bromide — the order printed in the primer, and the order Kodak’s 1949 handbook explains: the Elon first because it is only slightly soluble in a sulfite solution without alkali; the sulfite next; the second agent under its protection; the alkali last so no dissolved agent waits in an alkaline solution; and the bromide wherever suits you, because it does not react with the agents.

The primer’s own table starts with 500 mL of water at about 52 °C (125 °F) and finishes with cold water to a litre. That is a real instruction rather than a formality: 105 g of sulfite and 52.5 g of carbonate in one litre is a lot of solid, and the second half of the volume is what makes it up.

⚗Carbonate in three forms, and a factor of two and a half

Kodak’s 1928 primer sets out the three forms of sodium carbonate on the market — the decahydrate at 37 per cent carbonate, the monohydrate at 85 per cent, and the dry powder at 98 per cent — and recommends the dry salt because the composition of the crystals is uncertain.

Kodak Limited’s 1949 handbook gives the practical rule for anyone with the wrong jar: where a formula specifies carbonate, use the anhydrous salt, and if crystals are used the quantity must be increased to two and a half times. Note what that means in this formula: 52.5 g of the anhydrous salt becomes about 131 g of the crystals. Getting it wrong by using crystals gram for gram would leave you with about a third of the alkali the formula calls for, in the developer whose whole behaviour is set by its alkali.

Behaviour

Five minutes at 18 °C, undiluted. Fast, and the speed is the alkali.

No capacity or keeping figures are published for this formula, because the 1928 primer carries no such table. Kodak Limited’s 1949 table does, for D-19b, and those figures belong to that formula rather than to this one — 6.3 g/L of bromide against 4.0 and 105 g/L of sulfite against 72 are differences large enough that the course will not transfer a capacity between them. If you mix this one, count sheets yourself and keep a control strip.

Image characteristics

Contrast: high, and everything else on this list is subordinate to it. Grain: coarse — 105 g/L of sulfite is a solvent load, but development is over in five minutes at a pH where the grains are reduced before the solvent has much time to work, and the primer’s own observation about D-76 covers the case: substituting carbonate for a weak alkali accentuates graininess. Speed: unpublished, and 6.3 g of bromide per litre is a strong reason to expect a raised threshold rather than full speed. Tonality: a short scale with a firm toe, which is what a document or a radiograph wants and what a portrait does not.

The mechanism

One agent does nearly all the work here, and it is the one that does almost none of it in D-76.

9.8 g/L ÷ 110.11 g/mol = 0.089 mol/L

Hydroquinone

52.5 g/L ÷ 105.99 g/mol = 0.495 mol/L

Carbonate

105 g/L ÷ 126.05 g/mol = 0.833 mol/L

Sulfite

6.3 g/L ÷ 119.00 g/mol = 0.053 mol/L

Bromide

Half a mole of carbonate per litre, against five thousandths of a mole of borax in D-76. That is a hundredfold difference in the amount of alkali, and it is what changes hydroquinone from a reserve agent into the principal one: at carbonate pH a much larger fraction of the hydroquinone is in its active form, and there is twice as much of it as D-76 carries in the first place.

High contrast is what a hydroquinone developer gives when it is allowed to work. The superadditivity lesson puts the pattern plainly: across the whole Kodak range the primary agent stays between 2.0 and 3.1 g/L while the secondary is varied to set the energy and the contrast. Here the secondary is at 9.8 g/L in a bath with the alkali to use it.

The bromide is the tax on all of that. Kodak’s own general statement is that too much alkali tends to produce chemical fog; a bath at half a mole of carbonate would develop unexposed grains without help. Six point three grams per litre is the most bromide of any developer in this batch — Part VIII’s restrainer table puts the range at 0.5 g/L for the general-purpose formulas and 4.0 g/L for D-19b — and it does a second job besides fog control. Bromide restrains hydroquinone far more strongly than it restrains metol, so a heavy dose sharpens the difference between an exposed grain and an unexposed one, which is contrast.

The sulfite is doing a defensive job rather than a fine-grain one. At 105 g/L in a strongly alkaline bath containing 0.089 mol/L of hydroquinone, aerial oxidation is a far bigger threat than it is in a borax developer, and the preservative load is sized for that.

Function of every ingredient

Metol, 2.5 g. The primary agent, and here it is very nearly a starter rather than a developer. It gets development going in the shadows and it is what makes the pair superadditive; the density is built by the hydroquinone behind it. More metol would fill the shadows and lower the contrast, which is the opposite of the point; less would slow the whole bath down, because the second agent works best after the first has begun. It is the ingredient that sets this page at Level B alongside the hydroquinone.

Sodium sulfite, 105.0 g. Preservative first, at a dose sized for a large hydroquinone load in a strongly alkaline solution — the conditions under which a developer oxidises fastest. It also contributes buffer capacity, though here the carbonate is carrying most of that. Its silver-solvent action is present but has little time to act in a five-minute development. More would improve keeping and slightly soften the image; less and the bath would go brown in the bottle.

Hydroquinone, 9.8 g. The working agent of this formula. It supplies the density and the gradient, and it is the reason the bath is high-contrast. More hydroquinone raises the gradient further and the fog risk with it; less moves the formula towards a general-purpose developer. Its heavy classification — Danger, with suspected carcinogenicity and mutagenicity and serious eye damage — is the reason this is the most hazardous formula in this batch to weigh out.

Sodium carbonate, anhydrous, 52.5 g. The alkali, and the ingredient that makes the hydroquinone usable. Half a mole per litre is a very large reserve as well as a high pH, so the bath holds its activity as it works rather than drifting the way a borax developer does. Kodak’s 1928 rule applies: the quantity of alkali governs the energy of a developer, too much tends to produce chemical fog, too little makes it slow, and alkalis soften the gelatin. That last clause matters at five minutes in a warm darkroom, because a softened emulsion is easy to damage. More carbonate means more energy, more fog and more swelling; less moves the formula towards DK-50 and away from its purpose.

Potassium bromide, 6.3 g. The restrainer, at the largest dose in this batch. It holds the development threshold up so that a bath this energetic does not develop unexposed grains, and because it acts much more strongly on hydroquinone than on metol it also steepens the curve. More bromide means a cleaner base, a higher threshold and lost shadow speed; less means fog, quickly. Kodak’s 1949 handbook offers a 10 per cent solution as an alternative way of measuring bromide in formulas of this family, and explains why it prefers solutions to drops: a drop is an uncertain quantity that can vary by as much as 150 per cent with how it is measured.

Water to 1000 mL. Half of it hot to get the solids in, the rest cold to make up.

Interactions

Alkali and secondary agent are the pair that defines this developer. Carbonate at half a mole per litre is what allows 9.8 g of hydroquinone to behave as a developing agent rather than as a reserve, and neither ingredient means much without the other.

Bromide against the two agents, unequally. This is the interaction that makes a heavy restrainer a contrast tool rather than merely a fog control, and it is Kodak’s own observation about the two agents.

Alkali against gelatin. The primer names it and it is a physical rather than a chemical interaction: alkalis soften the gelatin, so a carbonate developer at any warmth leaves a more delicate emulsion than a borax one does. It is a reason for a firm stop bath and careful handling rather than for a change to the formula.

Sulfite against the oxidation products. More important here than in any milder developer, because the rate of aerial oxidation rises with pH and with the amount of agent available to oxidise.

Variants

D-19b is Kodak’s later revision, printed in Kodak Limited’s 1949 handbook, and it lowers every quantity: metol 2.2, sulfite 72, hydroquinone 8.8, carbonate 48 and bromide 4.0 g/L. It is not recorded here as a variant, because Kodak published it as a formula in its own right with its own designation, its own replenisher and its own keeping table.

Why the course prints both. They are two published states of one design, they disagree, and Rule 6 forbids silently choosing. The page for each says what the other holds. Where the rest of the course needs a single high-contrast formula to cite, it cites D-19b.

The 1924 printing. Kodak’s 1924 primer carries a D-19 in avoirdupois measures only, and the course’s mirror of that scan has lost the sodium carbonate quantity to a scanning fault. It is cited here as evidence that the formula predates the 1928 edition and for nothing else; no quantity on this page comes from it, and the course does not reconstruct a missing line.

Safety

Level B, and this is the most hazardous set of powders in the film-developer section. Hydroquinone at 9.8 g/L carries a Danger classification — serious eye damage, suspected genetic defects, suspected cancer, and very high aquatic toxicity — and metol is a skin sensitiser. Sodium carbonate, sodium sulfite and potassium bromide are Level A materials, but half a mole of carbonate per litre makes this the most alkaline developer here and a real splash hazard for eyes. See the classification rubric.

Weigh the hydroquinone with extraction or in an enclosure. Splash goggles rather than glasses for mixing, because the alkalinity and the hydroquinone’s eye classification compound each other. Tongs, not fingers, in the dish.

What is not a hazard here. Nothing evolves a gas while the developer is being used as a developer — the carbonate will release carbon dioxide if it meets an acid, which is a reason to keep the stop bath separate rather than a hazard of the tank. Nothing is heated beyond the 52 °C mixing water. There is no sensitising alkali and no cyanide chemistry, and the ventilation requirement is for dust while weighing rather than for vapour.

Storage

Tightly corked, filled full, small bottles. Kodak published no keeping figure for this printing of the formula; the figures for D-19b are six months in a full stoppered gallon bottle and three months half-filled, and the course does not transfer them to a different formula. Date the bottle and treat an amber solution as suspect.

Store the dry carbonate away from acids and keep it dry: the anhydrous salt takes up water from the air, and a jar that has caked has also changed in concentration. The labelling SOP covers the rest.

Incompatibilities

Acid, with a specific consequence here: carbonate and acid give carbon dioxide, and a film carrying a carbonate developer into an acid fixing bath can blister as the gas forms inside the swollen gelatin. That is exactly the failure Kodak’s metaborate developers were designed to avoid, and the metaborate page records Kodak’s statement of it. Use a proper stop bath and do not let this developer go straight into the fixer.

Fixer, in either direction, on the usual grounds.

Oxidising agents — ferricyanide, dichromate, permanganate, persulfate — never with a developing agent. See chemical incompatibilities.

Waste

A strongly alkaline solution carrying a large hydroquinone load, and hydroquinone’s aquatic-toxicity classification is the reason this is the developer waste to be most careful with. Its own labelled bottle, kept out of the fixer, which goes for silver recovery. Do not attempt to neutralise it before disposal. The disposal caveat governs, the general chemical waste SOP gives the procedure, and local regulation decides.

Troubleshooting

Everything black, including what should be clear film. Chemical fog from an over-alkaline bath. Check that the bromide went in, and check whether you weighed anhydrous carbonate or crystals — the one substitution that raises rather than lowers the alkalinity is weighing anhydrous where crystals were intended, and both errors are easy.

Contrast much lower than expected. The reverse case: crystals weighed gram for gram where the formula wanted the anhydrous salt gives about a third of the alkali.

Shadows missing entirely. 6.3 g/L of bromide raises the threshold substantially. That is the formula working; if you want the shadows, you want a different developer or more exposure.

Frilling or a soft, easily marked emulsion. Alkalis soften gelatin, and this is the most alkaline developer in this section. Keep the temperature down, use a stop bath, and handle the film by its edges.

A bath that goes brown within days. Aerial oxidation, which is fastest exactly here — high pH and a large hydroquinone load. Small full bottles, and mix less at a time.

Experiments

Take the bromide out. One litre as published and one with no bromide at all, matched strips, same five minutes. The prediction is fog on the second and a lower gradient with it, which tests both jobs the restrainer is doing at once. Run it as part of the activity series.

Bridge D-76 and D-19 in four steps. Mix four litres holding the metol at 2.5 g/L and taking the alkali from borax through to 52.5 g/L of carbonate, with the hydroquinone and the bromide moved to match, and develop the same wedge in all four. You will have built a family of developers along the axis that separates the two ends of this reference.

Compare the two printings. D-19 as published here against D-19b as published in 1949, same film, same five minutes at 18 °C. Kodak revised the formula and did not say why; the difference on the film is a piece of evidence about what the revision was for, and it belongs in the developer laboratory report with the caveat that one comparison on one modern film is not a conclusion about 1949 materials.