Kodak D-76d

Put this formula beside D-76 and almost nothing has moved. The same 2.0 g of metol, the same 100 g of sulfite, the same 5.0 g of hydroquinone. Kodak changed one thing: it quadrupled the borax and then added an equal weight of boric acid, an ingredient D-76 does not contain at all. That is a single-variable experiment published as a formula, and what it changes is not the developer’s strength but its grip on its own pH.

Ingredient	Quantity	Form the source specifies
Metol	2 g	Kodak Limited calls it Elon
Sodium sulfite (anhydrous)	100 g or 200 g (crystalline heptahydrate, which is the 1944 booklet's main column)	anhydrous
Hydroquinone	5 g
Borax (sodium tetraborate decahydrate)	8 g
Boric acid	8 g
Water	to make 1000 mL
Added to the working bath, not to the stock
Potassium bromide	0.25 g per 1000 mL of working solution	Optional, and only for the initial fog of a freshly mixed bath: Kodak gives it as 15 grains per gallon (0.25 gram per litre) of the mixed developer

Purpose

To develop a negative whose density scale can be relied on to come out the same tomorrow. Kodak Limited’s own header is “Negative Developer — Buffered Borax”, and its Characteristics and Purpose note reads, in full: “A low contrast dish or tank developer for motion picture negatives and variable density sound records.”

The second half of that sentence is the reason the formula exists. A variable-density sound record carries the sound as a modulated density along the film rather than as a modulated width, so the developer is not just making a picture — it is setting the transfer function of an audio recording, and a bath that drifts as it works puts that drift into the sound. No source in this course’s corpus covers optical sound recording, so this page names the application and does not attempt to teach it. What it can say is what the chemistry is for, and the chemistry is for constancy.

Recommended uses

Undiluted, in a dish or a tank, for continuous-tone negative material, where you are developing enough film that the bath will season noticeably before you throw it away. That is the case Kodak built it for and it is the only case in which the extra ingredient earns its place: a bath thrown away after one film has no time to drift, and a buffer that prevents drift has nothing to prevent.

It is also the right formula to reach for when you want to hold one variable still. Because the two developing agents and the sulfite are identical to D-76’s, a matched pair of strips developed in the two baths isolates the alkali system and nothing else, which is what Part IX asks of an experiment.

!What Kodak does not publish for this formula

There is no development time, no temperature, no capacity and no keeping figure for D-76d in the 1944 booklet, and no other printing of the formula in this course’s corpus to supply them. Kodak gives times for other formulae on the same page — D.82 develops “about 5 minutes at 65 °F (18 °C)” — so the absence is the booklet’s, not the scan’s.

That has a practical consequence you should plan for before you weigh anything. You will have to establish your own time, by control strip or by a test roll, and you cannot borrow D-76’s: the arithmetic below says this bath sits at a lower pH than a plain borax one, and a lower pH means a different time. D-76d is a formula for somebody who is already running a process with a control strip in it.

When another formula is preferable

• If you want documented times, capacities and keeping figures, use D-76. It is the most thoroughly published developer in this reference and D-76d is one of the least. That is not a statement about which is the better developer; it is a statement about which one you can check your results against.
• If you want a tank held at constant activity across a hundred rolls, use D-76 with D-76R. Kodak publishes a replenisher for D-76 and publishes none for D-76d. A buffer slows the drift of a working bath; a replenisher replaces what the bath has lost. They are different remedies for different halves of the same problem, and only one of them puts metol and hydroquinone back.
• If you want the pH held higher rather than lower, DK-20 and DK-50 use Kodalk — sodium metaborate — which supplies the same borate pair as base only, with no acid half beside it. That is the opposite move from this one, made with the same element.
• If you want a bath that both holds its pH and works quickly, a carbonate developer such as D-19b carries about twice this bath’s reserve — 0.453 mol/L of carbonate against 0.213 mol/L of borate pair — and holds it a full pH unit higher, because the carbonate pair’s pK_a is 10.33 against boric acid’s 9.27. Kodak’s 1928 primer states the price plainly: substituting carbonate in a developer of this type increases the rate of development and accentuates the graininess of the negative. Buffering and speed are separable; buffering and grain are not.

Mixing

Elon, sulphite, hydroquinone, borax, boric acid. Kodak’s own instruction under the formula is the one line “Dissolve the chemicals in the order given”, and the reasoning is set out in the successor handbook of 1949: Elon is readily soluble in warm water but only slightly soluble in a sulphite solution that has no alkali in it, so it goes in first; the sulphite follows, so that the agents are protected before the alkali arrives and aerial oxidation has no window; the second agent next; and the two borate solids last, borax then boric acid in the order Kodak prints them, because a developing agent left sitting in an alkaline solution without its preservative oxidises while you wait.

Two practical notes that belong to this formula rather than to D-76:

Buy boric acid as crystals, not as powder. Kodak’s own toning publication says so in a footnote — “avoid using powdered boric acid; it does not dissolve easily” — and 8 g in a litre is a small enough quantity that a stubborn powder floating on the surface is easy to declare dissolved when it is not. Boric acid is not especially soluble: the figure on the boric acid page is 5.6 g per 100 mL at 20 °C, so 0.8 g per 100 mL is comfortable, but it dissolves slowly in cold water and quickly in warm.

Four times the borax dissolves more slowly than you expect. Borax is described by Kodak’s 1928 primer as forming “large crystals readily soluble in hot water”, with the emphasis on hot. Kodak’s 1928 directions for D-76 add the borax to sulphite solution at about 71 °C for this reason, and the same applies here with four times the quantity and a second solid behind it.

✕One column or the other, never a mixture

The 1944 booklet prints every formula twice, metric and avoirdupois, and the 1949 handbook carries the warning in capitals: the two columns “are not exact equivalents” and one or the other must be used exclusively. D-76d is a formula in which that matters more than usual, because two of its five solids have the identical imperial figure — 280 grains of borax and 280 grains of boric acid — and 8.0 g each in the metric column. Weigh the pair in grams or weigh them in grains. A litre mixed with the metric borax and the imperial boric acid is 8.0 g against 18.1 g — not a variant of this formula but a different developer, about three tenths of a pH unit below it on the arithmetic under The mechanism, and slower for it.

Behaviour

It is used exactly as it is mixed. Kodak publishes no dilution, no replenisher and no second working strength. The instruction is “Use without dilution”, and there is nothing else on the page.

It has a published adjustment, and the adjustment is the formula’s real subject. Kodak’s note under the quantities is worth reading twice:

By increasing the quantity of borax with a corresponding decrease in the boric acid content, the development rate is increased. By decreasing the borax and increasing the boric acid proportionately, the development rate is decreased.

Notice what is held constant: the total weight of borax plus boric acid. Kodak is not telling you to add more alkali, it is telling you to change the ratio of the two halves of one buffer pair while keeping the quantity of borate solids the same. That is a dial for development rate that never touches the agents, the sulfite or the silver-solvent concentration that sets the grain, and there is no other formula in this reference whose published instructions offer one. It is not quite free — a constant weight is not a constant number of moles, and moving the ratio also moves the buffer capacity, as the arithmetic under The mechanism shows — but everything that decides what the negative looks like apart from the pH is left alone. Kodak gives the direction and not the quantities, so the numbers for any particular setting are yours to establish and to record on a formula version record.

A freshly mixed bath may fog slightly, and Kodak says what to do about it. The note under the formula offers 15 grains of potassium bromide per gallon — 0.25 gram per litre — of the mixed developer, and is careful to describe the fog as “slight” and “initial”. It is an addition to the made-up bath, not an ingredient of the formula: the 1949 handbook’s general rule is that potassium bromide has no action on the developing agents, so it is immaterial at what stage it is added.

⚗Kodak's own two figures for the bromide do not convert into each other

15 grains is 0.972 g. Per imperial gallon, 4.546 L, that is 0.214 g/L; per US gallon, 3.785 L, it is 0.257 g/L. Kodak Limited prints 0.25 g/L beside it, so the metric figure is a round number chosen for the litre rather than a conversion of the imperial one — which is precisely the practice the 1949 handbook’s capitalised warning about the two columns is describing. Use whichever unit you are weighing in and do not convert across.

Image characteristics

Contrast. “Low”, which is Kodak’s whole published statement, given without a gamma, a curve or a time. The same booklet calls D-76 a “low-contrast fine-grain” developer in the entry immediately above, so the adjective does not distinguish the two.

Grain. Not stated for D-76d. What can be said is that the sulfite is at 100 g/L, unchanged from D-76, and that Kodak’s 1928 primer identifies the high sulphite of D-76 as a solvent for silver bromide which dissolves a little off each grain during development and so prevents neighbouring grains from clumping. That mechanism is concentration-dependent and the concentration has not changed, so there is no reason to expect the grain to differ from D-76’s for the same degree of development. This is an inference from an unchanged quantity, not a published claim about this formula.

Speed. Not published, and not inferable. Effective speed depends on where development begins in the shadows, which depends on the bath’s activity, which is exactly the quantity the buffer changes.

Tonality. The application Kodak names — variable density sound records — is one in which the repeatability of the density scale is the whole requirement. Read the formula as a design for consistency rather than for a look.

The mechanism

Everything on this page comes down to one arithmetic and one instruction, and they agree with each other.

Where borax puts you, and why boric acid moves you

Borax is disodium tetraborate decahydrate. Dissolved, one formula unit gives two boric acid and two borate, which is why a plain borax solution is a buffer with no second ingredient in it and why 0.01 molal sodium tetraborate is a certified pH standard. Part VIII establishes this for D-76 and this page uses its figures: molar mass 381.4 for the decahydrate, 61.84 for boric acid, and a pK_a of 9.27 from OpenStax’s ionisation constant of 5.4 × 10⁻¹⁰.

B(OH)₃ + 2 H₂O ⇌ B(OH)₄⁻ + H₃O⁺

The pair this whole formula is built on. Adding boric acid to the left-hand side pushes the equilibrium towards borate and hydronium, which is why an addition of acid to a borax bath lowers its pH and stiffens it at the same time

Now the two formulas, per litre:

8.0 g/L ÷ 381.4 g/mol = 0.0210 mol/L, giving 0.0420 mol/L of borate and 0.0420 mol/L of boric acid

Borax in D-76d

8.0 g/L ÷ 61.84 g/mol = 0.1294 mol/L, all of it the acid half

Boric acid in D-76d

So the finished bath holds 0.0420 mol/L of borate against 0.1713 mol/L of boric acid: a pair of 0.213 mol/L in total, mixed about one part base to four parts acid. D-76’s borax alone gives 0.021 mol/L of pair in equal halves. Two things have therefore changed at once, and they are independent:

	D-76	D-76d
Borate, the base half	0.0105 mol/L	0.0420 mol/L
Boric acid, the acid half	0.0105 mol/L	0.1713 mol/L
Size of the pair	0.021 mol/L	0.213 mol/L — ten times
Ratio, base to acid	1 to 1	1 to 4.1

🧮Both halves of Henderson and Hasselbalch, on one formula

The relation is

pH = pK_a + log₁₀([A⁻] ÷ [HA])

Henderson and Hasselbalch

and it has two inputs. Where the pH sits is the pK_a plus the logarithm of the ratio; how hard it is to move is set by the size of the pair.

Where. A borax bath is a 1 : 1 mixture, its logarithm is zero, and its borate system sits at the pK_a, 9.27. D-76d’s ratio is 0.0420 ÷ 0.1713 = 0.245, whose logarithm is −0.61, so its borate system sits at 9.27 − 0.61 = 8.66.

How hard. Buffer capacity is proportional to the size of the pair and to the product of the two fractions, β = 2.303 × C × f_A × f_HA. For D-76, 2.303 × 0.021 × 0.5 × 0.5 = 0.012 mol/L per pH unit. For D-76d, 2.303 × 0.213 × 0.197 × 0.803 = 0.078. Ten times the pair buys about six and a half times the capacity, not ten, because the ratio has been pushed off the pK_a where a buffer is strongest. That is the trade Kodak made: some of the tenfold increase was spent on lowering the pH, and only the remainder on holding it.

This is arithmetic on Kodak’s quantities, not a measurement of Kodak’s bath. It describes the borate sub-system alone and ignores the 0.79 mol/L of sulfite sitting beside it, which is itself a buffer pair. The course publishes no pH for D-76d, because none is published anywhere it has read. Note only, and for scale, that ILFORD’s measured 8.60 to 8.70 for ID-11 stock — the closest published figure for anything in this family — is within a twentieth of a unit of the number above, which is suggestive and is not evidence.

Why a maker would want this

Development is an acid-producing reaction. Every silver ion reduced leaves a bromide ion in the solution and every molecule of agent oxidised leaves hydrogen ions behind, so a working developer titrates itself downwards as it goes. Kodak understood this as a design problem long before the word buffer appears in its literature: the 1928 primer explains carbonate as “a sort of reservoir of alkali, only a small quantity of alkali being present at any time, but more being generated by dissociation of the carbonate as it is used up”, and concludes that the reservoir “enables us to employ a small concentration of alkali and yet to keep that concentration nearly constant during use”.

D-76’s problem is that its reservoir is tiny. Its borate pair is 0.021 mol/L against 0.79 mol/L of sulfite — a ratio of thirty-eight to one — and Part VIII’s treatment of the same case finds an acid load a carbonate developer would not notice moving a borax bath half a pH unit. That is why D-76R carries ten times the developer’s borax: the alkali is what a tank of D-76 runs out of first.

D-76d attacks the same fact from the other end. Instead of putting the alkali back after the film has taken it, it starts with ten times the pair, so the same acid load moves the pH about a sixth as far. The sulfite is no longer overwhelmingly the larger reserve:

Developer	Borate pair, mol/L	Sulfite, mol/L	Sulfite as a multiple
D-76	0.021	0.79	38×
D-76d	0.213	0.79	3.7×
DK-50	0.072 (base only)	0.24	3.3×

Read against Part VIII’s table of the same ratio across the formulary, D-76d moves out of the position that made D-76 the odd one out and into DK-50’s. The borax is no longer a trace ingredient whose only job is to set a region; it is a reserve in its own right.

And why the rate falls

The cost is on the page in Kodak’s own words. Lowering the ratio lowers the pH; lowering the pH slows the bath, because the developing agents work as their anions and a lower pH ionises less of them. Kodak states the direction empirically — more borax and less boric acid is faster, less borax and more boric acid is slower — and the Henderson–Hasselbalch arithmetic above states the same direction from the constants. Two independent routes to one claim is as close to confirmation as this page gets.

What the course will not say is by how much, or that D-76d is slower than D-76. That comparison needs a time, and Kodak publishes a time for neither formula in this booklet. The arithmetic points that way; it is an inference and it is labelled as one.

Function of every ingredient

Metol, 2.0 g. The primary developing agent, and identical to D-76’s. Kodak Limited calls it Elon and the 1944 booklet’s own glossary defines that as “a specially purified form of monomethyl paraminophenol sulphate”, also sold as Metol or Genol. It is the agent that starts the image in the thin shadow exposures and brings the whole frame up together, and it is the one that still works at this bath’s modest pH. It is unchanged from D-76 on purpose: changing it would have confounded the experiment the formula represents. More metol raises activity, shadow speed and eventually fog; less leaves the shadows thin and the hydroquinone with nothing to finish. It is a skin sensitiser, and sensitisation does not reverse.

Sodium sulfite, 100.0 g anhydrous — or 200.0 g of the crystalline salt, which is the 1944 booklet’s main column and the same amount of sulfite, the heptahydrate being almost exactly half water by mass. The 1949 handbook recommends the anhydrous form for greater stability, easier solution and smaller bulk. At 0.79 mol/L it does three jobs at once, exactly as in D-76: it is the preservative, scavenging dissolved oxygen and intercepting the oxidised agents; it is the silver solvent that makes a developer of this family fine-grained, which Kodak’s 1928 primer states explicitly of D-76’s sulphite; and it is a buffer pair in its own right, and by far the largest single reserve in the bottle. What is new here is that it is no longer the only meaningful reserve. More sulfite means finer grain, lower effective speed and better keeping; less means coarser grain, more sharpness and a bath that oxidises sooner. None of those three can be adjusted independently, which is why Kodak did not touch it.

Hydroquinone, 5.0 g. The secondary agent, again identical to D-76’s, and again mostly held in reserve because the pH will not ionise it: its first pK_a is near 9.9 and this bath sits below that. Its work is superadditive — the pair develops faster than either agent alone — and it is what keeps the bath going as the metol is consumed. The buffer makes it matter more, not less: hydroquinone’s contribution is the most pH-sensitive thing in the formula, so a bath whose pH drifts is a bath whose contrast drifts, and holding the pH holds the second agent steady. More hydroquinone raises contrast and useful life; less and the bath runs down sooner. It carries the heaviest hazard classification of the five solids.

Borax, 8.0 g. Four times D-76’s quantity, and the source of both halves of the buffer pair: 0.0210 mol/L of the decahydrate yields 0.0420 mol/L of borate and 0.0420 mol/L of boric acid. Its job here is to supply the base half of the borate pair — the part that neutralises the acid the film generates — and it is the only source of borate in the formula. Kodak’s 1928 primer gives the general trade: the quantity of alkali governs the energy of a developer, too much tends to chemical fog, too little makes it slow, and alkalis soften the gelatin. More borax at constant boric acid raises both the pH and the reserve and speeds the bath up; more borax with a matching cut in the boric acid is Kodak’s published adjustment, which speeds it up while leaving the agents, the sulfite and the grain untouched — though not, strictly, the reserve, because a constant weight of two solids of different molar masses is not a constant number of moles. Less borax and the bath is both slower and less able to hold its pH, which is the worst of both.

Boric acid, 8.0 g. The ingredient D-76 does not have, and the reason this page exists. It contributes nothing basic: 0.1294 mol/L of pure acid half, which does two things at once. It pushes the base-to-acid ratio from 1 : 1 down to about 1 : 4, lowering the pH by 0.61 of a unit on the arithmetic above; and it takes the total pair from 0.021 to 0.213 mol/L, multiplying the capacity by about six and a half. It is the same substance the course meets in Kodak’s F-5 fixing bath, and for the same underlying reason — Kodak’s 1928 primer’s point that the strength of an acid and the quantity of alkali it can neutralise are different quantities, so a very weak acid in bulk gives you capacity without acidity. In a fixer that keeps the bath inside a narrow window; here it holds a developer inside one. More boric acid at constant borax slows the bath and stiffens it further; less, and you converge on D-76. It is classified Danger for reproductive toxicity, which means this formula puts two such powders on the balance in one session rather than one.

Potassium bromide, 0.25 g per litre — optional, and added to the mixed bath. This is not one of the five solids Kodak prints in the formula. It appears in a note beneath it, offered against the “slight initial fog of a freshly mixed sample”, at 15 grains per gallon or 0.25 gram per litre — 0.0021 mol/L, a very small restraining dose beside the 4.0 g/L that D-19b carries. Bromide restrains by competing with development at the grain surface, which suppresses fog centres more than it suppresses image centres, so a little of it cleans a fresh bath’s highlights at a small cost in shadow speed. The 1949 handbook notes that potassium bromide has no action on the developing agents and may be added at any stage, which is why Kodak can offer it as an afterthought to the made-up litre. Add it only if you see the fog: a bath that has developed a few rolls has generated its own bromide and does not need any. Part VIII’s page on restrainers works the mechanism through.

Water to 1000 mL. Not inert. The 1949 handbook’s advice on stock solutions applies: iron in the water is the classic contaminant, and a solution stored cold enough to throw something down has lost the constituents you most need into the precipitate, which is redissolved by warming rather than decanted away from.

Interactions

Alkali and agent. The pH decides which of the two agents is actually working, and this formula moves the pH deliberately. Lowering it holds hydroquinone further in reserve and leaves more of the work to the metol, which is a contrast decision as well as a rate decision. It is the same lever DK-50 pulls in the opposite direction with a base-only alkali.

Alkali and alkali. The two borate ingredients are not two alkalis, they are the two halves of one pair, and this is the single most useful thing on the page to understand. Adding boric acid to a borax developer does not make it more alkaline in any sense; it makes it less alkaline and more stubborn. Anyone who reads “8 g of borax and 8 g of boric acid” as sixteen grams of alkali has the formula exactly backwards.

Alkali and sulfite. In D-76 the sulfite pair outweighs the borate pair thirty-eight to one, which is why Part VIII’s inference — that the borax sets the region and the sulfite carries the reserve — is a live one there. Here the ratio is under four to one, so the borate system is a real contributor to the reserve rather than a rounding error beside the sulfite. The inference about D-76 is not transferable to this formula, and this page does not transfer it.

Agent and agent. Superadditivity is unchanged in composition and changed in expression: the pair is the same 2 : 5 by mass as D-76’s, but the pH at which it is asked to work is lower.

Restrainer and time. The bath restrains itself as it works, on the bromide the film releases — which is the one form of drift a buffer does nothing about. A buffered developer holds its pH and still accumulates bromide, so the useful life of this bath is bounded by the halide it collects rather than by the alkali it loses. That is a real limit and it is the reason a buffer is not a substitute for a replenisher.

Variants

D-76 is the parent, and the two differ in exactly one subsystem. Printed side by side, the family reads as three answers to one question:

Ingredient	D-76	D-76d	D-76R
Metol	2.0 g	2.0 g	3.0 g
Sodium sulfite, anhydrous	100.0 g	100.0 g	100.0 g
Hydroquinone	5.0 g	5.0 g	7.5 g
Borax	2.0 g	8.0 g	20.0 g
Boric acid	—	8.0 g	—

D-76R is the replenisher for D-76, not for this formula; Kodak publishes no replenisher for D-76d in the 1944 booklet and the course will not improvise one.

Kodak’s own published adjustment — more borax and less boric acid for a faster bath, the reverse for a slower one, at constant total — is a family of variants the maker sanctions and declines to quantify. Any particular setting you arrive at is your formula and not Kodak’s, and belongs in the formula version record with the variable you changed and the result you got.

This is not a course variant. D-76d is Kodak’s own published formula with its own number and its own printed quantities, which is why it is filed as verified rather than as a variant of D-76. The formulary reserves the word variant for the course’s own modifications of somebody else’s formula, and this page contains none.

A note on what became of it. Kodak Limited’s 1949 handbook Chemicals and Formulae — the successor booklet in this course’s corpus, five years later — prints D-76 and D-76R and no buffered variant, and Kodak’s American formulary J-1, in the seventh edition of 1973 updated to 1977, prints D-76 and D-76R on page 37 and then an appendix of thirteen formulas “for developers which are no longer in general use” that does not include it either. So the formula was published and, on the evidence of the documents this course holds, not carried forward. Why is not stated in any of them, and the course does not guess.

✦A note for whoever writes the next Kodak page

The J-1 scan in this course’s corpus is the document the D-76 page had to record as unusable, because the mirror carries no extractable text layer. It is nevertheless perfectly legible: the file is fifty-six full-page JPEGs, one per page, and they can be read as images. The three statements about J-1 above were read that way, off pages 24, 37 and 51 to 53. Nothing on this page’s formula comes from it — the quantities are Kodak Limited’s 1944 booklet — but the claim that J-1 cannot be read is now only true of its text layer.

Safety

Level B, and by a slightly wider margin than D-76. Four of the five solids put it past Level A on their own: metol is a skin sensitiser; hydroquinone carries a Danger classification with suspected carcinogenicity and mutagenicity and causes serious eye damage; and both borax and boric acid are classified Danger for reproductive toxicity — boric acid at H360, may damage fertility or the unborn child. The classification rubric sets out what Level B assumes: splash goggles, ventilation better than a closed room, eyewash within reach, and experience with concentrated reagents.

The quantitative difference from D-76 is in the boron. D-76 carries 2 g of borax in a litre; this formula carries 8 g of borax and 8 g of boric acid, so the dry weight of reproductive-toxicant powder you handle per litre is eight times larger, and it arrives as two separate weighings rather than one. Weigh both with extraction running or inside an enclosure, never in a draught, and follow the weighing SOP. This is the one part of the job where the hazard is concentrated: once the five solids are in a litre of water the concentrations are low, though gloves and eye protection stay on because metol is a sensitiser at any dilution.

What is not a hazard here. Nothing in this formula evolves a gas in normal use. The bath is not strongly alkaline — it is less alkaline than D-76 — so it is not a corrosive-alkali risk, and nothing is heated beyond the water used to dissolve the borax. The ventilation requirement is for dust while weighing, not for vapour while developing.

Storage

Kodak publishes no keeping figure for D-76d, in this booklet or anywhere else the course has read, so the honest instruction is to treat it as you would D-76 and to expect no more: a full, tightly corked bottle with as little air space as the neck allows, several small bottles in preference to one large one, and a date on the label. For scale, Kodak’s figures for D-76 stock are six months in a full stoppered bottle, two months half-filled, one month in a tank under a floating lid and twenty-four hours in a dish, and those are D-76’s figures, quoted here as the nearest published comparison and not as this formula’s.

The buffer does nothing for keeping. Aerial oxidation of the agents is a reaction with oxygen, not with acid, and the sulfite is the ingredient that defends against it; a buffered bath in a half-empty bottle oxidises on the same schedule as an unbuffered one. Label it with the formula, the date mixed and the fact that it has no published development time, using the labelling SOP.

If a cold bottle has thrown down a crystalline deposit, warm it and redissolve rather than decanting the clear liquid off the top — with two borate solids in the bottle the precipitate is more likely here than in D-76, and the 1949 handbook’s point stands that a precipitate often contains the solution’s most important constituents.

Incompatibilities

Acid, deliberately and in quantity. The paradox of a buffered developer is worth stating: the buffer makes it harder for a small acid carry-over to change the bath, and makes it no safer to splash a stop bath into it. A tong that goes from the stop tray back into the developer still carries acetic acid, and 0.078 mol/L per pH unit of capacity is a reserve, not an immunity. See the stop bath part for what the acid is for and why it must stay there.

Fixer, in either direction. Thiosulfate carried into a developer is a far more aggressive silver solvent than sulfite and will fog and stain; developer carried into the fixer shortens its life and spoils a solution that would otherwise go for silver recovery.

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

Waste

Spent D-76d is a dilute, mildly alkaline solution whose environmental load is the developing agents, the sulfite and — much more than in D-76 — the boron. Count it: D-76 carries 0.021 mol of boron species per litre and this formula carries 0.213, a tenfold increase. Borate is a registered vegetation control and both developing agents carry aquatic-toxicity classifications, so spent developer does not go on the garden whatever its pH and does not go down a drain that a regulator has not agreed to.

Keep it in its own labelled bottle. It carries almost no silver, and pouring it into the fixer bottle ruins a solution that would otherwise go for silver recovery. The disposal caveat governs and the general chemical waste SOP gives the procedure. Local regulation decides, and this course cannot tell you what it says where you are.

Troubleshooting

A slight overall fog on a freshly mixed bath. This is the one fault Kodak anticipated on the page, and it published the remedy: 0.25 g of potassium bromide per litre of the mixed developer. Add it once, to the bath, and do not carry the habit forward to a bath that has already developed film.

The negatives are thin and the time was D-76’s. Expected. There is no published time for this formula and D-76’s is not transferable; the arithmetic says this bath sits lower in pH than a plain borax one. Establish a time with a control strip or a test roll before committing anything you care about.

Undissolved grit in the bottom of the bottle. Almost always the boric acid, and almost always because it went in as powder rather than crystals or the water was cold. Kodak’s own footnote warns against powdered boric acid. Warm the solution and stir it back in rather than filtering it out — what you would be filtering out is a quarter of the buffer.

The bath is far slower than expected and stayed slow. Check the two 280-grain lines. Borax and boric acid have identical figures in the imperial column and identical figures in the metric column, which makes them the easiest pair in the formulary to transpose or to weigh from different columns. Twice the boric acid and half the borax is a much slower developer, and it will be consistently slower rather than intermittently.

Contrast drifting upwards over a session. Not a buffer failure. Bromide accumulation restrains shadow development more than highlight development, so a seasoned bath of any formula tends to climb; the buffer holds the pH, not the halide. Count what has been through the litre.

A bath that has developed a lot of film and is now slow. The buffer has done its job and the formula has still run out of developing agent, because a buffer replaces nothing. There is no published replenisher for D-76d. Mix fresh.

Experiments

The pair against the parent. A litre of D-76 and a litre of D-76d, matched strips from one exposure batch, the same time and temperature in both. Every ingredient except the alkali system is identical, so any difference in density is attributable to the buffer and to nothing else. This is the cleanest single-variable comparison available anywhere in the formulary and it is worth running before any of the others. Record it on the developer laboratory report.

Kodak’s own dial, quantified. Mix four litres at a constant total of 16 g of borate solids — 4 + 12, 8 + 8, 12 + 4 and 16 + 0 grams of borax and boric acid — and develop matched strips for the same time. Kodak states the direction and not the magnitude, so what you are producing is the number the source withholds: a development-rate curve against buffer ratio. The prediction from Henderson and Hasselbalch is that the four baths sit at roughly pH 8.3, 8.7, 9.0 and 9.27, and that the densities order accordingly. Work the capacities out before you start as well, because they do not hold still — 0.044, 0.078, 0.097 and 0.097 mol/L per pH unit across the four — and the last two are level because the pair shrinks in moles as it approaches the equal-halves ratio where a buffer is strongest. Constant weight is not constant capacity, and the difference is the sort of thing a formula’s published instruction can hide.

Load the buffer and watch it hold. Season a litre of each formula with the same number of rolls, measuring pH after each one if you have a calibrated meter. The prediction is that D-76 drifts about six times as far as D-76d for the same load. This is the experiment that tests the whole claim of the formula, and it is the one nobody in the sources ran in public.

The boric acid alone. Take a litre of plain D-76 and add 8 g of boric acid to it — not the buffered formula, D-76 plus the acid. Compared with a control litre it should be slower and much harder to shift, which separates the effect of adding the acid half from the effect of raising the whole pair that D-76d does both of at once. It is also a warning worth feeling: two grams of a solid you might think of as inert will visibly change a developer’s speed.

Measure the pH of both and publish the number. The course cannot give you a pH for D-76d because none is published. If you have a meter and a set of buffers, you can produce one for your own bottle, label it as your own measurement, and put it in the lab notebook — which is exactly what Part VIII says it intends to do about the gap in this family’s published data.