Assignment: Reading a Developer Formula

Six developers sit in front of you: D-76, D-23, Rodinal, XTOL, Microphen and PMK. Every one of them is in current use, every one has a personality photographers argue about, and the composition of four of them is not public.

That is not an obstacle to this assignment. It is the assignment. What you are practising is the thing that separates a chemist from a person repeating a recipe: taking a formulation apart as far as the evidence goes, saying precisely where it stops, and still making a good decision from what is left.

Part 1 — The provenance ladder

Before any chemistry, sort the six by what the course actually holds. This is the course’s provenance rule applied as a piece of work rather than quoted as a principle.

Developer	What the course holds	Verdict
Kodak D-76	Kodak’s own 1928 primer, with the formula and its mixing directions; Kodak Limited’s 1949 handbook, with the same quantities independently; Kodak Alaris’s current J-78 sheet, with times, capacity and storage	Published. Printed in full.
Kodak D-23	Kodak Limited’s 1949 handbook, with the formula, the dissolving instruction and a development time	Published. Printed in full.
Rodinal	The Adox datasheet, fetched and unreadable; Foma’s sheet for the same developer type, disclosing the agent class; ILFORD’s film sheets, publishing times for it without composition	Proprietary. Class and behaviour only.
Kodak XTOL	Kodak Alaris’s J-109 sheet: “ascorbic acid-based”, “no hydroquinone”, pH 8.20 ± 0.05, specific gravity 1.085 ± 0.003, two-part powder, keeping, capacity, dilution	Proprietary. Two disclosed facts and a great deal of behaviour.
ILFORD Microphen	ILFORD’s technical sheet: pH 8.67 to 8.93, specific gravity 1.095, a claimed speed increase of up to half a stop, and grain behaviour attributed to low alkalinity	Proprietary. Behaviour and two measurements; no agent named.
PMK	Bergger’s 2020 datasheet: “pyrogallol-based”, two solutions, 1+2+100, capacity, temperature range, processing, hazards, a time chart	Documented by a manufacturer, composition undisclosed. One agent named, no quantities.

!The rule this page is built on, stated once

A formula is printed only where the course has read a document that gives it, and only where every ingredient’s function can be explained. Where a product’s composition is not disclosed, the course teaches it as behaviour and disclosed components and prints nothing else — not a composition from a secondary listing, not a reconstruction, not “essentially the same as”.

The temptation is real and worth naming. Compositions for all four of the closed products circulate, some of them probably close to right. The trouble is that a course which published them would have no way to tell you which ones were right, and a reader could not tell a sourced formula from a plausible one. The value of the two formulas this page does print comes from the fact that it declines to print the others.

The second half of the rule bites too. Even a published formula is printed only where every ingredient’s function can be explained. That is why D-76 and D-23 arrive here at the end of Part VIII rather than at the start: it took nine lessons to be able to say what each of their four ingredients does.

Part 2 — Two formulas, taken apart

Kodak D-76

Kodak’s 1928 primer gives it for four litres and Kodak Limited’s 1949 handbook for one, and the two agree exactly. Per litre:

Ingredient	Quantity	Class
Metol	2.0 g	developing agent (primary)
Sodium sulfite, anhydrous	100.0 g	preservative, buffer and silver solvent
Hydroquinone	5.0 g	developing agent (secondary)
Borax	2.0 g	alkali
Water to make	1 litre

Metol, 2.0 g. The primary agent: high reduction potential in Kodak’s own ranking, meaning it will develop against a good deal of bromide, and it works at a modest pH where hydroquinone barely works at all. It brings the image up quickly and gains density slowly, which is the behaviour that fills the shadows. More would raise activity and speed and eventually fog; less would leave the shadows thin and slow the whole bath, because the second agent cannot start what the first one has not begun.

Sodium sulfite, 100.0 g. Three jobs at once, which is why it is ninety-two per cent of the dry weight. It scavenges oxygen; it intercepts the oxidised agent; and — the job that makes D-76 what it is — it acts as a silver solvent, dissolving a little of every grain during development and breaking the contacts that would otherwise clump. More means finer grain, less speed and a rising risk of dichroic fog; less means coarser grain, better speed, sharper edges and a bath that keeps worse. It cannot be adjusted for one of those reasons without moving all of them.

Hydroquinone, 5.0 g. The secondary agent, at two and a half times the metol by mass. Kodak’s own 1928 ranking puts its reduction potential so low that “it is rarely used alone but is generally used with Elon”; alone at borax pH it is nearly inert. Its work here is superadditive: the pair develops faster than either alone. More raises contrast and the eventual capacity of the bath; less, and the developer runs down sooner, because there is less reserve behind the metol.

Borax, 2.0 g. The alkali, and a deliberately weak one — Kodak introduced it precisely for fine-grain motion-picture negatives. It holds the bath near pH 8.6, which is enough to ionise metol and not enough to make hydroquinone violent. Kodak’s own statement of the trade is unambiguous: 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. More alkali means faster development, more fog, more swelling and — Kodak’s own observation about this formula specifically — accentuated graininess, because a faster development gives the solvent less time to work before the grains are gone.

🧮What the ratios say before you read a word about it

Convert D-76 to moles, using the encyclopaedia’s molar masses, and the formula explains itself.

100 g/L ÷ 126.05 g/mol = 0.79 mol/L

Sulfite

5 g/L ÷ 110.11 g/mol = 0.045 mol/L

Hydroquinone

2 g/L ÷ 381.37 g/mol = 0.0052 mol/L

Borax

Sulfite outnumbers hydroquinone seventeen to one, and outnumbers the alkali a hundred and fifty to one. No account of sulfite as a preservative can justify seventeen equivalents, which is the arithmetic that forced the sulfite lesson to look for a second and third job. And 0.0052 mol/L of borax is a very small quantity of alkali, which is what a fine-grain developer wants and also why the bath has modest buffer capacity and drifts as it works.

Do this arithmetic for every formula you meet. It takes two minutes and it usually finds the design decision.

Kodak D-23

From Kodak Limited’s 1949 handbook, described there as an “Elon fine-grain developer for plates and films; a soft-working developer of simple formula giving normal emulsion speed”. Per litre:

Ingredient	Quantity	Class
Metol	7.5 g	developing agent, and the only one
Sodium sulfite, anhydrous	100.0 g	preservative, buffer, alkali and silver solvent
Water to make	1 litre

Two ingredients. No hydroquinone, and — this is the striking part — no alkali at all.

Metol, 7.5 g, nearly four times D-76’s dose, because there is no second agent to regenerate it and no borax to accelerate it. Everything the developer does, this does.

Sodium sulfite, 100.0 g, doing a fourth job it was only half-doing in D-76: it is the alkali. Sodium sulfite is the salt of a strong base and a weak acid, so its solution is alkaline; with bisulfite it also forms a buffer pair. Kodak’s own instruction is to use it undiluted and develop about 18 minutes at 18.3 °C.

What the omissions predict. Compare the two formulas rather than reading them separately, and the predictions fall out.

• Softer working, which is Kodak’s own word. One agent, no accelerator, low pH: the gradient climbs slowly, so highlights are restrained relative to shadows.
• Full speed, which Kodak also states — because the pH is low and there is no bromide, so the threshold is not raised, and metol at 7.5 g/L is plenty.
• Fine grain, from the same 100 g of sulfite as D-76.
• Long times. Eighteen minutes against D-76’s eight or nine on a modern film.
• Poor buffer capacity. There is no conjugate pair holding the pH except sulfite and whatever bisulfite forms as it oxidises, so the bath drifts as it works.

And the variant proves the reading. Kodak’s D-25 is D-23 plus 15 g/L of sodium bisulfite, and nothing else. The handbook describes it as an “extra fine-grain developer — a simple formula for minimum grain”, warns that it “requires 50 to 100 % increase in exposure”, and gives 18 minutes at 25 °C rather than 18.3 °C. Adding an acid salt lowered the pH, and the price was a stop of speed. One ingredient, one arrow, and Kodak printed both ends of it.

Part 3 — Four developers taught as behaviour

For each of the four closed products, the discipline is the same: list what is disclosed, list what can be inferred and label it as inference, and list what is unknown and stays unknown.

Rodinal, and the para-aminophenol class

Disclosed. Almost nothing, by the manufacturer of the branded product. The Adox datasheet in the course’s corpus was fetched successfully and carries no extractable text layer, so this course quotes nothing from it: no dilution, no pH, no keeping claim, no statement about stand development.

What the course does hold. Foma describes its FOMADON R09 as “a liquid concentrate of a fine-grain, normal-working para-aminophenol negative developer”, used at 1+25 or 1+50, with a capacity of 25 films per package. ILFORD’s own film sheets publish development times for “Agfa Rodinal” at 1+25 and 1+50 — 6 and 11 minutes for HP5 Plus at EI 400 — without saying what is in it. And Wall’s 1924 formulary records the period rodinal-type liquid developers, which are historical formulas and not Agfa’s.

Inference, labelled as inference. A single-agent concentrate used at 1+50 has very little of anything per unit volume of working solution, so it must exhaust locally, must be a one-shot, and must give strong adjacency effects. That prediction follows from the class, not from the product.

Unknown, and left unknown. The composition, the alkali, the sulfite level, the pH, and whether the current product is the 1891 formulation at all.

XTOL

Disclosed, and it is more than most. Kodak Alaris states in its features table that XTOL is an “ascorbic acid-based black-and-white film developer” and carries “no hydroquinone”. It is a two-part powder; one solution serves as both developer and replenisher; the correctly mixed working tank solution is specified at pH 8.20 ± 0.05 and specific gravity 1.085 ± 0.003 at 25 °C; it mixes in water at 18 to 30 °C; storage is six months in a full container and at least two months in a partially filled one, “because partially filled containers allow oxidation of the solution”.

What is claimed rather than measured. Very high image quality at full emulsion speed, fine grain and high sharpness, more emulsion speed than most developers, a contrast index similar to other developers, and stable performance across a range of temperatures, dilutions and agitation methods. These are the manufacturer’s claims about its own product, and the course labels them as such.

Inference, labelled. A pH of 8.20 sits in the same region as ILFORD’s borax-class developers, so the alkali is a mild one. Ascorbate’s oxidation chemistry has no sulfonate route, which the alternative-agents lesson establishes, so the way this developer fails when it fails will not look like an MQ developer’s slow browning.

Unknown. The second developing agent. Kodak names none, and although a superadditive partner is implied by everything the course knows about ascorbate developers, J-109 does not name one and neither does this page. Also unknown: the sulfite level, the buffer system, and any sequestrant.

Microphen

Disclosed. ILFORD publishes pH 8.67 to 8.93 and specific gravity 1.095 for the fresh stock solution, measured under controlled laboratory conditions, and advises users to make their own control measurements. It is a two-part powder mixed at about 40 °C. Its claimed behaviour is a speed increase of up to half a stop with most films and more with the faster ones, and the sheet gives its own explanation for the grain: “the low alkalinity of the developer reduces grain size and grain clumping”, so that Microphen “gives a speed increase while retaining much of the grain characteristics associated with fine grain developers”.

No developing agent is named anywhere on the sheet. ILFORD does name agents elsewhere — its paper developer sheet calls BROMOPHEN “a phenidone/hydroquinone developer” and MULTIGRADE and PQ UNIVERSAL “dimezone-s/hydroquinone” — which shows that the omission for the film developers is a choice, not an oversight.

Inference, labelled. The published pH of 8.67 to 8.93 is higher than ID-11’s 8.60 to 8.70, so ILFORD’s own phrase “low alkalinity” must be relative to the speed-increasing developers it is competing with rather than to its stablemate. That is worth noticing: a manufacturer’s adjective and its own table can point different ways, and the table is the harder evidence.

Unknown. Every ingredient.

PMK

Disclosed. “A pyrogallol-based developer… adapted to modern films by Gordon Hutchings in the 1980s”, supplied as two solutions of 250 mL and 500 mL, used at 1 + 2 + 100, capacity 1,000 cm² of film per litre, working range 21 to 27 °C, an hour of working-solution life in an open vessel, and a concentrate shelf life claimed at up to ten years even in half-filled bottles. The processing requirements are unusually specific and are all published: a 3 to 5 minute pre-wet, agitation every 15 seconds, a non-acid stop, a non-tanning fixer, a 20 to 30 minute wash and no hypo eliminator.

What is claimed rather than measured, and one place where the sheet contradicts itself: the prose claims increased film sensitivity while the sheet’s own time chart lists FP4 Plus at EI 80 and HP5 Plus at EI 200, both well below box speed. The staining lesson sets that out in full; the point for this assignment is that finding it is your job, and that a careful reader catches it by comparing the prose with the table on the same sheet.

Unknown. All quantities. Which agent is in which solution. The alkali. The sulfite level, although it must be low or there would be no stain.

Part 4 — Predicting behaviour from composition

The point of taking a formula apart is to predict what it will do before you mix it. Fill in this matrix for all six, and for each cell write the evidence class as well as the answer: published, inferred from composition, manufacturer’s claim, or not knowable from what is disclosed.

	Grain	Effective speed	Contrast character	Keeping	Edge behaviour
D-76 stock
D-76 1+1
D-23
Rodinal 1+50
XTOL
Microphen
PMK

Two rows are worked here so that the standard is clear.

D-76 stock. Grain: fine — published, Kodak’s own description, with the mechanism in the 1928 primer. Speed: full — published, “full emulsion speed” on J-78. Contrast: normal, adjustable by time, with a contrast index around 0.62 at eight minutes on the standard method — published, from the H-740 workbook, which notes that its standard developer is similar to D-76. Keeping: six months full, two months half-filled — published. Edges: moderate, and Kodak’s own route to more is dilution — published.

Rodinal at 1+50. Grain: coarser than a solvent developer — inferred from the class, since a single-agent concentrate at 1+50 carries almost no sulfite into the working solution. Speed: at or near box — inferred; ILFORD tabulates times for HP5 Plus at 1+50 at EI 400, which is published support for the inference but not a statement about speed. Contrast: compensating at high dilution — inferred from the class, and supported for the class by ADOX’s statement about FX-39 II. Keeping: concentrate excellent, working solution one-shot — not knowable for this product from the corpus. Edges: strong — inferred from the class.

Notice how much of that second row is inference. That is an honest reading of a closed product, and it is more useful than a confident one.

Part 5 — Mixing order, and why it is not arbitrary

Kodak Limited states the rule and the reason in one paragraph, and it is the best short piece of practical chemistry in the 1949 handbook:

When developers are made up, it is essential to dissolve the constituents in the order given in the formula if undesirable reactions are to be avoided. For instance, if the developing agent is dissolved first, and then the alkali is added, considerable aerial oxidation and formation of coloured oxidation products may occur before the preservative, sodium sulphite, is dissolved.

Then the specific rule for metol, which is the one that surprises people:

In the case of formulae containing the developing agent “Elon,” the “Elon” should be dissolved first, since it is readily soluble in warm water, but only slightly soluble in sulphite solutions without alkali. After the “Elon” is completely dissolved the sulphite should be added, followed by the other developing agents, and finally the alkali.

Three more rules from the same page, each with its reason:

• In other formulas the preservative goes first, then the agents, then — only when those are completely dissolved — the alkali.
• Potassium bromide’s position does not matter: “since the potassium bromide has no action on the developing agents, it is immaterial at what stage it is added”.
• Sodium bisulfite goes in with the sulfite.

✕The received wisdom, and what Kodak actually wrote

You will often be told to put “a pinch of sulfite” into the water before the metol, to stop the metol oxidising while it dissolves.

This course could not source that instruction to Kodak, and Kodak’s own two documents say something different. The 1949 handbook says the metol goes into warm water first, and gives a solubility reason rather than an oxidation one: metol is readily soluble in warm water but only slightly soluble in sulfite solutions without alkali. The 1928 primer’s directions for mixing D-76 are more specific still and put the sulfite in two portions: dissolve the Elon in a small volume of water at about 52 °C; separately dissolve about a quarter of the sulfite in hot water at about 71 °C and add the hydroquinone to it; then dissolve the remainder of the sulfite, add the borax, and combine.

The received practice may well work, and the reasoning behind it is not silly. But the course states what its sources state, marks the rest as unverified, and does not present a widely repeated instruction as a manufacturer’s. Part of this assignment is noticing that you had heard the “pinch of sulfite” rule and could not have said where it came from.

Now do the reasoning yourself. For each of the four closed products, ask: what does the mixing instruction reveal about the composition? XTOL is two parts and mixes at room temperature, which tells you the agents survive being packaged together with something. The ILFORD powders are two bags, A small and B large, with A dissolved first — and the small bag going in first is exactly the pattern Kodak’s rule predicts for a formula whose agent must precede the bulk sulfite. PMK is two liquids that are never combined until the moment of use, which is the classic arrangement for an agent that cannot tolerate its own alkali on a shelf.

Part 6 — Formula versioning

A result that cannot be tied to a specific mix is not evidence about a formula. The course therefore gives every mixed batch an identifier, in the form:

FORMULA-INITIALS-SEQUENCE

Formula version

so that the first litre of D-23 mixed by a student with the initials EB is D23-EB-001, and the second is D23-EB-002. The identifier goes on the bottle, in the notebook, and on every strip, negative and curve that came out of that bottle.

What must be recorded against the identifier, once, when the batch is made:

• The formula and the source it was taken from, by document and section.
• Every mass actually weighed, to the resolution of your balance — not the target mass.
• The water: its source, its temperature at each stage, and the final volume.
• The dissolving order used, and any deviation from the published one, with the reason.
• The measured pH and the temperature it was measured at.
• The date and time of mixing, the bottle, and how full it is.
• Any deliberate change from the published formula, stated as a change.

A version number changes when anything in that list changes. Substituting anhydrous carbonate for the crystalline salt is a new version, even at Kodak’s own conversion factor of two and a half. Mixing at a different temperature is a new version. Using tap water instead of distilled is a new version. The discipline is not bureaucratic: it is what makes a difference between two negatives attributable to something.

Part 7 — The chemistry selector

This is an educational model. It shows the direction a change moves a result and never its magnitude. It predicts no particular film, paper or developer. No number or recommendation read from it may stand in for your own measurement, and nothing it produces is a formulation that has been shown to be safe, stable or valid: anything you would actually mix goes through the course’s provenance rule and a hazard assessment first.

The selector takes a stated intention and returns the class of chemistry that answers it, with the reasoning shown. It is a table you read, not a machine that decides.

If your stated intention is…	…the chemistry that answers it	The reasoning, in one line
The finest grain I can get, and I can afford to lose speed	A high-sulfite, low-alkali developer at full strength	Solvent action breaks the contacts that make clumps, and the same reaction costs the marginal grains
The sharpest edges I can get, and grain is secondary	A single-agent, low-sulfite developer at high dilution, with restrained agitation	Local exhaustion at boundaries is the engine of edge effects, and it needs a small local reservoir
Every bit of speed the film has	A higher-activity developer of the speed-increasing class, at full strength	Speed is set at the toe, so anything that lowers the development threshold helps there first
Highlights held without flattening the shadows	High dilution and reduced agitation, or a two-bath arrangement	Compensation acts where consumption is fastest, which is the highlights, and nowhere else
A negative that prints easily on variable-contrast paper	A conventional MQ or PQ developer, developed to a stated contrast index	A neutral silver image has one density, readable the same way in every light
Reproducibility above all	Any developer, used one-shot at a stated dilution	A reused or replenished bath is a different solution on its second film
Long shelf life in a darkroom used twice a year	A two-part or concentrate product, stored full and dated	The oxygen a solution meets is set by the headspace, not by the preservative

The interactive chemistry selector implements these intentions and also routes fixer, paper-developer and toner decisions to the evidence now available in Parts XI, XVIII and XX. It returns a class with limitations, not a recipe or an approval of handling conditions.

Part 8 — The formula designer

Explore one change in the formula designer, then use the sourced table below to challenge its reasoning.

This is an educational model. It shows the direction a change moves a result and never its magnitude. It predicts no particular film, paper or developer. No number or recommendation read from it may stand in for your own measurement, and nothing it produces is a formulation that has been shown to be safe, stable or valid: anything you would actually mix goes through the course’s provenance rule and a hazard assessment first.

Move one variable, read the direction. Every arrow in this table has a source, and any relationship without one is missing rather than guessed.

Move this…	Activity	Contrast	Grain	Fog	Keeping	Source for the arrow
More alkali (higher pH)	↑	↑	↑ coarser	↑	—	Kodak 1928: the quantity of alkali governs the energy of a developer, too much tends to produce chemical fog and too little is slow; and adding carbonate to a high-sulfite developer increases the rate and accentuates graininess
More sulfite	—	—	↓ finer	↑ dichroic risk	↑	Kodak 1928: high sulfite dissolves a little of each grain and minimises clumping; an excess of sulfite may give dichroic fog; sulfite protects the developer from the oxygen of the air
More bromide	↓	—	—	↓	—	Kodak 1928: bromides are added to compensate for chemical fog; Hurter and Driffield’s Experiment 15 shows the whole curve displaced right and down as bromide rises
A second, superadditive agent	↑ more than the sum	↑	—	—	—	Kendall’s patent and Kodak’s 1928 account of the Elon–hydroquinone pair; the superadditivity lesson
More dilution	↓	↓ (compensating)	↑ slightly coarser	—	working solution ↓	Kodak J-78 and E-103CF: greater sharpness with a slight increase in graininess at 1:1; ADOX FX-39 II: 1+19 acts to reduce contrast for high-contrast subjects
Longer development time	—	↑	—	↑	—	Kodak H-740: contrast index 0.51 at 5 minutes, 0.62 at 8, 0.73 at 13
Higher temperature	↑	↑	—	↑ faster than image	Kodak 1928: the temperature coefficient, and the statement that the fog reaction has a much higher temperature coefficient than development

!Relationships this model refuses to assert, and why

An omission here is a decision, not an oversight. Each of these is a relationship photographers talk about and the course has no Tier-1 or Tier-2 source for the direction, so the designer leaves the cell empty rather than filling it plausibly.

• Bromide against effective speed. Kodak says a used, bromide-laden developer’s restraint is “analogous to cutting down the exposure”; Hurter and Driffield found that the retarding influence of bromide “can be fully compensated by time of development” and that the speed of the plate “is not really altered”. The restrainer lesson marks this contested and records that no source in the corpus gives a figure for speed lost per gram of bromide.
• Sulfite against contrast. Sulfite changes activity, grain and speed, and the course has no source stating a direction for contrast, so there is a dash in that cell.
• Sulfite or bromide against keeping, in a developer that already has enough. The preservative arrow above is about having some; whether more than enough helps is not sourced.
• Anything at all about magnitude. Not one number in this table is a quantity. “More alkali raises activity” is sourced; “0.5 g/L more borax raises activity by X per cent” is not, for any X, in any source this course holds.
• Interactions. Every arrow assumes one variable moving alone. Real formulation moves several, and the arrows do not add up. That is the honest limit of a one-variable model and the reason Part IX measures rather than predicts.

Part 9 — The curve family

This is an educational model. It shows the direction a change moves a result and never its magnitude. It predicts no particular film, paper or developer. No number or recommendation read from it may stand in for your own measurement, and nothing it produces is a formulation that has been shown to be safe, stable or valid: anything you would actually mix goes through the course’s provenance rule and a hazard assessment first.

Four levers, four ways a characteristic curve moves

1. 1More alkali — steeper, and the foot lifts: more contrast and more fog together
2. 2More sulfite — a small shift right: a little speed lost. The grain change is not on this axis at all
3. 3More bromide — displaced right, foot lower: threshold up, fog down
4. 4Longer development — pivots about the toe: steeper and higher, with the toe nearly fixed

No axis carries a number, and none may be added. The reference shape is taught rather than measured, and each panel moves one variable alone; a real change to a formula moves several at once.

Work through the four panels with the designer table beside you, and for each one write the sentence that joins them: this lever moves the curve this way because this ingredient does this to the reaction. A lever whose curve movement you cannot explain from Part VIII’s chemistry is a lever you have memorised rather than understood.

Part 10 — Art track: matching a developer to an intention

Three briefs. For each, choose from the six, and defend the choice from the chemistry rather than from reputation. There is no single right answer; there are answers with reasoning and answers without.

A portrait, in soft window light, to be printed at 16 × 12 inches. Skin is a subject of gradients and almost no true edges, and the print is large enough for grain to be visible. Consider what edge enhancement does to a face, and what a solvent developer costs you in speed when the light is already low.

A building, in hard sun, with a very long tonal range from lit stone to shadowed doorway. The subject supplies more contrast than the paper can hold, and it is made almost entirely of boundaries. Consider compensation, and consider what the sky will do at the top of the curve.

A city street at night, with lit windows against dark walls. Extreme range, low overall light, small bright sources. Consider which developer keeps shadow separation while stopping the windows blocking up, and consider that the failure of a dilute developer with restrained agitation on a scene like this is streaking below the bright areas — the bromide drag Part III described.

For each brief, write down three things: the developer and dilution, the one property that decided it, and the cost you are accepting. A defence with no cost in it is not a defence, because every lever on this page is a trade.

What to submit

1. The provenance ladder, completed in your own words: for each of the six, what the course holds, what verdict follows, and one sentence on how you would recognise the same situation with a product this page does not cover.
2. The completed function table for XTOL, with a row per ingredient the manufacturer discloses, a row for each ingredient class you can infer with the inference labelled, and an explicit list of what is not knowable from J-109. Mark every unknown; do not leave a blank that could be read as an absence.
3. The behaviour matrix, all seven rows, with the evidence class written in every cell.
4. A mixing-order justification for D-76, in your own words, citing the two Kodak documents and saying which one you would follow and why.
5. Your version-record template, filled in for the batch you are about to mix in the lab.
6. One art brief answered, with the developer, the deciding property and the accepted cost.
7. One paragraph on the thing you believed and could not source. Everyone has one. Naming it is the habit this assignment is really for.

Check your understanding

Question 1. Kodak’s J-109 sheet says XTOL is "ascorbic acid-based" and carries "no hydroquinone". What may a course legitimately print about XTOL’s composition on that basis?

• The full formula, since the agents are now known
• That it is ascorbate-based and contains no hydroquinone, and nothing further — the second agent, the sulfite level and the buffer are not named by Kodak and are not supplied by the course
• That it contains Dimezone S, since ascorbate developers need a superadditive partner
• Nothing at all, since the sheet is a marketing document

Show the answer and why

Answer: That it is ascorbate-based and contains no hydroquinone, and nothing further — the second agent, the sulfite level and the buffer are not named by Kodak and are not supplied by the course

A manufacturer sheet is Tier 1 evidence for what it states. Two disclosed facts are two disclosed facts, and they are genuinely informative: they tell you the oxidation chemistry has no sulfonate route, so this developer will not fail the way an MQ developer does. Filling in a superadditive partner is the tempting move and it is exactly what Rule 6 forbids — the inference may well be right, and a course that published it would give a reader no way to tell it from the sourced half.

Question 2. Kodak D-25 is D-23 plus 15 g/L of sodium bisulfite, and Kodak’s handbook states that it requires a 50 to 100 per cent increase in exposure. What single mechanism explains the whole difference?

• The bisulfite acts as a restrainer, raising the development threshold
• The bisulfite is an acid salt, so it lowers the pH; less of the metol is ionised, activity falls, and the price of the finer grain that lower activity brings is paid in effective speed
• The bisulfite dissolves more silver halide, costing speed
• The bisulfite reduces the sulfite’s solvent action

Show the answer and why

Answer: The bisulfite is an acid salt, so it lowers the pH; less of the metol is ionised, activity falls, and the price of the finer grain that lower activity brings is paid in effective speed

In D-23 the sulfite is the alkali as well as the preservative and the solvent, so adding an acid sulfite is a direct pH lever and nothing else changes. Lower pH means less of the metol present as the active ionised species, which slows development throughout and hits the toe hardest, where speed is decided. It is the cleanest single-ingredient demonstration in the Kodak formulary: one salt, one direction, and the manufacturer printing the cost alongside the benefit.

Question 3. Which of these belong in the formula designer as sourced direction-of-change arrows?

• More alkali raises activity and raises fog
• More sulfite gives finer grain
• Two grams per litre of bromide costs one third of a stop of speed
• Longer development raises contrast

Show the answer and why

Answer: More alkali raises activity and raises fog, More sulfite gives finer grain, Longer development raises contrast

The first, second and fourth each have a Tier-1 statement behind them: Kodak’s 1928 primer on the alkali governing energy and tending to produce chemical fog, the same primer on high sulfite dissolving a little of each grain, and the H-740 workbook’s contrast indices of 0.51, 0.62 and 0.73 at 5, 8 and 13 minutes. The third fails twice over — no source in the corpus gives a figure for speed lost per gram of bromide, and the model asserts no magnitudes for anything at all, only directions.

Question 4. Kodak Limited’s 1949 handbook says metol should be dissolved first because it is "readily soluble in warm water, but only slightly soluble in sulphite solutions without alkali". Why does that matter more than the oxidation argument usually given?

• Because oxidation is not a real risk during mixing
• Because it is a solubility constraint rather than a kinetic one: metol added to a strong sulfite solution may simply fail to dissolve, which no amount of stirring or speed will fix
• Because sulfite reacts with metol to form an insoluble salt
• Because warm water dissolves everything faster

Show the answer and why

Answer: Because it is a solubility constraint rather than a kinetic one: metol added to a strong sulfite solution may simply fail to dissolve, which no amount of stirring or speed will fix

The two arguments predict different failures. An oxidation argument says the metol will be damaged if it waits; a solubility argument says it will not go into solution at all. Kodak gives the second, and it is the one that decides the order for this class of formula. Note also that the primer’s own directions for D-76 split the sulfite into two portions and put the hydroquinone into the first of them, which is more specific than either the general rule or the received "pinch of sulfite" advice — and it is what a formula’s own instructions are for.

Question 5. ILFORD publishes Microphen’s stock pH as 8.67 to 8.93 and attributes its grain behaviour to "the low alkalinity of the developer", while publishing ID-11 at 8.60 to 8.70. What should a careful reader conclude?

• That ILFORD has made an error in one of the two figures
• That "low alkalinity" must be relative to the speed-increasing developers Microphen competes with rather than to ID-11, and that where an adjective and a table point different ways the table is the harder evidence
• That pH is not a good measure of alkalinity
• That Microphen contains a different alkali from ID-11

Show the answer and why

Answer: That "low alkalinity" must be relative to the speed-increasing developers Microphen competes with rather than to ID-11, and that where an adjective and a table point different ways the table is the harder evidence

Both figures are from the same table on the same sheet, measured under stated conditions, so neither is likely to be wrong. What the comparison catches is that a descriptive phrase always has an implied comparison class, and the sheet does not say what Microphen’s is. Reading the number against the adjective — rather than accepting the adjective — is the specific skill this assignment is training, and it costs nothing but attention.

Question 6. Why is every one of the three educational models on this page required to carry the same wording about direction, magnitude and validity?

• Because the course is legally obliged to disclaim
• Because a model that shows only direction can be mistaken for one that predicts values, and repeating the limit identically wherever the model appears is what stops a reader carrying a number away from it
• Because the models are unfinished
• Because the wording is required by the manufacturers cited

Show the answer and why

Answer: Because a model that shows only direction can be mistaken for one that predicts values, and repeating the limit identically wherever the model appears is what stops a reader carrying a number away from it

A teaching model earns its place by being simpler than reality, and the simplification is only honest if it is stated every time the model is shown rather than once at the top of a long page. Identical wording matters for the same reason a hazard pictogram is identical everywhere: a reader recognises it without reading it. The concrete danger here is specific — someone quoting a curve position or an arrow as though it were a measurement of their own film in their own developer.

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