Capstone Stage 2: Formulating and Documenting Your Chemistry

Purpose

To satisfy requirement 4 by mixing at least one working solution from individually weighed raw chemicals, requirement 6 by documenting it to the standard of a formulary page, and — the part that separates this from following a recipe — to verify it against a measurement before a single capstone negative is exposed.

What satisfies the requirement, stated as a boundary:

Satisfies it	Does not satisfy it
A solution mixed from raw chemicals you weighed, with a version identifier, a mixing record and verification data	A kit, however carefully used
A published formula reproduced exactly and cited to its source	A concentrate diluted, however precisely
A declared variant of a published formula, with the change stated and its consequence predicted before the test	A formula copied without understanding, where the evidence for understanding is the function-of-every-ingredient section

The reason for the strictness looks like purism and is not. The capstone is testing whether you can predict what a change will do, and a prediction is only meaningful about a composition you know. You know the composition you weighed. That is also why one solution is enough: the discipline is in the knowing, not in the number of bottles.

Learning objectives

By the end of this session you will be able to:

• decide what to formulate by arguing from the negatives the project needs rather than from preference;
• distinguish reproducing a published formula from declaring a variant of it, and do the second correctly;
• mix to a controlled procedure in which the dissolution order is justified from solubility and oxidation rather than followed;
• record actual weighed masses against nominal ones and say what a deviation is worth;
• verify a bath by pH and by a step-wedge development test read on your own densitometer, with a stated agreement rule fixed in advance;
• state a shelf life and a capacity only where a source gives one or you measured it, and mark the rest unmeasured;
• apply the course’s version-identifier scheme so that every negative traces to the bottle that processed it;
• argue the batch-size and bottle decision from aerial oxidation rather than from convenience.

Prerequisites

The project plan, with the developer characteristic already chosen and argued.

From Part VIII, reading a developer formula and mixing D-23 and D-76, which own the procedure this page executes; and alkalis, buffers and pH and aerial oxidation for the two mechanisms the storage decision turns on. From Part II, concentration and dilution. From Part III, measuring pH, which owns what a home meter can and cannot resolve. From Part XXVII, the developer comparison, whose matrix rows are half of your justification.

And the SOPs this session executes rather than restates: weighing a solid, mixing a developer, mixing to a final volume, pH meter calibration, labelling a container and formula versioning.

Safety classification

Level B, on the rubric’s criterion for repeated weighing of fine powders and the preparation of concentrated solutions. That is the activity that raises it, and it is a genuinely different activity from using a ready-made developer: a litre of D-76 stock means opening four containers of powder and weighing from each, and one of those powders is classified a suspected carcinogen and a skin sensitiser while another is classified for reproductive toxicity.

What is not a hazard here, and why. Nothing on this page is heated beyond the 71 °C of the mixing water, nothing is volatile at that temperature, no gas is evolved by any step of the procedure as written, and no reaction in it is exothermic enough to matter — dissolving 100 g of sodium sulfite in a litre is a mild endotherm rather than the exotherm a strong alkali would give. There is no acid in the session at all unless you are formulating a stop bath, which is why the sulfite and thiosulfate incompatibilities that dominate the waste corner do not arise at this bench. That absence is a property of this procedure: the same sulfite meeting a spilled acid is a room full of sulfur dioxide, and the same borax made into a 40 per cent solution for emulsion work is a different assessment entirely.

One raised step, named here rather than in the procedure. If your chosen formulation is a sulfide or selenium toner, this page’s controls do not govern it: the ventilation, separation and waste requirements of Part XX apply instead, and its waste is collected separately from the first drop. If it is an emulsion or a test solution containing silver nitrate, Part II’s silver nitrate rules come with it, including the eye hazard, which is the serious one; the staining is the least of its problems.

Hazards

Read from current safety data sheets, with the classification for the pure substance and the note that the product in your hand may be a different grade or hydrate whose supplier’s sheet is the authority.

Substance	Signal word	Statements that govern the handling
Metol	Warning	H302, H317 (allergic skin reaction), H373, H400, H410
Hydroquinone	Danger	H302, H317, H318 (serious eye damage), H341, H351, H400
Sodium sulfite	Danger	H302, H314, H315, H319
Borax	Danger	H319, H360 (may damage fertility or the unborn child)
Potassium bromide, if your formula has it	Warning	H315, H319, H335

Four consequences for the bench. Powders are not inhaled: weigh over a tray, away from draughts, and wipe spills up wet rather than brushing them, because brushing is how a spill becomes an aerosol. Skin contact is avoided rather than minimised: metol and hydroquinone are both skin sensitisers, and sensitisation is a one-way door — once acquired, the reaction happens at doses that never troubled you before. Hydroquinone’s H318 sets the eye protection: sealed splash goggles for the weighing and the dissolving, not spectacles. Borax’s H360 is the reason this is not a Level A material despite being mild in every other respect, and anyone pregnant or planning a pregnancy takes a formulation without it — D-23, which is metol and sulfite only, is the obvious substitution and it changes the project’s contrast behaviour in ways you can measure rather than guess.

Required PPE

Sealed chemical splash goggles, not safety spectacles, from the moment the first container is opened until the last one is closed. Nitrile gloves, changed if either powder touches them. An apron or dedicated overall. A particulate mask rated for fine dusts where the substance’s own safety data sheet calls for one — the control that matters most is the tray and the still air, and the mask is the backup. Eyewash within reach before the first jar is opened, and the first aid page read beforehand rather than during.

Ventilation

The control here is dilution ventilation for dust rather than for vapour, because nothing in this session produces one. An openable window with a fan drawing across the bench and away from you, or a local extractor if you have one, and never a sealed room — not because a vapour would accumulate but because still air lets a disturbed powder hang exactly where you are working. Switch the fan off while you are actually weighing, and on again for the rest: a draught across an open pan is a weighing error, and a fan running during the weighing is the commonest cause of a mass that will not settle.

Materials

Material	Quantity	Note
Distilled or deionised water, if you use it	2 L	See the water note under Preparation
Storage bottle, glass or HDPE, with a sealing cap	1 or 2, sized to the batch	The price file could not price these; they are named in its own gap list
Labels	3 or 4	One per bottle, one for the record, one spare for the working solution
Film for the verification strips, from the project’s own batch	2 strips of 135 mm	The same emulsion batch the capstone will use, or the verification means nothing
A 21-step transmission wedge	1	Already in the laboratory from Part XIII

Chemicals

The worked example is Kodak D-76, per litre, exactly as the 1949 handbook’s metric column gives it. Use it, or substitute your own formula and keep the columns.

Chemical	Quantity per litre	Form
Metol	2.0 g	Powder; Kodak calls it Elon
Sodium sulfite	100.0 g	Anhydrous. The 1949 handbook’s other column gives 200.0 g of the crystalline heptahydrate for the same amount of sulfite
Hydroquinone	5.0 g	Powder
Borax	2.0 g	Decahydrate
Water	to make 1000 mL	Mixed hot, made up cold — see Preparation

!One system of units, all the way down

The 1949 handbook prints every quantity twice, in avoirdupois and in metric, and carries a warning in capitals on the same page: the two columns are not exact equivalents. Weigh in grams or weigh in grains, and do not convert halfway down the list. The same rule applies to the sulfite: anhydrous or crystalline, one or the other, never a mixture of the two systems inside one batch.

Equipment

A balance reading to 0.01 g with a check mass, and the bench check run on the day. A pH meter with buffer standards and its calibration procedure. A thermometer you have verified. Two beakers, a 1 L graduate, a stirring rod, a spatula, a funnel and a wash bottle. The sensitometer and densitometer, with their certificates to hand, for the verification arm. A daylight tank. None of these is consumed and none appears in the table below.

Estimated cost

££ on the planner’s bands, and almost all of it is capital that already exists by this point in the course: the balance, the pH meter and its standards, the glassware and the instruments. The recurring cost is four jars of powder, and the powder jars are bought whole while the session consumes grams of each. The table below is the session; the planner has the capital.

Estimated consumables cost

Every figure with a source is the planner’s own dated UK price and every quantity comes from the Materials and Chemicals sections. The run costed is two litres of D-76 stock, plus the verification arm: two step-wedge strips exposed, developed, fixed and read.

Consumed	This session	Sourced price	Cost this session
Metol	4 g	£16.20 per 50 g	£1.30
Hydroquinone	10 g	£11.89 per 50 g	£2.38
Sodium sulfite, anhydrous	200 g	£13.68 to £19.98 per 1 kg	£2.74 to £4.00
Borax	4 g	£9.98 per 200 g	£0.20
Film, from the project batch	2 strips of 135 mm, about a fifth of a 36-exposure roll	£6.37 to £11.40 a roll	£1.27 to £2.28
Stop bath concentrate	20 mL	£10.66 to £12.18 per 500 mL	£0.43 to £0.49
Rapid fixer concentrate	60 mL	£21.05 to £25.98 per 1 L	£1.26 to £1.56
Wetting agent	3 mL	£28.70 per 1 L	£0.09
pH buffer standards at 4.01 and 7.00	2 sachets of each	Named in the price file’s own gap list as unpriced	—
Storage bottles, 1 L, with sealing caps	1 or 2	Named in the price file’s own gap list as unpriced	—

The priced rows come to about £9.66 to £12.28 for one run, and that is a floor and not a total, because two of the ten consumables have no sourced price. The number worth carrying into the project budget is the one per litre: £3.30 to £3.93 for a litre of D-76 stock, which at 1+1 one-shot is £1.65 to £1.97 for a litre of working solution.

Alternative route

The mixing half needs no darkroom at all. It is weighing, dissolving and measuring, done in a lit room at a bench with the window open, and it is the half that satisfies requirements 4 and 6.

The verification half needs darkness only to load film, and the course’s standard substitution covers it completely: a changing bag to load the step-wedge strips and a daylight tank to process them at a sink with the lights on. Nothing in the verification arm needs a safelight, because nothing here handles paper. That is the same route Part II established and Part XXVII’s measured programme runs on, and it costs nothing in evidence.

Without a sensitometer, run the verification with Part XIII’s enlarger exposure series instead. The cost is stated rather than hidden: the exposure axis becomes relative rather than absolute, so the contrast index survives intact — it is a ratio of a density difference to a log-exposure difference and both are relative in the same way — while any speed figure derived from the same strip is comparable only with your own other measurements. Say so in the record; do not present it as the same quantity.

Without a pH meter, the pH comparison is unavailable and narrow-range indicator papers do not replace it: Part III is blunt about their honest resolution, and half a unit of resolution cannot discriminate inside a ±0.3 window. Record the pH as not measured, with the reason, and lean the whole verification on the wedge — which is the stronger of the two tests anyway, because it measures what the bath does to film rather than what it does to an electrode.

Unable to handle a class of chemical. The substitution table in the specification governs, and one case is worth naming here because it is common: borax carries H360, so anyone pregnant or planning a pregnancy takes a formulation without it. D-23 — metol and sulfite only, no alkali beyond the sulfite’s own — is the direct substitution, and it changes the negatives’ contrast behaviour in a direction you can measure on the same wedge rather than guess at.

Waste streams

Alkaline developer, spent and surplus, collected separately from anything acidic. Spent fixer from the verification strips, silver-bearing, retained for silver recovery. Spent stop bath, acidic, kept away from the sulfite container and from the fixer. Used buffer standards, which are dilute salts and go to the general chemical waste route. Empty powder containers, rinsed into the developer stream rather than into the sink, because the rinse carries the last of the sulfite.

Local regulation governs disposal, and this page gives no jurisdiction-specific instruction. Read the disposal caveat: what the course can tell you is the chemistry and the general practice, and the permission is your water authority’s to give.

Preparation

Choose what to formulate, and write the paragraph. The film developer is the default for three reasons and they are worth stating rather than assuming: the negatives depend on it, its behaviour is measurable with the two instruments you already have, and it is the one bath whose change you can see in a curve rather than only in a print. A fixer, a stop bath, a print developer, a toner or an emulsion may be added, and a project centred on printing or on an alternative process may formulate there instead — provided the negatives are still processed in something whose composition is known, because the chemistry report’s developer sections have to be about something.

Decide between reproducing and varying, and the two have different obligations.

• Reproducing a published formula means the quantities exactly as the source gives them, the source cited with its edition and section, and no silent change. A historical formula is never quietly altered — that is a rule of this course rather than a preference, and the reason is that an altered formula published under the old name corrupts the record for everybody who reads it later.
• Declaring a variant means stating what was changed, why, and what you predict it will do — before the test. “Sulfite reduced from 100 to 60 g/L; I predict coarser grain, about a third of a stop more effective speed and sharper edges, and a bath that oxidises sooner.” A prediction written afterwards is an explanation, and an explanation cannot be wrong.

Run the balance and thermometer check on the day, and the pH calibration on the day. A verification made with an uncalibrated meter produces a number of unknown meaning, which is worse than no number because it will be believed.

Decide the water, and record it. The course found no manufacturer statement in its corpus about water hardness or dissolved iron for D-76, so it will not give you a rule. What it can tell you is what to record and how to test it if you suspect it: write down the water source and whether it stood before use, and if you want to know, run the arm Part VIII’s mixing lab already offers — a second half-litre mixed with distilled water on the same day from the same jars, developed alongside. That is an experiment rather than a rule, and it is the honest form of the advice.

Issue the version identifier before anything is weighed. By the versioning SOP, the code is STEM-INITIALS-SEQUENCE — D76-EB-001 — and it is written at the head of the record, on the label, and in the register before the bottle is filled. A code allocated afterwards is a code that has already failed at the one job it has.

Procedure

1. Open the record. Version code at the head, date, mixer, formula with its document and section, nominal masses in a column with an empty column beside them for what you actually weigh.
2. Set out the bench: balance and tray at one end, hot water and beakers at the other, the four jars closed until each is needed. One jar open at a time. Goggles and gloves on before the first lid comes off.
3. Weigh the metol by the weighing SOP, over the tray. Record the actual mass beside the nominal one — 2.03 g against 2.0 g, not “2 g”.
4. Dissolve the metol first, in a small volume of water at about 52 °C, and add it to the vessel. The order is a solubility problem rather than a convention: metol dissolves readily in warm water but only slightly in a sulfite solution with no alkali in it, so sulfite first leaves a good deal of the metol undissolved. Kodak’s general rule sits behind it — an agent put in before its preservative oxidises in the air while it waits.
5. Weigh and dissolve about a quarter of the sulfite in hot water at about 71 °C, add the hydroquinone, and stir until it has completely dissolved. Then add that solution to the vessel. The split matters: this quarter is there to protect the hydroquinone while it dissolves hot.
6. Weigh and dissolve the remaining sulfite in hot water at about 71 °C, add the borax, and when it has dissolved pour the whole solution into the vessel. By now the metol is in solution and past the point where sulfite could precipitate it.
7. Dilute to the final volume with cold water. Make up to the volume; do not add a volume of water to the solution. The two are different quantities and the SOP owns the distinction.
8. Let it come to room temperature, then measure the pH with the meter you calibrated today. Record the temperature with the reading, to one decimal place.
9. Label the bottle by the labelling SOP: name, version code, concentration, volume, date made, and the hazard statements that travel with the mixture.
10. Expose two step-wedge strips in the sensitometer, on film from the project’s own batch, plus one unexposed strip for base-plus-fog.
11. Develop one strip at the time your processing table gives for your target contrast index, at 20 °C, to your own agitation scheme. Keep the second strip for a repeat if the first is spoiled.
12. Stop, fix, wash and dry to your own SOP, and measure the clearing time on a film leader while you are there, because you need it for Stage 3 and this is the fresh-bath figure everything later is measured against.
13. Read all twenty-one steps on your densitometer, plus the unexposed strip, and plot.
14. Compare with the processing table, and apply the decision rule you wrote down in step 1.

Expected observations

During mixing. The metol solution is colourless and clears quickly at 52 °C. The sulfite is a large mass of powder for the volume — 100 g in a litre is 0.79 mol/L, and it looks like it — and it dissolves with mild cooling rather than heating. The finished stock is colourless to very faintly straw. A stock that is visibly yellow or brown when new has oxidised during mixing, and the usual cause is the metol standing in air before the sulfite arrived.

On the pH meter. A borax metol-hydroquinone stock of this family sits near pH 8.6. Expect the reading to be unsteady in the first thirty seconds and to settle; expect the second decimal place to be meaningless.

On the curve. A family you already recognise: a toe, a straight section and the beginning of a shoulder at step 3 or 4. What you are looking at is not whether the curve is right but whether it is where your processing table said it would be.

What is happening chemically

Two mechanisms decide everything on this page and both were taught elsewhere; what follows is the short form and the links.

The pH decision comes first and everything follows from it. Borax at 2 g/L is a very small amount of alkali:

2 g/L ÷ 381.37 g/mol = 0.0052 mol/L

Borax as a molar quantity

That puts the bath in a region where metol is fully active and hydroquinone is mostly held in reserve, because the two agents have different pH thresholds. Raise the pH and the hydroquinone wakes up and the contrast climbs; lower it and the metol slows. The superadditivity of the pair is the reason the combination develops faster than either alone, and Part VIII owns the mechanism.

The sulfite is doing three jobs at once, which is why 100 g of it is in a litre of a developer whose two agents total 7 g. It is the preservative, scavenging oxidation products before they can attack the agents. It is the acid-absorbing reserve, since 0.79 mol/L of sulfite dwarfs 0.0052 mol/L of borate. And it is a silver solvent, which is what makes this a fine-grain developer — the property people buy D-76 for is a side effect of the preservative. More sulfite means finer grain, lower effective speed and longer keeping; less means coarser grain, better speed, sharper edges and a bath that oxidises sooner. That sentence is the shape every function-of-every-ingredient paragraph should have.

And the reason the mixing order is chemistry rather than housekeeping is in step 4: an agent dissolved before its preservative is an agent oxidising in air, and a metol put into a sulfite solution with no alkali is a metol that partly stays a solid.

Data to record

Into the formula version record sheets, which already carry these fields:

• The batch record: version code, date, mixer, formula with document and section, nominal mass and actual mass for every ingredient, dissolution order as performed, the temperature of each dissolution, the time each solid took to dissolve, the final volume, the water source and whether it stood, and the measured pH with its temperature.
• The verification record: the strips exposed, the development time, temperature and agitation as performed rather than as intended, the twenty-one densities with their reading uncertainty, the base-plus-fog from the unexposed strip, and the fresh-bath clearing time.
• The variant record, if you declared one: the parent code, the change, the prediction written before the run, and the result.
• The decision: accept, or diagnose — and if diagnose, which of the four factors you will move.

Analysis

Three comparisons, each with a rule fixed before the data existed.

The pH, against the source’s figure where an authoritative one exists. For D-76 there is none: no Kodak publication the course holds gives D-76 a pH. ILFORD publishes 8.60 to 8.70 for the stock of ID-11, a packaged borax metol-hydroquinone developer of the same family, and the course treats that as the working region of the family and labels it an inference — ID-11’s composition is not disclosed, so the two are the same kind of solution rather than the same solution. So the rule here is not “hit 8.65”. It is: does your reading land in the region the family occupies, or is it a whole unit away?

🧮DO THE MATHS: what your meter can actually resolve at pH 8.6

Calibrate at 4.01 and 7.00 and a reading at 8.6 is an extrapolation — you are using a line fitted to two points, outside them. On top of that sits alkaline error: above about pH 9 the glass membrane responds to sodium and potassium as well as to hydrogen, so it reads low, and a sulfite-loaded developer is a sodium-rich solution.

Then read your meter’s own specification rather than its display. A pen meter that displays 0.01 commonly specifies ±0.2, and a session adds a calibration error and a drift on top of that.

So the tolerance this page states is ±0.3, recorded to one decimal place. A reading of 8.5 or 8.8 tells you the bath is in the right region. A reading of 8.62 is a display, not a measurement, and writing it down claims a precision three of your own uncertainties contradict. If you want it tighter, add a third standard near pH 10 to the calibration, which removes the extrapolation and leaves only the alkaline error.

The development test, against your personal processing table. Read the contrast index under the course’s construction, and compare it with the figure your table gives for that film, that dilution, that temperature and that time.

The agreement rule the course already uses is ±0.02 in contrast index, taken from Kodak’s own process-control window and adopted in Part XV as a defensible starting point. Convert it to minutes through the slope of your own contrast-index-against-time plot before you decide anything: if contrast index rises by 0.03 a minute, ±0.02 is ±0.7 minutes, and quoting a development time to the nearest fifteen seconds is spurious.

Then apply the decision rule, and it has three outcomes rather than two:

1. Inside the window. Accept the bath, write the working rule on the label, and go to Stage 3.
2. Outside the window, but reachable by time. Move the development time along your own slope and re-verify with the second strip. This is the ordinary outcome and it is not a failure; it is what the slope is for.
3. Outside the window and not reachable by time. Something is wrong with the batch. Diagnose it before remixing — a weighing error will show as an activity change, an oxidised metol as a raised base-plus-fog with normal contrast, and a wrong sulfite form as a systematic shift in both.

The clearing time, if you made a fixer. The fresh-bath figure is the reference every later measurement is taken against, under the Part XI fixing criterion: a bath is fit for use while a piece of the film being processed clears in no more than twice the time it took in that same bath when fresh.

Troubleshooting

What you see	Likely cause	What to do
The metol will not all dissolve	Sulfite went in first, or the water was too cool	Do not “help it” with more heat. Start again with the order right; the partly dissolved batch cannot be rescued because you no longer know what is in solution
The new stock is yellow or brown	Oxidation during mixing — the metol stood in air before the sulfite arrived	Discard it, and shorten the interval next time. A stock that starts oxidised will not keep to the published figures
A white precipitate on standing	Sulfite crystallising out in a cold room, or a hydrate confusion between the anhydrous and crystalline columns	Check which form the label on the jar names against which column you weighed from. Warm the bottle gently and see whether it redissolves
The pH reads a whole unit low	Extrapolation plus alkaline error, or a tired electrode	Recalibrate with a third standard near pH 10 and repeat. If it still reads low, check the electrode’s slope, which the calibration reports
The pH reading will not settle	A dirty or dry electrode, or a solution still cooling	Let the solution reach room temperature, rinse the electrode with distilled water rather than wiping it, and give it a full minute
The contrast index is far below the table at the table’s time	An underweighed agent, an overweighed sulfite, or a temperature that was not what you recorded	The actual-mass column answers the first two in seconds, which is why it exists. If the masses are right, the thermometer is the next suspect
Base plus fog is high but contrast is normal	Oxidised stock, or fogged film, and they are told apart by the unexposed strip from a different box	Develop an unexposed strip from a second box in the same bath. If it fogs too, the bath; if not, the film

Clean-up

Rinse every vessel that held powder into the developer waste rather than into the sink, and rinse the tray you weighed over. Wash the balance pan and the spatula, and dry them; a spatula left with metol on it is how sensitisation spreads to the next session. Cap every jar, and check the caps — a sulfite jar left ajar for a week is a jar of partly oxidised sulfite and its label no longer describes its contents. Remove gloves last, by the PPE procedure, and wash your hands after.

Storage

The bottle decision is argued from oxidation, not from convenience, and the published figures make the argument for you. Kodak give D-76 stock six months in a full, tightly closed bottle and two months in a half-filled one — the same four keeping figures in 1949 and in 2017, which is unusual enough to be worth recording — plus 24 hours in a tray and a month in a tank with a floating lid.

The explanation is the air space. A half-empty bottle is a slow oxidation cell, and every time you open a large bottle you refill the headspace. So for a capstone that runs over weeks the decision is not “one big batch or several small ones” in the abstract; it is:

• Several small full bottles beat one large one that is opened repeatedly, because each small bottle is opened once. Decant at mixing time, not at use time.
• One version identifier covers the lot if they were mixed in one operation from one weighing. That is the point of decanting at mixing time rather than mixing three batches.
• A bottle opened and half used gets a new date on the label, because its shelf life restarted at two months rather than six.

Label every bottle with name, version code, concentration, volume and the date it was made — and where it has been decanted, the date it was opened as well.

Disposal considerations

Spent developer is alkaline and carries the developing agents’ aquatic hazard classifications: metol and hydroquinone are both classified very toxic to aquatic life, and the developer is the stream that keeps them. It is collected separately from anything acidic, for the reason the incompatibility matrix gives: acidifying a sulfite regenerates sulfurous acid, which gives up sulfur dioxide, and the reaction is worse inside a capped waste bottle than in the open because you will unscrew that cap later.

Spent fixer from the verification strips is silver-bearing and goes to silver recovery. Rinses from the powder containers go with the developer.

What the course cannot tell you is where any of it may then go. The route is jurisdictional: sewer discharge is governed by your water authority, and household hazardous waste by your local authority. Check your local regulations; they govern, and the disposal page explains why this course states chemistry and general practice and stops there.

Documenting it to formulary standard

Requirement 6 asks for the formulary page template applied to your own solution. Twelve sections, and the one that carries the weight is the last.

What fills each part of your formulary-standard page, and where the evidence comes from

1. 1Identity and provenanceName, version code, and the document and section the formula came from. If it is a variant, the parent and the variance.
2. 2Purpose, and when another formula is preferableFrom your project plan's chemistry paragraph, and from your Part XXVII matrix rows.
3. 3The ingredient tableQuantity, form and function for every ingredient. Form is not decoration: anhydrous and crystalline are different weighings.
4. 4Mixing order, with reasonsFrom the source, and from the solubility and oxidation arguments above. Never reconstructed.
5. 5Working dilutions and behaviourAnd the conditions the behaviour was measured under — your temperature, your agitation, your film batch.
6. 6Image characteristics, as observedWhat you saw on your negatives, not what the literature says the formula is famous for.
7. 7Storage, shelf life and capacitySourced where a source gives it, measured where you measured it, and marked unmeasured otherwise. No third option.
8. 8Incompatibilities and wasteFrom the substances, and from the incompatibility matrix.
9. 9The function of every ingredientFor every one, not for the interesting ones. What it is, why it is there, what it does, what photographic consequence follows, what more or less of it does, and what it interacts with.

The last section is the heart of the page and it is where requirement 6 is actually assessed. An ingredient present for a reason that has nothing to do with reducing silver is the one whose paragraph proves you read the formula rather than copied it.

✕Three ways the documentation quietly stops being honest

Quoting a capacity you did not measure as though you had. Kodak’s unreplenished figure for D-76 is 16 sheets of 8 × 10 per US gallon with the time raised 15 per cent after every four sheets or rolls per gallon. That is Kodak’s number for Kodak’s conditions. Your own count, under your own criterion, is a different number, and where they disagree the difference is discussed rather than averaged.

Averaging a published figure with an observed one. If the maker says six months and your bottle was visibly oxidised at three, the honest entry is both figures and the conditions each was obtained under. An average of the two is a number nobody measured.

Writing a shelf life you have no evidence for at all. Then write unmeasured. A blank with an admission is a usable record; a plausible number is a trap for the version of you who reads it in two years.

Questions

1. Your batch record shows nominal 2.0 g of metol and actual 2.31 g. What has that done to the bath, what would you expect to see on the wedge, and is the batch usable?
2. Explain, from solubility rather than from tradition, why the metol goes into the water before the sulfite — and why Kodak nevertheless splits the sulfite into two portions.
3. Your meter reads pH 8.31 for a fresh D-76 stock. Write the sentence that goes in the record, including what you may and may not conclude.
4. You want to reduce the sulfite from 100 to 60 g/L. Write the variant declaration: the change, the reason, and four predictions — grain, effective speed, acutance and keeping — made before the test.
5. Which of D-76’s four ingredients is present for a reason that has nothing to do with reducing silver, and what are its three separate jobs?
6. Your project needs three litres of stock across eight weeks. Argue the bottle decision from the published keeping figures, and say what you would write on each label.

Further experiments

Run the water arm. Mix a second half-litre with distilled water on the same day from the same jars, develop a wedge in each, and read both. That is a measurement of a question this course could not answer from any source it holds, and it costs one strip.

Measure your own capacity instead of quoting Kodak’s. Develop one strip per film through a litre of stock, reading the contrast index each time, and find the point where it has fallen by more than your ±0.02 window. Compare with the published 16 sheets per gallon, and discuss the difference rather than resolving it.

Test the headspace claim. Fill two identical bottles from the same batch, one full and one half, seal both, and develop a wedge from each at two weeks, four weeks and eight. If the published figures are right, the half-filled bottle should show a rising base-plus-fog and falling contrast well before the full one. Whatever you get, it is your bottle in your room, which is the only version of the question that governs your project.

Predict, then test, one ingredient change. Before mixing, state what a 20 per cent change in one named ingredient would do to contrast, speed, fog and grain. Then test one of those predictions if the schedule allows. The prediction is the assessment; the test is the evidence.

Check your understanding

Question 1. You dilute a bought developer concentrate very precisely to make the working bath for your capstone negatives. Does that satisfy requirement 4?

• Yes, provided the dilution is recorded and a version identifier is issued
• Yes, because a working solution is a working solution however it was made
• No: requirement 4 asks for a solution mixed from individually weighed raw chemicals, because the point is to be able to predict what a change would do, and you can only do that for a composition you know
• No, because bought concentrates contain sequestering agents that interfere with the measurement

Show the answer and why

Answer: No: requirement 4 asks for a solution mixed from individually weighed raw chemicals, because the point is to be able to predict what a change would do, and you can only do that for a composition you know

The requirement is about knowledge rather than about effort or precision. A maker does not publish the composition of a concentrate, so a prediction about changing one of its ingredients is not available to you — and prediction is the capacity the capstone is testing, which is why requirement 6 asks for the function of every ingredient and why the failure conditions include a formula altered without saying so. The last option asserts a fact about concentrates that nothing in this course establishes, which is its own kind of error.

Question 2. Your pH meter, calibrated at 4.01 and 7.00 that morning, reads 8.62 for a fresh borax metol-hydroquinone stock. What may you write in the record?

• "pH 8.62, within ILFORD's published range of 8.60 to 8.70"
• "pH 8.6 ± 0.3 at 20 °C, calibrated two-point at 4.01 and 7.00 that morning; the reading is an extrapolation above the calibrated interval and the bath is in the region the borax metol-hydroquinone family occupies"
• "pH 8.62, confirming the formula was mixed correctly"
• "pH 8.62; no comparison is possible because Kodak publishes no pH for D-76"

Show the answer and why

Answer: "pH 8.6 ± 0.3 at 20 °C, calibrated two-point at 4.01 and 7.00 that morning; the reading is an extrapolation above the calibrated interval and the bath is in the region the borax metol-hydroquinone family occupies"

Three things have to survive into the record and only the second answer keeps all of them. The second decimal place is display resolution rather than accuracy — a pen meter that displays 0.01 commonly specifies ±0.2, and the session adds calibration error and drift. The reading sits above the interval the calibration covered, which makes it an extrapolation, and a glass electrode also reads low in a sodium-rich alkaline solution. And the comparison that is available is with the family rather than with the formula, because ILFORD publishes a figure for ID-11 whose composition is not disclosed, so the course labels the comparison an inference. The last option is right that no Kodak pH exists and wrong that this leaves nothing to say.

Question 3. Why does D-76 contain twenty times as much sodium sulfite as it does developing agent in total, and what follows for a variant that halves it?

• Sulfite is the alkali, so halving it would halve the pH
• Sulfite is the preservative, the acid-absorbing reserve and a silver solvent all at once; halving it gives coarser grain, better effective speed, sharper edges and a bath that oxidises sooner
• Sulfite is the restrainer, so halving it would raise fog
• The quantity is historical and has no current function

Show the answer and why

Answer: Sulfite is the preservative, the acid-absorbing reserve and a silver solvent all at once; halving it gives coarser grain, better effective speed, sharper edges and a bath that oxidises sooner

One ingredient doing three jobs is why the quantity looks disproportionate, and the fine grain the formula is famous for is a side effect of the preservative rather than a separate design decision. Borax is the alkali and 2 g/L of it is 0.0052 mol/L, against 0.79 mol/L of sulfite — which is also why the sulfite rather than the borate is the bath's acid-absorbing reserve. D-76 contains no restrainer at all: at this pH, with this little alkali, it does not need one. Predicting all four consequences of halving it, before the test, is exactly what a variant declaration asks for.

Question 4. Your verification wedge gives a contrast index of 0.54 where your processing table predicts 0.58 at that time and temperature. What is the correct next step?

• Remix the developer, since a 0.04 discrepancy is twice the accepted window
• Accept it and adjust the printing to suit, since 0.04 is a small difference
• Read the discrepancy against your own contrast-index-against-time slope, move the development time by the corresponding amount and re-verify with the second strip — the ordinary outcome, and what the slope is for
• Recalibrate the densitometer, since the instrument is the likeliest source of a 0.04 error

Show the answer and why

Answer: Read the discrepancy against your own contrast-index-against-time slope, move the development time by the corresponding amount and re-verify with the second strip — the ordinary outcome, and what the slope is for

The ±0.02 window is a tolerance on the development time, not a verdict on the batch: it exists so that a time can be accepted or moved, and 0.04 outside it is squarely in the range time can reach. If the slope is 0.03 of contrast index a minute, the correction is about a minute and a third, and the second strip — deliberately exposed alongside the first — is there to confirm it. Remixing throws away a usable bath before diagnosing anything; adjusting the printing accepts an unknown into the campaign; and while a densitometer can drift, its certificate's repeatability band is far tighter than 0.04 of contrast index, so it is a later suspect rather than a first one.

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