Lab: Mixing D-23 and D-76 from Raw Chemicals

Two litres of developer come out of this session, and they are not the point. The point is the record: two bottles with version numbers, a pH reading each, two control negatives, and a notebook entry complete enough that somebody — you, in three years — can tell whether a difference measured later belongs to the film, the developer or the day.

Part IX uses these two bottles as its controls, and Part XXVII re-measures the strips they produce. A batch you cannot identify afterwards is not a control.

Purpose

To make one litre each of Kodak D-76 and Kodak D-23 from raw chemicals, in the dissolving order Kodak published, to measure the pH of each, to bottle and label them so they can be identified years later, and to establish a first control negative in each so that Part IX has a baseline to work against.

Learning objectives

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

• Weigh four solids to a stated tolerance and say which of the four the tolerance actually matters for.
• State the dissolving order for a metol formula and the two different reasons Kodak gives for it.
• Explain what each of D-76’s four ingredients does, and what D-23 achieves by leaving two of them out.
• Measure the pH of a developer correctly, and say what you can and cannot compare the number to.
• Bottle, label and date a stock solution so that its identity survives without you.
• Assign and record a formula version, and list what must be recorded against it.
• Process a control roll with a published agitation scheme and describe the negative it produced.

Prerequisites

• Alkalis, buffers and pH, for what borax is doing at 2 g/L and why a developer’s pH is worth measuring.
• Sulfite: preservative, buffer, silver solvent, for why a hundred grams is not a preservative dose.
• Lab: processing your first film, for the tank, the loading and the agitation scheme, none of which is repeated here.
• Measuring pH, for calibration, temperature and electrode care.
• Laboratory safety and PPE, for the weighing discipline this page leans on hard.
• Assignment: reading a developer formula, which is where the version-record template comes from.

Safety classification

Level A: a standard home darkroom — with one step that is worked at Level B controls, and the assessment says so rather than averaging it away.

• Substances in solution. Both finished developers are alkaline solutions of an agent, a preservative and (in D-76) a weak alkali, handled by the litre. With gloves and eye protection that is Level A territory, and it is the same handling as the proprietary developer of Part VI’s processing lab.
• The weighing step, which is not. Three of the four solids are classified in this course’s encyclopaedia at Level B as substances: metol and hydroquinone as skin sensitisers with further health classifications, and borax on a reproductive-toxicity classification notified by 93.2 per cent of reports. The rubric assigns a level to a procedure, and its Level B criteria include “fine powders that must not be inhaled”, which is exactly what four open jars on a bench are. This page therefore works the weighing at Level B controls — a tray, still air, one jar open at a time, gloves, eye protection, a particulate mask, and no film or paper open in the room — inside an otherwise Level A session. Saying that is more useful than claiming the whole session is one letter.
• Borax and pregnancy. Borax’s classification is may damage fertility or the unborn child. A reader who is pregnant, breastfeeding or trying to conceive should read the borax page before opening the tub, and should take the alternative route below, which involves no borax at all.
• Temperature. Kodak’s 1928 directions call for water at about 71 °C, which is above the 50 °C ceiling in this course’s Level A criteria. The page prints Kodak’s instruction unchanged and works at a lower temperature for a reason it shows you the arithmetic for; see the note under Preparation.
• Waste. Spent developer in one labelled container; fixer and its first rinse, which are silver-bearing, in the silver container.

What is not a hazard here, and why. There is no risk of sulfur dioxide, although two hundred grams of sodium sulfite pass through your hands. Sulfite releases the gas when it meets an acid, and nothing in the mixing half is acid: both developers are alkaline from the first gram onwards. It becomes real only if a stop bath, an acid fixer or a descaling product reaches a sulfite-bearing solution or its waste — which is why those wastes have separate labelled containers and are never combined to save a bottle.

Equally, the finished developers present no dust hazard, and the sensitiser risk becomes a contact risk once the solids are in solution, met by gloves and by keeping fingers out of a tank. And nothing here is under pressure or near a flame: the warmest water is hand-hot.

Hazards

Metol and hydroquinone: skin sensitisation. Notified at 100 per cent of reporting notifiers for metol and above 99.9 for hydroquinone. Sensitisation is cumulative and does not reverse, and the dermatitis it produces is the classic reason people stop doing darkroom work. Gloves throughout, and never a finger in a tank.

Hydroquinone: serious eye damage, at 99.9 per cent with a harmonised CLP entry. Eye protection from the moment the first jar is opened until the last bottle is capped.

Borax: reproductive toxicity, and dust. H360 at 93.2 per cent of reports. HSE’s EH40 sets workplace exposure limits for the dust at 5 mg/m³ for the decahydrate and 1 mg/m³ for the anhydrous and pentahydrate forms, so the control is dust discipline: weigh without raising it, over a tray, and wash hands before eating.

All four solids are powders. The weighing is the only step where inhalation is a live route, and it is the only step at Level B controls.

Aquatic toxicity. Both agents are notified as very toxic to aquatic life with long-lasting effects, at or near unanimity, and two litres of developer contain everything you weighed of both — two rolls consume very little agent.

Warm water and a full jug. A litre at 50 °C will scald, and carrying it across a room is a bigger risk on this page than any of the chemistry. Warm the water where it will be used.

Working in the dark. Lay the bench out before the light goes off, and do not change it afterwards.

Required PPE

• Single-use nitrile gloves, 0.2 mm, the splash-resistant grade HSE’s COSHH essentials sheet P1 specifies for manual film development where the safety data sheet gives no more specific advice. Changed when contaminated, thrown away at the end.
• Eye protection for the whole session.
• A particulate mask for the weighing step, which is the control that lets a Level B weighing sit inside a Level A session. It does not replace the tray or the still air.
• An apron or overall kept for laboratory work, per the same HSE sheet’s instruction on clothing contamination.
• Dedicated, labelled utensils, never used for anything but photographic chemistry.

Ventilation

Nothing here evaporates, so ventilation is not being asked to remove a vapour. It is doing two jobs: diluting any powder that becomes airborne during the weighing, and meeting the general standard HSE sets for manual development work, which its COSHH essentials sheet quantifies as greater than five air changes per hour with a through draught. An openable window plus an internal door left open meets that in most rooms.

Order matters. Weigh in still air with the window shut, close every jar, and only then open the window. A draught over an open pan scatters powder around a room.

Materials

• Two 1-litre bottles with tight screw closures, preferably brown or opaque, plus two spares.
• Labels and a pen that both survive water.
• Two 1-litre jugs, a 250 mL measuring cylinder and a 1-litre one, and a stirring rod.
• A shallow tray to weigh over and to stand bottles in.
• A balance reading to 0.01 g.
• A thermometer reading to 0.5 °C, and a pH meter or narrow-range pH papers covering 7 to 10.
• A developing tank with two reels, a changing bag or a dark room.
• Two rolls of the same film, same batch, exposed on the same subject.
• Scrap film for the fixer clearing test.
• The notebook.

Chemicals

Chemical	Quantity	Form
Metol	9.5 g total	Solid: 2.0 g for D-76 and 7.5 g for D-23
Sodium sulfite, anhydrous	200.0 g total	Solid: 100.0 g for each litre
Hydroquinone	5.0 g	Solid, D-76 only
Borax	2.0 g	Solid, decahydrate, D-76 only
Rapid fixer	about 1 L of working solution	Proprietary ammonium thiosulfate fixer at the maker’s film dilution
Stop bath or plain water rinse	about 600 mL	At the maker’s dilution, or water at the process temperature
Wetting agent	as the maker states	Non-ionic surfactant for the final rinse

Kodak D-76, from Kodak’s 1928 primer and Kodak Limited’s 1949 handbook, which agree exactly:

Ingredient	Per litre
Metol	2.0 g
Sodium sulfite, anhydrous	100.0 g
Hydroquinone	5.0 g
Borax	2.0 g
Water to make	1000 mL

Kodak D-23, from the same handbook:

Ingredient	Per litre
Metol	7.5 g
Sodium sulfite, anhydrous	100.0 g
Water to make	1000 mL

🧮Weighing to 0.1 g, and the one ingredient where it hurts

The covers list for this lab says “weighing to 0.1 g and the tolerance that matters”, and the second half of that phrase is the teaching. Run the arithmetic on what a ±0.1 g error means for each ingredient:

e = Δm / m

Relative error

Ingredient	Mass	±0.1 g is
Sodium sulfite	100.0 g	±0.1 % — undetectable in any way you can measure
Hydroquinone (D-76)	5.0 g	±2 %
Metol (D-23)	7.5 g	±1.3 %
Metol (D-76)	2.0 g	±5 %
Borax (D-76)	2.0 g	±5 %

The two small weights are the ones that matter, and they matter for different reasons. A 5 per cent error in the metol is a 5 per cent error in the primary developing agent, which lands directly on the rate. A 5 per cent error in the borax is a 5 per cent error in the alkali, and Kodak’s own statement is that the quantity of alkali governs the energy of a developer.

So use a balance reading to 0.01 g and record what you actually weighed, which turns a ±5 per cent uncertainty into a ±0.5 per cent one and costs nothing. Recording the real figure matters more than hitting the target: a batch mixed at 1.94 g of metol and recorded as 1.94 g is a known quantity, and one mixed at 1.94 g and recorded as 2.0 g is a small permanent lie in your own data.

ILFORD makes the same point from the manufacturing side, about its own packed powders: always make the stock up to the volume stated on the pack, and “do not attempt to prepare smaller solution quantities by using fractional parts of each powder”. Dividing a packet by eye is exactly the ±5 per cent problem without the balance.

Equipment

The balance is the only instrument whose specification changes the result, and 0.01 g is the number to buy. The pH meter matters second: an electrode not calibrated on the day is a device for generating confident wrong numbers, and Part III’s procedure is the one to follow. Papers covering pH 7 to 10 are a legitimate fallback and are recorded as such — ILFORD says the same about its own figures. The thermometer is used more often than either: at the mixing temperature, at the pH reading, and at the start and end of development.

Estimated cost

Cost band £. Two litres of developer costs a few grams of four common solids; the dominant recurring cost of the session is the two rolls of film. The balance, the bottles and the pH meter are one-off purchases the rest of the course reuses. Dated prices live in the laboratory planner, where they can be kept current.

Estimated consumables cost

Two litres of developer for a few grams of four solids — and the developer is not the dominant cost of the session. The two rolls of film are. That inversion is the point of the lab: mixing your own developer is cheap, and proving that it works costs a film each time.

Consumed	This session	Sourced price	Cost this session
Metol	9.5 g: 2.0 g for D-76, 7.5 g for D-23	£16.20 per 50 g (£0.32 a g)	£3.08
Sodium sulfite, anhydrous	200.0 g: 100 g a litre, twice	£13.68–£19.98 per 1 kg, anhydrous	£2.74–£4.00
Hydroquinone	5.0 g, D-76 only	£11.89 per 50 g (£0.24 a g)	£1.19
Borax, decahydrate	2.0 g, D-76 only	£9.98 per 200 g, decahydrate	£0.10
Black-and-white film	2 rolls, same emulsion batch	£6.37–£11.40 per one 35 mm roll, 36 exposures	£12.74–£22.80
Rapid fixer concentrate	200 mL, to make 1 L at 1+4	£21.05–£25.98 per 1 L of ammonium thiosulfate concentrate, diluted 1+4 for film	£4.21–£5.20
Stop bath concentrate	about 30 mL, or a plain water rinse	£10.66–£12.18 per 500 ml of citric acid concentrate, diluted 1+19	£0.64–£0.73
Wetting agent	5 mL per litre of final rinse	£28.70 per 1 L of concentrate, diluted 1+200	£0.14
Disposable nitrile gloves	1 pair	£6.64–£14.99 per box of 50 to 100 disposable gloves (£0.13–£0.15 a glove)	£0.27–£0.30
Disposable FFP3 respirator	1, for the weighing	None. A named price gap: an FFP3 disposable respirator	—
Narrow-range pH papers	two or three strips, pH 7 to 10	None. A named price gap: a pH meter, buffer standards at 4.01 and 7.00, and narrow-range indicator papers	—

The priced rows come to £25.10 to £37.53 for one run of this session, at the retail ranges read on 5 September 2026 and recorded in the laboratory planner. That is a floor, not a total: 2 of the 11 rows carry no dated price, so they are counted as nothing here and are certainly not free. A priced entry is a dated range to plan against, never a quotation.

Every row but two is priced, which makes this the best-costed session in the course — and the two litres of developer it produces are the feedstock for most of Parts IX, X and XIII, so the solids figure above is not a per-session cost anywhere downstream. The balance, the bottles and the pH meter are equipment.

Waste streams

Two streams, and the labels go on the containers before the session starts.

1. Spent developer, which is any developer you discard and every rinse from the mixing vessels. Metol and hydroquinone are both notified as very toxic to aquatic life with long-lasting effects, and essentially all of what you weighed is still there.
2. Fixer and its first rinse, which are silver-bearing because the fixer has dissolved the undeveloped halide from two films, and go to the silver container Part II established.

Do not combine them. Kodak’s guidance for amateur photographers records that developer solutions carry negligible silver, so the mixture recovers nothing and spoils a stream that could have been recovered.

The stop bath, if you use an acid one, is a third container and never goes into the first: an acid meeting a sulfite-rich developer waste is the one reaction on this page that produces a gas.

Alternative route

If you cannot weigh under the conditions described above — no tray, no still air, no mask, nowhere to work without film or paper in the room — do not weigh. There are two routes to most of this session’s learning that involve no powder.

Route A: mix a packed powder instead. Kodak D-76 and ILFORD ID-11 are both sold as packed powders, and mixing one gives you the pH measurement, the bottling and labelling discipline, the version record and the control roll. What it loses is the ingredient-by-ingredient reasoning, so read the packet’s instruction against Kodak’s published order and note where they differ. ILFORD’s — part A, the smaller bag, into about three-quarters of the volume at about 40 °C, then part B added gradually while stirring — is the pattern Kodak’s rule predicts, and noticing that is worth something.

Route B: mix D-23 only. D-23 has two ingredients and neither of them is borax. It is the whole of the pH work, the whole of the bottling and record-keeping, and one control roll, at half the weighing exposure and with the reproductive-toxicity classification removed entirely. The cost is that you lose the comparison, which Part IX will want; the honest way to recover it is to buy packed D-76 or ID-11 for the second bottle and record it as a bought batch rather than a mixed one.

Neither route is a lesser version of the lab. Choosing the route your conditions actually support, and recording which you chose, is itself the assessment discipline this part teaches.

Preparation

1. Label everything first. Two bottles, three waste containers, two jugs. A bottle labelled after it is filled is a bottle that spent five minutes unlabelled.
2. Draw the water and let it stand. ILFORD’s instruction, and a chemical one: mains water is highly aerated and dissolved oxygen consumes developing agent. Draw two and a half litres, let it stand a few minutes, and use it for everything.
3. Set the bench out: tray, balance, spatula, the four jars closed, jugs, cylinder, thermometer, with the waste containers beside the tray and not in it.
4. Weigh all six masses before dissolving anything, into six labelled containers, in still air with the mask on, one jar open at a time, recording every reading to 0.01 g as you take it.
5. Then open the window and put the mask away.

!Kodak's temperatures, this course's temperature, and the arithmetic between them

Kodak’s 1928 Directions for Mixing D-76 specify water at about 52 °C (125 °F) for the metol and about 71 °C (160 °F) for the sulfite portions. This course prints that instruction unchanged, because the course never silently modernises a historical formulation.

71 °C is above the 50 °C ceiling in this course’s Level A criteria. The course is not going to pretend Kodak wrote something else, and it is not going to send you to a Level A page with a Level B step hidden in it. So here is the arithmetic that decides what to do, from the solubilities in the encyclopaedia:

• Sodium sulfite: 22 g per 100 mL at 20 °C, which is 220 g/L. The strongest intermediate solution this procedure makes is the remaining 75 g in about 400 mL, which is 187 g/L — under the cold limit already, and comfortably under it at 45 to 50 °C.
• Metol: 4.7 g per 100 mL at 15 °C, which is 47 g/L. Two grams in 200 mL is 10 g/L; seven and a half grams in 200 mL is 37.5 g/L, still under the cold figure.
• Hydroquinone: about 70 g/L at ordinary temperatures. Five grams in 250 mL is 20 g/L.
• Borax: about 51 g/L at 20 °C, and far more when hot. Two grams in the remaining volume is under 5 g/L.

Every dissolution in this procedure is possible below 50 °C, and Kodak’s higher temperature was speed and convenience at a four-litre commercial scale, not necessity at one litre. This lab therefore works at 45 to 50 °C, which is hot-tap temperature, and says so as a stated deviation with its reason — not as a correction to Kodak.

What is not altered is the order or the quantities. Those are Kodak’s, unchanged, and they are the part that carries the chemistry.

Procedure

The dissolving sequence for D-76, and why each step is where it is

1. 1Metol into warm water — readily soluble warm; only slightly soluble in sulfite without alkali, so it cannot wait
2. 2A quarter of the sulfite, then the hydroquinone — the second agent meets a preservative at once
3. 3Combine — both agents now in the same preserved solution
4. 4The rest of the sulfite, then the borax — alkali last: no agent ever stands in unpreserved alkali
5. 5Cold water to one litre — makes the volume and brings the temperature down

The order and the quantities are Kodak's, from the 1928 primer's Directions for Mixing, unaltered. The temperature is this page's, for the reason given above it.

Stage 1 — mix D-23 (about 25 minutes)

1. Warm about 700 mL of the standing water to 45 to 50 °C and check it with the thermometer.
2. Put about 200 mL in a jug and dissolve the 7.5 g of metol completely — no crystals and no haze against the light. Give it the stirring it needs rather than the stirring you planned.
3. Add the 100 g of sodium sulfite in three or four portions, stirring each in before the next. All at once makes a lump that takes longer than the rest of the stage.
4. Make up to 1000 mL with cold water, stir, note the temperature and the time. This batch is D23-XX-001, with your own initials in place of XX.

Stage 2 — mix D-76 (about 35 minutes)

Follow the five stages of the drawing. In detail:

1. Metol 2.0 g into about 200 mL at 45 to 50 °C, dissolved completely.
2. In a second vessel, 25 g of the sulfite — a quarter of the total — into about 250 mL of the same warm water, then the 5.0 g of hydroquinone, stirred until completely dissolved.
3. Combine the two.
4. In the second vessel again, the remaining 75 g of sulfite into about 400 mL of warm water, then the 2.0 g of borax. Borax is much slower cold than warm; if it will not go in, the water is too cool.
5. Combine everything, make up to 1000 mL with cold water, and note the temperature and time. This batch is D76-XX-001.

Stage 3 — measure the pH (about 15 minutes)

1. Calibrate the meter on the day with the buffers, following Part III’s procedure, and record the buffer values and the slope if your meter reports one.
2. Bring both developers to 20 °C, or as close as the room allows, recording the actual temperature with each reading. A pH reading without its temperature is not a measurement.
3. Read D-76, rinse the electrode, read D-23, rinse again, and re-read D-76 to check the meter has not drifted. Record all three numbers.
4. If you are using papers rather than a meter, record the range you could resolve and say so in the notebook. A reading of “between 8.5 and 9” honestly recorded is worth more than a spurious 8.63.

Stage 4 — bottle, label and date (about 10 minutes)

1. Fill each bottle as full as it will go, leaving only a small air space. Kodak Limited’s reason for a small space rather than none is mechanical: solution volume changes with temperature, and a bottle with no headspace can loosen its stopper or burst.
2. Cap tightly. Kodak’s handbook notes that glass stoppers are undesirable for developers, because the alkali tends to make them stick.
3. Label: the formula, the version number, the date and time of mixing, the volume, who mixed it, the measured pH with its temperature, and the words “developer — not for drinking, keep away from food”. Every one of those has been needed by somebody.
4. Store in a cool, dark place. Kodak’s storage table gives D-76 stock six months in a full tightly closed bottle and two months half-filled, and states the reason: partially filled bottles allow some oxidation.

Stage 5 — one control roll in each (about 90 minutes)

The tank, the loading and the agitation are Part VI’s lab and are not repeated here. What is specific to this session:

1. Two rolls of the same film and batch, exposed on the same subject, in the same light, at the same meter setting. Include a grey card and a step wedge in the frame if you can; otherwise photograph one scene running from open shadow to lit white.
2. D-76 first, at its published time. ILFORD publishes, for Kodak D-76 at full strength in a spiral tank with intermittent agitation, 8 minutes at 20 °C for FP4 Plus at EI 125 and 7½ minutes for HP5 Plus at EI 400.
3. Agitation: the scheme your published time assumes, and no other. ILFORD’s is four inversions in the first ten seconds and four again at the start of every subsequent minute, tapping the tank to dislodge bubbles; Kodak’s D-76 sheet gives its small-tank times against agitation at 30-second intervals. Write down which you used, because a time means nothing without it.
4. D-23 second, and here the course has to be honest with you.

📓D-23's development time, and why this page gives you a derivation instead of a number

No source in this course’s corpus gives a development time for D-23 with a current film. Kodak Limited’s 1949 handbook gives one instruction for the formula — “Develop about 18 mins. at 65 °F (18.3 °C)” — for the plates and films of 1949, which are not the films you can buy.

So you have two defensible starting points, and the page asks you to choose one, write down which, and treat the negative as a first data point rather than a correct exposure.

Option 1: Kodak’s own figure, unadjusted. 18 minutes, accepting that your bath is at 20 °C rather than 18.3 °C and that the film is not the film Kodak meant. Simple, and the deviation is recorded.

Option 2: Kodak’s figure, temperature-adjusted. ILFORD’s powder-developer sheet gives a rule of thumb of about 10 per cent per degree C for its own products. Applying it across 1.7 °C:

t₂ = 18 min × (1 − 0.10)^1.7 ≈ 15 min

A rule-of-thumb adjustment, applied outside the product it was written for

That is an extrapolation and the page labels it one. ILFORD’s rule is written for ILFORD developers; nothing establishes that D-23’s temperature coefficient matches, and the kinetics lesson is explicit that the coefficient belongs to the developer rather than to development in general.

Either way, the number goes in the notebook with its derivation and its status, and Part IX is where it becomes a measurement. Being the person who determines D-23’s time for a current film is the point of this part of the course, not a failure of it.

5. Stop, fix, wash and dry as in Part VI, within 5 °C of the developer temperature. Find the fixer’s clearing time on a scrap of the same film and fix for twice it, which is ILFORD’s instruction.
6. Hang, dry and sleeve both rolls, labelled with the developer, the version, the time, the temperature and the agitation scheme.

Expected observations

• The metol dissolves quickly and completely in warm water, colourless. If it refuses, the water is too cool.
• The sulfite dissolves with a faint cooling and gives a clear solution. A hundred grams briefly looks as though it cannot possibly go in.
• The hydroquinone dissolves more slowly, also colourless. If it goes yellow while you watch, the order has gone wrong: that colour is oxidation product, and it means an agent met alkali before it met the preservative.
• The borax dissolves slowly and warm, and is the one most likely to be left as a haze in a jug.
• Both finished developers are clear and colourless or very nearly so. Write down any tint you can see, because it is the zero reading against which every later look at that bottle is judged.
• Both pH readings will be alkaline, and D-76 should be the higher, because it has an alkali in it and D-23 does not.
• The D-76 negative should look normal at the published time: full shadow detail, separation left in the highlights.
• The D-23 negative probably will not, at whichever time you chose, and that is expected. Softer and thinner is the likely direction, since Kodak calls D-23 soft-working; grossly under-developed means the time was shorter than the derivation allowed for.

What is happening chemically

Why metol first. Kodak Limited gives a solubility reason, not an oxidation one: metol “is readily soluble in warm water, but only slightly soluble in sulphite solutions without alkali”. That is a different and stronger claim than the usual one — the risk is not that the metol is damaged while it waits, but that it does not go into solution at all. The encyclopaedia’s figure of 4.7 g per 100 mL at 15 °C is for plain water; nothing in the corpus quantifies the reduction in a sulfite solution, so the course follows the instruction without being able to put a number on it.

Why the alkali last. Kodak’s general rule and its reason, from the same page: dissolve the agent first and add the alkali before the sulfite is in, and “considerable aerial oxidation and formation of coloured oxidation products may occur”. Alkali is what makes a developing agent active, and an active agent with no silver to reduce reduces oxygen instead.

C₆H₆O₂ → C₆H₄O₂ + 2 H⁺ + 2 e⁻

Hydroquinone oxidised: the electrons go to oxygen when there is no silver, which is why the order of dissolution is chemistry and not custom

Why the sulfite is split in two. The 1928 directions put a quarter of it with the hydroquinone and the rest with the borax. The first portion is there so the hydroquinone is never alone in solution; the second carries the borax, which needs the warmth and the volume.

Why D-23 needs no alkali. Sodium sulfite is the salt of a strong base and a weak acid, so its solution is alkaline on its own. At 100 g/L that is enough to ionise metol usefully and not enough to make it violent, which is what “soft-working” means in Kodak’s description. The alkalis lesson has the arithmetic; the consequence to carry into the tank is that D-23 has very little buffer capacity, so its pH falls as development releases acid, and a second film in the same bath is not developed in the same solution as the first.

Why the two bottles will behave differently on the shelf. Both carry 100 g/L of sulfite, so both are protected the same way; what differs is the pH. D-76 sits higher, and a higher pH means a more active agent, which reacts faster with oxygen as well as with silver. Kodak’s published storage life is for D-76; the course has no published storage life for D-23, which your own records will eventually supply.

Data to record

This is the section the rest of the course depends on. Part IX reads it as its baseline and Part XXVII re-reads it years later, so write it for a stranger.

The batch record, one per bottle.

Field	Why it is there
Formula and version, e.g. D76-XX-001	The identifier everything else is filed against
The source of the formula, by document and section	So a later reader can check the quantities you used
Every mass actually weighed, to 0.01 g	The real composition, not the intended one
The balance used, and when it was last checked	Systematic error lives here
Water source, and whether it stood before use	Aeration and hardness both act, and both vary
Water temperature at each dissolving stage	The deviation from Kodak’s temperatures, recorded
The dissolving order, and any departure with its reason	The order is chemistry; a departure is a different formula
Final volume, and how you determined it	A 3 per cent volume error is a 3 per cent concentration error
Measured pH, with the temperature it was measured at	Meaningless without the temperature
Meter or papers, calibration buffers, and the resolution you could actually read	The uncertainty of the number above
Colour and clarity of the fresh solution	The zero reading for every future look at the bottle
Date, time, bottle, and how full it is	Headspace is what sets shelf life
Who mixed it	Not vanity: two people weigh differently

The processing record, one per roll. Film and batch number; meter setting; subject and light; developer version; time; temperature at start and end; the agitation scheme written out; stop and fixer with their dilutions; the fixer’s clearing time; wash method and duration; drying conditions.

The negative record, one per roll, written before you scan anything: overall density against the other roll, shadow detail, highlight separation, base fog against a clear unexposed frame, grain by eye, and any defect with its position on the roll.

📓The archive package, and what it has to survive

When the session is finished, one physical package goes into the archive and one entry goes into the index. The package holds both sleeved negative rolls, labelled, and the notebook pages. The index entry holds the version numbers, the date, and where the package is.

The test is whether it can be read without you. Somebody who was not there, opening it in five years, must be able to say what was in the bottle, what was on the film, what number was measured, and what was uncertain. That means writing “pH 8.62 at 19.4 °C, meter calibrated on 7.00 and 10.01 buffers the same morning” and not “pH 8.6”; and it means writing “D-23 developed 15 min at 20 °C, time derived from Kodak Ltd 1949’s 18 min at 18.3 °C using ILFORD’s 10 per cent per degree rule, which is an extrapolation” and not “15 min”.

Part IX will re-measure these developers properly, with a step wedge and a densitometer. Its whole value depends on being able to say that its measurements were made on these bottles.

Analysis

1. Compare your measured pH values with each other. D-76 should be higher than D-23. By how much, and does the difference match what you expect from 2 g/L of borax against no added alkali at all?
2. Compare them with the only published figure the course can offer, and read the comparison carefully. ILFORD publishes ID-11 stock at pH 8.60 to 8.70. ID-11 is a different product with an unpublished formula, so a match does not confirm your mixing and a mismatch does not condemn it. It is a sanity check on the order of magnitude and nothing more. The corpus contains no published pH for D-76 or for D-23, which the alkalis lesson also records; your measurement is therefore the course’s own figure, and it is worth taking properly.
3. Compute the molar composition of each bath and put it in the record: sulfite 0.79 mol/L in both; metol 0.0116 mol/L in D-76 against 0.0436 in D-23; hydroquinone 0.045 mol/L in D-76 and none in D-23; borax 0.0052 mol/L in D-76 and none in D-23.
4. Compare the two negatives side by side on a light box, not one after the other. Which has more shadow detail, which more separation in the highlights, which is denser overall? Write the answers before you form an opinion about which is better.
5. Say what you cannot conclude. The D-23 roll was developed for a time you derived rather than one anybody published, so a difference between the two negatives could be the formula or could be the time. Naming that confound now is what makes Part IX’s compensated-time comparison worth running.

Troubleshooting

What you see	Likely cause	What to do
The hydroquinone solution turns yellow while you mix	An agent met alkali before it met the preservative, or the borax went in early	Note it, finish the batch, and mark the version as suspect. Kodak’s order exists for exactly this
Undissolved crystals in the bottom of the bottle	Water too cool, or made up to volume before something had dissolved	Warm the bottle gently in a water bath and shake. Kodak Limited’s advice for a precipitate is to redissolve by warming rather than discard, because the precipitate often contains the most important constituents
The borax will not dissolve	It is much less soluble cold, and you are working at the bottom of the range	Take out 200 mL, warm it, dissolve the borax in that, and return it. Record the deviation
pH reads far from what you expect	The electrode is out of calibration, or you read at a very different temperature	Re-calibrate and re-read. If it still disagrees, check your borax weighing before you doubt the meter
Both readings are identical to two decimals	The electrode was not rinsed between them, or it is not responding	Rinse, blot, re-read D-76 last as a drift check
The D-76 negative is thin and flat	Under-development, wrong dilution, or a weighing error in the metol or the borax	Check the record before the chemistry: the commonest cause is a time or temperature that was not what you wrote down
Both negatives are blank or nearly so	Fixer contamination of the developer, or the film was fixed before it was developed	ILFORD’s own warning: a trace of fixer in the developer gives inconsistent results or, at worst, completely blank film. Separate vessels, separate funnels, no exceptions
The negative has clear circular spots	Air bubbles that were never dislodged	Tap the tank against the bench after the first agitation, every time

Clean-up

Rinse every jug, cylinder and stirrer into the developer waste container, then wash and dry them. Do not rinse a developer vessel into a sink because it “only had a little in it”: a little is where the aquatic classification lives. Wipe the bench and the balance and put the cloth into the waste rather than a laundry basket, which is HSE’s instruction on contaminated cloth. Throw the gloves away, and wash your hands before you touch anything else.

Storage

The bottles. Full, tightly capped, labelled, dated, cool, dark and away from anything acid. Kodak’s published life for D-76 stock is six months full and two months half-filled; the course has no published figure for D-23, so treat the first sign of colour in that bottle as information rather than a nuisance.

The solids. Back into tightly closed containers with the date of opening on each, cool, dry and dark, away from oxidisers and acids. Kodak Limited’s point about part-used containers applies to jars as much as to bottles: the air space grows every time one is opened.

The negatives. Sleeved, labelled with the version number, and filed with the notebook pages as one package.

Disposal considerations

Three labelled containers, and the reason for three rather than one is chemistry rather than tidiness.

Developer waste. Both agents are notified as very toxic to aquatic life with long-lasting effects, and a developer that has processed two films has consumed almost none of its agent — what you weighed is essentially all still there. ILFORD’s advice to domestic users in the United Kingdom is to bottle each waste chemical separately, label it and take it to a Household Waste and Recycling Centre; the disposal page sets out why the answer is jurisdictional.

Fixer and its first rinse. Silver-bearing, and kept for the silver stream. Kodak’s guidance records that developer solutions carry negligible silver, so combining the two containers recovers nothing and spoils the recoverable one.

Acid stop bath, if you used one. Its own container, and never poured into the developer waste. A sulfite-rich alkaline waste meeting an acid is the one gas-producing reaction available on this page.

Check your local regulations. They govern, they differ between authorities within one country, and they change.

Questions

1. Kodak gives two different reasons for dissolving metol first — one about solubility, one about oxidation. Which reason applies to D-23, which has no other agent and no alkali, and what would you expect to see if you ignored the order?
2. Your D-76 measured pH 8.4 and your D-23 measured pH 9.0. Which of those is more surprising, and what would you check first?
3. You weighed 2.13 g of borax instead of 2.00 g. Estimate the direction of the effect on activity and on fog, from the designer table in the assignment, and say whether the batch should be discarded, used, or used with a note.
4. Both developers carry 100 g/L of sulfite. Name three separate jobs that sulfite is doing in D-23, and say which of them D-76 does not need it for.
5. Why does this page insist that the agitation scheme is recorded alongside the development time, rather than just the time?
6. Part IX will ask you to run the same two developers against a step wedge. What in today’s record would make that measurement interpretable, and what in it would you have to have written down at the time because it cannot be recovered afterwards?

Further experiments

Make D-25. Kodak’s D-25 is D-23 plus 15 g/L of sodium bisulfite and nothing else, and Kodak publishes the consequence alongside: an extra fine-grain developer requiring a 50 to 100 per cent increase in exposure, developed about 18 minutes at 25 °C. One added salt, one pH change, one stop of speed, all published by the manufacturer. Mixing it and measuring its pH against your D-23 is the cleanest single-variable experiment in this whole part.

The headspace pair. Split one of your litres into a full 500 mL bottle and a half-filled one, both capped and dated, and read the colour and a fogged-strip activity test at intervals for two months. Kodak publishes the endpoints — six months full, two months half — and publishes nothing in between.

The water arm. Mix a second half-litre of D-23 with distilled water, the same day and from the same weighings, and compare the pH. Kodak’s 1928 primer is notably unimpressed by water-quality folklore, and this is a two-hour test of whether yours is doing anything at all.

The 71 °C question. Mix one batch at Kodak’s published temperatures instead of this page’s cooler ones, with the Level B controls the higher temperature needs, and compare pH, clarity and the control negative. The arithmetic here says it should make no difference. Finding out beats being told.

Check your understanding

Question 1. Kodak Limited says metol should be dissolved first because it is "readily soluble in warm water, but only slightly soluble in sulphite solutions without alkali". Why is that a stronger argument than the oxidation one?

• Because oxidation does not happen at mixing temperatures
• Because it predicts a different failure — the metol simply will not dissolve, which stirring and speed cannot fix — rather than a degradation that might be tolerable
• Because the sulfite reacts chemically with metol
• Because warm water dissolves everything

Show the answer and why

Answer: Because it predicts a different failure — the metol simply will not dissolve, which stirring and speed cannot fix — rather than a degradation that might be tolerable

The two arguments are about different failure modes. An oxidation argument says the agent may be damaged while it waits, which is a matter of degree. A solubility argument says it may not enter solution at all, which is a matter of kind: you would end up with a developer of unknown, lower metol concentration and undissolved solid in the jug. Kodak gives the second, and the course follows the instruction while noting that no source it holds quantifies how much the sulfite reduces metol’s solubility.

Question 2. This page prints Kodak’s mixing temperatures of 52 °C and 71 °C and then works at 45 to 50 °C. Why is that not a silent modernisation of the formula?

• Because temperature is not part of a formula
• Because the quantities and the dissolving order — the parts that carry the chemistry — are unchanged, the deviation is stated as a deviation with its reason, and the sourced solubilities are shown to permit it
• Because Kodak’s figures were in Fahrenheit
• Because the difference is small

Show the answer and why

Answer: Because the quantities and the dissolving order — the parts that carry the chemistry — are unchanged, the deviation is stated as a deviation with its reason, and the sourced solubilities are shown to permit it

Rule 5 forbids changing a historical formulation without saying so. What that protects is the composition and the procedure that makes it, and both are printed here exactly as Kodak gave them. The temperature is a working choice, and the page earns it three ways: it prints Kodak’s figure, it states its own and why, and it shows the arithmetic — sulfite at 220 g/L against a required 187, borax at 51 g/L against a required 2 — that makes the cooler water sufficient. A deviation you can see and check is not a modernisation.

Question 3. A ±0.1 g weighing error is ±0.1 per cent on the sulfite and ±5 per cent on the metol and the borax in D-76. Which of these follow?

• A balance reading to 0.01 g is worth having for the two small weights
• The mass actually weighed should be recorded rather than the target mass
• The sulfite can be weighed casually because the tolerance is generous
• A 5 per cent error in the borax lands on the developer’s energy, because the quantity of alkali governs it

Show the answer and why

Answer: A balance reading to 0.01 g is worth having for the two small weights, The mass actually weighed should be recorded rather than the target mass, A 5 per cent error in the borax lands on the developer’s energy, because the quantity of alkali governs it

The first, second and fourth are the argument. The third is a trap of a familiar kind: the tolerance on the sulfite is indeed generous, but sloppiness in weighing 100 g is usually sloppiness about which sulfite — the anhydrous salt or a hydrate — and that is a factor-of-two error, not a one per cent one. Generous tolerances make the identity of a chemical matter more, not less.

Question 4. You measure your fresh D-76 at pH 8.62 and compare it with ILFORD’s published 8.60 to 8.70 for ID-11 stock. What does the agreement establish?

• That you mixed D-76 correctly
• Very little: ID-11 is a different product with an unpublished formula, so this is a sanity check on the order of magnitude and not a confirmation of anything
• That D-76 and ID-11 are the same formula
• That your meter is calibrated

Show the answer and why

Answer: Very little: ID-11 is a different product with an unpublished formula, so this is a sanity check on the order of magnitude and not a confirmation of anything

This is the discipline the whole part has been building. The corpus contains no published pH for D-76 or D-23, so there is nothing to check against; ID-11 is a borax-class ILFORD powder developer whose composition ILFORD does not publish. An agreement is reassuring about magnitude and proves nothing about composition, and a disagreement would condemn nothing either. Your measurement is the course’s own figure, which is why the record has to carry the temperature, the buffers and the resolution.

Question 5. Why does the page give a derivation for D-23’s development time instead of a number?

• Because Kodak never published one
• Because Kodak published one for the films of 1949 and none for a current film, so any modern figure is an extrapolation and the page shows the extrapolation rather than hiding it inside a number
• Because development time cannot be predicted
• Because D-23 is not intended for roll film

Show the answer and why

Answer: Because Kodak published one for the films of 1949 and none for a current film, so any modern figure is an extrapolation and the page shows the extrapolation rather than hiding it inside a number

Kodak Limited’s 1949 handbook does give a time — about 18 minutes at 18.3 °C — but for the plates and films of that period. Carrying it to a current film and a different temperature requires assumptions, and the largest of them is that ILFORD’s 10-per-cent-per-degree rule of thumb, written for ILFORD developers, transfers to a metol-sulfite bath. Printing "15 minutes" would bury all of that. Printing the derivation with its status makes the first negative an honest first data point, which is exactly what Part IX needs it to be.

Question 6. D-23 has no alkali listed in its formula. What holds its pH up, and what is the practical consequence for a second film in the same bath?

• Nothing does; D-23 works at neutral pH
• Sodium sulfite: it is the salt of a strong base and a weak acid, so its solution is alkaline — but with little buffer capacity, so the pH falls as development releases acid and the second film is not developed in the same solution as the first
• The metol itself is basic
• Dissolved carbon dioxide from the water

Show the answer and why

Answer: Sodium sulfite: it is the salt of a strong base and a weak acid, so its solution is alkaline — but with little buffer capacity, so the pH falls as development releases acid and the second film is not developed in the same solution as the first

A hundred grams per litre of sodium sulfite is enough alkalinity to ionise metol usefully, which is what makes a two-ingredient developer possible and what Kodak means by calling D-23 soft-working. What it is not is a buffer with a conjugate pair in reserve, so every mole of acid development releases moves the pH. That is the chemical reason a reused bath is a different bath, and the reason this course develops one-shot whenever it means to measure something.

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