Experiment: The Solvent Series - Sulfite, Dilution and Agitation

Three knobs on a developer look like three different subjects. Sulfite is a preservative that happens to dissolve silver halide. Dilution is an economy that happens to change the negative. Agitation is a housekeeping chore that happens to decide how even the result is.

They are one subject. Every one of them changes how much developing agent, and how much solvent, is present at the surface of a crystal at the moment it is being developed — one by putting more solvent in the bath, one by putting less of everything in the bath, and one by deciding how fast what has been used up is replaced. That is why they belong in one session, and it is also why running them in one session is dangerous. Three variables in five hours is exactly how a confounded experiment gets made.

The strip layout and the order of processing are what keep them apart. Read those two things carefully; they are the content of this page as much as the chemistry is.

Purpose

To measure what happens to grain, speed, contrast, evenness and edge sharpness when the solvent concentration is changed at constant pH; when the whole developer is diluted; and when the rate at which fresh developer reaches the film is changed — and to keep those three answers separable.

Hypothesis, arm A. Raising the sulfite from 10 to 100 g/L in a metol bath held at one pH gives progressively finer grain and progressively less speed, because dissolution of halide during development both breaks the contacts between crystals and removes the marginal specks that carry the toe. The threshold step should fall as the sulfite rises. The magnitude is open: Part VIII establishes the mechanism and states plainly that the course has no formation constant for a silver–sulfite complex and no measured solubility of silver bromide in sulfite solution, so nothing here can be calculated in advance.

Hypothesis, arms B and C. Diluting the developer and slowing the agitation both make the developer next to the emulsion locally different from the developer in the vessel, so both should increase adjacency effects and compress highlights, and both should cost evenness. Dilution should do it in proportion to how little agent is present; reduced agitation should do it in proportion to how long the by-products are left where they were made.

The controls. Four, and they do four different jobs.

• S100, the metol bath at 100 g/L of sulfite, is arm A’s control: the other two cells differ from it in sulfite and in nothing else. It is also, by design, the same composition and the same time as cell A2 of the activity series, so the two sessions share a cell — with one difference that has to be written down: A2 was made by adding borax to a D-23 base that had been standing in a bottle since Part VIII, and S100 is mixed fresh from solids. Any difference between the two strips is therefore a difference in the age of the bath before it was anything else, which is a result about keeping and not about sulfite.
• D-stock at 16 minutes is arm B’s control: the dilute cells differ from it in dilution and in nothing else, the time being held.
• D-1+3 intermittent is arm C’s control: the other two agitation cells differ from it in the agitation script and in nothing else, the dilution, the volume, the vessel and the time being held. All three come out of one jug, so they cannot even differ in mixing.
• The shared reference strip, D-76 1+1 for 11 minutes at 20 °C, the standard condition set by the test-negative lab. It controls nothing inside the session. Its job is to tie this session to the others, and to be a replicate of the compensated 1+1 cell so that the session contains one honest estimate of its own repeatability.

The one variable that changes. Sulfite concentration in arm A, dilution in arm B, agitation script in arm C. The arms do not cross. Arm A is a metol-only bath and arms B and C are metol–hydroquinone, so no cell in arm A may be read against any cell in arm B as though the two differed in one thing. The page draws them on one field at the end for their directions, and says again there that it is not a grid.

!Three things this session cannot do, said before you start

It cannot separate sulfite from ionic strength. A hundred grams of sodium sulfite per litre is 0.79 mol/L, and ten grams is 0.079. Arm A therefore changes the bath’s whole ionic strength by a factor of ten along with its solvent power, and ionic strength changes how far the gelatin swells and therefore how fast anything diffuses through it. “Sulfite” in arm A means sulfite, and whatever a tenfold change of salt concentration does to a gelatin layer.

It cannot separate sulfite from preservation. Sulfite is the antioxidant as well as the solvent, so the 10 g/L cell is also the least-protected cell. The mitigation is procedural rather than chemical: all three cells are mixed within the same half hour, kept full and capped, and developed in one batch, so they stand for the same length of time. If the low-sulfite cell comes out weak, part of that may be agent lost to air rather than solvent action withheld, and the week-long keeping jars set up at the same time are what will tell you how large that part could be.

It cannot give you a number for grain. Grain is ranked here, by eye and under magnification, at matched density. A granularity figure needs a densitometer with a defined aperture, and Part IV is explicit that Kodak’s own figures carry an aperture, a magnification, a density and a developer. The strips are archived so that Part XXVII can put numbers on this ranking.

Learning objectives

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

• Design a three-arm session whose arms share a bench and a batch without sharing a variable, and say in one sentence for each arm what its control is.
• Compute the pH of a sulfite–borate bath from published dissociation constants, and show that a borate buffer holds it still across a tenfold change in sulfite.
• Trim three cells to a common measured pH with boric acid, and record the trim as a change of composition rather than as an adjustment.
• Work out the minimum volume of a diluted developer from a manufacturer’s published figure for a roll, scaled to a strip, and catch the cell where the obvious volume falls below it.
• Run continuous, intermittent and reduced agitation to written scripts, at one time and one dilution, and predict which will fail and how.
• Compare grain between two strips at matched density rather than at matched step, and explain why the distinction is the whole comparison.
• Find and describe a Mackie line on an edge-target strip.
• State what a compensated-time pair does and does not hold constant.
• Archive fourteen strips so that Part XXVII can read them without asking you anything.

Prerequisites

• Lab: preparing standard test negatives, which produced the exposure batch, the standard condition, the notch discipline and your resolution limit.
• Experiment: the activity series, whose cell A2 this session repeats, and whose pH arithmetic it extends rather than restates.
• Solvent action, physical development and grain, which owns the solvent mechanism, the speed loss and the gaps in both.
• Acutance, adjacency and compensation, which owns edge effects, compensation, stand development and the published failure modes.
• Measurement and uncertainty and concentration and dilution.
• Buffers and buffer capacity and measuring pH.
• The SOPs for opening the laboratory, mixing from a stock, calibrating a pH meter, checking the balance, labelling a container and closing the laboratory.

Safety classification

Level A: a standard home darkroom, with one weighing step worked at Level B controls.

• The solutions in use. Alkaline developers, handled by the hundred millilitres in open cylinders, with gloves and eye protection. That is the same handling as Part VIII’s mixing lab and the same as the activity series before it.
• The weighing step, which is not. Forty grams of sodium sulfite, fifteen of borax and a few of boric acid are weighed out. Borax and boric acid are Level B substances in this course’s encyclopaedia on a reproductive-toxicity classification, and the weighing is done with the Level B controls Part VIII sets: a tray, still air, one jar open at a time, gloves, eye protection, a particulate mask, and no film open in the room. A reader who is pregnant, breastfeeding or trying to conceive should read the borax and boric acid pages before opening either tub, and should take the alternative route below.
• The long unattended cell. The semi-stand vessels stand on the bench for a quarter of an hour with a strip in them. Label them, set a timer, and do not let a standing vessel of developer be mistaken for a fresh one — that is a housekeeping control, not a chemical one, and it is the only thing this arm adds to the risk assessment.
• Waste. Alkaline developer in one labelled container; fixer and its first rinse, which are silver-bearing, in another. Never combined.

What is not a hazard here, and why. There is no sulfur dioxide risk, although the arm-A cells carry up to 0.79 mol/L of sulfite. Sulfite releases the gas on meeting an acid, and this session contains no acid step at all: the stop is a plain water rinse, chosen for that reason among others, and the fixer is met only afterwards and goes to its own container. Boric acid is an acid by name and a very weak one by behaviour — its pK_a of 9.27 makes it a far weaker proton donor than the bisulfite already in the bath, which is precisely why it can be used to trim the pH of a sulfite solution without gassing it. The real acid risk in this session lives one bench along, in the waste bottles, which is why the two streams are never combined.

Equally, nothing is heated beyond a 20 °C water bath, and the inhalation route exists for about six minutes at the balance and is controlled there.

Hazards

Metol: skin sensitisation. H317, may cause an allergic skin reaction, in every ECHA notification that classifies it. It is present in all three arm-A cells and, as part of D-76, in every other cell. Sensitisation is cumulative and does not reverse. Gloves throughout, and no finger in a cylinder.

Hydroquinone: serious eye damage and aquatic toxicity. Present in every arm B and C cell as part of D-76. Eye protection from the first container opening to the last one capped.

Borax and boric acid: reproductive toxicity, and dust. Borax carries H360 at 93.2 per cent of the reports that classify it, and boric acid the same statement. HSE’s EH40 sets a workplace exposure limit for borates. The control is dust discipline at the balance and gloves on the hands that touch the jar.

Sodium sulfite: eye and respiratory irritation at the balance. Forty grams of a fine powder is the largest single weighing in this session, and it is the one most likely to raise dust. It goes on the tray with the rest.

Aquatic toxicity of the whole waste stream. Metol and hydroquinone are notified as very toxic to aquatic life with long-lasting effects, and this session produces about 1.8 litres of alkaline developer waste carrying nearly everything that was weighed or poured into it, because fourteen small strips reduce very little silver — about 1.8 litres, with another 150 ml a week later when the keeping jars are finished with.

Required PPE

• Single-use nitrile gloves, 0.2 mm, per HSE’s COSHH essentials sheet P1, changed when contaminated.
• Eye protection from the first jar opening to the last container capped.
• A particulate mask for the weighing step, which is what allows a Level B weighing inside a Level A session. It does not replace the tray or the still air.
• An apron or overall kept for laboratory work.
• Clean dry hands, or lint-free gloves, for the film itself — the Library of Congress handling guidance, and a control on the archive rather than on you.
• Dedicated labelled utensils, and a separate set for fixer.

Ventilation

Nothing in this session evaporates in a way that puts a substance into the air, so ventilation is not being asked to remove a vapour. It is doing two jobs. The first is dilution during the six minutes when powder jars are open, which is a general-ventilation duty: HSE’s COSHH essentials sheet P1 sets more than five air changes an hour with a through draught for manual film development, and that is the standard here. The second is amenity over a five-and-a-half-hour session, most of it the ammonia smell of a rapid fixer.

Part II’s laboratory layout owns how a room is light-tight and ventilated at once.

Materials

Item	Quantity	Note
Wedge strips from the Part IX exposure batch	10	Datum-notched; identity nips applied at allocation
Edge-target strips, cut from the same film	4	Exposed separately in the Preparation; their own batch block
Negative sleeves and card label slips	14	One slip per strip, eight fields each
Opaque tin	1	Holds the unused batch while the light is off
Small clear stoppered jars	3	For the week-long keeping observation on the arm-A cells
Random reading cards	14	Shuffled, for blind reading
Opaque card with one clean straight edge	1	The edge-target mask; taped to the contact glass, never laid on the film

Running total against the part’s budget. The overview allows about 41 strips for the whole of Part IX and budgets roughly eight for this session. The design as written spends ten from the wedge batch — the two extra are the compensated cell and the shared reference — plus four edge targets that are not wedge-exposed at all and so do not come out of that count. With the four control strips and the ten of the activity series, that leaves about seventeen for the agent comparison and the break/fix, which is enough with a margin. Count them before you cut anything.

Chemicals

Chemical	Quantity	Form
Metol	5.64 g	Solid, for the three arm-A cells at 7.5 g/L
Sodium sulfite, anhydrous	40.0 g	Solid: 2.50 g, 12.50 g and 25.00 g into three 250 ml cells
Borax	15.0 g	Solid, 5.00 g per arm-A cell, weighed at Level B controls
Boric acid	2 g, as needed	Solid, for the pH trim only; most of it will not be used
D-76 stock (metol, hydroquinone, sodium sulfite, borax), from Part VIII’s lab	520 ml	Solution, one bottle, one version number
Rapid fixer (ammonium thiosulfate type)	750 ml at 1+4	Fixed for twice the clearing time
Wetting agent	1 L at 1+200	Final rinse
Water, at 20 °C	about 6 L	Dilution, rinse and wash

Note what is not in that table: no potassium bromide is added to anything. Bromide appears in this session only because the film puts it there, which is the whole of arm C’s subject.

Equipment

Eight measuring cylinders of 100 ml, and six vessels that hold 120 ml at a depth of at least 150 mm — about 35 mm across, which is the size of a 250 ml measuring cylinder. Check every one with water and a scrap of film before you commit developer to it; a strip that stands proud of the surface for the last 20 mm has a variable in it that no notebook will record. A balance reading to 0.01 g, checked against a reference. A pH meter with pH 7 and pH 10 buffers, or the best indicator strips you have. A thermometer to 0.1 °C. A tray deep enough to serve as a water bath for the whole rack. One 1 L jug for the 1+3 batch. Three shallow trays for the rinse, the fixer and the wash, each long enough to lay a 135 mm strip flat. Tongs, one pair per solution, and a separate set for fixer. A stopclock with a lap function, or two timers. A drying line, a lightbox, a loupe or a digital microscope, and a flatbed scanner.

📓What magnification the grain work needs, and how to find out before you buy

Part IV already costed this out and the arithmetic is not repeated here. The short version is that the structure you are looking for is the mottle Kodak measure through a 48 µm aperture, that it should span about ten sensor pixels to be seen comfortably, and that the question to ask of any digital microscope is therefore how many micrometres of the subject one pixel covers — 5 µm per pixel or better will show granularity, 50 µm per pixel will not. A good loupe over a lightbox will rank the three arm-A strips; it will not settle a close call between two of them, and the ranking is what this session needs.

Estimated cost

££, and almost all of it is the D-76 stock and the film. The solids consumed amount to about 40 g of sulfite, 15 g of borax, 6 g of metol and a gram or two of boric acid. The 520 ml of D-76 stock is the real expense: check the bottle before the session, because Kodak’s storage-life table gives six months for a full, tightly closed bottle and two months for a half-filled one, and a bottle that has been open since the activity series may be at the end of its second month. The planner carries the numbers.

Estimated consumables cost

Almost all of it is the D-76 stock and the film, both costed elsewhere. What this session consumes on its own account is about 40 g of sulfite, 15 g of borax, 6 g of metol and a gram or two of boric acid.

Consumed	This session	Sourced price	Cost this session
Metol	5.64 g, three arm-A cells at 7.5 g/L	£16.20 per 50 g (£0.32 a g)	£1.83
Sodium sulfite, anhydrous	40.0 g across three cells	£13.68–£19.98 per 1 kg, anhydrous	£0.55–£0.80
Borax	15.0 g, 5.00 g a cell	£9.98 per 200 g, decahydrate	£0.75
Boric acid	up to 2 g for the pH trim; most will not be used	None. The planner carries no item for this substance at all	—
D-76 stock, from Part VIII	520 mL — check the bottle date before the session	Costed in Part VIII’s mixing lab	—
Wedge and edge-target strips	14, from the Part IX exposure batch	Costed in preparing-standard-test-negatives	—
Rapid fixer concentrate	150 mL, to make 750 mL at 1+4	£21.05–£25.98 per 1 L of ammonium thiosulfate concentrate, diluted 1+4 for film	£3.16–£3.90
Wetting agent	5 mL, for 1 L at 1+200	£28.70 per 1 L of concentrate, diluted 1+200	£0.14
Negative sleeves and card label slips	14 pockets, 14 slips	None. A named price gap: sleeving that passes the Photographic Activity Test	—

The priced rows come to £6.42 to £7.42 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 9 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.

The 520 mL of D-76 stock is the real expense and it is costed in Part VIII, but it is not free: Kodak’s storage-life table gives six months for a full, tightly closed bottle and two months for a half-filled one, so a bottle opened for the activity series may have to be remixed for this session. Budget the mixing lab twice if your sessions are more than two months apart.

Waste streams

1. Alkaline developer, about 1.8 L, carrying all the metol, hydroquinone, sulfite, borate and dissolved silver the session used, plus 150 ml more when the keeping jars are read out. One labelled container, routed per the general waste SOP.
2. Spent fixer and the first rinse after it, silver-bearing, to the silver stream. The arm-A fixer is worth a thought of its own: a solvent developer puts silver into the developer, so stream 1 is more silver-bearing here than in a normal session and stream 2 slightly less.
3. Rinse and wash water. The rinse that follows the developer carries developer and goes with stream 1; the first change of wash water after fixing goes with stream 2, and the rest to the general stream.

Never combine streams 1 and 2. Stream 1 is a concentrated sulfite solution and stream 2 is acidic.

Alternative route

The session needs darkness for one operation only: taking ten strips out of the tin and giving each its identity nips, which is about fifteen minutes with the light off. The edge targets are exposed in the Preparation, which needs darkness for about the same again.

The orthochromatic route. If the batch was made on ILFORD ORTHO Plus, both of those quarter hours happen under a deep red safelight instead — ILFORD’s 906 filter with a 15 W bulb at not less than 1.2 m — and the rest of the session runs in room light with the strips in closed vessels. Whichever film the batch is on, it stays on it.

The route without borax. A reader avoiding borax and boric acid on the reproductive classification can run arms B and C unchanged, because D-76’s own borax is already in the bottle mixed in Part VIII and nothing is weighed for them here. Arm A cannot be run at constant pH without a borate buffer, and the honest options are to drop it or to run it unbuffered and record the pH of each cell as a second variable you did not control. The second is worth something and the page would rather say what it costs than pretend the substitution is free: an unbuffered sulfite ladder spans about 1.3 pH units, and the activity series has already shown you what a pH ladder does on its own.

Preparation

About 90 minutes, the evening before. The 330 minutes on this page is the Procedure.

Working out the buffer before you weigh anything

The arm-A base is Kodak’s D-23 with the sulfite treated as the variable: metol 7.5 g/L throughout, sulfite at 10, 50 and 100 g/L. Left alone, that is not a sulfite series at all. It is a pH series with a sulfite series inside it, and here is why.

Metol is a hemisulfate, (C₇H₉NO)₂·H₂SO₄ at 344.39 g/mol, so 7.5 g/L is 0.0218 mol/L and its sulfuric acid converts about 0.0436 mol/L of sulfite to bisulfite at the moment of mixing. That pool does not change when the sulfite does. What changes is how much sulfite is left beside it.

pH = 7.19 + log([SO₃²⁻] / [HSO₃⁻])

Predicted pH of an unbuffered metol-sulfite bath, from Henderson-Hasselbalch with pKa₂ = 7.19

Sulfite	Total sulfite	Left as sulfite	As bisulfite	Predicted pH, unbuffered
10 g/L	0.0793 mol/L	0.0357	0.0436	7.10
50 g/L	0.397 mol/L	0.353	0.0436	8.10
100 g/L	0.793 mol/L	0.749	0.0436	8.43

A spread of 1.33 pH units, which the activity series measured as the difference between a bath with no alkali and a bath with a real one. Run that series and you would be measuring pH, not sulfite.

So the pH is pinned with borate. Borax is Na₂B₄O₇·10H₂O, and each mole of it supplies two moles of borate and two of boric acid — a buffer that arrives already half-neutralised, centred on boric acid’s pK_a of 9.27.

B(OH)₃ + H₂O ⇌ B(OH)₄⁻ + H⁺

Boric acid and borate: the couple that holds arm A still while the sulfite changes by a factor of ten

At 20 g/L — the quantity Kodak puts in the D-76R replenisher, and the quantity the activity series used — borax gives 0.105 mol/L of borate and 0.105 of boric acid. Conserve protons across both couples and solve for the pH at which the sulfite couple and the borate couple agree, and the three cells come out at 8.90, 8.96 and 9.00.

🧮A tenfold change in sulfite, a tenth of a pH unit

The reason the buffer works so well is not that the borate is strong. It is that the thing it has to overpower — the 0.0436 mol/L of bisulfite — does not change across the series, because it comes from the metol and the metol is held constant. Borate at 0.105 mol/L takes about 0.032 mol of that pool in the 100 g/L cell and about 0.042 in the 10 g/L cell, and once the bisulfite is nearly gone the borate couple sets the pH by itself.

A spread of 0.10 units is inside the ±0.2 specification of a teaching electrode, which means you will not be able to prove the cells are at the same pH; you will only be able to fail to prove they are not. That is a weaker statement than it looks like and it belongs in the report in those words.

Every number here assumes ideal behaviour in a solution running from 0.08 to 0.8 mol/L, where the assumption is poor at one end and much worse at the other — and the two ends are not equally wrong, which is the awkward part. Read them for direction and magnitude and let the meter decide.

The rest of the preparation

1. Open the laboratory to the SOP, and check the balance and thermometer against a reference.

2. Mix the three arm-A cells, 250 ml each, all within the same half hour, at Level B controls for the solids. Dissolve in this order and no other: metol first, in about 200 ml of water at 45 to 50 °C, because Kodak’s own handbook records that the agent is only slightly soluble in sulfite solutions without alkali; then the sulfite, in two or three portions; then the borax, which is slow in cold water; then make up to 250 ml with cold water.

   Cell	Metol	Sulfite	Borax	Water to
   S10	1.88 g	2.50 g	5.00 g	250 ml
   S50	1.88 g	12.50 g	5.00 g	250 ml
   S100	1.88 g	25.00 g	5.00 g	250 ml

   Record every mass actually weighed, not the target mass, and give each cell a formula version code per the scheme Part VIII sets. These are variants, not D-23, and their codes should say so.

3. Calibrate the pH meter at 7 and 10 per the SOP, bracketing the samples rather than sitting to one side of them, and measure all three cells at 20 °C, rinsing the electrode between and reading only when the display has settled.

4. Trim to the lowest reading. Take whichever cell reads lowest as the target and bring the other two down to it with boric acid in 0.10 g additions to the 250 ml, stirring and re-measuring after each. Trimming downwards only is deliberate: it needs one reagent, it is monotonic, and it cannot overshoot into a second alkali. Record every addition. The trimmed cells are new versions, and “pH held constant” now means “pH held constant, and whatever the boric acid brought with it” — a little more borate buffer and a little more ionic strength in two of the three cells.

5. Fill the keeping jars. Take 50 ml of each trimmed cell into a small clear stoppered jar, filled about half, labelled with the cell, the sulfite level and the date. Stand all three together, out of direct sun, where you will see them daily.

6. Expose the four edge targets. Rebuild the contact rig to the geometry recorded in the test-negative lab — the same lamp, the same 1.00 m, the same everything — and record it as a separate batch block, because these strips are not part of the wedge-exposed batch and must never be filed as though they were. Cut four strips at 135 mm, datum-notch each, and expose each one for the batch time with the opaque card taped to the glass so that it masks half the strip lengthwise. That gives a strip whose one half saw the full lamp and whose other half saw nothing, with 135 mm of clean boundary between them. Give them their identity nips now, in the dark, one to four, and put them in the tin with a note of which is which.

✕Why the edge target is a full-exposure boundary and not a gentle one

An adjacency effect is driven by how different the two neighbouring regions are in how fast they consume developer. The strongest possible case on this film is bare exposure against no exposure, so that is what the target is, and if a Mackie line does not appear there it will not appear anywhere in this session.

The cost is that the bright side is developed past the shoulder, where the emulsion has stopped responding to exposure and the local chemistry has already run itself down. So the target answers “is the effect present, and in which cell is it strongest” and does not answer “how big is it at a normal subject brightness range”. The second question needs a densitometer trace across the boundary, and Part XXVII is where these same four strips get one.

Procedure

Fourteen strips, three arms, three equal times, and one order of processing that keeps them apart. The 330 minutes divides as 35 to bring the bench to temperature, 30 to mix the dilutions, 15 in darkness allocating strips, 130 for the four wet batches and the wash, 60 while the strips dry, and 60 for the first blind reading. The microscopy and the scanner pass come afterwards and are not in that number.

The design, in one picture

The cells actually run, and the cells deliberately not run

1. 1Arm A — sulfite — three cells, one variable, pH pinned with borate and trimmed with boric acid
2. 2Arm B — dilution — three cells at one time, plus one compensated cell at the published time
3. 3Arm C — agitation — three cells at one dilution and one time; the intermittent cell is shared with arm B
4. 4The grid not run — nine cells of dilution against agitation would need two sessions; the dilute column is where the effect is
5. 5Edge targets — four strips, own vessels, same solutions, same times

Every line in this drawing is a decision that could have gone the other way, and the ones that were declined are drawn as well, because an experiment is defined as much by the cells it does not run.

Why the equal time is 16 minutes, and what it costs

Every cell in arms B and C gets 16 minutes at 20 °C, which is ILFORD’s published time for Kodak D-76 at 1+3 with FP4 Plus at EI 125. Their published times for the same pair are 8 minutes at stock and 11 at 1+1.

The equal time is set by the most dilute cell rather than by the middle one, and the reason is worth stating because it is a choice the reader could sensibly have made differently. Everything fragile in these two arms — the Mackie lines, the unevenness, the grain comparison at matched density — lives in the dilute cells. An under-developed dilute strip shows none of it. So the dilute cells are developed properly and the stock cell pays for the design by being given twice its published time.

The price, named in advance. The stock cell at 16 minutes is over-developed by any normal standard: it should come back dense, contrasty and short in scale, possibly with the top steps run together. That is a predicted outcome and not a spoiled strip, and it is exactly why the compensated cell exists.

Stage 1 — the bench, about 35 minutes

1. Bring the whole bench, cylinders and solutions to 20 °C, holding it within 0.3 °C — the limit Kodak’s process-control publication sets before temperature affects the result. A five-hour session drifts; check it between every batch, not once at the start.
2. Re-measure the pH of S10, S50 and S100 on the day and record all three again with the electrode’s stated accuracy beside each. A metol bath that stood overnight has begun to oxidise, and the pH is one of the two places you find out.
3. Look at the three keeping jars and write the first colour entry: a colour and an intensity, water clear, faint straw, clear yellow, never “the same”.

Stage 2 — mix the dilutions, about 30 minutes

4. Mix 800 ml of D-76 at 1+3 in one jug: 200 ml of stock into 600 ml of water at 20 °C, stirred. Split it six ways at 120 ml into the six deep vessels. All three agitation cells and their edge strips now come from one mixing, so mixing variation cannot appear as an agitation effect.
5. Mix 160 ml of D-76 at 1+1: 80 ml of stock into 80 ml of water. Split it into two 100 ml cylinders at 80 ml each — one is arm B’s 1+1 cell at 16 minutes, the other is the shared reference at 11.
6. Measure 240 ml of neat stock into three 100 ml cylinders at 80 ml each: two for the stock cell at 16 minutes and its edge strip, one for the compensated stock cell at 8 minutes.
7. Measure 80 ml of each arm-A cell into its own 100 ml cylinder.

🧮The volume that would have been wrong, and the arithmetic that catches it

Kodak publishes a minimum for D-76 at 1:1 rather than a rule: one 135-36 roll — 80 square inches — in 473 ml of diluted developer, or 237 ml with a 10 per cent increase in time. Take the first figure, which is the unqualified one. It contains 236 ml of stock, so the published requirement is about 2.96 ml of stock per square inch of film.

A 135 mm strip of 35 mm film is 47.3 cm², which is 7.32 square inches. So one strip needs about 21.7 ml of stock, however much water is around it.

Now check the obvious volume. Eighty millilitres was the right answer for every cell of the activity series and it is the right answer for the stock and 1+1 cells here — 80 and 40 ml of stock respectively. At 1+3 it contains 20 ml of stock, which is below the published minimum. The strip would not obviously fail; it would simply develop a little less than the arm’s other cells, and the deficit would be read as an effect of dilution, which is precisely the variable under test.

Hence 120 ml at 1+3: 30 ml of stock, 1.4 times the minimum. The minimum developer volume is not about drowning the film. It is about how many molecules of developing agent are in the vessel, and dilution is the one operation that takes them away without looking as though it has.

Stage 3 — allocate the strips, in darkness, about 15 minutes

8. With the light off, take ten strips from the batch tin. Working from the datum notch, give each its identity nips: one to five on the top edge for S10, S50, S100, D-stock-16 and D-1+1-16; one to five on the lower edge for D-1+3-int, D-1+3-cont, D-1+3-stand, D-stock-8 and the reference.
9. Take the four edge targets out too. They already carry their nips and are told from the wedge strips at a touch by the mask boundary, but check the note you wrote in the Preparation before the light goes on rather than after.
10. Close the tin, put it away, and only then turn on the light. Lay each strip beside its vessel.

Stage 4 — the wet run, in four batches, about 130 minutes

One agitation script, written out, for every intermittent cell in the part: lower the strip in and move it gently up and down for the first 30 seconds; then lift, drain for two seconds and re-immerse once at the start of each subsequent minute. The same words as the control set, the same words as the activity series.

The other two scripts are written out here because arm C is nothing but the difference between them.

• Continuous. Move the strip gently up and down for the whole 16 minutes, without pause, at about one cycle per second. ILFORD’s own instruction for continuous agitation is to reduce a spiral-tank time by up to 15 per cent, so at equal time this cell is expected to over-develop relative to the intermittent one, and the size of that expectation is published.
• Semi-stand. Move the strip gently up and down for the first 30 seconds, then leave it entirely alone except for a single 10-second agitation at 8 minutes 30 seconds — offset by half a minute so it does not collide with the intermittent cells’ lift.

Four wet batches, and where the hands are

B1 — 1+3 int, wedge + edge

develop 16 min, one-minute scriptrinsefix

B1 — 1+3 semi-stand, wedge + edge

develop 16 min, two agitations onlyrinsefix

B2 — 1+3 continuous, wedge + edge

develop 16 min, hands throughoutrinsefix

B3 — stock 16, wedge + edge

develop 16 minrinsefix

B3 — 1+1 at 16 min

develop 16 minrinsefix

B3 — stock at 8 min, compensated

develop 8 minrinsefix

B4 — S10, S50, S100

develop 10 minrinsefix

B4 — shared reference

develop 11 minrinsefix

0 min255075100

The continuous cell has a batch to itself because it occupies both hands for a quarter of an hour, and the semi-stand cell shares a batch with the intermittent one because it occupies neither. That is the whole of the scheduling problem, and it is why the batches are not four equal quarters.

11. Batch 1: the intermittent and semi-stand 1+3 cells, four vessels, started one minute apart in the order int-wedge, int-edge, stand-wedge, stand-edge. Run the intermittent pair on the one-minute script and the stand pair on its two agitations. Lift each at its own 16-minute mark.
12. Batch 2: the continuous 1+3 cell, wedge and edge, two vessels, hands on both for the full 16 minutes. Start them together; there is no script collision to avoid.
13. Batch 3: the stock cell and its edge strip, the 1+1 cell at 16 minutes, and the compensated stock cell at 8 minutes. Four vessels on the one-minute script. Start the first three a minute apart and the 8-minute cell eight minutes after the last of them, so that all four come out within three minutes of each other.
14. Batch 4: the three arm-A cells and the shared reference, four vessels, one minute apart. Arm A at 10 minutes, the reference at 11.
15. After each batch: rinse one minute in two changes of plain water, then fix for twice the clearing time measured on a scrap of the same film.

⚗Water rinse, not stop bath, for the whole of Part IX

Two of this part’s developers are alkaline with sodium carbonate, and carbonate carried into an acid bath makes carbon dioxide inside a warm swollen gelatin layer; Part VIII draws what happens next. No cell on this page contains carbonate — but treating this session’s strips differently from the rest of the part’s would put a difference between sessions into an archive that Part XXVII is going to read as one set.

So every strip in Part IX gets the same plain water rinse. ILFORD name the cost rather than hiding it: a water rinse may be substituted for a stop bath but increases the risk of processing marks and stains. That is the trade, and it is made once for the whole part.

16. Wash all fourteen together, 5 to 10 minutes in water within 5 °C of the developer, final-rinse in wetting agent at 1+200, and hang in still, dust-free air. Do not squeegee. A drying mark on a step is read as density, and these strips have a densitometer in their future.

Stage 5 — while they dry, about 60 minutes

17. Pour each used cell into a labelled clear jar as you finish with it, and stand the fourteen jars in order. The colour of a used developer is a datum and it will not survive the evening.
18. Write up the notebook while the deviations are still fresh. This is the section that is worth the most and gets written the least.
19. Close the laboratory to the SOP as far as the wet bench goes, leaving only the drying line and the lightbox.

Stage 6 — the first reading, about 60 minutes

20. When the strips are bone dry — not before — read them, blind, as the Analysis section sets out.

Expected observations

Arm A, as the sulfite rises. The 100 g/L strip should look the finest-grained and the slowest: its threshold step lower down the wedge than the 10 g/L strip’s, because the marginal specks that carry the toe are the ones a solvent dissolves first. The 10 g/L strip should look coarsest and fastest. Contrast should move least of the three readings, because the pH is pinned and the agent is unchanged.

Arm A, the surprise to watch for. A green or reddish veil in the shadow end of the 100 g/L strip, which looks like one colour by reflected light and another by transmitted light, is dichroic fog — Kodak’s 1928 primer attributes it to a developer containing an excess of sulfite, and records that it concentrates in the shadows where no bromide has been liberated to restrain it. If it appears, it is the arm’s most interesting result and not a spoiled strip.

Arm B, as the dilution rises. The stock strip dense and short in scale from its doubled time; the 1+3 strip at normal contrast; the 1+1 strip between them and over-developed by about 45 per cent. At matched density, the more dilute strips should read grainier and sharper — which is Kodak’s own published outcome for the 1:1 dilution, stated as greater sharpness with a slight increase in graininess.

Arm C, as the agitation falls. The continuous strip denser than the intermittent one, by the up-to-15 per cent that ILFORD’s own instruction implies. The semi-stand strip less dense, and the first place to look for trouble: streaks running downwards from the dense steps is bromide drag, and a general blotchiness with no direction is mottle. Both are published failure modes of reduced agitation and both are results.

The edge strips. Along the boundary, a narrow lighter band on the dense side and a narrow darker band on the thin side. The dark band is the Mackie line. Expect it faint on the stock strip, clearer at 1+3, and clearest of all on the semi-stand strip — and expect to need a loupe and raking light to be sure of any of it.

Everything. Expect the differences to be smaller than you hope, and expect at least one cell to be spoiled by something you did not plan for. Fourteen strips in one session is a lot of handling.

What is happening chemically

Arm A: dissolving a little of everything

The mechanism belongs to the solvent lesson and is not re-derived. In one paragraph: a silver solvent in the developer dissolves a small fraction of every crystal while development proceeds, which breaks the contacts that let an unexposed crystal be dragged into development by a developing neighbour — Kodak’s 1928 primer describes graininess as exactly that clumping — and which also takes away the smallest latent-image specks before they can work, and takes silver out of the image altogether. The first effect is the fine grain. The second and third are the speed loss. They are the same reaction, which is why no formulation separates them.

The dissolved silver does not leave. Some of it is reduced again on the filaments already growing, which is physical development happening inside chemical development; some is reduced in the gelatin between the grains, which is the dichroic fog above.

What this page cannot write down. There is no reaction equation for the sulfite complex on this page, and its absence is deliberate. Part III found no formation constant for a silver–sulfite complex in a source it had read, and Part VIII found no measured solubility of silver bromide in sulfite solution. Writing AgBr + n SO3^2- with a guessed coordination number would be inventing chemistry to fill a hole in a page layout. What arm A therefore measures is the effect, in three steps of concentration, which is the honest thing a bench can contribute where the constant is missing.

Arms B and C: the same shortage, arrived at two ways

AgBr + e⁻ → Ag + Br⁻

Every crystal developed hands a bromide ion back to the solution, and in a still bath it stays near where it was made

Development consumes agent and produces two things that slow it down: oxidised agent and bromide. In a brightly exposed region both are produced fast. Whether they matter depends on whether they are carried away faster than they are made, and that is a transport question with two answers.

Dilution changes the supply. Every dissolved species falls in the same ratio, so the reservoir at any point in the emulsion is smaller and runs down sooner, and there is less sulfite to mop up the oxidised agent and less buffer to hold the pH where it was. Local exhaustion arrives earlier and goes further.

Agitation changes the removal. Kodak states the purpose in one line: agitation removes the by-products of development from the surface of the film so that fresh developer can act on the exposed halide. Slow it down and you are deliberately leaving the by-products where they were made.

Both routes end at the same place — a boundary layer next to the emulsion that is chemically different from the bulk — and that boundary layer is what an adjacency effect is made of. Beside a heavily exposed area, spent developer and released bromide diffuse sideways into the lightly exposed area and hold it back: a light band. Beside a lightly exposed area, unspent developer diffuses the other way and pushes the dense side further: a dark band. That pair is the Mackie line, and it is the same physics as compensation at the scale of a highlight rather than an edge.

The failure modes are the same physics with nothing to organise it. A layer of spent developer that is denser than the bulk sinks, and retards development in whatever it flows over: bromide drag. A layer that is neither refreshed nor allowed to settle gives mottle. Kodak’s own troubleshooting table lists streaks of non-uniform density against excessive or uneven agitation and mottle against inadequate agitation, so both ends of the range fail and they fail differently.

📓Why this session's semi-stand cell is not stand development

Stand development as it is practised changes two things at once: it reduces agitation and extends the time, often several-fold. This session holds the time at 16 minutes and changes only the agitation, which makes arm C a clean single-variable comparison and makes its semi-stand cell not the thing photographers mean by the phrase.

That is the right trade for an experiment and it should be labelled honestly in the report. Wall’s 1924 formulary is worth having beside it: he records stand development as an old method whose only advantages are fine grain and uniform results “if the developer be frequently agitated” — a qualification which is the whole of modern semi-stand practice, arrived at a century early. Bostick and Sullivan publish schemes with real numbers for Pyrocat-HD, and Part VIII is explicit that a scheme published for one developer is not evidence about another, so they are not transplanted here.

The long version is in Further experiments and it is one strip.

Data to record

Session header, as the design lesson sets out, plus two batch blocks copied by name: the wedge exposure batch, and the edge-target batch made in the Preparation.

The pH table. One row per arm-A cell: predicted pH from the arithmetic, measured the evening before, every boric acid addition with its mass, measured after trimming, measured again on the day, and the electrode’s stated accuracy written next to every reading rather than once at the bottom.

The cell table. One row per strip, fourteen rows: strip name, notch code, random reading number, developer and its version code, dilution as used, actual volume in the vessel and the stock-equivalent it contains, time, temperature at start, middle and end, agitation script by name, vessel.

The reading table. One row per wedge strip: threshold step, scale length in steps, a written description of the masked patch against clear fixed base, grain rank with the density it was judged at, evenness score, and the date of the reading. One row per edge strip: whether a Mackie line was found, on which side, how wide in millimetres, and under what magnification and lighting.

The colour of the used cells, ranked in one sitting against a white card, fourteen entries.

The keeping log. Three colour entries a day for seven days, in the same light, from the same distance.

The deviations. Every one. A vessel knocked, a lift missed, a strip that touched its neighbour, the thermometer found reading 0.4 °C low after batch 3, the two minutes the continuous cell was left alone because the phone rang.

Analysis

1. Read blind. Shuffle the cards, assign a random number to each strip, read all fourteen in one sitting in random order on the same lightbox, and open the key only when the table is full.
2. Apply your resolution limit before you look at any pattern. It came from the control set. Any difference smaller than that limit is not reported as a result, and if that rules out most of an arm, say so. A null result honestly bounded is worth more than a trend read into noise.
3. Check the reference against the control set, and against the 1+1 cell at 11 minutes. These are two different checks and both matter. The first is between-session drift. The second is within-session repeatability: two strips from one batch, one developer, one time, one script, developed in the same session. If those two disagree by more than your resolution limit, your resolution limit was optimistic and every conclusion in the session inherits the wider one.
4. Plot arm A: threshold step against sulfite concentration on a logarithmic axis, because the levels are a tenfold ladder and a linear axis will hide the shape.
5. Rank grain at matched density, not at matched step. This is the step people skip and it is the whole comparison. On each strip, find the step whose density matches a chosen mid-tone on the reference strip — by eye against a lightbox, sliding one strip over the other until the two patches disappear into each other. Then examine that step. Different developers reach the same density at different steps, so comparing step 12 to step 12 compares two different densities, and Part IV is explicit that mottle is strongest at middle densities and weakest at both extremes. Record the step number you used on each strip; it is a datum in itself.
6. Score evenness on a written scale you define before you look — for example: 0, no visible non-uniformity; 1, faint mottle in the mid-tones only; 2, mottle plainly visible; 3, directional streaks from the dense steps; 4, unusable. A scale invented after the strips are dry is a scale fitted to the result.
7. Examine the four edge strips under magnification in raking light and again in transmission. Look for the light band on the dense side and the dark band on the thin side, measure the width of whichever you can see, and rank the four. Write your prediction of the order down before you look; the design lesson asks for this and it is the cheapest guard against seeing what you expect.
8. Read the compensated pair as its own experiment. D-76 stock at 8 minutes against D-76 1+3 at 16 minutes are the two conditions the manufacturer publishes for the same average contrast on this film. If the two strips do come back at similar scale length, then contrast is held and the remaining differences — grain at matched density, edge effects, the fog floor — are what dilution buys and costs when it is not confounded with development time. Say what the pair still does not hold constant: the time itself is different, so anything that depends on how long the emulsion is wet is not controlled.
9. Scan everything in one pass with the wedge included and every automatic function off, and repeat steps 4 and 5 on the scanner’s numbers. Where the eye and the scanner disagree about the order of two cells, that pair is inside the resolution of both and neither has separated it.

Arm A: what to write down before you develop anything

• Predicted threshold step (lower = slower)
• Predicted scale length, steps

Show the numbers behind this plot

Two predicted lines drawn against sulfite concentration at ten, fifty and one hundred grams per litre. The upper line is the threshold step, falling from about 18 at ten grams per litre through 17 at fifty to about 15.5 at one hundred, which means the developer needs progressively more exposure before it will put down any density at all as the solvent concentration rises, and that is the speed loss. The lower line is the scale length in steps, drawn almost flat at about 11 across the whole series, because the pH is pinned and the developing agent is unchanged, so the prediction is that contrast is the reading that does not move. The gap between a falling line and a flat one is the shape of the hypothesis: solvent action is predicted to cost speed without buying or spending contrast. Both lines are drawn shapes rather than measurements, printed so that the reader can lay three of their own points over them. Grain is deliberately absent from the plot because it is ranked rather than measured in wedge steps and cannot honestly share this axis.

Series	Sodium sulfite in the cell, g/L	Reading, in wedge steps
Predicted threshold step (lower = slower)	10.00	18.00
Predicted threshold step (lower = slower)	50.00	17.00
Predicted threshold step (lower = slower)	100.00	15.50
Predicted scale length, steps	10.00	11.00
Predicted scale length, steps	50.00	11.00
Predicted scale length, steps	100.00	10.80

Drawn, not measured: the shapes the hypothesis predicts, printed so that your three points can be laid over them. If your threshold line runs flat, the solvent effect on this film at these levels is below what a step reading can see, and that is the result. The curve is drawn to show the shape, not measured from a real material. Your own materials will differ, and measuring them is what the sensitometry part of the course is for.

Reading the three arms against each other

Three routes to one shortage, and the two readings that still tell them apart

1. 1Stock, full agitation — the even, unremarkable corner every published starting point sits in
2. 2The sulfite path — less solvent: coarser grain, more speed — and the sharpness claim is the least sourced of the three
3. 3The dilution path — less of everything: sharper, less even, published by two manufacturers
4. 4The agitation path — slower replacement: sharpest and least even, with the failure modes published alongside

The paths start together and are run on two different developer bases, so this is a map of directions and not a two-factor grid. Anyone who reports it as one has confounded the solvent with the agent set.

What a photographer does with this

Four working rules come out of these strips, and they are yours rather than the course’s because they rest on your own readings.

• Sulfite is the grain control and speed is its price. ILFORD say the same thing in a product description rather than a caveat: PERCEPTOL is for use when very fine grain is wanted and a decrease in film speed is not important, and their own chart offers a 400-speed film at EI 250 in it. If you want finer grain from a developer you already have, more solvent is the route, and you will pay at the toe.
• Dilution is the sharpness control and evenness is its price. ILFORD’s own table names ID-11 at 1+3 for maximum sharpness and PERCEPTOL at stock for finest grain — one manufacturer, one film, two recommendations pointing in opposite directions, which is the trade written down.
• Agitation is the same control with a steeper slope and a worse failure mode. It buys the most edge effect per unit of nothing, and it is the one that produces drag and mottle if you get it wrong.
• Choose two of the three and let the third follow. These levers do not add up independently: a dilute bath given little agitation is not “dilute plus quiet”, because the shortage each creates is the same shortage. The photographer’s version of that sentence is that a compensating scheme is a package, and changing one part of it changes what the others were doing.

Troubleshooting

What you see	Likely cause	What to do
The three arm-A pH readings differ by more than 0.2 after trimming	The trim was not stirred in, or the electrode is drifting between readings	Re-read all three in one sitting, in reverse order, and take the pair of readings for each cell. If they still differ, record the spread as a variable you did not control and say so in the report
The 10 g/L cell is visibly yellow before you use it	Aerial oxidation, which is what 10 g/L of preservative buys	Expected, and the reason the three cells are mixed together and used together. Record the colour with the time, and read the arm knowing the low cell had less protection
All three arm-A strips look alike	Either the solvent effect is below your reading resolution at these levels, or the metol did not dissolve in one of them	Check the mixing notes first, then report the null result against the resolution limit. The wider ladder is in Further experiments
The stock-at-16 strip is black from step 1 to step 10	Predicted: twice the published time	Not a fault. Read the steps that are separable, note where the strip runs together, and lean on the compensated cell for the dilution comparison
The semi-stand strip has streaks running down from the dense steps	Bromide drag, the published failure mode of reduced agitation	A result, not a fault. Photograph it, score the evenness, and note that it is the thing the manufacturers warn about
The continuous strip is no denser than the intermittent one	The continuous agitation was not actually continuous, or the effect is below the resolution limit	Fifteen per cent of development time is roughly one wedge step. If your limit is one step, this comparison was always marginal and the report should say so
No Mackie line anywhere, including on the semi-stand edge strip	Insufficient magnification, wrong lighting, or the effect is genuinely small on this film in this developer	Try transmitted light with a loupe first, then raking reflected light. If nothing shows, record the negative result: it is evidence about this film and this bath
Two vessels of the 1+3 batch developed differently	They were not from the same jug, or one was not deep enough	Check the volumes. This is the failure the one-jug rule exists to prevent, and if it happened, arm C is confounded and must be re-run
Drying marks read as density	Squeegeed, or the wetting agent was wrong	Re-wash and re-dry. Never squeegee a strip that Part XXVII will measure

Clean-up

Pour each vessel into its labelled jar for the colour reading, then into the alkaline developer container; rinse each vessel twice into the same container and only then into the sink. Fixer and its first rinse go to the silver container. Wash the developer utensils and the fixer utensils separately and keep them separate — Kodak’s troubleshooting publication names mixing equipment that has not been thoroughly cleaned as a leading cause of solution contamination, and a developer contaminated with fixer is a session lost. Wipe the balance and the tray. Throw the gloves away. Close the laboratory to the SOP.

Storage

Do not keep the fourteen working solutions. The 1+3 and 1+1 cells are one-shot by the maker’s own instruction: Kodak’s sheet says to dilute just before use and discard after one batch, and ILFORD’s says diluted developers are not reused and are not kept beyond 24 hours. The arm-A cells are experiments in what a sulfite level does, which includes what it does to keeping, and the keeping jars are where that question is asked properly.

Keep the three keeping jars for a week, and then discard them into the developer waste.

Keep the D-76 stock, capped as full as you can make it, dated, with its version number legible. The agent comparison and the break/fix both draw on it. Note the headspace when you put it away: a half-filled bottle has a two-month life on Kodak’s own table against six months for a full one.

Archive every strip. This is the deliverable and it matters more than any number you wrote down today.

📓The archive, and the extra field this session adds

Each strip is fixed for twice its clearing time, washed to the published standard, dried untouched, and filed in a sleeve with the card slip whose eight fields the test-negative lab sets out — with this session’s specifics filled in: arm and cell, sulfite level or dilution, the agitation script by name and in full, the measured pH with its temperature, the version code of the developer, the volume in the vessel and the stock-equivalent it contained, the time and the temperature range.

The extra field is the batch. Ten of these strips came from the wedge exposure batch and four did not. An edge target filed as though it were a wedge strip is worse than a lost strip, because Part XXVII will read it and get an answer. Write the batch name on every slip.

Two honest gaps carried forward from the activity series and not closed here. The course cannot yet cite a residual-thiosulfate limit for archival permanence, because Part XII owns washing and has not been written; and it has not verified that silver density on a properly fixed and washed strip is stable over months to better than the uncertainty budget Part XXVII will work to. The mitigation is structural: the shared reference strip in every session, so that drift can be measured later rather than argued about.

Disposal considerations

Two containers, labelled with contents and date, never combined.

The alkaline developer waste, about 1.8 L, carries all the metol and hydroquinone that went into it, because fourteen small strips reduce very little silver. Both agents are notified as very toxic to aquatic life with long-lasting effects. It also carries a great deal of sulfite — the arm-A cells alone contribute about 10 g — and borate from every cell.

It also carries dissolved silver, and this session more than most. That is the point of arm A: a solvent developer takes silver off the crystal and holds it in solution, so some of the silver that would normally leave in the fixer leaves in the developer instead. The course has no figure for how much, and does not offer one. What follows practically is that stream 1 is not a silver-free stream on this page, and it should be labelled accordingly rather than treated as ordinary spent developer.

The fixer and its first rinse are silver-bearing and go to the silver stream, where the silver can be recovered.

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. That is one country’s answer. The disposal page sets out why the question is jurisdictional and why this course gives no universal instruction. Check your local regulations; they govern, and they differ between authorities within one country.

Questions

1. Your three arm-A cells measure 8.85, 8.91 and 8.94 before trimming. The arithmetic predicted 8.90, 8.96 and 9.00. Is the trim worth doing at all? Answer with reference to your electrode’s stated accuracy, and say what you would write in the report either way.
2. A reader proposes running arm C at 1+1 instead of 1+3, “because 1+1 is the dilution people actually use”. What would that change about the result, and what would it change about the chance of getting a readable result at all?
3. The compensated pair — stock at 8 minutes against 1+3 at 16 — comes back with the same scale length. Write the two sentences you would put in the report: one saying what the pair has now held constant, and one saying what it still has not.
4. Your semi-stand strip is the sharpest at the edge and the worst for evenness, and you want that character for a landscape negative. Name the one change you would make first to keep most of the sharpness and recover some of the evenness, and say what published evidence you are leaning on.
5. Eighty millilitres of D-76 at 1+3 contains 20 ml of stock. Kodak’s published minimum works out at about 21.7 ml of stock for a strip this size. If you had used 80 ml anyway, in which direction would the error have pushed the 1+3 strips, and why would it have been almost impossible to detect from the strips alone?
6. The 100 g/L strip shows a faint green cast in the shadow end by reflected light. What is it, why is it in the shadows rather than the highlights, and what does it tell you about how much silver went into the developer waste?

Further experiments

The wider sulfite ladder. If the three cells came back inside your resolution limit, the levels were too close together for the reading method rather than wrong. Run 5, 25 and 125 g/L instead, with the same borate buffer and the same trim, and expect the low cell to oxidise visibly during the session.

Stand development, properly. One strip, D-76 at 1+3, agitated for the first 30 seconds and then left entirely alone for an hour. It changes two variables against this session’s semi-stand cell — time and agitation — so it is a demonstration rather than a comparison, and it is the version photographers actually mean. Wall’s warning applies: a large surface of dilute developer standing for an hour is a large surface oxidising for an hour.

The compensated grid. The compensated pair on this page is two cells. The full version is three: stock at 8, 1+1 at 11 and 1+3 at 16, all at their published times, so that contrast is held across the whole dilution range and grain, sharpness and fog are read against dilution alone. It costs one extra strip and it is the cleanest single experiment in this part.

The sulfite-and-sharpness question Part VIII would not assert. That a low-sulfite developer gives stronger edge effects is a mechanism the course has not found stated in any source it holds. Arm A’s cells are metol-only and were not run with edge targets. Repeat arm A with an edge strip in every cell, and you have made a direct test of a claim the literature repeats and this course declined to.

The film that changes the answer. Every number here is for one emulsion. A modern tabular-grain film has a different surface area per unit of silver, and a solvent acts on surface. Run the three arm-A cells on a second film from the same session and you have a two-factor result that is worth more than either alone.

Check your understanding

Question 1. Why does arm A add 20 g/L of borax to every cell, when the sulfite series would have been simpler without it?

• Because borax is needed to dissolve the metol
• Because an unbuffered metol-sulfite series spans about 1.3 pH units from 10 to 100 g/L, so it would be a pH series with a sulfite series hidden inside it
• Because borax increases the solvent action of sulfite
• Because Kodak’s D-76 contains borax and the cells must match it

Show the answer and why

Answer: Because an unbuffered metol-sulfite series spans about 1.3 pH units from 10 to 100 g/L, so it would be a pH series with a sulfite series hidden inside it

The bisulfite that sets an unbuffered bath’s pH comes from metol’s sulfuric acid and stays at about 0.044 mol/L whatever the sulfite is; what changes is how much sulfite is left beside it. The Henderson-Hasselbalch ratio therefore swings from roughly 0.8 to 17 across the ladder, which is pH 7.10 to 8.43. Since the previous experiment measured what a pH ladder does on its own, running this one unbuffered would have produced a result nobody could attribute. Borate at 0.105 mol/L overpowers a bisulfite pool that does not change, and pins the three cells within about a tenth of a unit.

Question 2. A student mixes the three 1+3 agitation cells separately, one jug each, to avoid measuring out a large volume. What has that cost?

• Nothing, provided each is mixed to the same ratio
• The three cells can now differ in mixing as well as in agitation, so any difference between them is attributable to either — and mixing variation is invisible in the strip
• The cells will be at different temperatures
• The developer will oxidise faster in three vessels than in one

Show the answer and why

Answer: The three cells can now differ in mixing as well as in agitation, so any difference between them is attributable to either — and mixing variation is invisible in the strip

Arm C exists to attribute a difference to the agitation script and nothing else. Three separate mixings introduce three separate measuring errors in the stock-to-water ratio, and a two or three per cent difference in developer strength is far below what a step reading can see — which is exactly why it would never announce itself and exactly why it has to be removed rather than tolerated. One jug split six ways costs one extra vessel and makes the comparison unambiguous.

Question 3. Grain is to be compared between the stock strip and the 1+3 strip. Why is it wrong to look at step 12 on both?

• Because the wedge steps are not exactly 0.15 apart
• Because the two strips reach different densities at the same step, and Part IV establishes that mottle is strongest at middle densities and weakest at both extremes, so a step-for-step comparison compares grain at two different densities
• Because step 12 is too dense to examine
• Because the scanner cannot read step 12 accurately

Show the answer and why

Answer: Because the two strips reach different densities at the same step, and Part IV establishes that mottle is strongest at middle densities and weakest at both extremes, so a step-for-step comparison compares grain at two different densities

Granularity is a property of a density, not of an exposure. Kodak read their own figures at a net diffuse density of 1.00 through a 48 micrometre aperture for precisely this reason. Two strips developed differently place that density at different steps, so the honest procedure is to find the matching step on each strip first — by sliding one over the other on a lightbox until the two patches disappear into each other — and then examine the steps you matched, recording which step number each turned out to be.

Question 4. The equal time for arms B and C is set at 16 minutes, which is twice the published time for the stock cell. What is the argument for that choice, and what does it cost?

• It is a compromise between the three published times and costs nothing
• The fragile readings — Mackie lines, unevenness, grain at matched density — all live in the dilute cells, so those are developed properly and the stock cell pays by being over-developed and short in scale
• It matches the time used in the activity series
• Longer development always gives more reliable readings

Show the answer and why

Answer: The fragile readings — Mackie lines, unevenness, grain at matched density — all live in the dilute cells, so those are developed properly and the stock cell pays by being over-developed and short in scale

An equal time cannot suit three dilutions whose published times are 8, 11 and 16 minutes, so the question is which cell should absorb the mismatch. Everything arm C is looking for needs a properly developed dilute strip; an under-developed one shows no edge effect and no mottle worth scoring. The stock cell therefore takes the hit, its over-development is predicted in advance rather than discovered afterwards, and the compensated cell at the published 8 minutes is added so the dilution comparison still has an uncompromised member.

Question 5. What does the shared reference strip do here that the 1+1 cell at 16 minutes cannot?

• It develops for a shorter time
• It ties the session to the control set and to every other session in the part, and — because it is the same condition as the compensated 1+1 cell — it also gives the session its one within-session estimate of repeatability
• It is the control for arm B
• It is the only strip that is archived

Show the answer and why

Answer: It ties the session to the control set and to every other session in the part, and — because it is the same condition as the compensated 1+1 cell — it also gives the session its one within-session estimate of repeatability

An internal control answers "what did the dilution do", because it differs from its cells in one thing. It cannot answer "is this session comparable with the last one", because everything in it moved together with everything else in the session. The reference is held at one fixed condition across the whole part so that it can. Its second job here is quieter and just as useful: it duplicates a cell, and two strips developed identically in one session are the only honest measure of how well the session repeats itself.

Question 6. Arm A is a metol-only bath and arms B and C use D-76. What may not be concluded from the session as a result?

• Nothing may be concluded about sulfite at all
• No cell in arm A may be read against a cell in arm B as though the two differed only in solvent or dilution, because they also differ in the agent set — so the three arms give directions, not a two-factor grid
• The arms cannot share an exposure batch
• The arms cannot share a reference strip

Show the answer and why

Answer: No cell in arm A may be read against a cell in arm B as though the two differed only in solvent or dilution, because they also differ in the agent set — so the three arms give directions, not a two-factor grid

Sharing a batch and a reference is exactly what makes the three arms comparable in the weak sense: same film, same exposure, same session, same reader, same day. What it does not buy is the strong sense. A metol-only bath at 100 g/L of sulfite and a metol-hydroquinone bath at 1+3 differ in the solvent, in the agent set, in the pH and in the buffer, so any difference between them has four candidate causes. The map at the end of the analysis plots directions for that reason, and labels itself as not a grid.

Check my answersClear