ILFORD PQ UNIVERSAL developer

This is a product page, not a formula page. Every other developer in this library arrives as a column of weights with a source beside it and an account of what each weight is doing. Nobody outside Harman knows the weights in this bottle. What follows is what its maker publishes, which for a product asked to do two different jobs runs to two pages of dilutions, times, exposure indices, average gradients, capacities and a working pH; what its maker’s own safety data sheet discloses, including two substances it discloses in a section most readers never reach; what the two documents together still leave unknown; and the open formula that does the same two jobs with its quantities on the page.

HARMAN technology Limited (ILFORD Photo) — sold as liquid concentrate

Components the maker discloses — from the safety data sheet, which classifies hazards and does not state a formula

Component	Concentration as the sheet gives it	Hazard codes
Sodium sulfite (anhydrous)named on the sheet as Sodium sulphiteCAS 7757-83-7	10-30%
Potassium carbonate (anhydrous)named on the sheet as Potassium carbonateCAS 584-08-7	5-10%	H315, H319, H335
pentasodium (carboxylatomethyl)iminobis(ethylenenitrilo)tetraacetateCAS 140-01-2	<3%	H290, H319, H332, H361
Hydroquinonenamed on the sheet as 1,4-dihydroxybenzenehydroquinonequinolCAS 123-31-9One of the two developing agents ILFORD names in the product description	1-5%	H302, H317, H318, H341, H351, H400, H410
Sodium hydroxidenamed on the sheet as sodium hydroxidecaustic sodaCAS 1310-73-2	<1%	H314
Dimezone Snamed on the sheet as 4-(hydroxymethyl)-4-methyl-1-phenylpyrazolidin-3-oneCAS 13047-13-7The other developing agent ILFORD names; the product description calls this a dimezone-s/hydroquinone developer	<1%	H302
BenzotriazoleCAS 95-14-7Named as present in three places outside the composition table, with no concentration given	—
Potassium bromideCAS 7758-02-3Named in the regulatory section and not in the composition table, with no concentration given	—

Not disclosed. HARMAN publishes no composition for PQ UNIVERSAL. The safety data sheet names six components in its composition table and gives each a concentration band for the purpose of classifying a hazard, which is not an assay: section 11 records that every classification on the sheet was calculated from those bands, so they are chosen to make a conservative classification and not to describe a bottle. Even at their upper limits they account for about half of it and the sheet names nothing else, not even water; two further substances appear in the regulatory section with no figure at all. No quantity, no ratio between the two developing agents, no split between the two alkalis, no restrainer or sequestrant loading, no pH or density for the concentrate itself and no formulation date is published anywhere in ILFORD's literature. A reader who needs to change one term at a time, and see what it does, has to mix an open formula instead of buying this one.

Nearest open formula. Kodak D-163 — Both are single baths sold on doing two jobs. Kodak Limited's own product list calls D-163 a universal developer for papers at normal or high contrast that also serves as a dish developer for negative materials; ILFORD calls this one UNIVERSAL and gives it a page of paper times and a page of sheet-film times. D-163 is published in full and mixed from five weighed chemicals whose quantities can each be read and changed — metol against seven times its mass of hydroquinone, the largest sulfite reserve in the paper library, sodium carbonate and a bromide. PQ UNIVERSAL is a concentrate whose maker names a pyrazolidone and a hydroquinone, two alkalis, a sequestrant, a bromide and an organic antifoggant, and quantifies none of them. Where D-163 changes dilution for working life and publishes no gradient for film, PQ UNIVERSAL changes dilution for contrast and publishes an average gradient and an exposure index for four films at each of its two film dilutions, along with a working pH, a specific gravity and a keeping life of two years unopened that a hand-mixed stock cannot approach. The exchange is a better-documented performance from a bottle you cannot alter against five quantities you can.

Purpose

One bottle, two jobs. ILFORD describes PQ UNIVERSAL as “a liquid concentrate dimezone-s/hydroquinone developer suitable for the dish/tray developing of all RC and FB black and white photographic papers”, used at 1+9, “clean working” with “excellent keeping properties” and giving “a slightly warm of neutral image tone with most papers”. Then it adds the sentence the other two developers on that sheet do not get: “In addition PQ UNIVERSAL can be used to dish/tray process ILFORD and some other technical films. It is also suitable for dish/tray developing of general purpose sheet films when a fast working, high contrast developer is needed and a high degree of enlargement is not required.”

That second paragraph is the product. A darkroom that prints and also shoots sheet film can keep one bottle instead of two, mix one working solution at one dilution for both, and use the same tray, the same thermometer and the same twenty degrees. ILFORD is careful about the boundary of the offer: not general purpose 35 mm and roll film, not high temperature, not machine processing, and not where the negative will be enlarged a great deal. Inside those limits it is the only bath in the ILFORD catalogue that develops a print and a negative from the same measured jug.

The name deserves a sentence of its own before anything else. PQ is the old shorthand for phenidone and quinol — a pyrazolidone paired with hydroquinone — and the maker’s own product description names not Phenidone but Dimezone S, and its safety data sheet gives CAS 13047-13-7 rather than the 92-43-3 that Phenidone carries. The trade name records a class of chemistry rather than the substance now in the bottle. That reading is the course’s; HARMAN prints the name and the description side by side and offers no comment on the difference between them. Its stablemate BROMOPHEN is the one that still says phenidone, and it is a powder.

Recommended uses

Dish or tray printing at 1+9, at 20 °C, mixed for the session and thrown away at the end of it. Two minutes for a resin-coated print, and two minutes recommended on fibre within a range of one and a half to three. That is the use every published paper figure on this page belongs to. ILFORD asks for the working solution to be prepared directly before it is needed, for enough of it to fill the dish about half full, and for every solution in the sequence to be within one degree of the working temperature.

Dish development of sheet and technical film, at 1+9 when contrast is wanted and 1+19 when it is not. ILFORD publishes a time, an exposure index and an average gradient for FP4 Plus, HP5 Plus, DELTA 100 Professional and ORTHO Copy Plus at both dilutions, and states that the developer will also handle the technical and sheet films of other manufacturers. The technique is the one described for paper, with one flat exception: do not interleave film. ILFORD says so directly, and adds that even with great care it may damage the emulsion.

On ILFOBROM GALERIE FB, where this is the developer the maker measured the paper in. GALERIE’s own sheet says its glossy grades 1 to 4 and matt grades 1 to 3 are developed in PQ UNIVERSAL or MULTIGRADE at 1+9 for two minutes, and prints its characteristic curves with that same caption beneath them. A paper’s published curve is always the curve of a paper-and-developer pair, and this is the one pairing in the ILFORD corpus where the curve on the sheet and the developer on the shelf are the same choice. If you are working from those curves, use this developer.

On HARMAN Direct Positive Paper, at 1+9 for one and a half to three minutes, which is the sheet’s own second option beside MULTIGRADE WARMTONE.

Where one bottle has to cover everything. This is the honest case for buying it. A litre of concentrate makes ten litres of working solution and will take seven hundred resin-coated prints, or four hundred and fifty fibre prints, or a hundred sheets of 8 × 10 film — and it keeps two years unopened and six months once it is opened. Nothing you mix by hand keeps like that.

Not for general purpose 35 mm and roll film. ILFORD states it twice on one sheet, once on page 1 and once on page 4, which is as close to underlining as a technical sheet gets. The reason is in the offer itself: a fast working, high contrast developer used where a high degree of enlargement is not required. For a 35 mm negative that has to stand enlargement, this is the wrong bath and D-76 is the shape of the right one.

When another formula is preferable

• When you want to understand a universal developer rather than use one, mix D-163. Kodak Limited built the same offer out of five weighed chemicals and printed all five, and it is the comparison this page is built around.
• When the print is the only job and the shortest time is the object, MULTIGRADE developer does a resin-coated sheet in one minute against this bottle’s two, from the same maker at nearly the same published pH.
• When the warmest image tone is the object, ILFORD’s own answer is BROMOPHEN or the HARMAN warm-tone developer, both of which it names on the MULTIGRADE FB WARMTONE sheet where this developer is merely listed.
• For a warm tone from a formula you control, D-156 cuts the alkali and raises the bromide, and D-166 goes further with twelve and a half grams of bromide to the litre.
• For the coldest blue-blacks, D-158 is the chloride-paper developer with the most alkali and the least bromide in the paper library.
• For high contrast on film from a published formula, D-19 is Kodak’s own answer and every quantity in it is on the page, including the four times D-76’s hydroquinone that makes the contrast.
• For a 35 mm negative that will be enlarged, this developer is excluded by its own maker; the fine-grain end of the library begins at D-76.
• When the darkroom cannot be held at 20 °C. ILFORD is explicit that these developers are for ambient room temperature, that high temperatures reduce the solution life considerably, and that they can shorten development to the point where uneven processing appears.
• When you want to change one thing and see what happens. Every open formula in this library scales to any volume and opens to any single change. This bottle offers three variables and no fourth.

What the maker publishes

For an undisclosed product this is a great deal, and it is worth setting out at length, because the quantity of it is exactly what makes a page about a secret formula useful rather than merely careful.

The mixing method, in the order it is done. Work out how much working solution the session needs, making sure it is at least enough to fill the dish half full. Measure the concentrate with the smallest cylinder that will hold it — ILFORD’s own reasoning is that 100 mL is more accurately measured in a 100 mL cylinder than in a 1000 mL one. Put the concentrate in the mixing vessel, and ILFORD suggests a large measuring jug so the total is checked as you go. Measure the dilution water, using hot and cold to arrive at 20 °C. Rinse the concentrate cylinder out into the mixing vessel with some of the dilution water, then add the rest and stir. That rinse is not housekeeping: a film of viscous concentrate left in a cylinder is a measurable fraction of a 100 mL dose.

The water advice, which also reads as housekeeping and is chemistry. Water from a pressure main comes out full of dissolved air, so ILFORD asks the printer to draw off what is needed and leave it standing for a few minutes before making a developer up with it.

The pH and the specific gravity, for the working solution. ILFORD prints a table for fresh solutions and this developer’s row reads 10.48 to 10.58 at 1+9 with a specific gravity of 1.022 at 20 °C; at 1+19 it gives a specific gravity of 1.011 and leaves the pH column empty. It adds that the figures came from controlled laboratory conditions, that a user’s own measurements may differ slightly, and that the right use of the table is to make your own control measurement on your own fresh solution and compare later ones against it. A pH meter is preferred and sticks covering pH 7 to 10 are accepted; a hydrometer covering 1.000 to 1.200 is suggested for the specific gravity.

The paper times, two minutes for resin-coated at 1+9 and two minutes recommended on fibre within a range of one and a half to three, all at 20 °C ± 1. Five ILFORD and HARMAN paper sheets repeat those figures for their own papers and none of them disagrees.

The emergence time and the plateau. On correctly exposed fibre prints ILFORD says the image will begin to appear after 35 seconds with these developers, and that development “may be extended to 6 minutes without any noticeable change in contrast or fog”. The second sentence is worth more than the recommended time, because it says the recommended time sits inside a wide flat region rather than on a slope — Part XVIII draws the two curves that make it true.

The batch-printing advice: to hold print-to-print consistency through a long run on either paper base, reduce exposure slightly and extend development, which moves the working point further into that flat region.

The film times, and with them the numbers a formula page would call sensitometry. This is the part of the sheet no other ILFORD paper developer gets. At 1+9 and 20 °C: FP4 Plus at EI 125–200 for 4 to 8 minutes, average gradient 0.85 to 1.00; HP5 Plus at EI 400–800 for 4 to 8 minutes, 0.90 to 1.00; DELTA 100 at EI 125–200 for 4 to 8 minutes, 0.80 to 1.00; ORTHO Copy Plus at EI 50–80 by daylight or 25–40 by tungsten, 4 to 12 minutes, 0.80 to 1.00. At 1+19 and 20 °C the four films get a single time each and a single gradient: FP4 Plus at EI 64 in 4 minutes, HP5 Plus at EI 320 in 4½, DELTA 100 at EI 80 in 4, ORTHO Copy Plus at EI 25 by daylight or 12.5 by tungsten in 4, all at Gbar 0.62. ILFORD calls the times a guide that may be adjusted for individual preference, which is the standard hedge and is still more than most makers give.

The capacities, per litre of working solution: 70 resin-coated or 45 fibre 8 × 10 prints, and 10 8 × 10 sheet films at 1+9 or 5 at 1+19. Those are the figures you can check in your own tray by counting.

The keeping, in four figures. A full unopened bottle keeps two years at 5–20 °C. Once opened, use the concentrate completely within six months and keep the bottle tightly sealed. Working solution lasts one working day in an open dish and 24 hours in a capped bottle.

The sequence around it, which is easy to skip and is part of the product’s documentation: ILFOSTOP or ILFOSTOP PRO at 1+19 for ten seconds; ILFORD RAPID FIXER or HYPAM at 1+4 for half a minute on resin-coated paper and a minute on fibre; two minutes’ wash for resin-coated paper in running water above 5 °C, and a warning that wet times beyond fifteen minutes cause edge penetration and curl. For film, an acid stop, a non-hardening fixer, a five to ten minute wash, and ILFOTOL at about 1+200 as a final rinse.

🧮The one row on this sheet where the arithmetic closes exactly

ILFORD’s availability section says a 1 litre bottle of PQ UNIVERSAL “makes enough working strength solution at 1+9 to process 700 20.3 × 25.4 cm (8 × 10 in) sheets of RC paper or 450 of FB paper or 100 8 × 10 in sheet films”.

Follow it through on the sheet’s own numbers. A litre of concentrate at 1+9 is ten litres of working solution. At the published capacity of 70 resin-coated prints per litre that is 700. At 45 fibre prints per litre it is 450. At 10 sheet films per litre it is 100. Three figures, three exact agreements, no rounding.

That matters beyond this page, because the same section of the same sheet gives BROMOPHEN — a 1+3 product with an identical per-litre capacity of 70 and 45 — the identical totals of 700 and 450, where the arithmetic gives 280 and 180 instead. These totals and that comparison are the course’s arithmetic on ILFORD’s printed figures, and the conclusion the course draws is narrow and useful: this is the row that is right, and it is very probably the row the other one was copied from. Use the per-litre figures for both products and count sheets rather than trusting a total.

What is not disclosed

The formula. Not the quantity of anything. Not the ratio between the two developing agents. Not how the alkalinity is divided between the carbonate and the hydroxide, both of which are named. Not the bromide loading, not the antifoggant loading, not the sequestrant loading, and not the date the current formulation was fixed. ILFORD names two developing agents in a product description; the safety data sheet names four more substances and two others in a regulatory list; and that is the whole of it.

What the rest of the bottle is. The composition table names six substances and stops. Unlike its MULTIGRADE stablemate’s sheet, this one gives no line for water — so the largest part of the bottle is named nowhere on either document. The obvious guess is not a disclosure, and the callout below is about why the guess cannot be tightened into one.

The concentrate’s own pH and density. Section 9 of the safety data sheet is a column of the words Not known: appearance “Liquid”, colour not known, odour not known, pH not known, density not known, relative density not known, solubility not known, viscosity not known. The technical sheet’s pH and specific gravity are for the diluted working solutions, which are different solutions. So the number you would measure if you put a meter in the bottle is published by nobody, and neither is what the bottle weighs.

Two substances that are disclosed without a figure. Benzotriazole and potassium bromide are named in the regulatory and other-hazards sections and are absent from the composition table. That they are present is HARMAN’s statement. How much of either is present is not published in any form.

Why it is twice MULTIGRADE’s time. The two products come from the same company on the same sheet at almost the same published pH, and one develops a resin-coated print in a minute and the other in two. Nothing in ILFORD’s literature says what accounts for that, and the components disclosed for the two are, name for name, the same six.

!Why the bands cannot be totalled, and why they cannot be topped up either

The temptation with two products is different from the temptation with one. Here the composition table’s bands do not overflow the bottle — they fall a long way short of filling it — and the urge is not to solve for the excess but to fill the gap.

Add the upper limits: 30, 10, 3, 5, 1 and 1 come to about 50 per cent. Add the lower limits and you get about 16 per cent. Both totals are the course’s arithmetic on HARMAN’s printed figures, and neither is a composition. Somewhere between half and five-sixths of the bottle is named by no substance on the sheet, and the sheet does not say what it is.

The reason the gap cannot be closed with a guess is written into the document itself. Section 11 records that every toxicological classification on this sheet was reached by “calculation method”, with a calculated acute toxicity estimate of 18347.95 for ingestion and 383.57 for inhalation. The bands exist to feed that calculation. A band is chosen so that the worst case it permits still classifies the mixture correctly and conservatively, which makes it wide by design — hydroquinone’s 1 to 5 per cent is a fivefold range — and a band selected to be safely wide is useless for mixing. A safety data sheet read as a hazard document is evidence. Reassembled into a recipe it is a fabrication with citations attached, and calling the missing half “water” would be the first line of one.

Nothing about why. No source in the corpus says why HARMAN uses potassium carbonate here rather than the sodium carbonate of the powder, why it keeps Phenidone in BROMOPHEN and Dimezone S in this bottle, why the working pH sits at 10.5 rather than 10.2 or 10.9, or what makes a bath that is “slightly warm of neutral” on paper into a “fast working, high contrast” developer on film. Those are the interesting questions and the literature does not touch them.

Disclosed components

Every component in the table above, the six from the composition table in the order the sheet prints them and then the two it discloses elsewhere. The concentration against each is the band that sheet states and not a quantity, and a function line appears only where the maker gives one.

Sodium sulphite, CAS 7757-83-7, 10–30 %. Sodium sulfite heads the composition table and carries the widest band on it, a factor of three from end to end. It is also the only component the sheet records as not classified — no hazard statement, no pictogram, nothing in section 15. In a developer its established work is preservation: it takes up dissolved oxygen and intercepts the quinone that hydroquinone becomes, which is what Part VIII’s lesson on sulfite and preservation sets out. A concentrate that must survive two years sealed and six months with a growing air space above it is asking rather more of a preservative than a tray mixed for one evening, and asking it of a developer that also has to hold still in a film tray for eight minutes. That reading is the course’s; HARMAN gives the substance no function at all.

Potassium carbonate, CAS 584-08-7, 5–10 %. Potassium carbonate is the alkali, classified H315, H319 and H335 — the only respiratory-irritant classification on the sheet. Carbonate against bicarbonate is a real buffer pair, and buffering is what a developer in an open tray needs, because every print and every sheet of film that goes through it returns acid to the bath. Two further points are worth marking as inferences rather than statements. The choice of the potassium salt over the sodium salt is the ordinary one where a concentrate has to stay in solution in a cold store — potassium carbonate is markedly the more soluble — and ILFORD does not say so. And that it is here as the buffering alkali at all is the course’s reading of a component list, not an ILFORD statement.

pentasodium (carboxylatomethyl)iminobis(ethylenenitrilo)tetraacetate, CAS 140-01-2, less than 3 %. Behind the mouthful is the pentasodium salt of diethylenetriaminepentaacetic acid, DTPA, a chelating agent from the same family as the EDTA salts the course meets elsewhere and whose behaviour is Part III’s subject. It has no plausible photographic role except sequestration: locking up calcium, magnesium and above all iron so that hard tap water does not throw a precipitate in the tray or supply the trace metal that catalyses aerial oxidation of a developing agent. It is the component with the most crowded classification on the sheet — H290, H319, H332 and H361 — and the mixture as a whole is not classified for reproductive toxicity, which is what a band below 3 per cent buys and is a small lesson in how the two halves of a safety data sheet relate to each other. The substance’s class is not in doubt; its reason for being in this particular bottle is an inference, and HARMAN states no function for it.

1,4-dihydroxybenzenehydroquinonequinol, CAS 123-31-9, 1–5 %. This is hydroquinone, and the mangled name is the sheet’s own — three synonyms run together with no separator, and printed again on the label element in section 2.2, so it is what a reader holding the bottle actually sees. It is one of the two developing agents ILFORD names, and it is where almost the whole hazard classification of the product comes from: H302, H317, H318, H341, H351, H400 and H410, and with them the suspected-mutagen and suspected-carcinogen labels the mixture carries. Note the shape of the band. It is the only closed range on the sheet below 10 per cent — a figure with a floor as well as a ceiling — and the floor is what tells you the substance is present in quantity rather than as a trace. What it does not tell you is how much, and a fivefold range is not a quantity.

sodium hydroxidecaustic soda, CAS 1310-73-2, less than 1 %. Sodium hydroxide, with two synonyms again run together, is the only component classified corrosive — Skin Corr. 1A, H314 — and the only one carrying an occupational exposure limit besides the hydroquinone. Below one per cent of a concentrate that is then diluted tenfold it is not what makes the working solution hazardous. What it is doing is setting a pH that carbonate alone will not reach, which is the standard reason a small hydroxide dose appears beside a carbonate in a developer. That is an inference from where hydroxide sits in developer formulation generally, and ILFORD does not say it.

4-(hydroxymethyl)-4-methyl-1-phenylpyrazolidin-3-one, CAS 13047-13-7, less than 1 %. This is Dimezone S, and here the maker does say what it is for: the product description calls PQ UNIVERSAL a dimezone-s/hydroquinone developer. It sits in the sheet’s narrowest band, sharing it with the sodium hydroxide, and it is the substance that makes the developer work — which is the signature of a superadditive pair and not a sign that it hardly matters. The chemical page carries the full account of the molecule and of the substitution for Phenidone, including what ILFORD does and does not say about it.

Benzotriazole, CAS 95-14-7, no concentration given. Benzotriazole is named three times on this sheet and never in the composition table. Section 2.3, other hazards, states that “This product contains: 95-14-7 (Endocrine disrupting properties)”. Section 12.6 records it as listed for evaluation for endocrine disruption under EU legislation. Section 15.1 names it in the UK REACH Annex XVII line and again on the European CoRAP line, where it stands beside hydroquinone as one of the two substances in this product under a Community rolling action plan. It is the organic antifoggant that Part VIII’s lesson on restrainers treats as the one that holds fog down without the shadow-speed cost a bromide exacts. That it is present is HARMAN’s statement, made four times over. How much, and what it is doing here, is not published.

Potassium bromide, CAS 7758-02-3, no concentration given. Potassium bromide appears in exactly one place: the Annex XVII line in section 15.1, where the sheet lists the substances in this product that appear on a UK REACH restrictions list. Every other name on that line is a component from the composition table, so the course reads its presence there as HARMAN naming a constituent. That is a reading of the document’s structure rather than a statement in the composition table, and it is marked as such here and in the table above. A developer containing bromide is entirely ordinary — the classical inorganic restrainer, doing the work Part VIII describes.

⚗What section 15 discloses that section 3 does not

The composition table names six substances. The Annex XVII line in section 15.1 names seven — 140-01-2, potassium carbonate, hydroquinone, potassium bromide, Dimezone S, benzotriazole and sodium hydroxide — of which five are in the table and two are not. Sodium sulphite, meanwhile, is in the table and on neither regulatory line, because it is not classified at all.

The two sections are answering different questions. Section 3.2 lists the hazardous ingredients that have to be declared at the concentrations present; a substance below its declaration threshold does not appear there at all. Section 15 lists what the mixture contains that a named piece of legislation cares about, and legislation about restricted substances and endocrine disruptors has thresholds of its own. So a composition table is a floor on what a product contains, not a list of it — and this sheet proves it out of its own mouth, by naming two substances in one section that its composition section leaves out.

That reading of how the two sections relate is the course’s, and the practical lesson is a reading habit rather than a chemical one: when you file a safety data sheet, read sections 2.3, 12 and 15 as well as section 3, because a maker sometimes discloses in the regulatory sections what it is not obliged to disclose in the composition table. The course’s procedure is recording a safety data sheet.

Behaviour

On paper it is the slow one of the pair. Two minutes for a resin-coated print at 1+9 is double what ILFORD asks of MULTIGRADE at the same dilution, and the same as BROMOPHEN’s at 1+3. On fibre the difference disappears entirely: all three developers get two minutes recommended within a one and a half to three minute range. The doubling shows on the base that soaks up least and gives up its solution fastest, and ILFORD offers no explanation of the difference on either base.

On paper it develops to completion; on film it develops to a gradient. This is the split that the word Universal is hiding, and it is the single most useful thing to understand about the product. In a print tray, two minutes is a point inside a plateau — the six-minute claim says the black has finished rising while the base has not started to lift, so a sheet left an extra minute comes out the same and a sheet snatched at ninety seconds comes out thin and blotchy rather than lighter. In a film tray the time is the contrast: ILFORD publishes 4 minutes and 8 minutes for the same film at the same dilution against average gradients of 0.85 and 1.00, and doubling the time is the whole difference between them. The same jug of liquid, obeying two different rules on two different materials, is Part XIII’s distinction between a paper curve and a film curve made physical.

Dilution is the film contrast control and nothing else’s. ILFORD’s own words: 1+9 “gives higher contrast but also an increase in granularity”, and 1+19 “is recommended for pictorial contrast, Gbar 0.62, and lower grain but there is some loss of film speed”. On paper there is no second dilution at all — 1+9 is the only one published, where MULTIGRADE gets two.

It exhausts by counting, not by looking. Seventy resin-coated 8 × 10 prints to a litre, forty-five on fibre, ten sheets of 8 × 10 film at 1+9 and five at 1+19. The film capacities are the ones worth staring at: a litre of working solution is finished after ten sheets of film, and the same litre would have taken seventy prints. A sheet of film asks perhaps seven times as much of the bath as a sheet of paper of the same size, which is the cost of running development to a chosen gradient rather than to completion.

It has three clocks and they are unusually generous. Two years for a sealed bottle, six months for an open one, one working day for the tray. Compared with a hand-mixed stock — three months full and one month half-full for D-163 — the concentrate’s advantage is not subtle, and it is the strongest practical argument for buying rather than mixing.

It is formulated for one temperature. Twenty degrees, plus or minus one, is the whole tolerance. A cooler tray can be worked with a longer time and a warmer one shortens development until covering the sheet evenly becomes difficult; ILFORD adds that high temperatures reduce the effective solution life considerably.

⚗Two ILFORD developers at one pH, and twice the time

Set the sheet’s own two rows for the 1+9 dilution beside each other.

	MULTIGRADE 1+9	PQ UNIVERSAL 1+9
Published pH at 20 °C	10.45–10.55	10.48–10.58
Specific gravity at 20 °C	1.022	1.022
Resin-coated paper time	1:00	2:00
Fibre paper time	2:00, range 1:30–3:00	2:00, range 1:30–3:00
Capacity per litre, RC / FB	100 / 50	70 / 45
Components disclosed	the same six, plus two named elsewhere	the same six, plus two named elsewhere

The alkalinity is the same to within the width of the bands. The specific gravity is identical to three decimal places. The disclosed component list is the same list. And one bath takes half as long on resin-coated paper and goes half as far again before it dies.

Whatever separates them, therefore, is not the pH, and it is not anything either published document contains. It is in the quantities — the dose of the pyrazolidone, the hydroquinone loading, how much restrainer is in each — and those are precisely what is not published, for either product.

The comparison is the course’s, drawn from ILFORD’s own table; ILFORD makes no statement about the difference between its two developers. It is put here because it is the clearest demonstration on this site of what an undisclosed composition actually costs a reader. Two bottles from one company, at one pH, with one component list between them, behaving measurably differently — and no document anywhere that can tell you why. On D-163 the equivalent question is answered by reading down the column.

Image characteristics

Image tone: slightly warm of neutral, on most papers. ILFORD’s own phrase, and it is a claim about the product rather than a measurement. It is also not a claim to being the warm one: the identical sentence is given to BROMOPHEN on the same sheet, and when ILFORD wants to name a developer for the warmest tone on Warmtone paper it names BROMOPHEN and the HARMAN warm-tone developer, leaving this one in the ordinary list.

Contrast on paper: set by the filter, not by the tray. If six minutes changes neither contrast nor fog, then on a variable-contrast paper the grade is decided by the filtration and the exposure and by nothing that happens in the developer. That is a property worth having rather than a shortcoming — it is what makes split-grade printing repeatable from one sheet to the next.

Contrast on film: published, in two numbers. Average gradient 0.85 to 1.00 at 1+9 and 0.62 at 1+19, and on ORTHO Plus a straight 0.80 at four minutes rising to 1.00 at twelve. This is the only developer in the ILFORD paper-developer sheet that gets an average gradient at all, and it is a real one: Part XIII’s account of gamma, contrast index and average gradient is what those figures mean and how to measure your own.

Speed on film: bought and sold with the dilution. Every exposure index on the sheet is paired with a dilution and a time, and the pattern is consistent: 1+19 costs speed. FP4 Plus drops from 125–200 to 64, DELTA 100 from 125–200 to 80, HP5 Plus from 400–800 to 320. Those are ILFORD’s figures for ILFORD’s development, and Part XIII on film speed and exposure index is where the difference between a box speed and a working index is worked out.

Grain: the maker’s own trade-off, stated in one sentence. Higher contrast and more granularity at 1+9; lower grain at 1+19. And underneath both, the boundary condition: this is a developer for sheet film “when a high degree of enlargement is not required”.

Maximum black on paper: reached at the recommended time, and for one paper the published curve is this developer’s. ILFOBROM GALERIE FB is the exception in the corpus. Its characteristic curves for glossy grades 1 to 4 and matt grades 1 to 3 were made in PQ UNIVERSAL or MULTIGRADE at 1+9 for two minutes, which means that for that paper the maker’s published curve and the maker’s recommended developer are the same choice — the opposite of the situation on MULTIGRADE FB WARMTONE, whose curves were made in a developer other than the one ILFORD recommends for it. Part XIII on paper sensitometry explains why the pairing matters.

Fog: low, on the maker’s word and on the disclosed component list. “Clean working” is ILFORD’s phrase. The disclosed presence of both a bromide and an organic antifoggant is consistent with a bath built to hold its whites through a long session — though how much of either is present is not published, and consistency is not evidence.

The mechanism

Everything in this section that goes past the two agent names is marked as what it is.

What the maker states. PQ UNIVERSAL is a liquid concentrate dimezone-s/hydroquinone developer, diluted 1+9 for all black and white papers and 1+9 or 1+19 for technical and sheet films, working at 20 °C, reaching pH 10.48 to 10.58 at 1+9, developing a resin-coated print in two minutes, showing the image at about 35 seconds on a correctly exposed fibre print, holding contrast and fog steady out to six minutes on paper, and giving average gradients of 0.85 to 1.00 and 0.62 on film at its two dilutions.

What follows without needing anything else: it is a PQ developer in the modern sense. A pyrazolidone with hydroquinone is the classical superadditive pair, and superadditivity is the central mechanism of Part VIII’s lesson. The fast agent — here Dimezone S — reduces silver at the latent-image site and is itself oxidised; the hydroquinone regenerates it from solution, so a very small quantity of one substance transforms the behaviour of a much larger quantity of another. That is consistent with the pyrazolidone sitting in the sheet’s narrowest band and the hydroquinone in a band five times higher. Two hazard bands are not a ratio and this page does not treat them as one.

Why the name and the description disagree. Dimezone S is a 4,4-disubstituted 1-phenyl-3- pyrazolidone — the same ring as Phenidone with two substituents on the four position. The trade name PQ belongs to the phenidone–quinol generation and the bottle now holds a different member of the same family. The course reads the name as a survival rather than a claim; HARMAN neither explains it nor corrects it, and the company’s own powder developer, BROMOPHEN, still uses the original. Part XVIII reads the split between the two as a solution-stability decision and marks that as the course’s inference, because ILFORD names the substances and explains nothing.

Two alkalis rather than one. The sheet names potassium carbonate and sodium hydroxide, in bands of 5–10 per cent and below 1 per cent. The standard reading is a buffer plus a trim: the carbonate supplies the reserve that holds pH through a session of prints, and the small hydroxide dose lifts the starting point above where carbonate alone would sit. That reading is the course’s, and Part VIII on alkalis and buffers is where it comes from. ILFORD publishes the pH and names the substances and connects the two nowhere.

A sequestrant, which a 1949 formula does not have. DTPA below 3 per cent is the component that marks this out as a modern concentrate rather than a modern printing of an old formula. A bath mixed this evening from weighed chemicals is used in whatever water it was mixed in and discarded; a concentrate has to survive two years of storage and then be diluted in water the maker has never seen. Reading the sequestrant as an answer to those two problems is the course’s inference, and Part III on complex formation is the chemistry behind it.

Why one bath does two jobs. A print developer diluted far enough is a vigorous negative developer, which is the observation Kodak Limited made when it published paper stock D-72 with instructions for plates and films, and D-163 with a line for negative materials. ILFORD does something stranger and more interesting: the same 1+9 dilution serves for both, developing a print in two minutes and a sheet of FP4 in four to eight. The difference is not in the bath but in the material — a print emulsion runs to completion in a fraction of the time a film emulsion takes to reach a chosen gradient. That account is the course’s reading of the sheet’s two tables; ILFORD prints them on facing pages and draws no connection between them.

What is unknown and stays unknown. The ratio of Dimezone S to hydroquinone. The absolute loading of either. The split of alkalinity between carbonate and hydroxide. The bromide and benzotriazole loadings. The sequestrant loading. What fills the half of the bottle nothing names. The concentrate’s own pH and density. And why the sister product at the same pH develops a print in half the time.

✕Reading this safety data sheet, and what its defects teach

This sheet has the same three visible faults as its MULTIGRADE and BROMOPHEN stablemates, and noticing them is part of the skill the course is trying to build.

It runs synonyms together. Hydroquinone is printed as “1,4-dihydroxybenzenehydroquinonequinol” and sodium hydroxide as “sodium hydroxidecaustic soda”, each a string of synonyms concatenated with no separator. The first of those is also on the label, in the “Contains:” line a user actually reads. The CAS number is the field to trust, every time, which is why every line in the table above carries one.

Its dates disagree with each other. Date of issue 18 July 2024; date of revision 17 July 2027, three years in the future. That is almost certainly a review date in the wrong field, and it is the kind of thing to record when you file the sheet rather than to correct silently.

Its physical properties are almost entirely absent. For a liquid whose diluted pH and specific gravity the same company publishes on a technical sheet, “pH: Not known” and “Density: Not known” are striking. They are not a contradiction — the two documents describe different solutions — but they are a reminder that a safety data sheet is written to classify a hazard and not to describe a product.

The nearest open formula

Kodak D-163, and the choice is not the obvious one, so it is worth saying why. The obvious comparison for an ILFORD paper developer is D-72, and that is the right comparison for MULTIGRADE and BROMOPHEN, which develop paper and nothing else. This product is sold on doing two jobs, and the formulary contains a published formula sold on doing the same two: Kodak Limited’s own product list calls D-163 a universal developer for papers giving normal or high contrast, suitable also as a dish developer for negative materials. Two makers, forty years apart, arriving at the same offer.

	Kodak D-163	ILFORD PQ UNIVERSAL
Composition	Published in full, per 1000 c.c.	Not published
Developing pair	Metol 2.3 g/L with hydroquinone 17 g/L — a ratio you can read	Dimezone S and hydroquinone, both named by the maker, neither quantified
Preservative	Sodium sulfite 75 g/L, the largest in the paper library	Sodium sulphite named at 10–30 % of the concentrate
Alkali	Sodium carbonate 65 g/L anhydrous	Potassium carbonate and sodium hydroxide named; no quantities, and their roles inferred
Restrainer	Potassium bromide 2.8 g/L	Potassium bromide and benzotriazole named outside the composition table; no quantities
Sequestrant	None	DTPA, below 3 % of the concentrate
Sold as	Five chemicals you weigh	500 mL, 1 L or 5 L of concentrate
Paper dilution and time	1:3, 2 minutes at 18 °C on bromide papers	1+9, 2 minutes at 20 °C on RC, 1½–3 on FB
Second paper dilution	1:1, for working life, at the same 2 minutes	None published
Film dilution and time	1:3, 5 to 10 minutes at 18 °C on negative materials	1+9 for 4 to 8 minutes, or 1+19 for 4 to 4½, at 20 °C, per film
Published gradient on film	None	0.85 to 1.00 at 1+9; 0.62 at 1+19
Published exposure indices	None	Four films, at both dilutions
Published pH	None	10.48 to 10.58 at 1+9
Keeping	Stock 3 months full, 1 month half-full	Concentrate 2 years unopened, 6 months open
What you can change	Any of five quantities, one at a time	The dilution, the time and the temperature

Two rows in that table need a caution rather than a comparison. The capacities are not measured the same way and are not put side by side here. Kodak gives 30 8 × 10 prints per 160 imperial fluid ounces of working solution in a narrow dish, which is about six or seven prints to the litre; ILFORD gives seventy. Those two numbers cannot both be describing the same thing, and the difference is almost certainly in what each maker counts as the end of a solution’s useful life rather than in the chemistry. The course does not reconcile them and does not average them. And the temperatures differ: Kodak’s paper times are for 18 °C and ILFORD’s for 20, so a comparison run in one evening has to pick a temperature and record which.

The rest of the table is the argument. Buying the bottle gets you a bath that keeps for two years, publishes a pH, a specific gravity, a print capacity, a film capacity, an exposure index for four films and an average gradient for each — a body of published performance no 1949 formula comes near — and exactly three variables you may touch. Mixing D-163 gets you a bath with no pH, no gradient and a capacity figure you cannot compare with anybody’s, and five quantities you chose, in any volume you like, each of which can be changed on its own to find out what it does. Part XVIII’s comparison session puts them in adjacent trays with one negative, which is the only way to find out what that exchange is worth to you.

Safety

Level B, and the reasoning belongs on the page rather than in a database.

What HARMAN classifies it as. Skin Sens. 1B, Eye Irrit. 2, Muta. 2, Carc. 2, Aquatic Acute 1 and Aquatic Chronic 2, with the signal word Warning, pictograms GHS08, GHS07 and GHS09, and hazard statements H317, H319, H341, H351 and H410. Its precautionary statements include P405, store locked up, and P102, keep out of reach of children.

Skin sensitisation is what puts it past Level A. Sensitisation is not reversible: it is acquired over many small exposures and it is permanent once acquired, and a Level A page on the classification rubric assumes substances that are at most irritant at the concentrations handled. The suspected-mutagen and suspected-carcinogen classifications are read against the Level C criterion and do not meet it, because that criterion turns on a fume cupboard or specialist disposal being the recognised control, and HARMAN’s own control is ventilation, gloves and eye protection. Level B.

The concentrate is what to be careful with, and it is what you handle. Measuring 100 mL of an undiluted developer into a cylinder is the moment of highest exposure in the whole process, and it is the moment when the sodium hydroxide is at its full concentration rather than a tenth of it. The mixture is classified Eye Irrit. 2 rather than Eye Dam. 1 — a milder classification than BROMOPHEN’s part A — but splash goggles rather than spectacles are still the right answer for a liquid that is poured, and goggles are a Level B assumption.

What a liquid does not ask for. There is no dust here, which is the one hazard a powder developer adds and the reason this product is easier to live with than the carton. The sheet says so in its own way: “Normally no personal respiratory protection is necessary.” Note that this sits beside section 6, which asks for full personal protection including respiratory protection during removal of spillages — the two statements are about two different situations and both are on the sheet.

Personal protection, as the sheet specifies it. Eye protection with side protection to EN ISO 16321-1. Impervious gloves to EN 374, with the breakthrough time taken from the glove maker rather than assumed — the course’s glove selection page is where that goes. Protective clothing. Hands and exposed skin washed thoroughly after handling; contaminated clothing off and washed before it is worn again; contaminated work clothing not allowed out of the workplace. Obtain special instructions before use, and do not handle until they have been read and understood.

Ventilation and eyewash. The sheet asks for use with ventilation, local exhaust ventilation or breathing protection, and for a washing facility or water for eye and skin cleaning to be present. A darkroom with an extractor running and an eyewash within reach meets that; a sealed bathroom does not.

Tongs, on every sheet. Sensitisation is built out of many small contacts rather than one memorable splash, and an evening spent lifting prints out by hand is far more skin exposure than a spilt tray would ever give. Two components on this sheet are classified as sensitisers or worse and the tray is where you meet them.

Published exposure limits, quoted by the sheet from EH40/2005, fourth edition, 2020: hydroquinone at 0.5 mg/m³ and sodium hydroxide at 2 mg/m³, both as long-term eight-hour limits. They are workplace air limits for the pure substances and neither is a limit for a tray of diluted developer; they are here because the sheet prints them.

⚠Every hazard statement on this sheet was calculated, not measured

Section 11 is worth reading once in full, because it says something about the whole document. Against every toxicological endpoint — acute toxicity by three routes, skin corrosion, eye damage, skin sensitisation, mutagenicity, carcinogenicity, reproductive toxicity, aspiration — the sheet records “Calculation method”, and for two of them it prints the calculated acute toxicity estimate: 18347.95 for ingestion, 383.57 for inhalation.

Nobody tested this mixture. Its classification was computed from the classifications of its components and the concentration bands in section 3.2, by the rules the CLP regulation lays down. That is entirely proper and it is how most mixtures are classified. It has two consequences worth carrying away.

The first is that the classification is as conservative as the bands are wide — the calculation is run so that the worst case a band permits is still covered — which is exactly why the bands are not an assay.

The second is a small comfort. The classification is not a measurement of what this developer does to a person; it is a statement about what its ingredients are capable of at the concentrations declared. Handle it as the sheet says and the arithmetic behind the label is on your side.

Storage

The unopened bottle, in cool conditions at 5–20 °C, keeps two years. That figure and the six-month one below it are the strongest practical argument for a bought concentrate over anything you can mix, and they are worth writing on the bottle rather than trusting to memory.

Once opened, six months — use the concentrate completely within that time and keep the bottle tightly sealed until it is used. ILFORD gives one figure here and not two, so unlike BROMOPHEN’s stock there is no published penalty for a half-empty bottle. That is not the same as there being none: the air space above a developing agent is what oxidises it, and a bottle three-quarters empty for five of its six months is not what the figure was measured on. Decanting a dwindling concentrate into smaller bottles is the standard answer and it is the course’s suggestion, not ILFORD’s.

The safety data sheet adds two instructions the technical sheet does not: store locked up, and keep out of reach of children. In a domestic darkroom that means a cupboard with a key, not a high shelf.

The working solution is not stored at all. Dilute what the session needs and pour it away at the end of it. The 24-hour figure for a capped bottle is a concession rather than a plan, and it is a five-hundredth of what the concentrate beside it will keep for.

Label everything, with the product, the dilution and the date, using the labelling SOP — and for this product put the date the bottle was opened on the bottle itself, because that is the date the six months runs from and nothing about the liquid will tell you later. A tray of clear solution in a darkroom is indistinguishable from three other trays of clear solution, and an unlabelled or undated container is the failure that costs a whole session.

Incompatibilities

Acid, and the stop bath above all. ILFORD’s own instruction is to keep both stop bath and fixer out of the developer and to wash every vessel after use. Acetic or citric acid carried back on a pair of tongs does not merely weaken this bath: it drops it out of the pH region where a pyrazolidone–hydroquinone pair works at all, and the working pH is one of the few numbers ILFORD gives you to check.

Fixer, travelling in either direction. Thiosulfate reaching the developer tray dissolves silver and stains; developer carried forward into the fixer shortens the fixer’s life and stains at the other end instead. On this product it is a waste problem as well, because the fixer is the bath a refiner will pay for and a developer tipped into it spoils that.

Metal, for the concentrate specifically. The sequestrant line is classified Met. Corr. 1, H290 — may be corrosive to metals — the only metal-corrosion classification on the sheet. The mixture as a whole is not classified corrosive to metals and the sheet’s section 10.5 says incompatible materials are not known, so this is a caution rather than a finding. Measure and store the concentrate in glass or plastic, which costs nothing and is what a darkroom does anyway.

Strong oxidisers. Ferricyanide, dichromate, permanganate and persulfate must not meet a developing agent on a shelf, in a tray or in a drain. The chemical incompatibilities page lists the pairs and the reaction behind each.

✕What section 10 says, and why it is not the last word

Section 10.5 of this sheet gives incompatible materials as “Not known”, section 10.4 gives conditions to avoid as “None anticipated”, and section 7.2 gives incompatible materials as “None known”. Read literally, those three lines say that a photographic developer has no chemical incompatibilities — which is false in a darkroom where the next tray is an acid and the one after it is a thiosulfate.

The sheet is answering a narrower question than the one a printer is asking: what makes this product, sitting closed in its own bottle, unstable or dangerous. It was never a compatibility chart for a processing sequence. What governs here is the course’s incompatibilities page together with HARMAN’s technical sheet, which says in plain words that developer solutions must not be contaminated with stop bath or fixer, and that all utensils are to be washed thoroughly after use.

Waste

Bottled separately, and never tipped into the fixer. Spent developer from this product is alkaline, carries negligible silver from paper and a little more from film, and contains both developing agents in their oxidised forms.

What HARMAN classifies the waste as. Aquatic Acute 1 and Aquatic Chronic 2 — very toxic to aquatic life, toxic with long lasting effects — carried almost entirely by the hydroquinone’s H400 and H410. Section 6.2 asks that spillages or uncontrolled discharges into watercourses be alerted to the appropriate regulatory body, which is a strong hint about the drain. The benzotriazole adds a second environmental consideration of a different kind: it is listed under EU legislation for evaluation as an endocrine disruptor, and is one of two substances in this product on the European rolling action plan.

What the sheet says to do with it: dispose of the contents in accordance with local, state or national legislation; send to a licensed recycler, reclaimer or incinerator; dispose of the material and its container to a hazardous or special waste collection point.

ILFORD’s own advice, on its health and safety pages, is to bottle each waste chemical separately and label it, and — for domestic users in the United Kingdom — to leave it in the chemical cupboard at a Household Waste and Recycling Centre. Business and trade users are told to use a licensed waste disposal operator, and are reminded that silver recovery from used fixer, film and paper is a key part of the treatment. Different waste chemicals are not to be mixed.

The film tray is a different waste stream from the print tray. A litre that has developed ten sheets of film has taken far more silver into itself than a litre that has developed seventy prints, and Part XII on silver recovery and waste streams is where that distinction is worked out.

Empty bottles are not clean. A film of concentrate remains. Rinse the bottle into the working solution while you are diluting it, which is where that material belongs and which is the same rinse ILFORD already asks you to do with the measuring cylinder.

The disposal caveat governs, and the rule where you live decides. The general chemical waste SOP is the procedure this course follows.

Troubleshooting

Prints thin in the blacks, a little warm and patchy. Nine times in ten this is development cut short rather than a fault in the bath, and muddy print from snatched development sets out the whole diagnosis. Give it the full two minutes on resin-coated paper and change the exposure instead.

The image takes far longer than 35 seconds to appear on fibre paper. Either the print is underexposed or the developer is going. Count the prints that have been through the litre against the published capacity of 45 before blaming the bath, then check the temperature, then mix fresh.

Highlights going grey and flat late in a session. That is developer exhaustion and the exhausted developer entry has the general case. Seventy prints to the litre is HARMAN’s figure for HARMAN’s papers; the number that matters is the one you measure, and it falls on fibre and falls further in a tray standing open.

Grey where the paper base should be white. Three suspects and one test that separates them: slide an unexposed offcut straight into the tray, in the dark, with the safelight off. If it comes up grey the bath is at fault and developer fog on paper is the entry; if it stays clean, the fog was made before the print reached the developer, by the safelight or by how the paper has been stored. On this developer the first suspect is worth taking seriously late in a bottle’s six months rather than early.

Prints from one session do not match prints from the next. Check the dilution first: 1+9 is 100 mL of concentrate into 900 mL of water, not 100 into a litre, and a misread dilution ratio changes the time and the capacity together. Then the temperature. Then the date the bottle was opened. If the drift runs gradually through one evening rather than between sessions, it is session exposure drift and the bath is not the cause.

The concentrate has gone dark in the bottle. Oxidation of the developing agents, which is what oxidised developer covers. A bottle past its six months, or one that has stood mostly empty, should be tested against a control strip before a print you care about goes near it.

The negative comes out too contrasty to enlarge. That is the product working as advertised: 1+9 is ILFORD’s high-contrast dilution and gives an average gradient up to 1.00. Go to 1+19 for 0.62, drop the exposure index as ILFORD directs, and expect blocked highlights to be the symptom you were chasing.

Uneven or mottled development on a sheet of film. Almost always the interleaving habit carried over from paper. ILFORD does not recommend interleaving for film at all, and says even careful handling may damage the emulsion. Develop one sheet at a time with continuous gentle rocking and see uneven density across a strip and surge marks for the two ways it goes wrong.

Streaks running one way across a fibre print. Agitation, not chemistry, and usually too many sheets interleaved at once — ILFORD warns that too many sheets with too little agitation gives uneven processing. See mottled development.

Two ILFORD sheets give different film times for the same film. They do, and the difference is real: the ORTHO Plus film sheet prints a note that dish or tray development with continuous agitation should be 15 per cent shorter than its table, while the developer sheet gives those same times for dish development. The course does not resolve it. Run a test strip, record which sheet you followed, and put both in the formula version record.

Experiments

Measure the pH and the specific gravity of the fresh 1+9 solution, then measure the concentrate. The first is the control measurement ILFORD explicitly asks for: a meter calibrated that day against its published 10.48 to 10.58, and a hydrometer against 1.022. The second is the interesting one, because nobody publishes it — put the meter in the undiluted concentrate, carefully, and write down a number this page could not give you.

Put the two ILFORD developers at one pH side by side. One paper, one negative, two trays: MULTIGRADE at 1+9 for one minute against this bottle at 1+9 for two. Then swap the times and run it again. Their published pH differs by 0.03 and their published times by a factor of two, so whatever you can see is a difference the maker’s own numbers cannot account for. Judge maximum black, base white and image tone, dry before you judge, and record everything.

Test the six-minute plateau on paper. Five identical sheets from one negative at one exposure, developed for 1, 1½, 2, 4 and 6 minutes at 1+9. The prediction from the maker’s claim is that the last four are indistinguishable in maximum black and only the first is weak. If the six-minute print has a grey base you have found the far end of the plateau on your paper and your safelight, which is worth knowing.

Test the dilution-as-contrast claim on film, and measure it. One box of sheet film, one step wedge, two dilutions: 1+9 for the sheet’s time and 1+19 for its. Read the wedges and calculate the average gradient by the method in Part XIII, then set your two numbers against ILFORD’s 0.85–1.00 and 0.62. This is the single best use of the developer as a teaching object, because it is the one place a bought product hands you a published sensitometric prediction you can test with a densitometer you built.

Count the film capacity down. Ten 8 × 10 sheets to the litre is a small number and easy to verify. Develop ten identically exposed step wedges through one litre at 1+9, one after another, plotting the average gradient of each against its position in the run. Where the gradient starts to fall is where the litre ended, and it will not be exactly ten.

The comparison that matters most: this against D-163, twice. Once on paper, same negative and same session, the bottle at 1+9 for two minutes and the mixed developer at 1:3 for two — noting that Kodak’s time is for 18 °C and ILFORD’s for 20, so the temperature is a decision you have to make and record. Then again on a sheet of film, the bottle at 1+9 and D-163 at 1:3 for its five to ten minutes. Two baths, two jobs each, one of them fully published. Part XVIII’s session sets the print half up properly with a control. Record all of it in the formula version record — a bought product earns a line there too, with its dilution, the date the bottle was opened, and how much had already gone through the tray, because those are the only variables you have.

Keep a column for the emergence time. Write down the second at which the image appears on fibre paper, beside the print number and the age of the bottle, and compare it with ILFORD’s 35 seconds. It costs nothing to record and after a month of printing it will warn you that a bath is failing before a ruined print does.