ILFORD PERCEPTOL developer

This is a product page, not a formula page, and on this product the difference is at its sharpest. Everything else in this library is a list of quantities with a source attached and an account of what each quantity is doing. Nobody outside Mobberley knows the quantities in these two bags. What the two safety data sheets disclose between them is two substances — a metol salt and sodium sulphite — which is the shortest disclosed-component table in this library, and the shortness is the trap. Two named substances look like a formula. They are not one, and most of this page is about the distance between the two things.

What follows is what HARMAN publishes, which for pH, specific gravity, dilution, time, capacity and keeping is a great deal and in one respect more than Kodak published for the open formula this page compares it with; what the hazard sheets name; what the two documents together still leave unknown; and the developer with exactly those two ingredients that you can weigh out yourself.

HARMAN technology Limited (ILFORD Photo) — sold as two part powder

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
Metolnamed on the sheet as bis(4-hydroxy-N-methylanilinium) sulphateCAS 55-55-0The only substance named anywhere in ILFORD's literature for this product, on the one line of part A's composition table and on part A's own product identifier	50-65%	H302, H317, H373, H400, H410
Sodium sulfite (anhydrous)named on the sheet as Sodium sulphiteCAS 7757-83-7	60-80%

Not disclosed. HARMAN publishes no composition for PERCEPTOL, and its nine-page technical sheet does not name a developing agent for any of its three powder developers. The only documents that name anything are the two safety data sheets, and between them they name two substances: a metol salt at 50–65 per cent of the small bag and sodium sulphite at 60–80 per cent of the large one. Those are hazard bands chosen to support a classification, not an assay — each leaves a third to a half of its own bag unaccounted for by any named substance, and nothing published anywhere states what mass of part A meets what mass of part B, so the two tables cannot be combined into a formula even in principle. No alkali is named, no restrainer, no second developing agent, no antifoggant, no sequestrant, no quantity, no ratio, no working-solution pH at either dilution and no formulation date. Nor is there any account of the two things a reader most wants explained: how much film speed the developer actually costs, and why a litre of it does four films where a litre of ID-11 in the same table does ten. A reader who wants to know rather than to buy — or to move one term and watch what happens — has to mix an open formula instead.

Nearest open formula. Kodak D-23 — D-23 is the one formula in this library whose entire published composition is the two substances HARMAN discloses: 7.5 g of metol and 100 g of sodium sulfite in a litre, with no second agent, no added alkali and no restrainer. Both are slow, soft-working, solvent fine-grain film developers worked in a tank at ordinary room temperature, and both put a large sulphite load around a small quantity of metol. They then differ in every way that matters to a reader. D-23's quantities are printed and can each be moved one at a time; PERCEPTOL's are two bands on two hazard sheets with no stated ratio between the bags. Kodak claims D-23 gives normal emulsion speed, where HARMAN designs PERCEPTOL for use "when a decrease in film speed is not important" and publishes no time at box speed for either of its 400-speed films — so a reader who assumes the product is the formula has already contradicted one of the two makers. PERCEPTOL publishes a stock pH, a specific gravity at three dilutions, times for ten films, a reuse ladder and six keeping figures where no Kodak printing in this corpus gives D-23 a pH or a dilution at all; D-23 can be mixed at any volume you care to weigh, where PERCEPTOL is sold only in one-litre cartons and its own sheet forbids making up a fraction of a pack. The formula that matches PERCEPTOL's published speed-for-grain trade rather than its component list is D-25, which is D-23 with sodium bisulfite added, and the body sets both comparisons out.

⚠Which bag carries the label, and why it is the opposite of MICROPHEN

The two bags are classified separately, and only one of them is classified at all.

Part A, the small bag, is Acute Tox. 4, Skin Sens. 1, STOT RE 2, Aquatic Acute 1 and Aquatic Chronic 1, signal word Warning, pictograms GHS08, GHS07 and GHS09, statements H302, H317, H373 and H410. The whole of that comes from the one substance in its composition table.

Part B, the large bag, is “Not classified as dangerous for supply/use” — no pictogram, no signal word, no hazard statement, and a single precautionary statement, P102, keep out of reach of children.

That is the reverse of MICROPHEN, where both bags are labelled Danger and the more serious warning is on the large one. A milder signal word is not a milder handling rule: part A is a skin sensitiser at 50 to 65 per cent, sensitisation is permanent, and the dry powder is where the exposure happens. See Safety.

Purpose

To develop a negative with the finest grain ILFORD’s powder range can give, accepting that you will rate the film below its ISO speed to get it. HARMAN’s own words: PERCEPTOL “is an extra fine grain film developer which gives excellent image quality. It is designed for use when very fine grain negatives are required and a decrease in film speed is not important. It has been specially formulated to get optimum results from high resolution lenses.”

That is a trade stated in one sentence, and it is the only sentence of its kind in ILFORD’s powder literature: ID-11 is sold as fine grain “without loss of emulsion speed” and MICROPHEN as fine grain with a speed increase. PERCEPTOL is the one that asks for something back. The sheet adds that it “exploits the superb grain structure of ILFORD medium and slow speed films, 100 DELTA PROFESSIONAL, FP4 Plus and PAN F Plus, and produces significantly finer grain in ILFORD fast films, DELTA 400 PROFESSIONAL, HP5 Plus and DELTA 3200 PROFESSIONAL, compared with a standard fine grain developer”, and that negatives developed in it “are capable of producing sharper and better-quality enlargements than those produced using a standard fine grain developer”.

Read that last claim carefully, because it is easy to turn into something HARMAN did not say. It is not an acutance claim. PERCEPTOL appears in no ILFORD sheet’s Maximum sharpness row — that row goes to a diluted ID-11, to MICROPHEN on DELTA 3200, or to a liquid concentrate. The claim is about the print: a finer-grained negative survives more enlargement before grain becomes the limit. The two statements are consistent and they are about different things, and the reconciliation in this paragraph is the course’s reading rather than HARMAN’s sentence.

How much speed does it cost? HARMAN never says. The maker’s own table does arithmetic the maker declines to write down, and Behaviour below sets out exactly how far that arithmetic can honestly be taken. Part XIII’s film speed lesson is where criterion speed, ISO speed and exposure index are separated, and it is the lesson to read before you believe or disbelieve a stop.

Recommended uses

A slow or medium film in a spiral tank at 20 °C, at stock strength, rated at or a stop below box speed. This is the use the whole of ILFORD’s literature points at. Seven film sheets in this course’s corpus carry a Choosing the best ILFORD developer for the job table with a Finest grain row — DELTA 100, DELTA 400, DELTA 3200, FP4 Plus, PAN F Plus, HP5 Plus and SFX 200 — and PERCEPTOL is named in that row on all seven. It is named in almost nothing else: the only other row it appears in anywhere is DELTA 3200’s Best overall image quality, at EI 400/27 and EI 800/30.

And on DELTA 400, read the row twice. That sheet splits Finest grain into two lines, and the unqualified one gives ID-11 (stock); PERCEPTOL appears on the second, Finest grain (EI 200/24) — a stop below the film’s ISO speed. HARMAN is saying, on its own sheet, that at box speed the finer-grained negative comes from the other powder, and that PERCEPTOL wins only once you have rated the film down. Nothing on this page states the speed-for-grain trade more plainly than that row does.

At EI 100 on DELTA 100, diluted 1+1 rather than at stock. DELTA 100’s sheet splits Finest grain by dilution rather than by developer: PERCEPTOL (1+1) at EI 100/21 and PERCEPTOL (stock) at EI 50/18. A maker recommending its own developer diluted for finest grain at box speed, and undiluted only when the film is rated down, is a distinction worth having, and ILFORD offers no explanation for it anywhere.

A fast film deliberately used well below its name. DELTA 3200 Professional has an ISO speed of 1000/31°, and its own sheet names PERCEPTOL (stock) as the best overall image quality powder at EI 400/27 and at EI 800/30, handing EI 1600/33 and above to MICROPHEN. That is the clearest statement in ILFORD’s literature of what this developer is for: not the film’s nominal speed, but the picture you take when you have chosen to give the film more light than its name suggests.

Rescuing an accidentally over-exposed film. The HP5 Plus and FP4 Plus sheets each carry a table the powder sheet does not — Manual processing, accidental exposure only — and in the over-exposed column the only ILFORD powder given a time is PERCEPTOL. HP5 Plus gets 9, 9 and 11 minutes at EI 50/18, 100/21 and 200/24; FP4 Plus gets 8½ minutes at EI 25/15 and below. On the FP4 Plus sheet MICROPHEN holds the opposite column, at EI 400/27 and above. Two products, two directions, one carton range.

Diluted 1+1 or 1+3 as a one-shot developer, mixed from the stock immediately before use and thrown away. Note how little of the table this covers: PERCEPTOL has a 1+3 time for five films only — DELTA 100, DELTA 400, PAN F Plus, FP4 Plus and HP5 Plus — and each of those at one or two meter settings, where ID-11 and MICROPHEN carry 1+3 times across most of the range. SFX 200, DELTA 3200, ORTHO PLUS and both Kentmere films get no 1+3 time at all.

Sheet film in a dish or tray, at stock strength only, with continuous agitation and the times cut by about 15 per cent. Higher temperatures are explicitly not recommended for dish work because the times become too short and lead to uneven processing.

Deep tanks with a floating lid, where the stock keeps four months against one month without it, using ILFORD’s own manual agitation: lower the rack, tap it, lift it out and return it immediately, then at the end of each minute lift, tilt, return, three times, alternating the direction of tilt.

Rotary tube processors, at stock, 1+1 or 1+3, with no pre-rinse — ILFORD says a pre-rinse can lead to uneven development — and the times reduced by around 15 per cent for the continuous agitation.

Not for anything ILFORD does not document. The nine-page sheet is a film sheet. It carries no paper instruction, no plate instruction and no reversal instruction, and this page supplies none.

When another formula is preferable

• When you want to weigh out this developer’s disclosed components and see what they do, mix D-23. Metol and sodium sulfite, nothing else, every quantity printed and movable one at a time. It is the comparison this page is built around.
• When you want the extra-fine-grain-for-speed trade published, mix D-25 — D-23 with 15 g of sodium bisulfite added, which Kodak sells as minimum grain at a cost of one to two stops of exposure. That is PERCEPTOL’s own trade, printed as three quantities, and D-25R replenishes it where PERCEPTOL has no replenisher at all.
• When you want a silver solvent you can point at, DK-20 adds a thiocyanate and publishes how much. PERCEPTOL names sulphite and stops.
• When you do not want to lose the speed, D-76 is the fine-grain standard that costs nothing on the meter, and ILFORD’s own answer in the same carton range is ID-11, whose composition it does not publish either.
• When you want speed rather than grain, MICROPHEN is the sibling product and the open equivalents are D-76 or, for a real acutance gain, Beutler’s two-solution developer and Rodinal.
• For high contrast, D-19. No fine-grain solvent developer does contrast, and this one is the slowest of them.
• When you need a replenished tank rather than a reused one. PERCEPTOL has no replenisher, and its reuse ladder stops at four films where ID-11’s runs to ten. The open equivalent is D-76 with D-76R, which restores capacity with no time increase at all.
• When you cannot use a whole litre at a time. The sheet forbids making up part of a pack, and PERCEPTOL is sold in one-litre cartons only: ID-11 is the only one of the three powders with a five-litre carton, and neither PERCEPTOL nor MICROPHEN has one. If your darkroom develops two films a month, an open formula you weigh is the only way to mix 300 mL.

What the maker publishes

A great deal, and on one point more than Kodak ever published for the open formula below.

The pH and the specific gravity. ILFORD prints a table for fresh solutions of all three powder developers. PERCEPTOL stock reads pH 7.68 to 7.82 with a specific gravity of 1.110 at 20 °C. At 1+1 the sheet gives 1.058 and at 1+3 1.028 — and no pH at either dilution, which is a gap and not a rounding. ILFORD adds that the figures were obtained under carefully controlled laboratory conditions, that a user’s own measurements may differ slightly, and that the right use of the table is to measure your own fresh solution and compare later ones against it. That is better advice than the number.

Two things about that row are worth pausing on. It is the lowest pH and the highest specific gravity of the three powders — ID-11 runs 8.60 to 8.70 at 1.090 and MICROPHEN 8.67 to 8.93 at 1.095. And it is a figure the open formula this page recommends does not have: no Kodak printing in this course’s corpus gives D-23 a pH at all. A bought product can be better documented than an open one on a specific point, and pretending otherwise would be as dishonest as pretending the composition were published.

Enough of the table to check the table. The three specific gravities are not independent, and the arithmetic takes two minutes. A stock of specific gravity 1.110 has a density excess over water of 0.110. Halve it for 1+1 and you predict 1.055; the sheet prints 1.058. Quarter it for 1+3 and you predict 1.0275; the sheet prints 1.028. Three parts and half a part in a thousand — close enough to confirm the dilutions, and not exact, because volumes of solutions are not strictly additive. The same test on the ID-11 and MICROPHEN columns behaves the same way. That arithmetic is the course’s, on HARMAN’s printed figures.

The mixing method, in enough detail to be a procedure. Dissolve part A, the smaller bag, in about three quarters of the total solution volume of warm water at about 40 °C. Stir until most of it has dissolved, then keep stirring while gradually adding part B. Keep stirring until no more powder dissolves — and ILFORD says plainly that it is normal for a few grains to remain undissolved, and that discoloured or darker particles in the white powder are normal and will not affect development. Add cold water to the final volume, stir, and let it cool to 20 °C. Two further instructions that are chemistry rather than housekeeping: never make up a fraction of a pack, though multiples of whole packs are allowed; and draw your water off and let it stand a few minutes first, because most water from a pressure main is highly aerated.

Development times for ten ILFORD and Kentmere films, at up to three dilutions, with the contrast they are meant to produce stated: negatives of normal contrast, “typically around a G-bar of 0.62”. That figure ties the whole table to Part XIII’s account of average gradient, and it is what makes the times adjustable rather than magical.

A temperature rule with a worked example. The developers may be used from 20 to 24 °C. Increase the time 10 per cent for each 1 °C drop and decrease it 10 per cent for each 1 °C rise, or use the time–temperature graphs. ILFORD’s own example: 6 minutes at 20 °C becomes 4½ at 23 °C and 9 at 16 °C. With PERCEPTOL’s long times that rule matters more than it does for its siblings — a 15-minute time becomes 11 at 23 °C.

Four agitation regimes, each specified. Spiral tank: four inversions in the first 10 seconds, four inversions in the first 10 seconds of every subsequent minute, tap the tank after each. Dish: continuous gentle rocking, times cut by about 15 per cent. Deep tank: lift, tilt, return, three times at the end of each minute, alternating the tilt. Gas burst: nitrogen for the developer, never air, 0.3 to 0.9 bar, two seconds on and eight off as a starting point. And a general instruction — drain the developer ten seconds before the end of the time.

The reuse scheme, and it is the figure that most distinguishes this product. A litre of stock does 4 roll films if reused, against 10 for both ID-11 and MICROPHEN in the same three-column table. The compensation is 10 per cent more time for each successive film, and where the siblings’ ladder runs to a tenth film at N+90 per cent, PERCEPTOL’s prints NR — not recommended — after the fourth. The same shape scales: in a 5-litre tank, films 1–5, 6–10, 11–15, 16–20, then NR. ILFORD offers no reason for the difference anywhere in nine pages, and it is the most interesting unexplained number on the sheet.

Six separate keeping figures, which on this product are planning constraints rather than trivia: the unopened carton keeps indefinitely at 4 to 20 °C, the stock six months in a full bottle but only one in a half-full one, a deep tank four months with a floating lid and one without, and any dilution 24 hours. Set those against a four-film capacity and the arithmetic of owning this developer is already decided for you.

Every other bath in the sequence, with its own capacity. ILFOSTOP at 1+19, ten seconds, fifteen films to the litre. RAPID FIXER or HYPAM at 1+4, two to five minutes, twenty-four films to the litre — six times the developer’s four, so on this product the developer is the bottle that runs out first by a wide margin, which is the opposite of most darkroom arithmetic. Then five to ten minutes of running water, or ILFORD’s own frugal substitute of three fills inverted five, ten and twenty times; ILFOTOL at 5 mL per litre; and drying at 30 to 40 °C.

And the availability line, which is a fact about your darkroom. PERCEPTOL is sold in cartons of one litre only. ID-11 comes in one and five; MICROPHEN in one. Combine that with the ban on fractional packs and the four-film capacity, and the planning unit for this developer is fixed: one litre, four films, or one litre thrown away as a one-shot dilution.

What is not disclosed

The formula, and further than usual. ILFORD’s paper-developer sheet at least calls BROMOPHEN a phenidone/hydroquinone developer in its product description. The powder film developer sheet names no developing agent at all, for any of the three products, in nine pages. Not the agents, not the alkali, not a quantity, not a ratio, not a restrainer, not a sequestrant, not the date the formulation was fixed.

So the only ILFORD document that names anything is a hazard sheet — and it names one substance per bag. Everything in the table above was published because the law requires a mixture’s hazards to be communicated, not because HARMAN chose to describe its product. That inversion is worth noticing every time it appears, and here it is at its starkest: two documents, two composition tables, one row each.

!Why two named substances are not a two-ingredient formula

This is the product on which the temptation is strongest, because the two disclosed substances happen to be exactly the two ingredients of a real published developer. Three separate things stop that reading, and the third finishes it.

First, each band leaves most of a third of its own bag unnamed. Part A’s metol salt is given as 50–65 %, so between 35 and 50 per cent of the small bag is not accounted for by any named substance. Part B’s sodium sulphite is given as 60–80 %, so between 20 and 40 per cent of the large bag is not either. Those subtractions are the course’s arithmetic on HARMAN’s printed bands, and they are not a composition — they are a measure of how much the sheets do not say.

Second, absence from a composition table is not absence from the bag. A safety data sheet names what the classifier needed to name. HARMAN’s own practice is not even consistent about that: part B’s sodium sulphite is marked Not classified, with no pictogram and no hazard statement, and is listed anyway — as is boric acid on MICROPHEN’s part A sheet — so a substance can appear without driving the classification, and can equally be present without appearing. No conclusion about what is not in these bags can be drawn from these tables, and this page draws none.

Third, and decisively, there are two tables and no bridge between them. These are the compositions of two separate bags. Nothing published anywhere states what mass of part A meets what mass of part B. Even if both tables were assays — and they are not — they could not be combined into a formula for the litre, because the mass ratio of the small bag to the large one is not published. The two sheets share a product code, 1960529, and that is the entire link between them.

A concentration band on a safety data sheet exists to support a classification: it is chosen so the mixture’s hazard can be calculated conservatively, and a band wide enough to do that is far too wide to mix from. A safety data sheet read as a hazard document is evidence. Reassembled into a recipe it is a fabrication with citations attached, and this page does not attempt it.

No alkali is named, in either table. Nothing in ILFORD’s literature says what raises the pH of this developer to 7.68–7.82, or whether anything does beyond the sulphite itself.

No restrainer, no antifoggant, no sequestrant and no second developing agent is named. Whether that is because there are none, or because whatever is present falls below the concentration at which a sheet must name it, is not published and this page does not guess.

And an absence with a sibling to compare it to. MICROPHEN’s part A discloses sodium metabisulphite at 30–40 per cent and carries the supplemental label statement EUH031, contact with acids liberates toxic gas. PERCEPTOL’s part A discloses no metabisulphite, no bisulfite and no EUH031. That is a real difference between two labels written by the same company on the same day, and it is worth recording — but it is not evidence that PERCEPTOL contains no acid sulphite, for the reason set out in the callout above. It is evidence about what HARMAN had to classify, and nothing more.

Every measurable property, refused. Section 9 of both sheets is a column of the words Not known: appearance “Solid”, and then colour, odour, pH, melting point, density, solubility, partition coefficient, decomposition temperature — all “Not known”. The company that publishes a stock pH band to two decimal places and a specific gravity to three in its technical sheet declines to publish either in its hazard sheets.

Nothing about why. No source in this course’s corpus says how much film speed PERCEPTOL costs, why it costs it, what its alkali loading is, whether a second developing agent is present at all, why a litre does four films where a litre of ID-11 does ten, or what the formulation looked like when the name was registered. Those are the interesting questions and the literature does not touch them.

Disclosed components

Two components, one from each sheet, in the order the two safety data sheets print them: part A first, the small bag, then part B. The concentration against each is the band the sheet states and not a quantity, and a function is given only where HARMAN names one or where the identification is not in doubt.

Part A — the smaller bag

bis(4-hydroxy-N-methylanilinium) sulphate, CAS 55-55-0, EC 200-237-1, 50–65 %. This is metol, and the name is the sheet’s own: the anilinium-salt spelling of what Kodak called Elon and what the encyclopaedia files as 4-(methylamino)phenol hemisulfate. A reader who did not already know the substance would struggle to look that name up, and it is a standing argument for the rule this library follows — the CAS number is the field to trust, every time.

It is the only substance in part A’s composition table, the only substance named on part A’s product identifier, and the sole source of that bag’s entire classification: Acute Tox. 4 (H302), Skin Sens. 1 (H317), STOT RE 2 (H373), Aquatic Acute 1 (H400) and Aquatic Chronic 1 (H410), with the signal word Warning and the pictograms GHS08, GHS07 and GHS09. HARMAN gives it no function, no occupational exposure limit — section 8.1 of both sheets says none is assigned — and no physical property.

Its band is 50 to 65 per cent, which leaves a third to a half of the small bag named by nobody.

That a metol salt at this concentration is a developing agent is not in doubt, and this page says so: the metol page sets out its place at the top of Kodak’s reduction-potential ranking and why it is the agent that can work in a bath with very little alkali. What HARMAN does not say, and what this page therefore does not say, is that it is the only developing agent in the carton. A second agent present below the concentration at which it must be named would not appear in this table, and nothing published rules one out.

The other thing the metol page carries, and it belongs here rather than only in Safety: metol is the substance that gave darkroom dermatitis its name. Sensitisation is permanent, and the bag you are tipping is half to two thirds metol salt.

Part B — the larger bag

Sodium sulphite, CAS 7757-83-7, EC 231-821-4, 60–80 %. Sodium sulfite is the only substance in part B’s composition table, and HARMAN marks it “Not classified”, with no hazard statement and no pictogram. That is why part B as a whole carries no label: section 2.1 reads “Not classified as dangerous for supply/use”, and its one precautionary statement is P102, keep out of reach of children. Section 12.1 records low toxicity to invertebrates, fish and algae.

That regulatory silence is the exact reverse of its photographic importance. In a fine-grain film developer, sulfite does three jobs at once: it consumes dissolved oxygen, it intercepts the oxidation products of the developing agent, and at high concentration it dissolves silver halide, which is what makes a developer fine-grain in the first place. Part VIII’s lesson on sulfite and preservation and its lesson on solvent action and grain are the accounts, and D-23 is where you can see the quantity: 100 g in a litre, published, doing all three jobs and the alkali’s as well. That the sulphite here is doing those jobs is the course’s reading of a component list against HARMAN’s own extra-fine-grain claim; ILFORD states none of it.

The band is 60 to 80 per cent, leaving a fifth to two fifths of the large bag unnamed.

What is in the table and what is not

Two components. No alkali, no restrainer, no antifoggant, no second agent — and, unlike MICROPHEN’s part A, no acid sulphite. Read the table for what it is: the substances HARMAN was obliged to name in order to classify two bags of powder. It is not a list of what is in PERCEPTOL. It is a list of what is in PERCEPTOL and needed saying for hazard purposes, which is a different and smaller set, and the difference is invisible from the table itself.

Behaviour

It is slow, and the sheet lets you count how slow. ID-11 and PERCEPTOL are printed in adjacent columns of one table at the same meter settings, so the comparison needs no assumption at all.

Film and meter setting	ID-11 stock	PERCEPTOL stock
PAN F Plus, EI 25/15	4 min 30 s	9 min
PAN F Plus, EI 50/18	6 min 30 s	14 min
DELTA 100, EI 50/18	7 min	12 min
DELTA 100, EI 100/21	8 min 30 s	15 min
FP4 Plus, EI 50/18	6 min 30 s	9 min
FP4 Plus, EI 125/22	8 min 30 s	12 min
DELTA 400, EI 200/24	7 min	10 min
DELTA 3200, EI 3200/36	10 min 30 s	18 min
SFX 200, EI 200/24	10 min	14 min 30 s

Across the nine settings above, PERCEPTOL takes between about 1.4 and 2.2 times ID-11’s time — the widest ratio on PAN F Plus, the narrowest on FP4 Plus and DELTA 400. Those ratios are the course’s arithmetic on HARMAN’s printed times, and the times themselves are corroborated film by film: DELTA 100’s, FP4 Plus’s, PAN F Plus’s, HP5 Plus’s, DELTA 400’s, DELTA 3200’s and SFX 200’s own sheets each reprint the powder sheet’s PERCEPTOL row, and every one of them agrees to the half minute. That is an unusually clean evidential picture for a bought product, and it is worth saying so: almost nothing on this page’s time table rests on a single printing.

Almost. There is exactly one disagreement, and it is a blank against a number. The powder sheet’s ORTHO PLUS row prints dashes in all three PERCEPTOL columns — no stock time, no 1+1, no 1+3 — while giving ID-11 and MICROPHEN complete Normal and High contrast times. ORTHO PLUS’s own sheet gives PERCEPTOL stock 13 minutes to a G-bar of 0.62 and 16 minutes to a G-bar of 0.70 at 20 °C, and its ID-11 and MICROPHEN figures match the powder sheet exactly. So the two documents agree about everything except whether this developer has a time for this film at all. The course does not know which is current, and prints both.

The speed loss, taken exactly as far as the evidence goes and no further. HARMAN never states a number. What HARMAN does is choose which meter settings to publish a time for, and the pattern in that choice is the closest thing to a quantitative statement that exists:

• The slow and medium films get a box-speed time: DELTA 100 at EI 100, FP4 Plus at EI 125, PAN F Plus at EI 50, Kentmere PAN 100 at EI 100, SFX 200 at EI 200. Each also gets a time a stop down, and the Finest grain recommendation for DELTA 100 at box speed is the diluted developer.
• Neither 400-speed film gets one. HP5 Plus’s only stock time is at EI 250/25 and its diluted times are at EI 320/26; DELTA 400’s stock times are at EI 200/24 and EI 250/25 and its highest published setting anywhere is EI 320/26, at 1+1. Kentmere PAN 400 gets one time in the whole table, at EI 320/26, and it is a 1+1 time. ILFORD publishes no PERCEPTOL time at EI 400 for any film that is rated at EI 400.
• And DELTA 3200 breaks the pattern. Its ISO speed is 1000/31°, and PERCEPTOL is published for it from EI 400/27 all the way to EI 3200/36 — above the ISO speed, not below it. The film’s own sheet nevertheless recommends PERCEPTOL only at EI 400 and EI 800 and hands the higher settings to MICROPHEN.

So the honest summary is a range and a caveat, not a figure. On the fast films the maker’s own table stops between two thirds of a stop and one stop below box speed; on the slow and medium films it does not stop there at all; and on the one film ILFORD rates at 1000 it publishes times nearly two stops above. The course does not convert that into “PERCEPTOL costs one stop”, which is the sentence the internet will offer you. The way to find out what it costs on your film is in Experiments, and it takes one roll.

A second thing the table does that HARMAN does not explain: dilution buys back a meter setting. On HP5 Plus the stock column stops at EI 250 and the 1+1 and 1+3 columns are printed at EI 320. On DELTA 400 the stock column reaches EI 250 and the 1+1 column reaches EI 320. That is HARMAN’s table, not a reading of it. Why a weaker solution should be published at a higher meter setting is not stated anywhere, and it runs against the ordinary expectation that dilution costs effective speed. It is a genuinely open question with a two-hour answer, and it is in the experiments below.

Four films to the litre, and then stop. The reuse table is the sharpest practical difference between this developer and its siblings. A litre of ID-11 or MICROPHEN does ten roll films with a 10 per cent time increase each; a litre of PERCEPTOL does four, and the fifth is marked NR, not recommended. In a 25-litre deep tank the ladder is 1–25, 26–50, 51–75, 76–100 and then NR, where the other two continue to 250 films. No reason is published. It is consistent with a bath whose activity has little reserve behind it — but that is an inference and it is marked as one in The mechanism.

Diluted, it is one-shot and nothing else. ILFORD does not recommend reusing 1+1 or 1+3, does not recommend push processing in a reused developer, and gives every dilution a 24-hour life. It also prints an unusually candid paragraph arguing against reuse in general: reusing developer “lowers image quality slightly and increases the risk of physical damage”, the developer oxidises, precipitates may form, particles of emulsion from earlier films may be held in suspension, and there is a risk of miscounting. One-shot processing “eliminates or greatly reduces these problems”. A maker arguing against the economical use of its own product is worth quoting, and with a four-film capacity the economical case was thin to begin with.

Fog and clean working: nothing is published, and nothing is named. Neither composition table names an antifoggant of any kind, and ILFORD makes no clean-working claim for PERCEPTOL. A low-activity bath is the condition under which fog is least likely, which is a reason to expect clean negatives and not a reason to assert them. Run your own control strip — see Experiments.

Image characteristics

Grain: the finest ILFORD’s powder range offers, and the maker says so on seven sheets. Extra fine grain is HARMAN’s own class for this product, and PERCEPTOL is named in the Finest grain row of all seven ILFORD film sheets in this corpus that carry one — with the DELTA 400 qualification set out under Recommended uses. On the fast films the claim is explicitly comparative — “significantly finer grain … compared with a standard fine grain developer” — where the standard fine grain developer in ILFORD’s own range is ID-11, printed in the next column.

Sharpness: two claims that must be kept apart. HARMAN says negatives developed in PERCEPTOL are “capable of producing sharper and better-quality enlargements” than those from a standard fine grain developer, and that it was “specially formulated to get optimum results from high resolution lenses”. It also never puts PERCEPTOL in a Maximum sharpness row. Both are HARMAN’s. The reading that reconciles them — that a finer-grained negative enlarges further before grain is the limit, which is not the same as edge acutance in the developer — is the course’s, not the maker’s, and Part VIII’s account of acutance and adjacency effects is where the distinction is made properly. A solvent developer at high sulphite loading etches the grain boundaries that edge effects depend on, so a high-solvent bath giving high acutance would be a surprise.

Speed: a loss, unquantified. See Behaviour. The one thing that can be said without inference is that ILFORD states its films’ ISO speeds were measured in ID-11, so every PERCEPTOL meter setting in the table is a setting relative to a developer sold by the same company in the same carton range and printed in the adjacent column.

Contrast: normal. The times are set for negatives of normal contrast, typically around a G-bar of 0.62, the same target ILFORD gives for ID-11 and MICROPHEN, and the sheet says plainly that the times are a guide to be adjusted until the contrast you want is obtained.

Tonality: no published claim at all, and the course supplies none. PERCEPTOL is very widely described as a compensating or long-scale developer; no ILFORD document in this corpus says so, and the same caution appears on the D-23 page for the same reason. It is a good candidate for measurement rather than repetition.

Image colour and staining do not arise. Nothing in ILFORD’s literature claims a tone, a tanned relief image or a stain for this developer, and nothing in the two component tables would produce one. It is a conventional silver developer and the page treats it as such.

The mechanism

Everything in this section that goes beyond the two names on the two sheets is marked as what it is.

What the maker states. PERCEPTOL is an extra fine grain film developer giving excellent image quality; it is designed for use when very fine grain negatives are required and a decrease in film speed is not important; it was specially formulated for high resolution lenses; it gives significantly finer grain in fast films than a standard fine grain developer; its stock runs at pH 7.68 to 7.82 with a specific gravity of 1.110 at 20 °C; it is made from two bags, the smaller dissolved first in warm water; a litre reused does four films; and its times run between about 1.4 and 2.2 times ID-11’s.

What follows from the safety data sheets without needing anything else: it is a metol developer with a large sulphite load. Part A’s product identifier and its composition table both name a metol salt and nothing else; part B’s composition table names sodium sulphite at 60 to 80 per cent of the larger bag and nothing else. Both of those are HARMAN’s statements. What is not HARMAN’s statement is that those are the only two substances present, and the difference between “the sheets name these two” and “the product contains these two” is the whole of this page.

Inference, labelled as inference: the fine grain is solvent action. A large sulphite concentration dissolves silver halide during development, etching the grains as they are reduced and leaving a finer-appearing image — and the classical price of that etching is effective film speed, because the smallest developable specks are the ones dissolved away. Part VIII’s solvent action and grain lesson is the account. PERCEPTOL’s published behaviour is exactly the shape that mechanism predicts: extra fine grain, a speed loss the maker declines to quantify, long times, and the highest specific gravity of the three powders, which is what a heavily loaded solution reads. HARMAN says none of this. It names no mechanism, and the specific-gravity reading is a density and not an assay.

Inference, labelled as inference: the low pH, and what it can and cannot tell you. PERCEPTOL’s published stock pH of 7.68–7.82 is the lowest of ILFORD’s three powders — about nine tenths of a unit below ID-11’s 8.60–8.70, which on HARMAN’s own printed bands is roughly an eightfold difference in hydroxide concentration. The general rule that a developer’s energy follows the quantity of alkali present is set out in this library on the D-23 page and in Part VIII’s lesson on alkalis, buffers and pH, and a bath at pH 7.7 worked by a slow agent is a bath that takes a quarter of an hour — which is what the times show. What the pH cannot tell you is whether there is a separate alkali in the carton at all. A concentrated sulphite solution is itself mildly alkaline on hydrolysis — that is precisely how D-23 works with no added alkali whatsoever — so a low pH is consistent with a sulphite-only bath and with a lightly buffered one, and a pH is not a titration. ILFORD names no alkali and this page does not supply one.

Inference, labelled as inference: why part A dissolves first. ILFORD’s instruction is to dissolve the smaller bag in warm water and add the larger gradually afterwards. There is a rule that fits it exactly, and the metol page sets it out from Kodak’s own primers: sulfite dissolved before metol throws down a white precipitate, the sparingly soluble free base, because the sulfite has taken the acid away — so the metol goes into the water first and the sulfite after it. Dissolving part A into three quarters of the volume at 40 °C and only then raising the sulphite concentration with part B is that manoeuvre, performed by a carton. The instruction is HARMAN’s; the reason offered for it is the course’s, and it assumes part A is mostly what its sheet names, which is not established.

Inference, labelled as inference: the four-film capacity. A developer whose activity rests on a single agent has no reserve behind the front line — when the agent at the emulsion surface is spent there is no second agent to regenerate it or to carry on — and the D-23 page makes the same point about a single-agent bath’s steeper exhaustion curve. That is consistent with a capacity two and a half times shorter than ID-11’s. It is not evidence for it: HARMAN publishes neither the reason nor the composition that would let anyone check, and a bromide build-up, a lower alkali reserve or a sulphite consumed by solvent action would all produce the same table.

What is unknown and stays unknown. Whether a second developing agent is present. Whether there is a separate alkali, and what it is. Whether there is a restrainer. The mass ratio of the two bags. The metol loading in the litre, and the sulphite loading. The working pH at 1+1 and 1+3. How much speed is actually lost, on which film, at which dilution. And why four films.

!Reading these two sheets, and what their defects teach

Three things about this pair of documents are worth noticing, because noticing them is part of the skill this course is trying to build.

A composition table with one row is still a hazard document. The strongest impression a reader takes from part A’s sheet is that PERCEPTOL is simple. What the sheet actually establishes is that one substance drives the classification. Those are different claims and only the second one is supported.

Their dates do not agree. Both sheets give a date of issue of 18 July 2024 and a date of revision of 17 July 2027, three years in the future — the same defect as on the MICROPHEN pair. It is almost certainly a review date printed in the wrong field, and it is exactly the kind of thing to record when you file a sheet rather than to correct silently. The procedure is recording a safety data sheet.

The two halves of one product give contradictory storage advice. Part A’s section 2.2 carries P405, store locked up; part B’s carries only P102, keep out of reach of children; and section 7.2 of both asks merely for ambient storage. The carton contains both bags. The stricter instruction governs, and a reader who filed only the part B sheet would never see it.

The lesson is the same in all three cases: a safety data sheet is a document to read, not a document to trust. Read all sixteen sections of both sheets, cross-check the CAS numbers against the GHS and CLP reference, and record what you found.

The nearest open formula

Kodak D-23, and no formula in this library sits closer to a product’s disclosed component list than this one does.

D-23 is 7.5 g of metol and 100 g of sodium sulfite in a litre of water. There is no second developing agent, no added alkali, no restrainer and no buffer beyond what the sulfite provides on its own. Those two substances are, precisely, the two substances HARMAN’s two safety data sheets name. Kodak Limited’s 1949 handbook calls it “a soft-working developer of simple formula giving normal emulsion speed” and prints it complete in three lines.

	Kodak D-23	ILFORD PERCEPTOL
Composition	Published in full: two ingredients, both quantities printed	Not published, and not sketched in the technical sheet
Developing agent	Metol, 7.5 g per litre	A metol salt, named only on a hazard sheet, at 50–65 % of an unweighed bag
Sulfite	Sodium sulfite, 100 g per litre — preservative, solvent, alkali and, in use, buffer	Sodium sulphite named at 60–80 % of the larger bag; loading in the litre not published
Alkali	None added; the sulfite is the alkali	None named, and nothing published says whether one is present
Restrainer	None in the formula	None named on either sheet
Published pH	None, in any Kodak printing this course holds	7.68–7.82 for the stock; nothing for either dilution
Speed claim	Normal emulsion speed — Kodak’s own words	Designed for use when a decrease in film speed is not important; no box-speed time for either 400-speed film
Published times	One: about 18 minutes at 18 °C, for the materials of 1949	Ten films, up to three dilutions, with a G-bar target and a temperature rule
Working dilutions	Undiluted only; the handbook gives none	Stock, 1+1 and 1+3
Reuse	24 sheets of 8 × 10 per 160 fl oz in a dish, 36 in a deep tank	4 roll films per litre, +10 % per successive film, NR after the fourth
Replenished	Yes — D-25R serves both D-23 and D-25	No replenisher exists
Sold as a packed powder	Never. Kodak’s handbook marks the packed formulas with an asterisk and D-23 has none	Only as a packed powder, in one-litre cartons, with fractional packs forbidden
What you can change	Either quantity, one at a time	The dilution, the time, the temperature and the agitation

Two rows in that table deserve to be read against each other, because between them they are the argument of this whole page kind. Kodak claims normal emulsion speed for D-23; HARMAN designs PERCEPTOL for a reader to whom a speed decrease does not matter. If the product were the formula, one of the two makers would be wrong about its own developer. So either PERCEPTOL is not D-23 — the overwhelmingly likely case, and the one the evidence supports — or ILFORD’s meter settings are conservative in a way it has never explained. This course does not choose between those, and it does not assert that PERCEPTOL is D-23 or any relation of it. It has exactly the same standing as the claim that ILFORD’s ID-11 “is” D-76, which the D-76 page also declines to make.

The formula that matches the behaviour is the next one along. D-25 is D-23 with 15 g of sodium bisulfite added, and Kodak prints both ends of that trade in one entry: minimum grain, at a cost of one to two stops of exposure, with the bath run seven degrees warmer to keep the time the same. That is PERCEPTOL’s own trade — extra fine grain, rate the film down — stated as three quantities and a temperature. If what you want is the result this product is sold for, and you want it published, D-25 is the formula; if what you want is to see what the two disclosed substances do on their own, D-23 is. Mixing both and comparing them is one afternoon, and Part VIII’s D-23 and D-76 mixing lesson is where the technique is taught.

And one more, for the reader who wants the solvent named rather than inferred. DK-20 puts a thiocyanate silver solvent into a metol–sulfite bath and publishes how much of it there is. PERCEPTOL’s fine grain is attributed on this page to solvent action as a marked inference; DK-20 lets you test the mechanism against a formula where the solvent is a printed quantity rather than a reading.

Safety

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

The two bags are classified separately, and only one is classified at all. Part A is Acute Tox. 4, Skin Sens. 1, STOT RE 2, Aquatic Acute 1 and Aquatic Chronic 1, signal word Warning, pictograms GHS08, GHS07 and GHS09, statements H302, H317, H373 and H410. Part B is not classified as dangerous for supply/use — no pictogram, no signal word, no hazard statement, one precautionary statement, P102.

Why B and not A. Two Level B criteria are met outright by part A alone: a fine powder that must not be inhaled, and a sensitiser handled at high concentration — 50 to 65 per cent of the bag you are tipping into a jug. The dry powder is the whole of the hazard; the diluted working solution is a different exposure.

Why B and not C. Level C’s reagent criterion covers sensitisers and toxins “where a fume cupboard or specialist disposal is the recognised control”. HARMAN’s own recognised controls, in section 8 of part A’s sheet, are ventilation or local exhaust ventilation, a washing facility for eye and skin cleaning, eye protection to EN ISO 16321-1, impervious gloves to EN 374 and a dust mask or respirator with filter type P where appropriate — not a fume cupboard. Part B’s sheet asks only for adequate ventilation and eye protection, and records skin protection as not normally required.

⚠The sensitiser, and why the signal word is the least important thing on the label

Part A’s label says Warning, not Danger. That is a lower signal word than either MICROPHEN bag carries, and it is the wrong thing to steer by.

H317, may cause an allergic skin reaction, is the statement that matters, and metol is the classical cause of darkroom dermatitis — the reason the metol page exists in the form it does. Sensitisation is a threshold event and it is permanent: once you are sensitised, quantities that never troubled you before will bring on the rash, and no amount of care afterwards undoes it. The dose that sensitises is delivered by dust and by casual skin contact during mixing, not by a tank of working developer.

H373, may cause damage to organs through prolonged or repeated exposure, is on this label and is not on MICROPHEN’s part A. It is a repeated-exposure statement, which is exactly what a darkroom that mixes a litre a fortnight for years supplies.

So: impervious gloves to EN 374 with the breakthrough time taken from the glove maker rather than assumed — glove selection is where that goes — eye protection with side protection, and a type P dust mask or respirator for the tipping step. Wash hands and exposed skin thoroughly afterwards. Do not brush spilt powder; wipe it damp or vacuum it.

No occupational exposure limit exists to hold you to. Both sheets say plainly that none is assigned, and the metol page records that metol is absent from the HSE’s EH40 list altogether. Absence from a limit list is not a safety statement; it means nobody has set a number, and the control is the one in HARMAN’s section 8, not a concentration you can measure.

Ventilation and eyewash. Part A’s sheet asks for use with ventilation, local exhaust ventilation or breathing protection, and for a washing facility for eye and skin cleaning to be present. A darkroom with an extractor running and an eyewash bottle within reach meets that; a sealed bathroom does not. Eyewash use is the procedure. Note that part A is not classified for eye damage — unlike MICROPHEN’s part A, which is Eye Dam. 1 — so a splash here is not the medical emergency that one is; it is still a splash of a sensitiser.

Mix the powder the way the powder deserves. Tip low and slowly into the water, never water onto powder; do not dry-mix the two bags together; keep the jug below your face; and store the carton locked up, which is part A’s own P405 and matters in a house with children or pets. Weighing a solid, mixing a developer and PPE donning and removal are the procedures, and the last is the one people skip.

One line on the technical sheet to disagree with. ILFORD opens its mixing instructions with “Photographic chemicals are not hazardous when used correctly”, and then immediately recommends gloves, eye protection and an apron and points the reader at the safety data sheets — so the intent is clear enough. But the same company’s sheet classifies part A as a skin sensitiser with a repeated-exposure organ-toxicity warning and tells you to store it locked up. The classification is the fact. “Used correctly” is doing all the work in that sentence, and the safety data sheets are where it is defined.

Storage

The unopened packets, in their carton, cool and dry at 4 to 20 °C, keep indefinitely — and once a packet is opened ILFORD says to prepare the stock solution immediately. Both safety data sheets record the storage life as stable under normal conditions at ambient temperature, and part A adds store locked up.

The stock solution, in a full capped container: six months. In a half-full tightly capped container: one month — the loss is oxygen in the air above the liquid, which is why a bottle you decant into as you use it beats a bottle that empties. In a deep tank with a floating lid: four months; without one, one month.

The 1+1 and 1+3 dilutions: 24 hours, and ILFORD says to prepare them directly before they are needed and to stir them thoroughly. There is no case for keeping them.

And the planning consequence, which is particular to this product. One carton makes one litre; fractional packs are forbidden; a reused litre does four films; a diluted litre is one-shot. So the storage question here is not “how long will it keep” but “how will I use a litre before it is a month old”, and the honest answers are four films in a fortnight, or one-shot dilutions from a full bottle you keep capped. Stock check and labelling a container are the procedures; date the bottle on the day you mix it and put the film tally on the same label.

Incompatibilities

There is no EUH031 on this label, and that is a fact about the label rather than a licence. MICROPHEN’s part A carries “contact with acids liberates toxic gas” because it discloses a metabisulphite; PERCEPTOL’s does not disclose one and carries no such statement. That is not a finding that acid may safely meet this developer. Nothing published says what else is in the bags, sulphite solutions themselves evolve sulfur dioxide with acid, and the general rule stands: the incompatibilities page governs, and stop bath never goes into a developer bottle, a funnel or a graduate that has not been washed. Part X’s account of why stopping works is the process reason for keeping them apart.

Fixer, and the contamination runs both ways. Thiosulfate finding its way back into the developer dissolves halide and fogs — a particular waste on a bath already chosen for its solvent action — while developer carried forward shortens the fixer’s life and stains. Part XI’s account of how a fixer works is the process side. It is a waste problem as well: a fixer bottle with developer in it is no longer a bottle a refiner wants.

Strong oxidisers, and dry powder makes it worse. A bleach or a persulfate reaching a bottle of developer is one problem; reaching an open bag of a metol salt is a larger one, because a solid oxidiser meeting a solid reducing agent has no solvent to carry the heat away. Keep the cartons on a different shelf from anything that bleaches.

Air, during agitation. ILFORD’s own instruction for gas-burst agitation is that nitrogen must be used for the developer and air only for the stop bath, fixer and wash. That is the sulphite-preservation argument stated as an equipment rule, and with a bath that keeps six months in a full bottle and one in a half-full one it is not a small point.

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

Section 10.5 of both PERCEPTOL sheets gives incompatible materials as “Not known”, and section 7.2 of both gives them as “None known”. Read literally, that says a bag of metol salt and a bag of sulphite have no chemical incompatibilities at all.

A safety data sheet answers a narrow question — what makes this product itself unstable in its container — and it does not answer it about the tank sequence the product will be used in. Part A’s own section 5.2 already contradicts the spirit of it: the material “may decompose in a fire, giving off toxic and irritant vapours”. The course’s incompatibilities page governs here, and section-10 boilerplate is not evidence of safety.

Waste

Bottled separately, and never mixed into the fixer. Spent PERCEPTOL is weakly alkaline, carries the oxidation products of a developing agent, and carries whatever silver the film released as halide rather than as recoverable metal.

The two bags’ waste classifications are as different as their labels. Part A is Aquatic Acute 1 and Aquatic Chronic 1, H410 — very toxic to aquatic life with long lasting effects, and its sheet directs disposal in accordance with local, state or national legislation, to a licensed recycler, reclaimer or incinerator, or to a hazardous or special waste collection point; its section 6 adds that spillages or uncontrolled discharges into watercourses must be alerted to the appropriate regulatory body. Part B’s sheet records low toxicity to invertebrates, fish and algae, says “dispose at suitable refuse site” and adds that no special precautions are required.

The litre in your bottle is both bags, so part A’s classification is the one that governs it. A reader who filed only the part B sheet would reach the opposite conclusion, and this is the clearest practical reason to read both sheets for a two-part product.

What ILFORD tells United Kingdom domestic users on its own health and safety page: local authorities generally accept small quantities of chemical waste at Household Waste and Recycling Centres, usually in a “chemical cupboard”; chemicals should be bottled separately and appropriately labelled; and a few authorities collect on request. The same page says that where no such route exists, small amounts may be flushed away with plenty of water, that chemicals must not be mixed for disposal, and that septic tanks should be avoided. That concession is ILFORD’s and not this course’s, and it is written for the United Kingdom.

Local regulation decides, and the disposal caveat says why this course cannot decide for you. The general chemical waste SOP is the procedure followed here, and Part XII’s waste-stream lesson is where the reason for keeping two labelled bottles rather than one becomes obvious — spent fixer has a silver value and spent developer has none, and pouring them together destroys the first.

And the empty packets. Part A’s held a sensitiser at better than half its mass. Do not reuse them for anything, and do not shake them out over a bin.

Troubleshooting

Thin, flat negatives from a bottle that has done a few films. Almost always the tally rather than the developer, and with a four-film capacity the margin is much narrower than with ID-11. Four films to the litre is the published figure and 10 per cent per film is the compensation; ILFORD marks the fifth film NR, so a fifth negative is outside what the maker will stand behind at any time. See thin negative, flat negative and exhausted developer, and put a tally mark on the bottle before the film goes in the tank.

Under-exposed-looking negatives at box speed on a fast film. Check what meter setting you used against what ILFORD publishes. There is no PERCEPTOL time at EI 400 for HP5 Plus, DELTA 400 or Kentmere PAN 400 anywhere in HARMAN’s literature; the published stock settings are EI 250 and EI 200. If you shot at 400 and developed at the EI 250 time, you have under-exposed by two thirds of a stop in a developer that was already asking you to over-expose. Empty shadows and cut-off toe are where that is diagnosed properly.

Times that seem impossibly long. They are long: PAN F Plus at box speed is fourteen minutes at stock, DELTA 100 at 1+3 is twenty-two. Before you shorten one, check the temperature — ILFORD’s rule is 10 per cent per degree, so a bath at 22 °C wants 20 per cent off, and a bath you thought was at 20 °C and was actually at 18 wants 20 per cent on.

Grain no finer than you got in ID-11. Two checks before blaming the bath. Did you actually rate the film down, or did you use the box-speed time from the same column? And what are you comparing against — HARMAN’s claim is against “a standard fine grain developer”, which is a modest baseline, and the difference on a slow film enlarged to 8 × 10 may be genuinely invisible. Part XIII’s step wedge series plus a loupe on the negative is a better test than a print.

Uneven development, streaks and mottle. Long times are the forgiving direction, but twenty-two minutes is a long time to keep agitation honest, and 1+3 in a small tank is a thin solution doing a lot of work. Mottled development, surge marks and bromide drag are the three patterns and they are told apart by where they appear.

The stock has gone yellow or brown in the bottle. Oxidation, which oxidised developer covers. A half-full bottle past its one-month life should be treated as suspect and tested against a control strip before a film you care about goes in it — control strip processing and charting is how.

Powder that will not all dissolve. ILFORD says explicitly that it is normal for a few grains to remain undissolved and that darker particles in the white powder are normal. A large undissolved residue is different, and points at water that was too cold, part B added before part A had dissolved, or a packet that had been open. Stock crystallised in cold storage is the related fault and its test.

Negatives that do not match last month’s. Check, in order: the dilution — nine minutes at stock is seventeen at 1+3 on the same film, and a misread dilution ratio is the commonest cause; the film count on the bottle; the temperature; the date the stock was mixed; and which ILFORD document you took the time from — which matters on ORTHO PLUS, where one HARMAN sheet gives this developer a time and another leaves the column blank.

A whole film blank, or nearly so. Whatever caused that, a slow fine-grain developer did not: even four times over-used, this bath produces a thin negative and not an empty one. Part IX’s fault diagnosis is the sequence that separates a chemistry failure from a camera, a loading or a shutter failure before the bottle gets blamed.

Experiments

Measure the pH of a fresh litre of stock and compare it with ILFORD’s band. The cheapest possible calibration of your meter, your water and your mixing, and the one ILFORD explicitly asks for. Calibrate the meter the same day — the calibration procedure is the whole experiment’s validity — and record the figure. Every later measurement is compared against your own first one, not against 7.68 to 7.82.

Check the specific-gravity table with a hydrometer. Measure stock, 1+1 and 1+3. The prediction is that the density excess over water halves and then quarters: from 1.110 you should read about 1.055 and about 1.028, and ILFORD prints 1.058 and 1.028. If your stock reads well away from 1.110 you have found a mixing error before you have found it on a negative.

Measure the speed loss HARMAN will not state. This is the experiment this page exists to provoke. Shoot one roll of a film ILFORD publishes two PERCEPTOL settings for — DELTA 100 or FP4 Plus — with a step wedge in the corner of every frame, bracketing the same subject at EI 25, 50, 100 and 200. Develop the whole roll at the published time for the middle setting and plot the four curves. Part XIII’s step wedge series sets the exposures up and curve plotting is the sheet to record them on. Where the toe lands tells you what the developer costs on your film, which is the only number that matters and the only one nobody has published.

The comparison this whole page is about: PERCEPTOL against D-23 you mixed yourself. One film, one subject, a step wedge in every frame. Develop half the roll in PERCEPTOL stock at ILFORD’s time for your meter setting and half in D-23 at Kodak’s, at 20 °C, with the same agitation. Plot both, and look at grain under a loupe as well as at the curves. The two developers disclose the same two substances and their makers claim opposite things about film speed; the prediction from that is that the curves will not superimpose, and finding out how they differ is worth more than any reconstruction.

Then add D-25 and see what the acid salt buys. D-25 is D-23 with 15 g of sodium bisulfite, and Kodak states the price in stops. Run all three baths on matched films and you have measured, on your own materials, the trade PERCEPTOL is sold on. Part IX’s experimental design page is how to run that without fooling yourself.

Test the four-film ladder instead of trusting it. Take a litre of stock and put six films through it one at a time, each with an identical step wedge exposure, applying ILFORD’s 10 per cent per film and continuing past the NR into films five and six. If the compensation holds, the first four wedges match; where they start to drift is your capacity, and whether films five and six are usable is a question HARMAN has declined to answer.

Settle the dilution puzzle. ILFORD publishes HP5 Plus at EI 250 in stock and at EI 320 in 1+1 and 1+3. Shoot one roll at EI 320, cut it in three in the dark, and develop the pieces at the stock time, the 1+1 time and the 1+3 time. Either the diluted pieces really do hold the higher setting — in which case you have learned something the sheet implies and never explains — or they do not, and you have learned that too.

Run the sulphite series on a formula you can weigh. PERCEPTOL’s fine grain is attributed on this page to solvent action as a marked inference. Test the mechanism where the quantity is printed: mix D-23 at 50, 100 and 150 g of sodium sulfite per litre, develop matched films, and compare grain, speed and time. Part IX’s solvent series is the session, and it is the honest way to reason about a bath whose sulphite loading nobody outside Mobberley knows.

Write the bought bath down as carefully as a mixed one. A carton earns its line in the formula version record exactly as a weighed formula does: the date the stock was made, the dilution, the meter setting, which film in the sequence of four this was, and which ILFORD document supplied the time. With no composition to record, those five entries are the entire history of the bath — and they are enough to account for nearly every result you will get from it.