ILFORD HYPAM

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 bisulfitenamed on the sheet as sodium hydrogensulphite … % sodium bisulphite … %CAS 7631-90-5	<5	H302
Boric acidCAS 10043-35-3	2.6022	H360FD
Acetic acid (glacial)named on the sheet as acetic acid … %CAS 64-19-7	1.4475	H226, H314

Not disclosed. HARMAN publishes no composition for HYPAM. One sentence of the technical sheet names the fixing agent as ammonium thiosulphate and rules out sodium thiosulphate, and that is the whole of the composition stated outside the hazard paperwork — and, uniquely among the ILFORD products this course has read, the hazard paperwork does not repeat it. The safety data sheet's composition table names three components, none of them the fixing agent, because the table lists what drives a classification and an unclassified substance earns no line. It gives sodium bisulphite a band, and gives boric acid and acetic acid single figures to four decimal places, which are outputs of a classification calculation and not an assay; section 11 records that every toxicological endpoint on the sheet was reached by calculation from them. This page will not add those three figures up and call the remaining ninety-six per cent a discovery. What is published nowhere in ILFORD's literature is the thiosulphate concentration of the concentrate or of either working dilution, the molarity of anything, what the boric acid is there to do, whether it is the reason this product tolerates a hardener and its twin does not, whether any sulphite is present beyond the bisulphite the sheet names, what accounts for the ten points of specific gravity by which HYPAM exceeds RAPID FIXER at the same dilution, and any statement that the product described by the 2017 technical sheet is the product described by the 2024 safety data sheet. A reader who wants to know how many moles of thiosulphate are in the tank, or to move that number and watch the fixing time and the capacity move with it, has to mix an open formula rather than buy this one.

Nearest open formula. Kodak F-5 — F-5 is the open formula that publishes, with quantities, the acid system HYPAM's hazard sheet only names: 17 mL of glacial acetic acid and 7.5 g of boric acid in a litre, alongside 240 g of hypo, 15 g of sulphite and 15 g of potassium alum. Two of the three substances HARMAN discloses for HYPAM are two of the five Kodak prints for F-5, and they are the two doing the same job in both — an acid, and a very weak acid in quantity behind it as reserve. The two baths then part on everything else. F-5 is a sodium bath and slow, ten minutes on a fresh tray; HYPAM is an ammonium bath and fixes film in two to five. F-5 carries its hardener inside the formula, so it is a hardening fixer whether you want one or not; HYPAM is sold non-hardening and becomes a hardening fixer only if you add a third party's hardener to the diluted bath, which is the one thing its twin RAPID FIXER is forbidden to do. And the halves of the page are swapped, as they always are between a formula and a product: Kodak prints five quantities and one fixing time, ILFORD prints eleven fixing times, four capacities, two specific gravities, four replenishment rates and no quantities at all. A reader who wants a hardening fixer whose contents are known mixes F-5; a reader who wants one whose behaviour is documented buys HYPAM and a hardener, and accepts that the label is the composition.

Purpose

HYPAM is a non-hardening acid rapid fixer, sold as a liquid concentrate in five-litre bottles, for black-and-white film and paper. Its fixing agent is ammonium thiosulphate, and ILFORD states that it contains no sodium thiosulphate. It dissolves the undeveloped silver halide out of an emulsion in two to five minutes on film and half a minute on a resin-coated print, and it works over a temperature range — 18 to 40 °C — wide enough to cover a hand-processed tank in a cold room and a roller-transport machine running hot.

It is also, and this is the whole reason it exists as a separate product, the ILFORD fixer you are allowed to harden. Its twin, RAPID FIXER, carries a flat prohibition: it “must not be used with fix hardeners”. HYPAM’s sheet says the opposite in its second paragraph — a fixer hardener can be used to turn working-strength HYPAM into a hardening fixer for films — and then spends most of a page explaining why you probably should not.

!Two products, one sentence of difference

Everything ILFORD publishes about these two fixers agrees, number for number, with one exception each in the technical and the hazard literature. In the technical sheets the exception is the hardener rule, which is reversed, and the specific gravity, which is ten points higher for HYPAM at both dilutions. In the safety data sheets — issued on the same day, by the same company, through the same compiler — the exception is a single extra line of boric acid, and that line takes HYPAM from not classified as dangerous to Danger, GHS08, may damage fertility, may damage the unborn child.

Whether those two exceptions are the same fact seen twice is exactly what HARMAN does not say, and what is not disclosed is where this page stops guessing.

Recommended uses

Film, at 1+4, always. ILFORD publishes one dilution for film and no other. Two to five minutes at 20 °C in a fresh bath, agitated as for development: four inversions in the first ten seconds, repeated in the first ten seconds of each subsequent minute. The film sheets — DELTA 100 PROFESSIONAL among them — print “ILFORD RAPID or HYPAM fixers” as a single line with a single set of numbers, which is the maker’s own statement that the two are interchangeable on film when neither is hardened.

Paper, at 1+4 or 1+9, by hand; 1+4 in a machine. Half a minute for resin-coated at 1+4, one minute at 1+9; one minute for fibre-based at 1+4, two minutes at 1+9. The 1+9 dilution buys nothing in capacity — ILFORD’s table gives both dilutions the same eighty resin-coated or forty fibre-based sheets per litre — so it buys only concentrate, at the price of double the time.

Specialist, X-ray and graphic arts materials, at 1+4. Two to five minutes, one square metre per litre, and a referral to those manufacturers for anything more.

The case where HYPAM is the right choice and RAPID FIXER is not. ILFORD names four, and they are the only circumstances in which it still recommends a hardener at all: a film process running above 30 °C; poor drying performance; a need for shorter drying times; and a risk of physical damage, the example given being a roller-transport processor. Outside those four, the sheet’s own advice is that modern camera films are sufficiently hardened at manufacture and a hardener buys nothing.

And a fifth, which the sheet does not name. ILFORD no longer makes a fix hardener. If you have one — an old bottle, or another manufacturer’s — HYPAM is the only current ILFORD fixer whose own sheet permits it, because the twin’s sheet forbids it.

When another formula is preferable

When you are not going to harden anything, RAPID FIXER is the same bath without the classification. This is the most useful sentence on the page for most readers. The two products fix film in the same time, take the same dilutions, have the same capacities, keep for the same periods and cost roughly the same. But RAPID FIXER’s safety data sheet classifies it as not dangerous for supply or use — no pictogram, no signal word, no hazard statement — while HYPAM’s classifies it Repr. 1B, with the health-hazard pictogram, the signal word Danger, and an instruction to store it locked up. If hardening is not on your list, the twin does the identical job and brings a reproductive toxicant into the darkroom that this one does.

When you want a hardening fixer whose contents you know, mix Kodak F-5. It is the nearest open formula and the comparison runs below. F-6 is the same bath with sodium metaborate in place of the boric acid and far more acetic acid, made for a darkroom that objects to the smell rather than to the boron.

When you want an acid fixer with no boron and no alum at all, mix Kodak F-24. Hypo, sulphite and bisulphite in a litre: non-hardening by design, entirely published, and the comparison the twin’s page runs at length. It is slow, because it is a sodium bath, and it carries no published fixing time.

When permanence matters more than speed, consider an alkaline bath. TF-2 washes out of fibre-based paper faster than any acid bath because there is no acid to neutralise and no bisulphite to leave behind. HYPAM’s own sheet asks for sixty minutes of running water for fibre-based paper without a washing aid, and ten to twenty minutes for film if you have hardened it.

When the material is a printing-out image, none of these. A silver image formed by light rather than development is finely divided enough for an acid bath to attack it, and the plain hypo bath exists for exactly that case.

And when you are fixing paper, do not use a hardener at all. ILFORD says so twice on the same sheet: a hardener “is not recommended” for paper processing, and then, flatly, “Do not use a fix hardener when processing ILFORD photographic papers.”

What the maker publishes

A great deal — more than for any other fixer in this library, and more than for its own twin, because the hardened bath needs a second column everywhere the unhardened one needs a first.

The dilutions and what each is for. 1+4 for all film, and for paper in a machine; 1+4 or 1+9 for paper by hand. A hardener, where used, goes into the diluted bath, and the sheet’s instruction is absolute: never mix hardener with concentrated fixer.

How to mix it. Fixer concentrates “do not readily mix with water”, so the sheet tells you to measure both accurately, pour the concentrate into the vessel and add the water gradually, while stirring — the reverse of the usual advice, and the reason is that a fixer concentrate left in a layer at the bottom of a tank is a bath that is simultaneously too strong and too weak. A processor filled with fresh solution should be brought to temperature and left recirculating for at least ten minutes before anything is put through it.

pH and specific gravity, for both dilutions, at 20 °C.

Dilution	pH	SG at 20 °C
1+4	5.0–5.5	1.080–1.090
1+9	5.0–5.5	1.040–1.050

The sheet tells you what to measure them with: pH sticks covering pH 4 to 6 where a meter is not available, and a hydrometer covering 1.000 to 1.200. HARMAN’s own process-control primer works the figure into a weight, so that a reader can check it on a kitchen scale: since a litre of water weighs 1000 g, a litre of HYPAM at 1+4 with an SG of 1.08 to 1.09 weighs 1080 to 1090 g.

🧮The ten points that separate the twins

RAPID FIXER at 1+4 is SG 1.070–1.080. HYPAM at 1+4 is 1.080–1.090. At 1+9 the gap is the same ten points: 1.030–1.040 against 1.040–1.050.

At a fixed dilution, specific gravity tracks dissolved solids. So at the same 1+4, a litre of HYPAM carries roughly ten grams more dissolved material than a litre of RAPID FIXER — and the boric acid the hazard sheet discloses, at 2.6 % of a concentrate that is a fifth of the working bath, is worth only about five of them.

That arithmetic is a check, not a discovery. It says the difference between the two products is not only the boric acid; it does not say what else it is. ILFORD publishes neither concentrate’s composition, and the pH window the two share is identical, so whatever the extra solids are, they are not moving the pH. This page states the gap and stops.

Fixing times, in two columns. This is the table RAPID FIXER’s sheet cannot print.

Material	Dilution	Without hardener	With hardener
General purpose film	1+4	2–5 min	4–10 min
Specialist, X-ray, graphic arts	1+4	2–5 min	4–10 min
RC paper	1+4	½ min	n/a
RC paper	1+9	1 min	n/a
FB paper	1+4	1 min	n/a
FB paper	1+9	2 min	n/a

Every paper row reads n/a in the hardened column, because ILFORD does not recommend a hardener for paper. The film rows roughly double. And the wash time doubles with them: 5 to 10 minutes for an unhardened film, 10 to 20 minutes for a hardened one.

Washing, by material. Film, 5 to 10 minutes in running water within 5 °C of the process temperature; or the fill-and-invert method — fill, invert five times, drain; refill, invert ten, drain; refill, invert twenty, drain — which ILFORD says is faster, uses less water and still gives negatives suitable for long-term storage. Resin-coated paper, 2 minutes running, or 30 seconds vigorously when speed matters more. Fibre-based paper, 60 minutes, or the WASHAID sequence: five minutes of washing, ten minutes in 1+4 ILFORD WASHAID at 18–24 °C, five minutes of washing. WASHAID is itself a bought product; the open formulas that do the same job are the one per cent sodium sulfite washing aid and Kodak’s Hypo Clearing Agent, whose page has the chemistry of why a sulphite rinse shortens a wash at all.

!The fill-and-invert wash is only validated for the unhardened bath

ILFORD’s minimum-water washing sheet states that the method is validated for ILFORD films, papers and non-hardening fixers, and that hardening fixers “can significantly increase the required wash time”. Harden a film in HYPAM and the short wash is off the table, along with the sheet’s own 5-to-10 minutes: you are on 10 to 20, in running water.

Capacity, per litre of working solution, unreplenished. 24 films of 135-36 at 1+4; one square metre of specialist material; 80 resin-coated or 40 fibre-based sheets of 8 × 10 inches, the same at either dilution. The paper figures “may be exceeded whenever print stability is not critically important”, which is the only capacity figure in ILFORD’s chemical literature that arrives with permission to ignore it.

Replenishment, four rates and a method. 45 mL of working-strength fixer per 135-36 film, or 855 mL/m²; 250 mL/m² for resin-coated paper, 500 mL/m² for fibre-based; a machine range of 300 to 450 mL/m² for resin-coated; and a reduction of 50 to 75 per cent where a silver recovery system is properly set up. For a deep tank the sheet gives a procedure rather than a rate: calculate the replenisher needed, remove more than that volume of used fixer, add the replenisher, and top the tank back up with some of the fixer you removed, stirring throughout.

Two-bath fixing, which the sheet calls “an extremely efficient method”: two baths of equal volume, half the time in each, and when the first reaches capacity you discard it, promote the second, and mix a fresh second. The material is then always finished in relatively fresh fixer.

A whole page of process control. The ILFOSTOP table, reproduced inside the fixer’s own sheet, with 1+19, 18–24 °C, ten seconds at 20 °C, and capacities for ILFOSTOP and ILFOSTOP PRO side by side (15 against 22 films per litre; 60 against 90 resin-coated sheets; 30 against 45 fibre-based). How to bring a drifted bath back: a few drops of 50 per cent acetic acid, gradually and with stirring, if the pH has risen — and “do not lower the pH of the fixer bath too far”. How to correct specific gravity in both directions: fresh concentrate, thoroughly stirred, if the bath is too dilute; water, if a high-temperature processor has evaporated it up.

The clearing-time test, and the rule that governs it. Fix for twice the clearing time, and discard the bath when the clearing time in used fixer exceeds twice the clearing time in fresh. The method is on the sheet and runs in room light.

Three silver limits and a chemical test to check them. 8 to 10 g/L in a film bath; below 2 g/L for commercially permanent fibre-based prints; not above 0.5 g/L for prints needing maximum long-term stability; and 4 to 6 g/L for resin-coated paper, whose base “is protected on both sides by an impervious polythene coating”. The test is 2 g of sodium sulphide in 125 mL of water, diluted 1+9 — which is, ingredient for ingredient, Kodak’s ST-1.

Silver recovery, and its failure mode. Electrolytic recovery is recommended for maximum efficiency, with the warning that too much current through a solution whose silver has already fallen low will break down the fixer’s active ingredients, plate silver sulphide onto the cathode (“sulphiding”) and, if vigorous, release hydrogen sulphide. Around 50 to 100 ppm is commonly achievable; secondary and tertiary ion-exchange and metal-exchange units take an overflow to around 3 ppm.

Keeping, seven figures. Concentrate: two years full and unopened at 5–20 °C, six months once opened. Working strength: six months in a full tightly capped bottle, two months in a tank or tray with a floating lid, one month in a half-full capped bottle, seven days in an open tray. A properly replenished tank: a very long life, but replace it after twelve months.

And the arithmetic of a bottle. Five litres at 1+4 makes 25 litres, and 25 × 24, 25 × 80 and 25 × 40 give exactly the 600 films, 2000 resin-coated prints and 1000 fibre-based prints the availability paragraph claims. The sheet checks out against itself.

What is not disclosed

The composition, entirely — and on this product the hazard sheet withholds more than its twin’s does.

The technical sheet’s one compositional sentence is that the fixing agent is ammonium thiosulphate and that the product contains no sodium thiosulphate. That is the whole of it across seven pages.

The safety data sheet names three substances. None of them is the fixing agent. Ammonium thiosulphate does not appear anywhere on HYPAM’s sheet — not in the composition table, not in the exposure limits, not in section 15 — because a hazard document lists what drives a classification, and ammonium thiosulphate drives nothing. Its twin’s sheet, issued the same day, does list it, at 35–50 %, marked Not classified. One compiler, one company, one date, and two different answers to the question of whether to name a substance that carries no hazard.

⁇What that asymmetry does and does not license

It tells you something real about safety data sheets: the composition table is discretionary below the classification threshold. A substance can be half the bottle and absent from the sheet.

It tells you nothing about HYPAM. The absence of ammonium thiosulphate from this sheet is not evidence that HYPAM contains less of it than RAPID FIXER, or more, or the same. The technical sheet says the fixing agent is ammonium thiosulphate; the hazard sheet declines to mention it; neither states a quantity, and the difference between the two documents is an editorial one.

What no ILFORD document states, anywhere:

• the thiosulphate concentration of the concentrate, or of either working dilution, or the molarity of anything at all;
• what the boric acid is for. It is disclosed, at 2.6022 %, with a CAS number and a hazard class, and with no function whatever;
• whether the boric acid is the reason this product tolerates a hardener and its twin does not;
• what accounts for the ten points of specific gravity by which HYPAM exceeds RAPID FIXER at the same dilution;
• whether any sulphite is present beyond the bisulphite the sheet names;
• whether there is a sequestrant, an anti-sludging agent or anything else that carries no hazard and therefore earns no line;
• and whether the product described by the 2017 technical sheet is the product described by the 2024 safety data sheet. Seven years separate them and neither mentions the other.

The two figures printed to four decimal places are not an assay. Boric acid at 2.6022 and acetic acid at 1.4475 look like measurements and are not. They are the inputs a classification calculator was given, printed at whatever precision it carries internally; section 11 records that every toxicological endpoint on the sheet was reached by calculation method from exactly these numbers, including the acute toxicity estimate of 12930.25. A number to four decimal places in a hazard document is a spreadsheet’s precision, not a chemist’s.

And this page will not sum them. 2.6022 plus 1.4475 plus something under 5 leaves something over ninety per cent unaccounted for, and naming what fills it — however obvious the answer feels — would be reconstructing a formulation from a hazard document. That is the one thing this page kind exists to refuse.

Disclosed components

Three, in the order the safety data sheet prints them, each with the concentration the sheet states against it and not a quantity anybody measured.

Sodium bisulphite, CAS 7631-90-5, EC 231-548-0, <5. The sheet does not name it that way. It prints “sodium hydrogensulphite … % sodium bisulphite … %”, and the ellipses are not a redaction: that is the CLP Annex VI entry name for a solution of unstated strength, carried verbatim into the composition table, and the same name appears again in section 15.1 under the UK REACH Annex XVII restrictions line. The course’s encyclopaedia calls it sodium bisulfite and the sheet’s hazard line is Acute Tox. 4, H302, pictogram GHS07; EH40/2005 gives sodium hydrogen sulphite a long-term workplace limit of 5 mg/m³, which section 8.1.1 reproduces. Its function in an acid fixing bath is not in doubt and is not peculiar to this product: bisulphite supplies both the sulphite and the acid a fixing bath needs. The sulphite half keeps thiosulphate from being thrown out as sulphur when it meets acid; the acid half is part of what makes the bath an acid bath. F-24’s page traces that dual role to Kodak’s 1928 handbook and is built around it. What HARMAN does not say is how much of each job this <5 is doing.

Note the band itself: <5, where the twin’s sheet prints 1-5% for the same substance under the same name. Whether HYPAM contains less bisulphite, or the same amount described more loosely, the sheets do not settle.

Boric acid, CAS 10043-35-3, EC 233-139-2, 2.6022. This is the line that makes HYPAM a different product from its twin in every respect that matters to a person rather than to a negative, and it is worth being precise about what it is and is not.

What it is. Boric acid is a very weak acid — pK_a 9.27 — which in a fixing bath means acid reserve without acid strength: almost all of its hydrogen is still on the molecule, available to replace hydrogen ions as carried-over developer consumes them, without ever making the bath acid enough to throw sulphur out of the thiosulphate. That is precisely the role Kodak’s F-5 gives it, at 7.5 g in a litre, and it is why F-5 keeps for a month in a tank. Its encyclopaedia page has the chemistry and the history.

What it does to the label. Boric acid is classified Repr. 1B, H360FD — may damage fertility, may damage the unborn child — and it is on the UK REACH Candidate List of Substances of Very High Concern, which section 15.1 of this sheet records by name. At 2.6022 % it carries the entire mixture into that classification. Everything alarming on HYPAM’s label — the GHS08 pictogram, the signal word Danger, H360FD, “store locked up”, “obtain special instructions before use” — comes from this one component. The bisulphite and the acetic acid, which sound worse, contribute nothing to the mixture’s classification at these levels.

What HARMAN says it is for. Nothing. The composition table has a function column for no component, and the technical sheet does not mention boron at all.

Acetic acid, CAS 64-19-7, EC 200-580-7, 1.4475. Printed as “acetic acid … %”, the same Annex VI naming convention, and it carries the harshest-looking hazard line on the sheet — Flam. Liq. 3 with H226, Skin Corr. 1A with H314, pictograms GHS02 and GHS05 — while contributing nothing to the mixture’s own classification, because it is far below the threshold at which a corrosive substance makes a mixture corrosive. That gap is the subject of the GHS and CLP page. Its encyclopaedia page has the properties; the International Chemical Safety Card records that a solution in water is a weak acid and that the substance attacks many metals, forming flammable hydrogen. EH40/2005 gives it 10 ppm long-term and 20 ppm short-term, both reproduced in section 8.1.1.

It is also the same acid ILFORD tells you to add, at 50 per cent, to a bath whose pH has drifted upward — a rare case of a maker naming, in its own technical sheet, a substance it also lists on its hazard sheet. What the acetic acid is doing in the bottle, HARMAN does not say, and neither will this page beyond the obvious. It is an acid in an acid fixer. Whether it sets the pH, buffers it with the bisulphite and the borate, or is a residue of manufacture is not stated.

And what is not in this table. The fixing agent, for one — the substance the technical sheet names in its first paragraph is absent from the hazard sheet altogether. Beyond that, commercial rapid fixers are often sold with a sequestrant or an anti-sludging agent. Nothing of the kind appears here, and the absence proves nothing either way, because the table lists what drives a classification. The one thing established about this formulation beyond the three names is negative and comes from the technical sheet: it contains no sodium thiosulphate, and as supplied it hardens nothing.

Behaviour

It is fast, and the speed is the ammonium ion. Two to five minutes for film at 1+4, thirty seconds for a resin-coated print. The previous lesson in Part XI makes the comparison with a sodium bath and is candid that no open source this course holds explains the mechanism.

It is tolerant of temperature. 18 to 40 °C is a range wide enough that most darkrooms never leave it, and the sheet notes that machine paper baths habitually run at 25 to 40 °C, where fixing times fall below the published minima without causing trouble. The one constraint is relative, not absolute: keep all process solutions within 5 °C of the developer.

It exhausts three ways at once, and the sheet says so plainly: silver and halide build up, solutions carried over from the preceding bath dilute it, and the same carry-over raises the pH. Those are three different failures with three different symptoms and one shared remedy — a stop bath, which is why ILFORD prints the whole ILFOSTOP table inside a fixer’s technical sheet.

Its exhaustion is measurable at the bench, and the measurement is the same one that sets the fixing time. Clearing time doubles as the bath ages; fix for twice it; discard at twice the fresh figure. Everything a reader needs is on the sheet, and Part XI’s clearing-time and capacity experiment runs it.

Hardened, it becomes a slower and thirstier bath. Fixing goes from 2–5 minutes to 4–10; washing from 5–10 minutes to 10–20; and the short fill-and-invert wash is no longer validated. The hardener buys mechanical toughness and a faster dry, and it costs process time at both ends.

It keeps better in a bottle than in a tray, by a factor of about twenty-five. Six months full and capped; seven days in an open tray. Air is the variable, and a floating lid recovers most of the difference.

Image characteristics

A fixer makes no image, and a correctly used one leaves no trace of itself. There is no tonality, no colour and no grain to attribute to this product. What it decides is what remains: silver halide gone or not gone, thiosulphate washed out or not washed out, gelatin hardened or not hardened.

Underfixing shows up years later, not on the day. Residual silver halide prints as a slow overall stain and a loss of highlight separation. ILFORD’s silver limits are pitched at that timescale, which is why the strictest of them — 0.5 g/L, about ten 8 × 10 fibre-based prints in a litre — is eighty times tighter than the film figure.

Overfixing shows up on paper. A thiosulphate bath left long enough begins to attack the image silver, and finely divided print silver goes first. ILFORD’s paper times are half a minute to two minutes; they are minima with a ceiling not far above them, which is the argument for two-bath fixing rather than for a longer single bath.

Hardening changes the surface, and it is the only image-side choice this product offers. A tanned gelatin layer swells less, dries faster and scratches less; it also takes toner more slowly and washes more slowly. For paper ILFORD forbids it outright, which is a statement about print permanence rather than about handling.

The mechanism

The fixing reaction is the ordinary one, and neither the counter-ion nor the buffer enters it.

AgBr + 2 S₂O₃²⁻ → [Ag(S₂O₃)₂]³⁻ + Br⁻

Thiosulfate takes the silver out of the halide's solubility equilibrium

How fixer works derives it, and complex formation is the general case. Nothing in that argument changes because the cation is ammonium, which is why ILFORD’s description of the product can be one sentence long.

Why the bath must be acid, and why the acid must be weak. Alkaline developer walks in on every film and every sheet; an acid bath neutralises it on arrival, which keeps the fixer’s own chemistry inside its window. But thiosulphate in strong acid decomposes and throws out sulphur — the bath goes milky, then sludges — so the acid is chosen weak and accompanied by sulphite. Kodak’s 1928 primer states the requirement directly: a fixing bath needs a large quantity of a weak acid, which is a description of a buffer written before the word was common in the trade. Part XI’s account of sulfurisation carries the equation. ILFORD’s own correction instruction carries the same logic in one clause: add acetic acid gradually with stirring, and “do not lower the pH of the fixer bath too far”.

So the window has a floor and a ceiling. A ceiling, because a bath whose acid is spent stains prints brown, and because an ammonium bath pushed alkaline gives off ammonia. A floor, because sulphur comes out. ILFORD publishes the window — 5.0 to 5.5 — and, unusually, publishes it as unchanged between 1+4 and 1+9, which is the behaviour of a buffered solution rather than of a diluted acid.

⚗What the disclosed components let this page say, and where it stops

A bath disclosing a bisulphite, acetic acid and boric acid, holding pH 5.0 to 5.5 at two dilutions five parts apart, is in the ordinary vocabulary of photographic chemistry a buffered acid fixing bath. That the product is a non-hardening acid rapid fixer is not an inference at all: ILFORD’s technical sheet uses those exact words.

The inference begins one step later, and this page marks it as one under Rule 7:

Inference 1 — that the three disclosed substances are the buffer system. A weak acid, a bisulphite and a very weak acid in quantity are exactly the components a formulator would use to hold a fixing bath at pH 5, and a pH that does not move between 1+4 and 1+9 is what a buffer does. Consistent, not conclusive. HARMAN states no buffer, no ratio and no conjugate base, and a fourth substance carrying no hazard would carry no line in the table.

Inference 2 — that the boric acid is there because this is the fixer you may harden. This is the tempting one, and it is the weakest. The case for it: boric acid’s established role in an acid fixing bath is acid reserve, F-5 uses it for exactly that in a bath that carries alum, Kodak’s 1928 chapter ties the reserve to sludging, and the one ILFORD fixer that discloses boric acid is the one ILFORD says a hardener may be added to. The case against: HYPAM contains no alum. It is sold non-hardening, HARMAN says so in the first paragraph, and a buffer cannot be doing a job for a hardener that is not in the bottle. The most that can be said is that a bath intended to survive the addition of alum would need more acid reserve than one that is not, and that this is a hypothesis about a formulator’s intention, from outside, with no statement from the maker at either end.

Inference 3 — that RAPID FIXER contains little or no boric acid. Its sheet lists none and classifies the product as not dangerous for supply or use, and a component that carries a mixture into Repr. 1B must be declared once it passes the threshold CLP sets. So the twin is below that threshold. This is a deduction about a classification, not a measurement of a bottle, and this course does not hold a source for the numerical threshold, so it states the direction and not the figure.

Naming a buffer pair, a ratio or a purpose here would be reconstructing a formulation out of a hazard document, which is precisely what this page kind exists to refuse.

Why the hardened bath needs longer, at both ends. Alum tans gelatin by cross-linking it, and a cross-linked layer is a tighter network: the thiosulphate takes longer to get in and reach the halide, and the thiosulphate and its silver complexes take longer to get out again in the wash. ILFORD’s two doubled figures — 4 to 10 minutes fixing, 10 to 20 minutes washing — are the same physical fact counted twice. Potassium alum’s page has the chemistry and the reason this whole apparatus is now a corner of a sheet rather than the default.

Why silver limits are so much tighter for paper than for film. Paper has a fibrous base that holds solution; film has an inert support. ILFORD’s own numbers say it — 8 to 10 g/L in a film bath, below 2 g/L for commercially permanent fibre prints, 0.5 g/L for maximum stability — and then say why, by giving resin-coated paper 4 to 6 g/L because its base “is protected on both sides by an impervious polythene coating”. The polythene is the whole of the difference: the limit is about the base, not the emulsion.

Why the sulphide test works. Sodium sulphide converts residual silver compounds to brown silver sulphide, which is sepia toning run deliberately on the silver that should not be there. A well-fixed, well-washed print gives a barely visible cream tint; anything yellower is underfixed. It has to be run on a washed print, because a print straight from the fixer is covered in the thing being looked for.

Why electrolytic recovery can poison the bath it is cleaning. Drive too much current through a solution whose silver has already fallen low and the cell starts reducing something else: the fixer’s active ingredients break down, silver sulphide plates onto the cathode, and in the worst case hydrogen sulphide comes off. ILFORD names all three. It is the clearest published statement in this corpus that a fixer is a chemical system rather than a consumable.

The nearest open formula

Kodak’s F-5 — the tropical acid hardening fixing bath — because it is the only open formula in this library that publishes, with quantities, the acid system HYPAM’s hazard sheet only names, and because it is the bath a reader is actually choosing against when they buy HYPAM and a hardener rather than mixing one.

F-5 is 240 g of crystalline hypo, 15 g of anhydrous sodium sulphite, 17 mL of glacial acetic acid, 7.5 g of boric acid and 15 g of potassium alum, made to a litre. Two of the three substances HARMAN discloses for HYPAM are two of the five Kodak prints for F-5, doing the same job in both: an acid, and a very weak acid in quantity behind it as reserve.

	Kodak F-5	ILFORD HYPAM
Composition	Five ingredients, every quantity printed	Three substances, none of them the fixing agent; amounts not published
Fixing agent	Sodium thiosulphate, 240 g/L, weighed by you	Ammonium thiosulphate, named on the technical sheet, absent from the hazard sheet, quantity nowhere
The acid	Acetic acid, 17 mL of glacial	“acetic acid … %”, 1.4475
The acid reserve	Boric acid, 7.5 g	Boric acid, 2.6022 — purpose not stated
Preservative	Sodium sulphite, 15 g anhydrous	A bisulphite at <5, supplying sulphite and acid together
Hardener	Potassium alum, 15 g — in the formula	None. Added by you, from another maker, to the diluted bath only
Speed	Sodium bath: 10 minutes, fresh	Ammonium bath: 2–5 minutes unhardened, 4–10 hardened
Published fixing times	One	Eleven, across two columns and six materials
Published pH	None	5.0–5.5 at both dilutions; 5.1 for the concentrate
Published density	None	SG 1.080–1.090 at 1+4, 1.040–1.050 at 1+9; 1.34 for the concentrate
Published capacity	120 sheets of 8 × 10 per 4.55 L	24 films, or 80 RC or 40 FB sheets per litre
Replenishment	None published	Four rates, a machine range and a silver-recovery reduction
Keeping	1 week in a dish, 1 month in a tank	Seven figures, from 7 days to 2 years
Classification	Level B, on the boric acid and the alum	Level B, on the boric acid — labelled Repr. 1B, Danger
What you can change	The thiosulphate, the acid, the reserve, the hardener — everything	The dilution, the temperature, the time, and whether to harden

The last row is the argument. Kodak prints a complete composition and one fixing time. ILFORD prints eleven fixing times, four capacities, two specific gravities, four replenishment rates, seven keeping figures and no composition. Neither document is dishonest and neither is sufficient.

And note what the comparison shows about the boric acid. F-5 does not merely contain it — Kodak puts it there for a stated reason, and this course’s page on the formula explains what more and less of it does. HYPAM contains a comparable proportion and states nothing. The same substance is a teachable ingredient in one document and a hazard line in the other, and that difference is the difference between the two kinds of page in this formulary.

If you do not want to harden anything, the honest nearest formula is F-24, which is non-hardening by design and is the comparison the RAPID FIXER page runs at length. It is the better match on that axis; F-5 is the better match on this product’s actual distinguishing feature, and on the chemistry its hazard sheet discloses.

The measurement that closes the gap runs in both directions, and ILFORD publishes it on this very sheet: the clearing time, and the rule that fixing time is twice it. Part XI’s clearing-time and capacity experiment runs it against both baths and the clearing-time SOP is the procedure. Do that, and F-5 acquires a fixing time for your film while HYPAM acquires a capacity for your work — exactly the half each document is missing.

Safety

Level B, and unlike its twin this is not a formality.

⚠This is a labelled reproductive toxicant. Its twin is not.

HARMAN’s 2024 safety data sheet classifies HYPAM Repr. 1B, pictogram GHS08, signal word Danger, hazard statement H360FD: may damage fertility, may damage the unborn child, with P405: store locked up and P201: obtain special instructions before use.

The RAPID FIXER sheet, issued by the same company on the same day, classifies that product not classified as dangerous for supply or use, with no pictogram, no signal word and no hazard statement.

The two products fix film in the same time at the same dilution with the same capacity. If you are not hardening, there is no photographic reason to have this bottle rather than that one.

Where the classification comes from. Boric acid, at 2.6022 %, and nothing else. It is on the UK REACH Candidate List of Substances of Very High Concern, which section 15.1 names explicitly, and the Annex XVII restrictions line records it as toxic to reproduction category 1B. The bisulphite (Acute Tox. 4, H302) and the acetic acid (Skin Corr. 1A, H314) look more frightening on the component rows and contribute nothing to the mixture’s classification at these concentrations.

Why Level B and not A. The course rubric caps Level A at a classification “at most irritant, harmful if swallowed, or corrosive at the concentrations actually handled”. Reproductive toxicity is outside it, and a product whose own label says store locked up is not a Level A product. This is the same level F-5 carries, and for the same substance.

Why Level B and not C. Level C assumes a fume cupboard, controlled waste and supervision. The controls the sheet itself specifies are within a well-run home darkroom: ventilation, local exhaust ventilation or breathing protection; eye protection with side protection to EN ISO 16321-1; protective clothing and impervious gloves to EN 374, with the breakthrough time taken from the glove maker; and a filter type A mask to EN 14387 or EN 405 as possibly appropriate. No fume cupboard is asked for.

What the maker’s own two documents say about hazard, seven years apart. The 2017 technical sheet says: “Photographic chemicals are not hazardous when used correctly. It is recommended that gloves, eye protection and an apron or overall are worn when handling and mixing all chemicals.” The 2024 safety data sheet says: obtain special instructions before use, do not handle until all safety precautions have been read and understood, wear protective gloves, clothing and eye or face protection, store locked up, keep out of reach of children. Both documents are HARMAN’s, both are current on their website, and this course reports the difference rather than resolving it. Where they disagree, follow the hazard sheet: it is the newer document and the one written for the purpose.

⚠Safety

Nitrile gloves, splash goggles rather than spectacles, and an apron. Mix in a ventilated space and keep your face out of the vapour path when pouring the concentrate — the sheet describes the odour as slightly pungent and asks for ventilation, local exhaust or breathing protection.

Store it locked, and away from anyone who might be pregnant or trying to conceive. That is not this course editorialising: it is P405 plus H360FD off the maker’s own label. ILFORD’s health and safety guidance addresses pregnancy separately, and a reproductive toxicant with a Candidate List entry is the case it is written for.

Do not decant it into an unlabelled bottle. A yellow-green liquid that looks exactly like its unclassified twin is the worst possible candidate for an unlabelled bottle in a shared darkroom.

First aid, in the sheet’s own words for every route — inhalation, skin, eye, ingestion — is to get medical advice or attention and treat symptomatically. Take the sheet with you.

In use, diluted, the hazard falls but the substance does not disappear. At 1+4 the boric acid is about half a per cent of the working bath. The classification thresholds are written for the product as supplied, and a diluted bath is not a labelled reproductive toxicant; the boron is still there, still goes down the drain, and still argues for gloves on a print tray.

Storage

Concentrate: two years full and unopened, at 5 to 20 °C. Six months once opened. Keep bottles tightly sealed. The safety data sheet adds store locked up and keep out of reach of children, and records the product as stable under normal conditions at ambient temperature.

Working strength, four figures, and the variable is air.

Container	Life
Full, tightly capped bottle	6 months
Tank or tray with a floating lid	2 months
Half-full, tightly capped bottle	1 month
Open tray	7 days

A half-full bottle keeps a sixth as long as a full one, which is the clearest statement in ILFORD’s literature that headspace, not time, is what ages a fixer. Decant into smaller bottles as you use it.

A replenished tank: a very long life, but replace it after twelve months — a calendar limit rather than a chemical one, and the only figure on the sheet that is not tied to a measurement.

Label the bottle. With the product name, the dilution, the date mixed, and — because this one is classified where its twin is not — the hazard. A working-strength bath is not the labelled product, but a shared darkroom should not have to guess which of two identical yellow-green liquids is in the jug.

Incompatibilities

Never mix a hardener with the concentrate. ILFORD’s instruction is unqualified and it is the only absolute prohibition on the sheet. A hardener goes into the diluted bath.

Never let a fixer meet a strong acid. Thiosulphate in strong acid decomposes to sulphur and sulphur dioxide. This is the reason the bath’s pH window has a floor and the reason the sheet warns against lowering it too far when correcting a drifted bath.

Never let it meet a sulphide. The residual-silver test uses sodium sulphide precisely because sulphide and silver-thiosulphate meet enthusiastically; a sulphide toner and a fixer bath in the same tray is hydrogen sulphide. Keep the test solution’s dropper away from the working baths, and see the incompatibilities page.

Do not push it alkaline. An ammonium thiosulphate bath made alkaline releases ammonia. Carried-over developer raises the pH a little, which the acid reserve is there to absorb; a deliberate addition of alkali is a different matter.

Boric acid is stored separated from strong bases — Chemical Safety Card 0991’s instruction for the substance, and also how it is ruined as an acid.

And the one that catches people: silver recovery run too hard. Excess current in an electrolytic cell breaks down the fixer’s active ingredients, sulphides the cathode and can release hydrogen sulphide. The bath and the recovery unit are not independent systems.

Rinse everything between products. The sheet asks for utensils, tanks, dishes and mixing vessels to be thoroughly cleaned before mixing a fresh batch, “particularly if it is being used for the first time”. Developer carried into a fixer on a stirring rod costs capacity; fixer carried into a developer on the same rod costs the developer.

Waste

It is silver-bearing, and the silver comes first. A spent fixing bath is the most concentrated silver stream a darkroom produces, and both the environmental and the practical arguments point the same way. The silver-bearing waste SOP is the procedure; ILFORD’s own sheet devotes a page to recovery and gives the achievable numbers — 50 to 100 ppm from a properly set up electrolytic unit, around 3 ppm after secondary and tertiary ion and metal exchange.

It is also boron-bearing, which its twin’s stream is not. Section 13 of the safety data sheet asks for disposal “to hazardous or special waste collection point”, where the twin’s sheet says only “dispose at suitable refuse site”. That is a real difference in the maker’s own disposal instruction and it follows the boric acid.

Do not pour it down a drain on this page’s authority. The disposal caveat explains why the answer is jurisdictional. ILFORD’s own guidance for domestic users in the UK is the chemical cupboard at a Household Waste and Recycling Centre, with chemicals bottled separately and appropriately labelled; for business users, that different waste chemicals must not be mixed but kept in separate, appropriately labelled containers. Section 6 adds that spillages or uncontrolled discharges into watercourses must be reported to the appropriate regulatory body.

Spills. Adsorb onto sand, earth or any suitable adsorbent and transfer to a container for disposal; provide adequate ventilation and full personal protection, including respiratory protection, while doing it.

Ecologically the sheet is reassuring and thin. Low toxicity to aquatic invertebrates, fish and algae; persistence, degradability, bioaccumulation and mobility in soil all recorded as not known. Read that as three answers and four blanks.

Troubleshooting

Negatives or prints show a milky or cream veil after fixing. Underfixed: residual silver halide. Refix in fresh solution and wash again. Then find out why — run the clearing-time test, and if the used bath clears in more than twice the fresh figure, the bath is finished.

The bath has gone milky or thrown a white precipitate. Sulphurisation: the thiosulphate has decomposed. Usually too much acid, from a stop bath carried in too strong or from an over-enthusiastic pH correction. Discard it. This is what the acid reserve exists to prevent and what “do not lower the pH too far” means in practice.

Prints stain brown after a few weeks. Either the bath’s acid was spent, or the silver level was over the limit for the paper, or the wash was short. ILFORD’s three figures — 2 g/L for commercial permanence, 0.5 g/L for maximum stability, 4 to 6 g/L for resin-coated — are the specification, and the sodium sulphide test is how you check the print rather than the bath.

Fixing times have crept up in a machine. Check specific gravity before anything else. A high-temperature processor evaporates water and concentrates the bath; a low SG means it has been diluted by carry-over. The sheet gives the correction in both directions: fresh concentrate, thoroughly stirred, or water.

The bath’s pH has risen. No stop bath, most likely. Add a few drops of 50 per cent acetic acid, gradually and with stirring, and stop inside the published window. Better: put ILFOSTOP or a citric acid stop in front of it, which is what the fixer sheet recommends and prints a whole table for.

Freshly mixed solution fixes badly. Almost always incomplete mixing. Fixer concentrates do not readily mix with water, and a concentrate layer sitting at the bottom of a tank is a bath that is too weak everywhere else. Stir thoroughly; in a processor, recirculate at temperature for at least ten minutes before running anything through.

Film is scratching or drying slowly, and you were told to harden. Check the four circumstances first — above 30 °C, poor drying, short drying times needed, roller-transport damage. Outside them, ILFORD’s own advice is that modern films are hardened at manufacture and the alum buys nothing while costing double the fixing time and double the wash.

You hardened, and now the negatives will not wash clean. Expected. Hardened film needs 10 to 20 minutes of washing, not 5 to 10, and the minimum-water fill-and-invert method is not validated for a hardened bath.

The bottle looks like the other bottle. It does. Read the label for the pictogram: HYPAM carries GHS08 and the word Danger; RAPID FIXER carries neither.

Experiments

1. Weigh the specific gravity difference. Mix a litre of HYPAM at 1+4 and a litre of RAPID FIXER at 1+4 and weigh each on a kitchen scale, tare against a litre of water. ILFORD predicts 1080–1090 g for HYPAM and 1070–1080 g for its twin. This is HARMAN’s own worked example from its process-control primer, run in reverse, and it is the cheapest published-number check in this library.

2. Run the clearing-time test on both twins, side by side. Same film, same temperature, same dilution. If the two products fix at the same rate — which ILFORD’s identical published times imply — then the ten points of specific gravity are not thiosulphate. That is a real inference about composition, obtained by measurement rather than by reading a hazard sheet, and it is the honest way to learn something ILFORD does not publish. The SOP is the procedure.

3. Measure the pH of the concentrate against the sheet. The safety data sheet gives 5.1 for HYPAM’s concentrate and records the twin’s as not known. A pH stick covering 4 to 6 costs almost nothing. Then measure both working dilutions and confirm that the 1+4 and the 1+9 really do land in the same 5.0–5.5 window — which is the observation the buffer inference rests on, and worth owning rather than borrowing.

4. Exhaust a litre deliberately, and plot the clearing time. Fix 8 × 10 sheets through a litre at 1+4, running the clearing-time test every fifth sheet, and plot clearing time against sheets. ILFORD says forty fibre-based sheets and says to discard at twice the fresh clearing time; find out whether those two limits arrive together for your paper. Part XI’s experiment has the full protocol.

5. Run the residual-silver test properly, and build the reference. Two grams of sodium sulphide in 125 mL of water, diluted 1+9. Make the reference tint first, on a print you two-bath fixed and washed thoroughly, because the test is a comparison and is worthless without it. Kodak ST-1 is the same solution with the chemistry explained.

6. Mix F-5 and compare it with a hardened HYPAM bath. This is the buy-or-mix comparison made real: an open hardening fixer whose boric acid you weighed yourself against a bought one whose boric acid you read off a hazard sheet. Compare clearing time, drying time, and the temperature at which a wet strip of each film’s gelatin softens. F-5 is Level B; read its page before you weigh anything.

7. Read both safety data sheets side by side. Not a bench experiment, but the most transferable exercise on this page. Two products, one maker, one issue date, one compiler. Note which substances each sheet names, which it omits, which bands are ranges and which are printed to four decimal places, and what the classification does to the label. You will not learn either composition. You will learn exactly what a safety data sheet is for, and why this library gives bought products a page kind of their own.