Foma FOMAFIX

This is a product page, not a formula page, and on a fixer 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 Hradec Králové knows the quantities in this bottle — and in this case nobody outside Hradec Králové has been told what the principal substance in it even is. What follows is what its maker publishes, which for dilution, time and capacity is a good deal; what its maker’s own safety data sheet discloses, which is four substances, none of them a fixing agent; what the two documents together still leave unknown; and the open formula to mix if you would rather know than buy.

Foma’s fixer sheet carries two products under one heading and they are not versions of each other. FOMAFIX is the liquid concentrate this page documents. FOMAFIX P is a two-component powder acid fixer, sold in boxes of two bags, for manual work only — and on Foma’s own table it takes ten minutes on a film where FOMAFIX takes three. The paper sheets treat the pair as alternatives and name them in the same breath: “For fixing, a common acid fixer (e.g. powder Fomafix P) or Fomafix rapid fixer should be used.” That sentence is the clearest thing Foma publishes about its own product’s class, and it is a comparison rather than a description.

FOMA BOHEMIA spol. s r.o., Hradec Králové — 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
Acetic acid (glacial)named on the sheet as Kyselina octováCAS 64-19-7The largest of the four and the one the concentrate smells of — the sheet gives the odour as mild and acetic, and the acid a fixing bath needs is a weak one	< 5 %	H226, H314
Borax (sodium tetraborate decahydrate)named on the sheet as Tetraboritan sodný dekahydrátCAS 1303-96-4	< 2 %	H360FD, H319
Trisodium nitrilotriacetate (Na3NTA) (Dissolvine A 92)CAS 5064-31-3	< 1 %	H302, H319, H351
Citric acid (anhydrous)named on the sheet as Kyselina citronováCAS 5949-29-1	< 1 %	H319

Not disclosed. Foma publishes no composition for FOMAFIX, and the gap here is wider than on any other product page in this library, because the substance that is missing is the one the product is for. The safety data sheet's composition table names an acid, a borate, a sequestrant and a second acid, and names no fixing agent at all: no thiosulphate, no cation for it, no concentration, and no sulphite either, although the same sheet warns that oxides of sulphur can be evolved. Each of the four bands it does print is one-sided, so the sheet states no lower limit for anything and their four upper limits together account for under a tenth of the bottle. Nowhere in Foma's literature is there a working-solution pH, a specific gravity for anything but the concentrate, a residual-silver limit, a replenishment rate, a two-bath scheme, a temperature range from the fixer's own sheet, a keeping time for the concentrate or the working bath, or a formulation date. A reader who wants to know how much thiosulphate is in the tray, or to change one term at a time and see what it does, has to mix an open formula instead of buying this one.

Nearest open formula. Kodak F-52 — Both are non-hardening acid fixing baths for films and papers alike, and the difference between them is which half of the page you can read. F-52 is 250 g of hypo and 25 g of potassium metabisulphite in a litre, used at working strength with no dilution, published by Kodak with both quantities on the page, three keeping figures and a capacity — and no fixing time at all. FOMAFIX is a concentrate whose fixing agent is not named in any document its maker publishes, diluted 1+5 by hand and 1+4 in a machine, published with eleven fixing times, four capacity figures, a concentrate pH and a concentrate density, and no keeping figure of any kind. Their acid systems are the interesting difference and are visible from both sides: F-52 makes its acid and its preservative out of one salt, so the sulphite that protects the thiosulphate is released by the same substance that lowers the pH, whereas FOMAFIX discloses two organic acids and a borate and no sulphite at all, while its own sheet warns that oxides of sulphur may come off on contact with a strong mineral acid. F-52 fixes in the ordinary time of a sodium bath and Foma's film sheets put FOMAFIX at three minutes against ten for a common acid fixing bath, so whatever is in the bottle is doing something F-52 cannot. One is a known composition with unmeasured speed; the other is a measured speed from an unmeasurable composition.

Purpose

To fix a black and white film or print — to dissolve the silver halide the developer did not reduce, and carry it out of the emulsion — in one to three and a half minutes at ordinary room temperature, from a bottle you measure rather than a powder you dissolve. Foma describes FOMAFIX as a “liquid concentrate of a rapid fixer featuring high efficiency, strong buffer ability and long-term stability”, designed “for the manual and automatic processing of all sorts of black-and-white films and papers”, diluted 1+5 by hand and 1+4 in a machine.

Four of those words are the whole product, and every one of them is a claim without a number behind it.

Liquid concentrate. Nothing to weigh, nothing to dissolve, no dust, and a half-litre bottle that makes three litres of working solution. Against FOMAFIX P — two bags dissolved in 600 mL of water at 40 °C, the bigger bag first — that is the entire practical argument for the liquid, and Foma prints both procedures on the same sheet so you can see what you are avoiding.

Rapid. The maker’s own word, used in the product description and again in every paper sheet’s recommendation line. Foma never says what makes it rapid. The film sheets say what it is rapid against: ten minutes in any common acid fixing bath, three minutes in this one.

Strong buffer ability. An unusual thing for a fixer sheet to boast about, and the one claim the safety data sheet’s composition table can be read against — because two of the four substances it names are acids and a third is an alkaline salt. What the claim is not accompanied by is a pH for the working bath.

Long-term stability. An adjective with no number behind it anywhere in Foma’s literature, and the single largest gap in what this maker publishes. There is no shelf life for the sealed bottle, none for the opened one, none for the tray.

Recommended uses

Hand fixing at 20 °C, at 1+5. That is the use Foma documents, the dilution every one of its paper sheets prints in its own processing table, and the one the published capacity belongs to.

Every material Foma makes, film and paper alike. The fixer sheet’s table covers eleven of them — five films and six papers — in two columns and one page. There is no separate film product and no separate paper product, and no separate dilution for the two. That is worth pausing on, because it is not how ILFORD sells the same class of bath: there the paper has a second, weaker dilution of its own and the film does not.

After a stop bath, which Foma’s paper sheets make part of the sequence rather than an option. Every one of them puts 2 per cent acetic acid or Fomacitro at 1+19 between the developer and this fixer, with a time — 20 to 30 seconds on the baryta papers, 10 to 20 seconds on Fomaspeed and Fomatone. The film sheets ask for a short rinse in distilled water or ten seconds in 2 per cent acetic acid. The open bath this course teaches for that step is the citric acid stop bath.

In a roller processor at 1+4. Foma gives the ratio, and the Fomaspeed sheet gives it a time and a temperature: 25 to 35 seconds at 30 °C, between a five-to-ten-second stop and a sixty-second wash. That is the only machine sequence in Foma’s literature and it is the reason the 5 litre canister exists.

On Fomatone MG Classic, with the stop bath treated as compulsory. The Fomatone sheet says in its own words that stopping development before fixing is “very important with this paper” and that neglecting it “can cause non-homogenities of gray areas on prints”. That is a maker naming a specific, visible failure and telling you which step prevents it.

Where a small quantity is the point. The half-litre bottle makes three litres of working solution, and a litre at a time is what a dish takes. Nothing is committed until you pour.

When another formula is preferable

• When you want to understand a fixer rather than use one, mix F-52. It is the same job done by two chemicals you can name, weigh and change, and it is the comparison this page is built around.
• When you need to know how much thiosulphate is in the tray. This is the reason to mix rather than buy that applies hardest here, and it is not a matter of curiosity: the clearing-time test calibrates a bath against its own fresh state, and a two-bath scheme, a replenishment rate and a silver limit all start from a concentration. F-52 publishes 250 g of hypo in a litre. Foma publishes no fixing agent at all.
• When you need a keeping figure. F-52 carries three from Kodak’s own table — a week in a dish, a month in a tank, three months in a stoppered bottle. Foma publishes none, for the concentrate or the working solution.
• When the print was made by printing out rather than developing out. An acid fixer bleaches a print-out image; the salted paper, albumen and Van Dyke side of this course uses a plain hypo bath or Reilly’s slightly alkaline one instead, and printed-out image bleached in the fixer is what happens when the wrong tray is used.
• When you want the shortest possible wash. TF-2 is held on the alkaline side deliberately, and its authors’ argument is that an alkaline bath washes out of a fibre base far faster than an acid one. Foma’s own washing times for a baryta paper are 30 minutes after this fixer and 45 after the powder one, which is the same argument made from the other end.
• When you want the emulsion hardened. Nothing in Foma’s literature says this bath hardens, and nothing says it does not. If hardening is the point, F-5 carries it in the formula and F-53 is the hardener stock that turns a plain bath into a hardening one, both with the alum weighed and published.
• When you want an acid system you can adjust. F-24 and the 1928 bisulphite bath publish theirs to the gram, and a bath whose pH you can move is a bath you can rescue. There is no published route to correcting a drifted tray of this one.

What the maker publishes

A concentrate gives its maker less to say than a powder does — there is no mixing procedure to write — and, exactly as with FOMATOL LQN, the surprise is how much of what Foma publishes about this product is in the paper and film sheets rather than the fixer sheet.

Two dilutions, and what each is for. Manual processing: one part concentrate to five parts water. Automatic processing: one part to four. Both are on the fixer sheet, in the FOMAFIX entry, and nothing else about strength appears anywhere.

A capacity, in four units at once. One litre of working solution at 1+5 fixes 17 perforated films of 135-36 or rollfilms of 120, or a corresponding amount of sheet film — up to 40 sheets of 13 × 18 cm — or 2 m² of baryta paper, or 4 m² of resin-coated. That is more capacity detail than any other document in this corpus gives for a fixer, and it is given for the hand dilution only.

Packaging. A polyethylene bottle of 0.5 litre and a polyethylene canister of 5 litres.

Times, for eleven materials, at 20 °C. The fixer sheet’s table gives the FOMAFIX column as: Fomapan 100 Classic 3 min; Fomapan 200 Creative 3; Fomapan 400 Action 3; Retropan 320 soft 3; Foma Ortho 400 3.5; Fomabrom 3; Fomabrom Variant 3; Fomaspeed 1.5; Fomaspeed Variant 1.5; Fomatone MG Classic 3; Retrobrom 3. Beside it, in the FOMAFIX P column, the same eleven materials take 10, 10, 10, 10, 11, 5, 5, 3, 3, 5 and 5.

The same times again, on the materials’ own sheets, with the dilution attached. This is where the fixer sheet’s gap is filled: its table header says only “Manual processing at 20 °C (minutes)” and names no dilution for either column. Fomabrom, Fomabrom Variant, Fomaspeed and Fomatone MG Classic each print “Fomafix (1 + 5)” in their own fixing row.

A washing time that depends on which fixer you used. This is the most interesting thing in the paper sheets and it is easy to read past. Every one of them gives two washing times side by side: after FOMAFIX, 30 minutes in running water for a baryta paper and 2 minutes for Fomaspeed; after FOMAFIX P, 45 minutes and 4 minutes. Foma is publishing, in its own processing tables, that the rapid fixer washes out of the paper in two thirds the time — or half of it, on resin-coated — that its powder acid fixer needs.

A temperature range, but only in the film sheets. The Fomapan datasheets give fixing as “at a temperature ranging from 18 to 25 °C for 10 minutes in any common type of an acid fixing bath, or for at least 3 minutes in Fomafix rapid fixer”. The fixer sheet itself gives one temperature, 20 °C, and no range at all.

A machine sequence, once. Fomaspeed’s machine table: stop 5 to 10 seconds, fix in Fomafix at 1+5 for 25 to 35 seconds, wash 60 seconds, all at 30 °C.

From the safety data sheet, the physical properties of the concentrate. A colourless to slightly yellowish liquid with a mild acetic odour; pH 5.5 to 5.8 at 20 °C; relative density 1.29 to 1.31 g/cm³ at 20 °C; vapour pressure below 20 mbar; non-flammable; not oxidising; freezing below 0 °C and boiling above 100 °C.

!What Foma publishes that ILFORD does not, and the other way round

Two makers, one class of product, and the two published pages barely overlap.

Foma publishes and ILFORD does not: a capacity in square metres as well as in films; a fixing time for eleven named materials of its own manufacture; a washing time that changes with the fixer used; a concentrate density and a concentrate pH.

ILFORD publishes and Foma does not: the name of the fixing agent, in the first paragraph of the sheet; a working-solution pH and specific gravity window for each dilution; residual-silver limits in grams per litre for film, for fibre paper and for resin-coated paper; four replenishment rates; four keeping figures; and the instruction for correcting a bath that has drifted.

The asymmetry is worth naming rather than scoring. Foma tells you what to do with its own materials in more detail than ILFORD does. ILFORD tells you what the bath is, and therefore how to measure it, replenish it, correct it and decide when it is finished. Neither sheet publishes a formula, and this page is not a complaint that Foma withholds one — it is a record of which questions each document lets a reader answer.

What is not disclosed

The fixing agent. Not its identity, not its cation, not its concentration, not its class. This is the silence that makes this page different from every other product page in the library: the composition table names four substances and not one of them fixes anything. A developer sheet that named its alkali and withheld its developing agents would be the same kind of document, and the FOMATOL LQN page is about a sheet that at least names its two.

Any sulphite. No sulphite, bisulphite or metabisulphite appears in the composition table, and a thiosulphate fixer without a preservative would not survive its own acid. Sections 5.2 and 10.6 warn that oxides of sulphur may be evolved on contact with a strong mineral acid, which is what a thiosulphate does and what a sulphite does; the table names neither.

Everything about the working solution. Foma measures the bottle. pH 5.5 to 5.8 is the pH of the bottle; 1.29 to 1.31 g/cm³ is the density of the bottle. Neither the 1+5 tray solution nor the 1+4 machine solution has a published pH, a published density or a published silver limit. The number you would actually meter in the dish is not in any Foma document.

Any keeping figure at all. No shelf life for the sealed bottle, none for the opened bottle, none for the tray, none for a capped bottle of working solution. The technical datasheet says “long-term stability” and stops; the safety data sheet asks for storage in the original container in a dry cool place away from foodstuffs and gives no time. For comparison, ILFORD publishes four such figures for RAPID FIXER on one page and Kodak publishes three for F-52.

Any way of telling when the bath is finished, other than counting. No clearing-time instruction, no residual-silver limit, no test. The capacity table is the whole of it, and a capacity is a prediction rather than a measurement.

Whether it hardens. Foma never uses the word about this product, in either direction, and the composition table names no aluminium salt. Whether that silence means a non-hardening bath is discussed under The mechanism below, and it is marked there as a reading of an absence.

A replenishment scheme, a two-bath scheme and a temperature range from the fixer’s own sheet. None of the three exists in Foma’s literature. The 18 to 25 °C range comes from the film sheets and is stated about fixing in general rather than about this product in particular.

!Why the four bands cannot be added up — and cannot be subtracted from either

A composition table with four numbers in it invites the same arithmetic every time, and here the invitation is unusually strong because the numbers are small and there is an obvious hole for the answer to go in. Doing the sum once is the cure.

Every band on this sheet is one-sided: less than 5, less than 2, less than 1, less than 1. There is no lower limit for anything, so the sheet is consistent with a bottle containing 4.9 per cent acetic acid and with one containing a trace. Add the four upper limits and you get about 9 per cent — which is not a shortfall to be explained, because none of the four is stated to be present in any particular amount at all. The table’s own foot says what most of the rest is: vodný roztok, an aqueous solution.

Now try the subtraction the arithmetic seems to offer. Ninety-one per cent of the bottle is unnamed; the product is sold as a fixer, so something in there dissolves silver halide; the maker’s own sections 5.2 and 10.6 put a sulphur species in there; and the sheet gives no upper bound, no lower bound and no classification for any of it. You cannot compute what is not there from what is, and the temptation is worse here than on a developer page precisely because a fixer has one obvious principal ingredient and a reader who has read Part XI can name three candidates for it. Naming one of them as a quantity would be reconstructing a formula out of a hazard document.

That is not sloppiness on Foma’s part, and it is not concealment either. A concentration band on a safety data sheet exists to support a classification — section 16 records that this mixture was classified by the calculation method — and a substance that carries no hazard classification contributes nothing to that calculation and therefore earns no row. Sodium and ammonium thiosulphate are both substances of that kind. 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.

Nothing about why. No source in the corpus says why Foma buffers with a borate rather than with the sulphite–bisulphite pair every open acid fixer in this library uses, why the concentrate sits at 5.5 to 5.8, when the sequestrant was put in, or why Fomatone MG Classic gets two different fixing times in two of its own documents. Those are the interesting questions and the literature does not touch them.

Disclosed components

The four substances the safety data sheet names, taken in the order its own table prints them. Each band is an upper bound on that substance’s share of the concentrate in the bottle, never of the solution in the dish, and the sheet gives no lower bound for any of them. Its wording is Czech and the names below are reproduced as it writes them; where the course has an encyclopaedia entry the link goes to it, and the CAS number is the field that carries across the language.

Before any of them, the thing to hold onto: this is the composition table of a fixer, and there is no fixing agent in it. Everything named below is an auxiliary. On an open formula page these four would be the last four lines of the ingredient list.

Kyselina octová, CAS 64-19-7, less than 5 per cent. This is acetic acid, the largest of the four, and it is what the concentrate smells of — section 9.1 gives the odour as “mírný, octový”, mild and acetic. An acid fixing bath needs an acid for a reason that belongs to the tray before it rather than to itself: alkaline developer walks in on every sheet and every film, and the acid neutralises it on arrival. Part XI’s account of fixer formulations sets out why the acid has to be a weak one, and the same substance at the same job is published to the millilitre in F-5 and F-6. That the acetic acid is here to arrest development and hold the bath acid is the course’s reading of where a weak acid sits in fixer formulation; Foma states no function for it. As a pure substance it is classified Flam. Liq. 3 (H226) and Skin Corr. 1A (H314), and section 8.1 quotes the Czech workplace limits of PEL 25 mg/m³ and NPK-P 35 mg/m³ — figures for the vapour of the glacial acid, not for a bottle at under 5 per cent.

Tetraboritan sodný dekahydrát, CAS 1303-96-4, less than 2 per cent. This is borax, sodium tetraborate decahydrate, and it is the substance that makes this sheet worth reading twice. A borate in a fixing bath is not an oddity — it is the whole design of F-6, where 15 g of Kodalk neutralises part of the acetic acid so that the bath holds a mildly acid pH instead of a sharply acid one, and 7.5 g of boric acid does the same job from the other side in F-5. That the borax here is the base half of the buffer Foma advertises is the course’s reading, and Foma states no function for it; what is not a reading is that the maker claims “strong buffer ability” in the same sentence in which it calls the product a rapid fixer, and that its sheet names two acids and one alkaline salt and nothing else.

Two things about this line have to be recorded rather than smoothed over. The sheet classifies borax Repr. 1B, H360FD — may damage fertility or the unborn child — and section 2.3 records it on the SVHC candidate list, the list of substances of very high concern. Foma nonetheless classifies the mixture as needing no classification at all, which is a statement about concentration limits and the calculation method rather than about the substance. The course does not derive a figure from that: the sheet’s band is “less than 2 per cent” and that is the only number there is. The practical consequence is in the safety section, and it is the reason gloves are not optional on a bath the maker labels with nothing.

Trisodium nitrilotriacetate (Na3NTA) (Dissolvine A 92), CAS 5064-31-3, less than 1 per cent. The sheet gives this one a trade name as well as a chemical one, exactly as the FOMATOL sheet does with its own sequestrant. NTA is a chelating agent — a smaller, cheaper relative of the EDTA salts the course meets elsewhere, and complex formation is Part III’s subject. It has no fixing role: reading it as an answer to hard water — locking up calcium and magnesium so that a borate-buffered bath does not throw a scum, and iron so that it does not catalyse the decomposition of what is dissolved in it — is the course’s inference, Foma states no function for it, and the course has no encyclopaedia page for the substance itself. It is also the only one of the four carrying a carcinogenicity classification, Carc. 2, H351, alongside H302 and H319, and section 8.1 gives it DNEL values for workers and consumers.

Kyselina citronová, CAS 5949-29-1, less than 1 per cent. This is citric acid — and note the CAS number, which is the monohydrate, not the 77-92-9 of the anhydrous acid that the course’s own encyclopaedia page is written around. The sheet prints no index number for it and classifies it Eye Irrit. 2 (H319) alone. Its presence is the second-most interesting thing on this table after the borax, because citric acid in a fixing bath is doing at least two things at once and Foma says which of them is intended: neither. It is a weak acid, like the acetic; it is also a chelating agent in its own right, weaker than NTA but not negligible; and it is triprotic, so it buffers over a wide span rather than at one point. All three of those are properties of the substance and none of them is a Foma statement about the product.

⚗The published pH band and the third dissociation constant

The concentrate’s published pH is 5.5 to 5.8. The course’s own citric acid page records, from the IUPAC compilation of dissociation constants, pK_a1 2.87, pK_a2 4.35 and pK_a3 5.68 at 20 °C — and 5.68 sits inside the published band, near the middle of it. The acetic acid page records pK_a 4.76 from the same compilation, which is a little under a pH unit below the band’s floor.

A conjugate acid–base pair holds a solution near its pK_a, so a bath at 5.5 to 5.8 is a bath sitting on the citrate’s third ionisation and on the upper shoulder of the acetate’s. That is an observation about three published numbers and it is consistent with the maker’s claim of strong buffer ability. It is not a formulation and it is not evidence of one. Foma states no buffer pair, no conjugate base and no ratio; the bands were chosen to classify a hazard; and there may be a substance in the bottle that carries no hazard, earns no row on the table, and does more of the buffering than either of these two.

The reason this matters to a printer rather than to a chemist is the floor. A fixing bath that goes too acid decomposes its own thiosulphate and throws out sulphur, and a bath whose acid is spent stains prints. The pH window of a fixer has a floor as well as a ceiling, which Part XI works through — and the number Foma publishes is for the bottle, not for the tray, so you cannot use it to tell where in that window your dish is sitting.

⚗The substance the composition table does not name

This is the most instructive absence in the corpus, and it is a lesson in what a safety data sheet is for rather than a discovery about the product.

No fixing agent appears in section 3.2. Foma’s technical datasheet calls FOMAFIX a rapid fixer; its safety data sheet calls it, in section 1.2, a “koncentrát kyselého ustalovače” — a concentrate of an acid fixer. Neither document names a thiosulphate. Both documents are Foma’s and neither is wrong: a composition table lists the substances that drive a mixture’s classification, and neither sodium thiosulphate nor ammonium thiosulphate carries a CLP classification that would put it there. A substance that is not hazardous does not appear on a hazard document, however much of it there is. The course’s reading is that the principal ingredient of this product is absent from its composition table for exactly that reason, and no quantity on this page bears on it.

A sulphur species is there on the maker’s own evidence. Section 5.2 warns of the “možná tvorba toxických plynů (oxidy síry)” — possible formation of toxic gases, oxides of sulphur — and section 10.6 repeats it as a decomposition product on contact with a strong mineral acid. Liberating sulphur oxides on acidification is what a thiosulphate does and what a sulphite does. That a sulphur species is present is the maker’s own statement in the form of a hazard; which species, and how much, is not in the document and is not inferred here.

The practical upshot is one line long and it is in the safety section below: do not put a strong acid, or a drain cleaner, or anything unidentified, into a container that has this concentrate in it. The maker has told you what comes off if you do.

Behaviour

It is fast, and Foma publishes the comparison rather than the reason. Three minutes on a Fomapan film at 20 °C against ten minutes in “any common type of an acid fixing bath” — the film sheets print both numbers in one sentence, which is a maker inviting the comparison. On paper the margin is smaller but goes the same way: 3 minutes against 5 on a baryta sheet, 1.5 against 3 on Fomaspeed.

It exhausts by area and by count, and Foma gives you both. Two square metres of baryta or four of resin-coated per litre — roughly 39 and 78 sheets of 8 × 10 inches by the arithmetic, which is the course’s and not Foma’s — or 17 films of 135-36, or up to 40 sheets of 13 × 18 cm film. Count against those figures rather than judging the tray by eye. Exhausted fixer is the entry, and Part XI’s capacity lesson is why a fixer fails gradually and invisibly rather than suddenly.

It has no published clocks at all, which is a behaviour in itself. The unopened bottle, the opened bottle, the tray and a capped bottle of working solution all have the same published life: none. In the absence of a figure, the honest working method is the one the course teaches anyway and which does not need the maker’s help — run the clearing-time test on the bath when it is fresh, write the number down, and retire the bath when the clearing time has doubled. Part XI’s clearing-time experiment is where that method is established. That is the course’s practice, not Foma’s, and here it is not a refinement but the only instrument you have.

It is published for two temperatures and two dilutions, and the four do not interchange. 1+5 at 20 °C by hand; 1+4 at 30 °C in a machine. There is no published time for 1+4 in a dish, none for 1+5 in a machine, and the only wider temperature range in Foma’s literature — 18 to 25 °C — is stated in the film sheets about fixing generally.

It washes out faster than the powder fixer, on the maker’s own tables. Thirty minutes against forty-five for a baryta print, two minutes against four for resin-coated. Foma offers no explanation and the course will not supply one it cannot source; what it will say is that a washing time is a property of the bath the material came out of, and that Foma has published that fact about its own two products.

Two of Foma’s documents disagree about Fomatone MG Classic, by a factor of two. The fixer sheet gives 3 minutes in FOMAFIX and 5 in FOMAFIX P; the Fomatone paper sheet gives 1.5 and 3. The course does not know which is right and prints both in the object above.

!The Fomatone disagreement, and the one clue in the documents

It is worth setting out, because it is the kind of thing a reader will meet again and because the evidence is more interesting than the answer.

The pair 1.5 and 3 that the Fomatone sheet gives for its two fixers is exactly the pair the fixer sheet gives for Fomaspeed, the resin-coated paper — and the fixer sheet’s own Fomatone row, 3 and 5, is exactly the pair it gives for the two baryta papers, Fomabrom and Fomabrom Variant. Fomatone MG Classic is a baryta paper.

And the Fomatone sheet contradicts itself in the same table: its washing row gives 30 minutes and 45, which is the baryta figure every other Foma baryta sheet carries, sitting one line below a fixing row that carries the resin-coated figures.

The course’s reading is that the fixing row in the Fomatone paper sheet is the anomaly, because it is the one line in either document that does not fit the pattern of the material it belongs to. That is a reading of two tables and it is not a Foma statement, so the object above carries both numbers and this page does not correct the maker. The safe practice needs no adjudication at all: fix for the longer time. Over-fixing a fibre print by ninety seconds costs a little more washing; under-fixing it costs the print, some years later.

Image characteristics

A fixer contributes nothing to the image and decides how much of it survives. There is no signature to describe in the way a developer’s is described. What there is instead is a list of failures the bath can leave behind, each with its own appearance and its own delay.

Under-fixing shows immediately and mildly, and permanently and badly. Undissolved halide leaves a milky or opalescent cast, visible against a light box on film and as a grey veil in what should be paper white. Left in place it darkens. Under-fixing and residual silver and yellow staining are the entries, and the residual hypo and silver tests are how you find out before it is too late. Foma publishes no residual-silver limit to test against, so the limits this course works to are ILFORD’s, quoted on the RAPID FIXER page, and they are another maker’s numbers for another maker’s bath.

Over-fixing has no published limit here, and the course does not invent one. Foma’s times are single figures rather than minimum times, and no upper bound appears anywhere in its literature. What is not in doubt is the general behaviour: a print left long enough in any fixer begins to lose delicate highlight densities, and a fibre print left long enough takes up thiosulphate the wash then has to remove.

Residual thiosulphate is the failure you cannot see for years, and this product gives you one clue about it. Residual thiosulphate is a wash problem rather than a fix problem, but the bath decides its size — and Foma’s own tables say this bath leaves a baryta print needing 30 minutes of washing where its powder fixer leaves one needing 45. That is the only quantitative thing the maker publishes about the interaction, and the physics of washing is where the mechanism behind it belongs. A hypo clearing agent or the open sodium sulfite washing aid shortens the wash further; Foma sells no equivalent and names none.

Whether the emulsion comes out hardened is not published, and it changes what you can do next. A hardened layer resists a toner, a selenium bath, a bleach and a redevelopment; an unhardened one swells more, dries more freely and is easier to damage wet. Since Foma says nothing either way, the practical answer is to find out on a test strip before a print you care about goes into a toner — and to read frilling and reticulation before a warm-weather session.

On a printed-out image it is actively destructive, which is not a defect of the product but a fact about acid fixers. The salted paper, albumen and Van Dyke side of this course reaches for a plain hypo bath instead, and printed-out image bleached in the fixer is the entry for what it looks like when the wrong tray is used.

The mechanism

Everything in this section that goes beyond the maker’s own two sentences is marked as what it is.

What the maker states. FOMAFIX is a liquid concentrate of a rapid fixer with high efficiency, strong buffer ability and long-term stability, for manual and automatic processing of all sorts of black-and-white films and papers, diluted 1+5 by hand and 1+4 in a machine, fixing in one and a half to three and a half minutes at 20 °C depending on the material, with a concentrate at pH 5.5 to 5.8 and a relative density of 1.29 to 1.31, containing acetic acid, sodium tetraborate decahydrate, trisodium nitrilotriacetate and citric acid in the four amounts the safety data sheet bounds from above, and evolving oxides of sulphur on contact with a strong mineral acid.

The fixing reaction itself is not in doubt and does not depend on any of that.

AgBr + 2 S₂O₃²⁻ → [Ag(S₂O₃)₂]³⁻ + Br⁻

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

How fixer works derives it properly. Nothing in the disclosed components enters that equation at all, which is another way of saying that this composition table tells you about the bath’s housekeeping and nothing about its work.

What follows from the maker’s own comparison: it behaves like a rapid fixer, and this page will not say why. Three minutes against ten for a common acid bath is the behaviour that the trade calls rapid, and in the ordinary chemistry of the trade a rapid fixer is an ammonium thiosulphate bath. That identification is an inference and this page marks it as one under Rule 7: Foma names no fixing agent and no cation, and a fixer can also be made fast by raising the thiosulphate concentration. The evidence that the ammonium ion accelerates fixing is set out on the ammonium thiosulphate page, which is careful to record what Wall established in 1924 and what he called a supposition. None of that evidence is about this product.

Why the bath is acid at all is about the bath before it, not this one. Alkaline developer walks in on every sheet and every film, and an acid bath neutralises it on arrival, which keeps the fixer’s own chemistry inside its window. That is why Foma’s own paper sheets put a stop bath between the two and give it a time, and why a stop bath pays for itself in fixer life rather than in print quality.

Why the acid is weak, and why the window has a floor. Thiosulphate in strong acid decomposes and throws out sulphur: the bath goes milky and then sludges. So the acid in a fixing bath is chosen to be weak, and in every open formula in this library it is accompanied by a sulphite that both preserves the thiosulphate and supplies the conjugate base — potassium metabisulphite doing both jobs in one salt in F-52, sodium bisulphite in F-24. FOMAFIX discloses no sulphite, and the course does not conclude from that that there is none: a sulphite carries a classification and would ordinarily earn a row, but the sheet’s own sulphur-oxide warning points the other way, and an absence on a hazard document is weaker evidence than a presence.

Why a borate, when the open formulas use a sulphite pair. This is the question the disclosed components actually raise, and the course can point at a published precedent without answering it. F-6 exists because F-5 smelled: replacing F-5’s 7.5 g of boric acid with 15 g of sodium metaborate neutralises part of the acetic acid before the bath is ever used, which raises the pH just enough to suppress sulphur dioxide while leaving the bath acid enough to work. That a borate in FOMAFIX is doing the analogous job is the course’s reading of a component list against a published formula, and it is not a Foma statement. What can be said without inference is that the maker advertises buffering, that a borate is an alkaline salt, and that its own sheet reports the concentrate’s odour as acetic rather than sulphurous.

Whether it hardens: a reading of an absence, offered as one. No aluminium salt appears in the composition table. Foma’s sheet for FOMAFIX H — a different product, a hardening solution added to the fixer for machine processing of X-ray film — names aluminium sulphate octadecahydrate at less than 70 per cent and sulphuric acid at less than 5 per cent, classifies the mixture as corrosive to metals and seriously damaging to the eyes, and prints “Obsahuje: kyselina sírová, síran hlinitý” on the label. So this maker does name an aluminium hardener when one is present at a classifiable amount. That FOMAFIX is therefore a non-hardening bath is the course’s reading, it rests on an absence rather than a statement, and Foma has never used the word about this product in either direction.

Inference, labelled as inference. The identification of the acetic acid as the arresting acid, of the borax as the base half of a buffer, of the NTA as a sequestrant for hard water, of the citric acid as a second weak acid and chelator, of an ammonium bath behind the word rapid, and of a non-hardening bath behind the missing alum are all readings of what those substances do in fixers generally, or of what a silence probably means. None of them is a Foma statement, and none of them carries a quantity.

What is unknown and stays unknown. The fixing agent. Its cation. Its concentration. Whether there is a sulphite and how much. The working pH at either dilution. Whether the bath hardens. The residual-silver limit at which it should be retired. Anything at all about keeping. Why this maker buffers with a borate where every open formula in this library buffers with a sulphite, which is the most interesting question the sheet raises and the one Foma answers least.

!Reading a safety data sheet in a language you do not have

This sheet is published only in Czech, as FOMATOL LQN’s is, and both are worth using as practice.

The structure is the same in every language, because the law fixes it. Sections 1 to 16 are the same sections in the same order in every REACH safety data sheet ever written. Oddíl 3, Složení is section 3, composition, wherever you find it; oddíl 9 is physical and chemical properties; oddíl 13 is disposal. The numbers, the CAS registry numbers and the H- and P-statements are the same tokens everywhere, and the course’s page on GHS and CLP decodes them.

Trust the CAS number over the name, always. It is what saves you here: the fourth row is kyselina citronová at CAS 5949-29-1, and the number tells you it is the monohydrate before you get anywhere near the Czech.

And read section 2 against section 3. This sheet’s section 2.1 says the mixture “shows no dangerous properties, need not be classified”, and its section 3.2 names a reproductive toxicant on the SVHC candidate list and a suspected carcinogen. Both statements are correct and they are about different things — one about a mixture at the concentrations present, one about substances. A reader who reads only the first has not read the sheet. Recording a safety data sheet is the procedure for filing what you find.

The nearest open formula

Kodak F-52, and the comparison is the reason this page exists.

F-52 is the shortest useful fixer in this library: 250 g of hypo and 25 g of potassium metabisulphite in a litre, used at working strength with no dilution and no stock, published by Kodak Limited for “papers, films and plates wherever hardening is unwanted”. FOMAFIX is the same class of bath doing the same job on the same range of materials — Foma’s own phrase is “all sorts of black-and-white films and papers” — with an unnamed fixing agent in place of the weighed hypo, two organic acids and a borate in place of the one bisulphite, a sequestrant that a 1949 formula has no equivalent for, and a bottle in place of a balance.

	Kodak F-52	Foma FOMAFIX
Composition	Published in full: two ingredients	Not published
Fixing agent	Sodium thiosulphate, 250 g in a litre	Not named in any document the maker publishes
Acid	Potassium metabisulphite, 25 g, which is the acid and the preservative in one salt	Acetic acid under 5 % and citric acid under 1 % of the concentrate; bands only
Preservative	The sulphite the metabisulphite releases, quantity published	None named; the sheet’s sulphur-oxide warning is the only trace of one
Buffer	The bisulphite–sulphite pair, inherent in the one salt	Borax under 2 % of the concentrate, and a maker’s claim of “strong buffer ability”
Sequestrant	None	Trisodium NTA, under 1 % of the concentrate
Hardening	None, by design, and the header says so	Not stated either way; no aluminium salt on the sheet
Sold as	Two chemicals you weigh	A 0.5 L bottle or a 5 L canister
Working strength	The formula is the working bath	1+5 by hand, 1+4 in a machine
Published pH	None	5.5 to 5.8, for the concentrate only
Published density	None	1.29 to 1.31 g/cm³ at 20 °C, for the concentrate
Published fixing time	None at all	Eleven materials, 1.5 to 3.5 minutes at 20 °C
Capacity	60 sheets of 8 × 10 in per 160 imperial fl oz (4.55 L) with a water rinse; 90 with a chrome alum bath	17 films of 135-36, or 2 m² FB, or 4 m² RC, per litre at 1+5
Keeping	Dish 1 week, tank 1 month, stoppered bottle 3 months	Nothing published, for anything
What you can change	Both quantities, one at a time	The dilution, the time and the temperature

Two rows carry the whole argument, and they point in opposite directions.

The fixing-time row is Foma’s. Kodak published a fixing bath and no fixing time for it, which is the ordinary state of a 1949 formula and is why Part XI’s clearing-time test exists. Foma published eleven times, for eleven named materials, at a stated temperature. If what you want is to fix a Fomabrom print correctly this evening, the bought bath tells you how and the open one does not.

The keeping row is Kodak’s, and so is every row above it. F-52 can be mixed in any volume you care to weigh, tested, corrected, halved, doubled, and retired on a published schedule. FOMAFIX cannot be made at all, cannot be adjusted, has no published life, and cannot be measured against its own fresh state without a test the maker never mentions.

The honest summary is that these two documents are complementary rather than competing, and a reader who has both is better off than a reader with either. Mix F-52 to understand what a fixing bath is; buy this one, or its ILFORD equivalents, when the job is to get eleven of one maker’s materials through a dish on a schedule the maker has already tested.

Safety

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

Foma classifies the mixture as not hazardous. Section 2.1 states that the mixture “shows no dangerous properties, need not be classified”, with “may slightly irritate the eyes” given as the most serious effect; section 2.2 carries no pictogram, no signal word, no hazard statement and no precautionary statement at all. That is the least hazardous product on any sheet in this course’s corpus, and it is why the level is A: the classification rubric’s Level A criterion asks for substances “at most irritant, harmful if swallowed, or corrosive at the concentrations actually handled”, and this mixture does not reach the first of the three.

That is not the same as harmless, and section 3.2 is why. The composition table names a reproductive toxicant on the SVHC candidate list and a suspected carcinogen, both at concentrations the maker judges too low to classify the mixture. The consequences are practical rather than alarming: wear gloves on a bath that carries no warning label, keep it off skin rather than wiping it off, and treat the borate as the course’s borax page treats it — the reproductive classification is a reason to keep the substance out of the mouth and off the skin rather than a formality. If you are pregnant or breastfeeding, this is a bath to handle with gloves and to ask a doctor about, and the maker’s blank label is not an answer to that question.

No dust, and that is the real difference from FOMAFIX P. Section 8.2 states that respiratory protection “is not needed in normal handling”. The two-bag powder fixer on the same technical sheet has to be dissolved from a bag into water at 40 °C, which is the one hazard a liquid concentrate avoids entirely.

Personal protection, as the sheet specifies it. Rubber (PE) gloves and safety goggles, both “recommended”; working clothing; local exhaust ventilation and running water for washing eyes, hands or contaminated skin, present at the workplace. Do not eat, drink or smoke while handling it; keep it away from food and drink; wash your hands with soap and water afterwards. The course’s glove selection page is where breakthrough time is taken from the glove maker rather than assumed.

Eyes first, and do not neutralise. The sheet’s first-aid instruction is to remove contact lenses, flush with water as soon as possible, force the lids open if they are clamped shut, avoid contaminating the unaffected eye with the washings, and not to attempt neutralisation. That is the instruction on the course’s eyewash procedure. For swallowing: calm the person, rinse the mouth with clean water, a glass of about 40 mL of water may be given, do not induce vomiting, do not give activated charcoal and do not give any neutralising agent. The first aid quick reference is the general page.

The one exposure limit the sheet quotes is for acetic acid, from the Czech regulation NV 361/2007 Sb.: PEL 25 mg/m³ with a ceiling of 35. That is a workplace air limit for the vapour of the pure acid and it is not a limit for a dish of fixer; it is here because the sheet prints it, and because a reader comparing this sheet with an ILFORD one should know the two quote different national lists.

⚠The one thing this sheet tells you that the label does not

Sections 5.2 and 10.6 both say the same thing: oxides of sulphur may form, and may be released on contact with a strong mineral acid.

A darkroom does not usually contain a strong mineral acid, and this is not a warning about the stop bath in the next tray: 2 per cent acetic acid, or Fomacitro at 1+19, is a weak acid and the sheet distinguishes the two. It is a warning about the concentrate, and about the shared waste container and the unlabelled bottle — the places where a fixer meets something that was never meant to meet it.

So: keep the concentrate away from anything you have not identified, never pour an unknown liquid into a container that has fixer in it, and rinse a funnel between baths. Sulphur dioxide is an acute respiratory irritant and a darkroom is a small room. This is also the practical reason an unlabelled or unknown container has a procedure of its own in this course.

Storage

The concentrate, in its original containers, in a dry cool place, away from foodstuffs. That is the whole of Foma’s storage instruction, and there is no keeping time attached to it — not for a sealed bottle, not for an opened one. The technical sheet’s “long-term stability” is a phrase and the safety data sheet’s section 10 says only that the product is stable under normal conditions and that high temperature is the condition to avoid.

In the absence of a figure, buy the size you will use. The 0.5 litre bottle makes three litres of working solution and the 5 litre canister makes thirty. The course’s advice, not Foma’s: for hand work the small bottle is the right purchase even at a worse price per litre, because a part-used bottle with no published life is a liability and a sealed one is not.

The working solution has no published life either, so measure it instead of guessing. Fix the clearing time of the fresh bath in your notebook on the day you mix it. That number, and not a date, is what tells you the tray is finished. A fixer differs from a developer here in a way that helps: it does not fail by oxidation in air so much as by filling up with silver and bromide, so a bottled working solution that has done little work is usually still good and a bottled one that has done a lot is not — and the test distinguishes them in two minutes.

Freezing. Section 9.1 gives the freezing point as below 0 °C and the density as 1.29 to 1.31 g/cm³, which is a heavily loaded solution; a concentrate like that will drop solids in an unheated outbuilding well before it actually freezes. A stock that crystallised in cold storage is the entry for what to do — warmth and patience, not a fresh bottle.

Keep the fixer bottle away from the developer bottle, and label both. Use the labelling SOP, and for this product write the date you first opened the concentrate on the bottle, because that is the only clock anyone can give you and you are giving it to yourself. A tray of clear liquid in a darkroom is indistinguishable from three other trays of clear liquid, and an unlabelled or undated container is the failure that costs a whole session. The stock rotation SOP is where an undated bottle stops being a recurring problem.

Incompatibilities

Strong mineral acids, which section 10.3 names as the hazardous reaction and sections 5.2 and 10.6 tie to the evolution of sulphur oxides. See the safety callout above. This is the one incompatibility Foma states.

High temperature, which section 10.4 gives as the condition to avoid.

No incompatible material is named, which is section 10.5 in full — neuvedeny, not stated. That is a smaller list than the same maker gives for its own paper developer, whose sheet names aluminium, and it is a gap rather than a clearance: the absence of a named material is not a statement that every material is safe.

Developer, in both directions. A splash of fixer in the developer tray dissolves silver out of the image and leaves a stain behind it; developer carried the other way neutralises the fixer’s acid and exhausts it sooner. Foma’s own paper sheets are built to prevent exactly that: every one of them puts a stop bath between the two and gives it a time. The chemical incompatibilities page has the general pairs.

Silver-bearing waste from other processes. A used fixer is a silver solution, and pouring toner chemistry, bleach or a ferricyanide into the same container turns a recoverable stream into a problem. Silver-bearing waste is the procedure and silver recovery is why it matters.

Oxidisers, and toner chemistry above all. Dichromate, permanganate, persulfate and ferricyanide have no business near a fixer bottle or in its waste container. Sodium sulphide toning is worse still: sulphide contamination of a fixing bath or of the air near one is what turns a print’s highlights brown weeks later.

Waste

Bottled separately, and never down the drain. Foma’s section 13 is direct: the product “must not be disposed of with municipal or other waste” and “do not flush into the sewer”. Spilt product is to be soaked into an inert absorbent and handed to an authorised person for disposal. Section 6.2 asks that it be kept out of soil, drains, surface water and groundwater, and that a large release be reported to the fire service.

The European waste codes, which are worth knowing because a waste contractor asks for them. 09 01 04* — fixer solutions. 15 01 10* — packaging containing residues of dangerous substances. The asterisk marks them as hazardous waste in the European List of Waste. Note that this is a different code from the one on the FOMATOL sheet, which is 09 01 01* for developer solutions: the two streams are separately classified, which is the regulatory expression of the practical rule that they go in separate bottles.

Used fixer is silver-bearing, and that is the whole reason it is worth handling properly. Foma publishes no residual-silver figure, so the arithmetic has to come from the capacity: a litre that has fixed 17 films or two square metres of baryta paper is carrying the silver those materials gave up. Silver recovery and waste streams is where the routes are set out, the silver-bearing waste SOP is the procedure, and the point of keeping this bottle uncontaminated is that a refiner will take it.

Empty bottles. Foma’s advice is that a thoroughly rinsed empty container may be reused or put out for plastics recycling. Rinse it into your own silver-bearing waste container, not into the sink, and let the rinsings go the same way as the bath.

The disposal caveat governs, and the rule where you live decides. The general chemical waste SOP is the procedure this course follows. Under any jurisdiction the developer bottle and the fixer bottle stay apart, because the fixer is worth something at a refiner and the developer is not.

Troubleshooting

A milky or opalescent cast on the film, or a grey veil in the paper white. Under-fixing, and with this product the first check is arithmetic rather than chemistry: how many films or how much paper has the litre already done, against Foma’s 17 films, 40 sheets of 13 × 18, 2 m² of baryta or 4 m² of resin-coated? Under-fixing is the entry and the clearing-time test is how you settle it in two minutes.

Yellow or brown staining that appears later. Residual silver and yellow staining is usually a bath worked past its capacity rather than a time that was too short, and exhausted fixer is the general entry. Because Foma publishes no silver limit, the honest test is the residual hypo and silver tests, and HT-2 is the open formula for the silver half of it.

Prints that will not tone evenly, or a selenium bath that does nothing. Consider whether the emulsion came out of the fixer hardened. Foma does not say, so test on a strip rather than assume, and read mottle revealed after toning before committing a print.

Fixing times that do not match the ones you read. Check which Foma document you read them in. The fixer sheet and the Fomatone MG Classic paper sheet disagree by a factor of two for that paper, and the fixer sheet’s own table carries no dilution in its header while the paper sheets do — so a time read from one document and a dilution assumed from another is a real trap. A misread dilution ratio is the entry, and 1+5 means 100 mL of concentrate into 500 mL of water, not into a made-up 600.

Purple or dark spots on a print, in a fresh bath. Air bubbles clinging to the paper where the fixer never touched it — purple spots from fixer air bubbles — and the cure is agitation on immersion, not a stronger bath.

A print-out image that vanished or went pale in the tray. The wrong fixer for the process: printed-out image bleached in the fixer. An acid bath does that to a print-out image, and the alt-process side of this course uses a plain hypo bath instead.

Grey, uneven patches in the mid-tones of a Fomatone print. Foma names this one itself: stopping development before fixing is “very important with this paper” and neglecting it “can cause non-homogenities of gray areas”. Use the stop bath and give it the published 10 to 20 seconds. See also mottled development.

A film that frilled or reticulated in warm weather. Frilling and reticulation are about the temperature difference between baths rather than about the fixer’s composition. Foma’s only published guidance on the point is the film sheets’ 18 to 25 °C range for fixing; keep the whole sequence inside it and inside a few degrees of itself.

A scum or a fine deposit in a freshly mixed tray. Hard water, most likely — and the sequestrant in the concentrate is there to prevent exactly this, at under 1 per cent of the bottle. It is dosed for the concentrate and not for your tap. Mixing with deionised water is the test that settles it in one session.

Milkiness or a sulphurous smell in the bath itself. Thiosulphate decomposing, which means the bath has been contaminated with something considerably more acid than a stop bath. Do not use it, and find out what went into the container.

Experiments

Measure what the sheet publishes, then measure what it does not. The concentrate should be pH 5.5 to 5.8 and 1.29 to 1.31 g/cm³ at 20 °C. The density needs a measuring cylinder and a balance and takes two minutes; the pH needs a meter calibrated that day. Then measure the 1+5 tray solution, which no Foma document gives, and write both numbers in your notebook. You have just produced a figure this page could not give you, and a check on your own meter at the same time.

Establish your own clearing time on day one, because the maker gives you nothing else. Run the clearing-time test on a fresh litre at 1+5 and record the seconds. Repeat it after every ten films or every twenty prints. The bath is finished when the clearing time has doubled, and Part XI’s experiment sets the method out properly. Plot it against Foma’s published capacity of 17 films to the litre and you will find out whether the maker’s figure is generous, conservative or exactly right for your water and your working habits.

Settle the Fomatone disagreement. Foma’s fixer sheet says 3 minutes for Fomatone MG Classic; Foma’s Fomatone sheet says 1.5. Fix five identical prints for 45, 90, 120, 180 and 300 seconds in one fresh litre at 1+5, wash them all identically, and run the residual silver test on each. The shortest time that leaves no stain is the answer for your bath, and it is worth more than either sheet because it is measured rather than printed.

Test the maker’s washing claim. Foma publishes 30 minutes of washing for a baryta print fixed in FOMAFIX and 45 for one fixed in FOMAFIX P. Fix two identical prints, one in each, wash them side by side in the same tray, and pull test strips from each at 10, 20, 30 and 45 minutes for a residual hypo test. If the claim holds, the FOMAFIX print clears the test a third sooner. Whatever you find is a number about your own water temperature and your own wash, which is what wash testing is for.

Find the time nobody publishes: 1+4 in a dish. Foma gives 1+4 only for a machine at 30 °C. If you want the stronger dilution in a tray — for a session where the bath must last a long evening — there is no published time and the course will not invent one. Mix it, run a clearing-time test against a 1+5 bath made the same day, and record both. That is how a maker’s silence gets turned into your own number.

Two baths, which Foma never mentions. The archival answer to a fixer with no published silver limit is not a stronger bath but a second one: the two-bath fixing rotation is the procedure, and the archival processing sequence is where it belongs in the workflow. Run a session both ways — one bath and two — and test the prints from each. Nothing in Foma’s literature tells you to do this, and nothing in it tells you not to.

The comparison that matters most: this against F-52. Mix a litre of F-52 and a litre of FOMAFIX at 1+5, and put identical strips of the same film through both, timing the clearing in each. You will have measured the thing Foma’s word rapid is a claim about, against a bath whose thiosulphate concentration is published. Record it in the formula version record — a bought product gets a line in that record too, with its dilution, the date its bottle was opened and how much material had already been through the bath, because those are the only variables you have.

Keep a column for the fixing count. Write down the number of films or sheets that have gone through the litre, beside the date the bottle was opened. Foma’s capacity figures are the only prediction you have and there is no keeping figure to fall back on, so the count is the record that matters. It costs nothing to keep, and after one winter it will tell you a bath is finishing before a ruined negative does.