Kodak F-54

Two lines, and the second of them is a formula rather than a substance. That is the point of this entry: F-53 is a bottle that keeps, hypo is a solid that keeps, and F-54 is what you make from them when you actually want a hardening fixer for paper.

Ingredient	Quantity	Form the source specifies
Warm water	500 mL	the hypo is dissolved in it first
Sodium thiosulfate	250 g	crystalline hypo
Kodak F-53 acid hardener stock	125 mL	added when the hypo solution is cold
Water	to make 1000 mL

Purpose

To fix prints, arrest development, and harden the paper’s gelatin layer — the same three jobs as F-5, reached by a different route and at a lower strength. Kodak Limited’s header is simply “acid hardening fixing bath for paper”.

The route matters more than it looks. The 1928 primer states the design principle: prepare the acid hardening solution as a separate stock solution and add this to the hypo solution as required, because a mixed acid hypo solution goes milky on keeping while its two halves do not. F-54 is that principle written out as a formula.

Recommended uses

Papers. Kodak publishes no fixing time for it, which is worth saying plainly rather than filling with a number from elsewhere. What the handbook publishes instead is a capacity — 120 sheets of 8 × 10 inches per 160 fluid ounces — and the clearing-time rule from the 1928 primer applies as it does to every bath in this section: time a test strip to clear, and fix for twice that.

Where a print will be dried on a heated drier or glazed, and the wet layer has to survive handling, squeegeeing and heat. That is what the alum is for.

Where you already keep a bottle of F-53 for other work. One stock serves this formula and F-54a.

When another formula is preferable

• When the print is going to be toned, F-52. A hardened layer takes sulfide, selenium and gold slowly and unevenly, and Kodak’s own advice elsewhere is to use a non-hardening fixer for prints intended for toning.
• When permanence is the priority, F-52 again, followed by a washing aid. A hardened fibre-base print holds thiosulfate longer and washes more slowly.
• For films and plates, F-54a — the same construction at 400 g of hypo and 185 mL of stock — or F-5, which needs no stock bottle. F-54a’s quantities are printed in full under Variants.
• For a printing-out paper, the alkaline bath. An acid hardening fixer is the wrong bath in two independent ways for a salted-paper or albumen print.
• When you want one bottle and one weighing session, F-5.

Mixing

Warm water, hypo, cool it, then the stock.

1. Dissolve 250 g of hypo in 500 mL of warm water. The handbook does not say how warm. Warm enough to dissolve a quarter-kilo of crystals in reasonable time, and remember that the dissolution is endothermic, so the solution cools itself as it goes.
2. Let it get cold. The handbook’s line is literally “to this, when cold, add”, and its general instruction for acid hardening baths says both solutions must be cold. The 1928 primer gives the penalty: if the hypo is not thoroughly dissolved and cool before the hardener is added, a precipitate of sulfur is likely to form.
3. Add 125 mL of F-53, slowly, with vigorous stirring. Not the reverse; not in one pour.
4. Make up to 1000 mL.

If you have the proprietary liquid hardener instead, the handbook’s first line is 50 mL of it. Whether you use 50 mL of that or 125 mL of F-53 is the handbook’s own choice to offer, and the ratio between them — two and a half — is the only number Kodak published about the product’s strength.

🧮What 125 millilitres of stock delivers, and how that compares

F-53 carries 50 g of anhydrous sulfite, 75 mL of glacial acetic acid and 100 g of potassium alum in a litre. At 125 mL to the litre of finished bath, that is:

50 g/L × 0.125 = 6.25 g per litre of F-54

Sulfite

75 mL/L × 0.125 = 9.4 mL per litre of F-54

Acetic acid

100 g/L × 0.125 = 12.5 g per litre of F-54

Potassium alum

250 g ÷ 248.19 g/mol = 1.01 mol/L, a 25 % w/v bath

Thiosulfate

Against F-5, which carries 15 g of sulfite, 17 mL of acid, 7.5 g of boric acid and 15 g of alum in a 24 per cent hypo bath, F-54 is the milder bath on every count except the hypo, where they are within a per cent of each other. It carries 42 per cent of F-5’s sulfite, 55 per cent of its acetic acid, 83 per cent of its alum, and no boric acid at all.

And yet Kodak’s keeping table gives the two baths almost identical figures, and gives F-54 the higher capacity in the one comparison where they differ. The course records that and does not explain it, because no source it read explains what the boric acid in F-5 is for. See the boric acid page, which says the same thing in the same words.

Behaviour

120 sheets of 8 × 10 inches per 160 fluid ounces, and this is the one row in Kodak’s fixing-bath table where all four capacity cells read the same number: dish or tank, water rinse or SB-3 hardening bath, the answer is 120. For F-52 the intermediate bath makes a difference of half as much again, and for F-5 the table’s own figures are inconsistent between dish and tank. F-54 is the least conditional capacity in the section.

It keeps three months in a full bottle and a fortnight in a half-empty one. That is a much sharper full-to-half penalty than F-52, which keeps three months either way, and it is what having alum and a smaller sulfite reserve in the bottle costs.

Its exhaustion has two visible ends. Like every alum fixer it can sludge with white aluminium sulfite when the acid has been neutralised by carried-over developer, and once it has gone alkaline the 1928 primer’s warning applies: prints fixed in it are likely to become stained brown. Like every acid thiosulfate bath it can also go milky with sulfur if it meets something more acid than itself.

No fixing time is published, and none is invented here.

Image characteristics

None of its own on a print used within the bath’s life. What it changes is the print’s future: a hardened fibre-base layer washes more slowly, holds residual thiosulfate longer, and takes a toner less evenly than an unhardened one.

That is a real trade rather than a defect. A hardened print survives a heated drier, a squeegee and a glazing plate; an unhardened one is more permanent if you wash it properly and more fragile if you do not. The choice between this bath and F-52 is where that trade is made, and it should be made deliberately.

The one visible fault the bath itself produces is the brown stain of a bath gone alkaline.

The mechanism

The fixing chemistry, the acid-against-thiosulfate problem, the sulfite that restrains it and the alum that tans the gelatin are all set out on F-5 and F-53, and this page links them rather than repeating them.

What is specific to F-54 is why the hardener arrives as a solution rather than as three weighings, and there are three separate reasons in the sources.

Keeping. A mixed acid hypo solution goes milky on standing; a hypo stock and a hardener stock do not. The 1928 primer’s recommendation to keep them apart until needed is the whole architecture.

Solubility. The same primer records that alum dissolves more readily in an acid-sulfite solution than in water. Making the hardener as its own concentrate is the easiest way to get 100 g of alum into a litre; adding 12.5 g of solid alum to a made-up hypo bath is a different and worse proposition.

Control of the dangerous step. The moment a hardening fixer can precipitate sulfur is the moment the acid meets the hypo. Delivering the acid as a measured, dilutable solution that is poured slowly into a cold bath makes that moment controllable in a way that tipping in glacial acid never would be.

Function of every ingredient

Sodium thiosulfate, 250 g of the crystals in 500 mL of warm water. The fixing agent, at 25 per cent w/v — the same hypo strength as F-52, and a little below F-5. It complexes silver out of the undeveloped halide, two thiosulfate ions to each silver. More would fix a little faster and leave more thiosulfate in the paper to be washed out; less moves the bath towards the region where the insoluble silver–thiosulfate complex forms, which is the failure that yellows prints years later. Note the form: the crystals are the pentahydrate at 248.19 g/mol, and 250 g of the anhydrous salt would give a bath half as strong again as Kodak’s.

Kodak F-53 acid hardener stock, 125 mL. Three ingredients arriving as one measurement, and each of them has to be accounted for.

• The sulfite it brings, 6.25 g per litre, is the preservative: it suppresses the acid decomposition of the thiosulfate by being that reaction’s own product, and it reduces oxidised developer carried in on wet prints so the bath does not brown. It is the smallest sulfite reserve of any acid fixer in this formulary, which is consistent with the sharp fall in this bath’s keeping figures once the bottle is half empty.
• The acetic acid it brings, 9.4 mL per litre, is what arrests development on contact and what holds the aluminium in solution and able to harden. More acid gives a longer-lived and slightly worse-hardening bath; less gives one that goes alkaline early and stains prints brown.
• The potassium alum it brings, 12.5 g per litre, is the hardener, tanning the gelatin so the wet layer survives handling and heat. More overshoots into brittleness; less fails to reach the minimum quantity that hardens at all.

Use more or less than 125 mL and all three move together, which is the price of the architecture: this formula has one dial where F-5 has three. That is also why the course does not offer a “reduced-hardening F-54” — cutting the stock cuts the preservative and the acid with it, and the result would be a bath with a shorter life and no published figures behind it.

Kodak Liquid Hardener, 50 mL, is the handbook’s first line and cannot be printed as an ingredient. Its composition is not disclosed anywhere in the handbook, and the course does not reconstruct proprietary formulations or infer them from a strength ratio. What is disclosed is that it is two and a half times stronger than F-53, which is a dosing fact and not a composition. Where a formula in the older literature calls for the liquid hardener, multiply by two and a half and use F-53.

Water, 500 mL warm and then to make 1000 mL. The split is part of the procedure. Dissolving the hypo in half the final volume gets it into solution quickly; the make-up water at the end is what brings the finished bath to strength after the stock has gone in.

Interactions

With F-53, which is half the formula. Everything on that page about mixing order, temperature and the aluminium sulfite sludge applies here at the moment the two meet.

With the developer, and with the tray before it. The bath’s acid is spent against alkali carried in on wet prints. The 1928 primer measured what a stop bath is worth for a print fixer of this class: its acid hardening bath F-1 fixes a hundred 8 × 10 prints per gallon after a thorough water rinse and a hundred and twenty-five after the acid rinse SB-1. A quarter more prints, from ten seconds and a little acetic acid.

With the wash after it, unfavourably, which is the cost of hardening. A hardened fibre-base print is the case where a washing aid earns its place most clearly.

With toners, unfavourably again, and deliberately avoided by choosing F-52 instead when toning is planned.

With F-54a, not at all. They are different strengths for different materials and should not be topped up into one another.

Variants

F-54a, the films-and-plates version, in the same handbook. Its quantities are printed here in full rather than summarised, because the course does not silently pick one of two published formulas:

Ingredient	F-54 (paper)	F-54a (films and plates)
Warm water	500 mL	500 mL
Sodium thiosulfate	250 g	400 g
Kodak Liquid Hardener	50 mL	75 mL
or F-53 stock	125 mL	185 mL
Water to make	1000 mL	1000 mL

F-54a is a 40 per cent hypo bath against F-54’s 25 — Wall’s ceiling for a fixing bath, and the strength plain hypo is published at — carrying 9.25 g of sulfite, 13.9 mL of acetic acid and 18.5 g of alum per litre. The course has not given it a separate entry in this batch; its keeping figures match F-54’s except that its tank and bottle cells carry the table’s temperature footnote, and its capacities are the same 120 sheets in every cell.

F-5 is the single-vessel alternative with boric acid, in the same handbook. Not a variant of this formula: a different formula for the same job.

Kodak Acid Fixing Salt with Hardener is offered by footnote as a powder alternative to mixing either of these baths, and its composition is not disclosed. Under the course’s rule on proprietary formulations it is taught as behaviour and disclosed components only, which here amounts to its name and its purpose.

No reduced-hardening variant is offered, for the reason given under Function of every ingredient: this formula’s single dial moves the preservative and the acid along with the alum.

Safety

Level B, and the step that earns it is measuring the stock rather than working the tray.

F-53 is a concentrate carrying 1.3 mol/L of acetic acid and 0.21 mol/L of aluminium. Measuring 125 mL of it and pouring it into a bath is a splash risk with a corrosive-classified liquid, and making the stock in the first place means handling glacial acetic acid, which is where the Level B criteria really bite. Splash goggles, gloves, an apron and an eyewash within reach for that step.

The finished bath is a much milder proposition — 25 per cent hypo with about 9 mL of acetic acid and 12.5 g of alum in a litre — and tray work with it meets the Level A criteria: gloves, eye protection, ordinary darkroom ventilation, dedicated utensils. The course assigns the higher level because a formula is assessed as written, and as written it begins with a concentrate.

What is absent, and why that is worth stating. There is no boric acid in this bath, so the H360 reproductive-toxicity classification that makes F-5 Level B on its ingredients alone does not apply here. If that classification is the reason you were looking for an alternative to F-5, this formula and F-52 are the two Kodak published.

And the standing hazard of every fixer. Nothing more strongly acid than the formula goes into this tray or its waste bottle; thiosulfate and sulfite both give sulfur dioxide when they meet a strong acid.

Storage

Three months in a full stoppered bottle, two weeks half full, one month in a covered tank and one week standing in a dish.

The full-to-half-full drop is the number to notice: a fortnight against three months. Store the working bath in bottles sized to what you have, rather than in one large bottle that spends most of its life half empty.

Keep the F-53 stock separately and expect the white incrustation of basic aluminium acetate that the handbook tells you to ignore.

Glass or plastic, never metal. Label the bath with the formula, the date and the sheet count, per the labelling SOP; label the stock as a stock, because a bottle of hardener mistaken for a working bath is a tray of concentrated acid.

Incompatibilities

Any acid stronger than its own, in the tray or in the waste bottle, which liberates sulfur dioxide from the sulfite and sulfur from the thiosulfate. See incompatibilities.

Alkalis and carbonates, which neutralise the acid, stop the hardening and precipitate aluminium sulfite.

Developer, in either direction. One pair of tongs per tray.

Oxidising agents — peroxide, persulfate, permanganate, hypochlorite — which attack both the sulfite and the thiosulfate.

Sulfide toners, which give hydrogen sulfide on meeting an acid bath, and whose waste is kept away from every acid stream.

Metals, which acetic acid attacks; plastic or glass throughout.

Waste

Silver-bearing, and carrying aluminium and sulfite as well: this is the same waste as F-5 minus the borate.

Silver recovery comes first where it is available; for a home darkroom the practical route is collection. The solution is oxygen-demanding and the silver is present as a soluble complex, so nothing about it is made safe to pour away by dilution.

Collect it, label it, keep it away from acid wastes, and follow the silver-bearing waste SOP, which cites the disposal ruling. Unused F-53 is a different stream — it carries no silver, and its acidity would decompose the thiosulfate in a silver waste container. Local regulation decides, and this course cannot tell you what it says where you are.

Troubleshooting

A milky bath the moment the stock went in. The hypo was warm, or not fully dissolved, or the stock went in too fast. That is sulfur and it does not redissolve; remake the bath cold.

A white sludge after a working session, and prints that no longer harden. Aluminium sulfite. The acid has been neutralised by developer carried in on wet prints. Use a rinse or a stop bath, and check the sheet count against the 120-per-160-fluid-ounces figure.

Prints staining brown. The bath has gone alkaline. The 1928 primer names the outcome directly.

Prints taking longer to clear than they did. Time a test strip; a bath whose clearing time has roughly doubled is at the end of its useful life whatever the sheet count says.

Prints brittle or curling badly when dry. Over-hardening. Check that 125 mL was measured rather than poured by eye, and that the stock is F-53 rather than the two-and-a-half-times-stronger liquid hardener.

Prints that will not wash clean. Expected to be slower than an unhardened print, but if it is severe, check whether the fixing time was extended: thiosulfate driven into paper fibres by over-fixing is close to unremovable, and a hardened layer makes that worse.

Experiments

Compare the two architectures. Mix a litre of F-54 and a litre of F-5, and run both to exhaustion on the same paper and the same developer, tracking clearing time and pH against the sheet count. Kodak’s table says they should behave similarly despite F-54 carrying less of everything but hypo. If your two curves separate, the boric acid is doing something, and you will have measured what no source in this course’s corpus explains.

Measure the hardening the stock buys. Fix matched print strips in F-54 and in F-52, wash and dry both, then heat each in water until the gelatin lets go. The 1928 primer’s melting-point test, applied to paper.

Test the toning cost. Fix two prints from the same negative, one in each of those baths, and tone both in the same selenium bath for the same time. The difference is the argument for choosing your fixer before you make the print rather than after.

Price the stop bath, again. The 1928 primer’s twenty-five per cent gain was measured on prints in an alum fixer. Run it on this one: a series after a water rinse and a series after SB-1, and count sheets to the same clearing time.

Scale F-54 to F-54a and see whether the hypo matters. Both baths take the same stock at proportionate doses; the substantive difference is 250 g against 400 g of hypo. Clear the same paper in both and find out whether the extra 150 g buys anything you can measure.