Kodak F-14

A deep tank is a bath that stands and is worked for weeks, and what kills such a bath is not the fixing — it is the slow neutralisation of its acid by developer carried in on the film, and the white sludge of aluminium sulfite that follows. F-14 is F-1 rebuilt against that failure: the same hypo, the same alum, half the sulfite and eight per cent more acid.

The hypo solution — the fixing bath itself

Ingredient	Quantity	Form the source specifies
Sodium thiosulfate pentahydrate	960 g	crystalline hypo
Water	4000 mL, added	"Water 4.0 liters", with no closing make-up line. The primer states its own convention: "cold water to make" is given at the end of a formula when a definite final volume is intended, so that the concentration is known each time it is mixed. F-14 has no such line.
Kodak's four-litre tank basis. A deep tank is a standing bath that will be worked for weeks, which is what the hardener below is proportioned for.

The hardener solution — the acid, the preservative and the hardener, made separately and used cold

Ingredient	Quantity	Form the source specifies
Sodium sulfite (anhydrous)	30 g	desiccated
Acetic acid (glacial)	208 mL of a 28% solution	28 per cent; the primer's footnote makes it from three parts of glacial acetic acid to eight parts of water
Potassium alum	60 g	powdered
Water	400 mL, added	No temperature is printed for this water on F-14's page, although the F-1a directions it refers the reader to specify about 52 degrees C for the same four ingredients. What is specified is that the hardener be cool when it is added.
"Dissolve in the order given following the directions for mixing the stock hardener (Formula F-1a)": the sulfite completely dissolved first, then the acid, then the alum with constant stirring.

Mixed in this order — the working fixing bath

1. Start with the whole of The hypo solution — cool, and thoroughly dissolved before anything is added
2. Then add the whole of The hardener solution — cool, added slowly with constant stirring

When thoroughly dissolved, add the following cool hardener slowly with constant stirring to the cool hypo solution.

The primer's stated failure for this operation is a precipitate of sulfur where the hypo is warm or incompletely dissolved. No volume is stated for the combined bath; the water and the acid alone come to 4,608 mL.

Purpose

To fix roll films in a deep tank. Kodak’s header is “Deep Tank Fixing Bath for Roll Films”, and as with the rest of this family that is the whole of the stated purpose — no time, no temperature, no capacity and no keeping figure appear on the page.

What the primer does explain, elsewhere in the same book, is the trade-off F-14’s proportions embody. It states that the hardening properties of an alum-acid fixing bath bear a relation to the bath’s tendency to precipitate aluminium sulfite: a bath containing an excess of acid may be used for a relatively long time before the sludge appears, and does not harden as well; a bath containing a minimum of acid hardens better and sludges after a much smaller volume of developer has gone into it.

F-14 is at the first end of that relationship and F-1 is nearer the second. That reading is the course’s, made from Kodak’s own general statement and Kodak’s own numbers; Kodak does not say it about F-14 on F-14’s page.

Recommended uses

A standing tank of fixer that will be worked over days or weeks, with film carrying developer into it continuously. That is the case the proportions answer.

Roll film, which is what the header names, and which is the material a deep tank existed for.

Where sludging has been the practical problem rather than under-hardening. If a bath keeps going cloudy and losing its hardening after a modest number of films, F-14’s proportions are Kodak’s published answer to exactly that complaint.

As the third term in the family comparison. F-1, F-2 and F-14 hold the hypo constant and move the hardener across a factor of five. F-14 is the one whose economy the primer explains.

When another formula is preferable

• When maximum hardening matters more than tank life, F-1, which is compounded for a published 54 to 77 °C melting range and carries twice the sulfite.
• When the bath is a tray mixed for one session, F-1 again. F-14’s whole advantage is spent on a problem a fresh tray does not have.
• When the darkroom is hot, F-5, which is built for it with boric acid. More acetic acid is not a tropical strategy.
• When hardening must not happen, F-52 or a plain hypo bath — before a toner, a reducer or an intensifier.
• When the emulsion should be hardened before it is fixed, the separate chrome alum hardening bath, which the primer prints as SB-3 and which raises a fixing bath’s film capacity by a third.
• When there is to be no alum in the tray at all, the primer’s own bisulphite fixing bath, which has nothing in it that can sludge.

Mixing

Two vessels, both cold when they meet.

1. The hypo solution. Dissolve 960 g of hypo in 4,000 mL of water — water added, not water to make. Let it dissolve completely and cool.
2. The hardener solution. In 400 mL of water, dissolve in this order 30 g of sodium sulfite, then 208 mL of 28 per cent acetic acid, then 60 g of powdered potassium alum, stirring constantly. The primer refers you to F-1a’s directions, whose substance is that the sulfite must be completely dissolved before the acid arrives and that the alum goes last because it dissolves easily in an acid-sulfite solution and badly in a plain sulfite one.
3. Combine. Hardener into hypo, slowly, with constant stirring, both cool. The primer’s stated failure is a precipitate of sulfur where the hypo is warm or incompletely dissolved.

🧮Two hundred and eight millilitres, and what they buy

Scale all three of the family’s hardeners to a common 960 g of hypo, which is the one basis on which they can be compared exactly:

	Sodium sulfite	28 % acetic acid	Potassium alum	Acid per gram of sulfite
F-1	60 g	192 mL	60 g	3.2 mL
F-2	12 g	72 mL	24 g	6.0 mL
F-14	30 g	208 mL	60 g	6.9 mL

F-14 carries the same alum as F-1 and more acid than either of the other two, and it is the most acid-rich of the three relative to its sulfite reserve. Read against the primer’s stated relationship — excess acid means a long life before the aluminium sulfite sludge and poorer hardening — this is a bath bought sludging life at the price of some hardening, with the alum left at F-1’s level so that the price is as small as it can be made.

4000 mL + 400 mL + 208 mL = 4608 mL

Liquid in the finished bath, at least

As with the rest of the family, no final volume is published, so no concentration can be stated exactly.

On the acid’s strength. The formula asks for 28 per cent, not glacial. The primer names the confusion between the two as a specific and consequential error, in the direction that matters here: using 28 per cent where glacial is called for gives less than a third of the intended acid. The reverse mistake, on this page, would give three and a half times it.

Behaviour

It fixes at the ordinary rate for its hypo strength. Nothing in the hardener changes what the thiosulfate does: fixation is twice the clearing time, 30 to 40 per cent hypo fixes fastest, and 18 °C is the recommended working temperature with 21 °C as the ceiling.

It should sludge later than F-1 and harden a little less. That is the design, on the primer’s own account of the trade — and it is the one claim on this page most worth testing, because Kodak publishes neither a capacity nor a hardening range for F-14 against which to check it.

Its sulfite reserve is halved, and its acid raised. The consequence is a bath whose margin against sulfurisation is narrower even as its margin against sludging is wider. The two failures pull in opposite directions, and F-14 has moved along that axis rather than escaped it.

When it does start to sludge, the primer has a remedy. At the first sign of a slight precipitate in a bath containing a minimum of acid, add about half as much acid again as the bath originally contained. That advice was written about baths in general; on a bath already carrying F-14’s acid it is worth weighing against simply replacing the tank.

A deep tank’s other enemy is evaporation and topping up, which changes proportions in a way no formula can defend against. Record what goes in.

Image characteristics

None of its own when it is working.

Under-hardening is this bath’s characteristic risk, by the primer’s stated relationship: frilling or reticulation in a warm wash, and a softer emulsion than F-1 would give.

Brown stains on prints mean the bath has gone alkaline and development is continuing in the fixing tank — although prints are not what this formula is headed for.

Fading years later is the consequence of a bath that has thrown sulfur, because the sulfur penetrates the gelatin and stays there.

Insoluble silver complexes are the consequence of using an exhausted bath rather than a weak one. Wall warns that a bath used too long takes longer to fix and forms insoluble transparent silver salts that are difficult to wash out; that is a reason to discard on the clearing time rather than on appearance.

The mechanism

Fixing is F-1’s chemistry, set out there and on how fixer works:

AgBr + 2 S₂O₃²⁻ → [Ag(S₂O₃)₂]³⁻ + Br⁻

The reaction the tank exists for

⚗Why a long-lived bath is an acid one

Aluminium(III) stays in solution only while the bath is acid enough. Every film that enters carries developer, and the developer’s carbonate consumes acetic acid:

CO₃²⁻ + 2 CH₃COOH → CO₂ + H₂O + 2 CH₃COO⁻

What every film spends

When the acid runs out, the pH rises and the aluminium comes down with the sulfite:

2 Al³⁺ + 3 SO₃²⁻ → Al₂(SO₃)₃

The white gelatinous sludge that ends an alum bath

So a bath with more acid takes longer to reach that point, and a bath with less sulfite has less of the other half of the precipitate to give. F-14 has moved in both directions at once. What it gives up is stated by the primer in the same breath: a bath with an excess of acid does not harden as well.

The competing failure has not gone away. The acid is also attacking the thiosulfate, and only the sulfite stands between:

S₂O₃²⁻ + 2 H⁺ → S + SO₂ + H₂O

What the halved sulfite reserve is holding off

Function of every ingredient

Sodium thiosulfate pentahydrate, 960 g in four litres of water. The fixing agent: it converts undeveloped silver bromide into a soluble thiosulfato-argentate complex so that it can be washed out. More fixes faster up to Kodak’s 30 to 40 per cent optimum, above which nothing is gained and Wall sets a 40 to 45 per cent ceiling; less fixes slowly and risks the insoluble intermediate complexes that no washing removes. The form is crystalline hypo, the pentahydrate. Note the wording of the line above it: the hypo is dissolved in four litres of water and not made up to four litres, and Kodak reserves “cold water to make” for the latter, so the working strength is somewhat below 240 g/L by an amount the source does not state.

Sodium sulfite, 30 g — half F-1’s dose against the same hypo. The preservative and the acid reserve: the thing the acetic acid attacks in preference to the thiosulfate. It is also one half of the aluminium sulfite sludge that ends an alum bath, and halving it is one of the two moves this formula makes to postpone that sludge. More would lengthen the bath’s life against sulfurisation and shorten it against sludging; less would leave almost no margin, and the primer names too little sulfite — or a stale tub that has oxidised to sulfate, which is not a preservative at all — as one of the three causes of a sulfur precipitate. The desiccated salt is meant, not the heptahydrate crystals, which would need about twice the weight.

Acetic acid, 208 mL of a 28 per cent solution — the most of the three baths, and the ingredient this formula is really about. Two jobs as always: arresting development by neutralising carried-in alkali, and holding aluminium(III) in solution so the alum can harden rather than precipitate. In a deep tank the second job is the one that runs out first, and the extra acid is a reserve against that. More acid means a still longer working life and still poorer hardening; less would give back the hardening and reintroduce the sludge this bath exists to postpone. The strength matters as much as the volume — glacial acid substituted volume for volume would put three and a half times the acid into the tank.

Potassium alum, 60 g, powdered — the same as F-1 against the same weight of hypo. The hardener: the aluminium(III) that tans gelatin and lifts its melting point so a film survives a wash. It is worth noticing what F-14 does not do, which is cut the alum the way F-2 does; the hardening this bath gives up is given up through the acid’s effect on hardening, not by leaving hardener out. More alum risks brittleness; less risks frilling. Powdered, because lump alum will not dissolve in a cold acid-sulfite solution in any reasonable time. Potash alum rather than chrome alum is the primer’s general preference for a bath in long use, since a chrome alum bath loses its hardening within days whether it is worked or not — an argument that applies with particular force to a deep tank.

Water, twice, and neither volume a make-up. Four litres for the hypo and 400 mL for the hardener, both printed as additions rather than as final volumes. No temperature is given for either on this page, although the F-1a directions the primer sends you to specify about 52 °C for dissolving the hardener’s three solids. The temperature instruction that is given is negative and is the important one: both solutions cold when they meet.

Interactions

With carried-over developer, which is the whole story of a deep tank’s life. Every film spends a little acid; F-14 simply starts with more of it. A rinse before the tank spends less, and the primer’s capacity figures for F-1 show what that is worth — a quarter more sheets, on the rinse alone.

With topping up, which a deep tank invites and which no published formula covers. Adding hypo restores the fixing power and not the acid; adding fresh bath restores both and dilutes the silver. Neither is a replenishment scheme, and Kodak publishes none for a fixing bath.

With warmth, badly. Above 21 °C the bath is apt to precipitate sulfur; above 29 °C it will not stay clear more than a few days.

With a second tank of itself, usefully: the two-bath rotation is the standard defence against the insoluble complexes a tired bath leaves behind, and it suits a deep tank better than it suits a tray.

With acid, in the waste bottle. See Incompatibilities.

Variants

F-1, the general-purpose bath. Twice the sulfite, eight per cent less acid, the same alum. Better hardening, a published hardening range, published capacities, and a shorter life before it sludges.

F-2, the motion picture bath. A fifth of F-1’s sulfite, three-eighths of its acid and two-fifths of its alum — the other economy in the family, and the one Kodak leaves unexplained.

F-1a, the hardener as a keeping stock. F-14’s hardener has its own proportions and is not obtainable by diluting F-1a, but F-1a’s mixing directions are the ones this formula tells the reader to follow.

F-16, the chrome alum bath on the facing page, offered for hot weather. Not written up here: it is a chromium(III) bath under the course’s chromium ruling, and its hardening dies within days with or without use, which makes it a poor choice for the one job — a standing tank — that F-14 is for.

No course variant is offered. The proportions are the formula’s argument, and adjusting them turns it into one of the other two published baths.

Safety

Level B, set at the mixing bench.

Two hundred and eight millilitres of acid per tank is the largest acid volume in this family. At 28 per cent acetic acid is corrosive enough to need gloves and eye protection, and the glacial acid its footnote sends you to in order to make it has a flash point of 39 °C and a vapour that reaches a harmful concentration in a small room by evaporation at ordinary temperatures. The course’s standing practice, from Part X, is to buy acid at a stated dilution and compute the volume.

A deep tank is a large volume of solution and that is itself a hazard class of its own. Four and a half litres of acid fixer is a spill that will not be mopped with a cloth; site it low, and have the spill response to hand before the tank is filled rather than after.

Sulfur dioxide is what this bath gives if a strong acid gets into it, and with half F-1’s sulfite it has less reserve to buffer an accident. Nothing acidic beyond the formula’s own acid goes in.

The solids carry no agreed GHS classification, which is an absence of one rather than a finding of safety; the potassium alum page records the exposure limit for soluble aluminium dust and sodium sulfite records what sulfite gives off in acid.

Storage

A deep tank is storage, and that is the problem this formula addresses. Cover it: an open tank evaporates, concentrates and picks up dust, and the primer’s warning about warmth applies to a standing bath more than to a tray.

No keeping figure is published for F-14. The only statement the primer makes about the keeping of acid fixing baths is the warning about 29 °C. For a formula whose entire design is longevity, that is a conspicuous silence, and this page will not fill it with a guess.

Keep a log against the tank, not a date on a bottle. With no published capacity, the only honest record of what is left is the number of films through it and the clearing time of a test strip. The clearing-time test is the procedure and the batch record is where it goes.

Glass, plastic or a lined tank, never bare metal. Label it per the labelling SOP — formula, strength, date, and the count.

Incompatibilities

Strong acids, which liberate sulfur dioxide and colloidal sulfur; the incompatibilities page treats this as the likeliest serious darkroom accident.

Developer, in either direction — one pair of tongs per tank, and a rinse between.

Ferricyanide baths and their waste, because acid on ferricyanide is the documented route to hydrogen cyanide.

Alkalis, which end the bath at once by putting the aluminium out of solution.

Sulfide toners, whose waste gives hydrogen sulfide on meeting an acid.

Chrome alum baths, a separate chromium(III) waste stream that must not be mixed into an aluminium one.

Waste

A deep tank is the largest single silver-bearing waste a small darkroom will produce, and it arrives all at once. Plan the container before the tank is dumped, not after.

Recovery before disposal where it is available. At darkroom scale the practical route is collection; Part XII sets out what is realistic and the silver-bearing waste SOP is the procedure.

Keep it away from acid wastes and ferricyanide wastes, follow the disposal ruling, and remember that local regulation decides. This course cannot tell you what it says where you are.

Troubleshooting

Milky as soon as the hardener went in. Warm hypo, undissolved hypo, or the hardener added too fast. The pale yellow slow-settling precipitate is sulfur and does not redissolve.

A white gelatinous sludge after long use. Aluminium sulfite, and on this formula it means the acid reserve really has run out. The primer’s remedy at the first sign is about half as much acid again as the bath originally held; once the sludge is general the tank is finished.

Films frilling or reticulating in the wash. The predicted cost of this formula’s design. Wash cooler, or harden separately before fixing with the chrome alum bath, or use F-1.

Fixing has slowed. Time a clearing test. Past 12 to 15 minutes for a slow film, discard the tank.

Froth on the surface, or general milkiness. Exhaustion signs in their own right, per the primer.

A transparent, hard-to-wash stain that appears after drying. Wall’s warning about a bath used too long: insoluble silver salts. Test the wash with the residual hypo and silver tests and shorten the tank’s life next time.

A sharp smell over the tank. Sulfur dioxide, which means acid has got in. Find it.

Experiments

Test the claim this formula is built on. Run F-1 and F-14 side by side, feeding each a measured dose of carbonate solution at intervals to stand in for carried-over developer, and record the number of doses before each throws its white sludge. The primer says the acid-rich bath should go further. Nobody has published the number.

Measure what it costs. Fix identical strips in F-1 and F-14, wash, and heat each in water until the gelatin flows off the support. F-1’s compounded band is 54 to 77 °C; F-14’s is unpublished, and the primer’s relationship says it should be lower. This is the missing half of the trade.

Establish the capacity Kodak did not print. Fix 8 by 10 sheets in a measured volume, timing a clearing test every few sheets, and stop at 12 to 15 minutes. Do it with and without a rinse bath. The clearing-time experiment has the method.

Try the primer’s rescue. When a bath first shows a slight precipitate, add half as much acid again as it originally contained and see how much further it runs — and whether the hardening survives. The advice is published; its result is not.

Weigh the wording. Dissolve 960 g of hypo in 4,000 mL of water and measure the volume you get. That difference is exactly what separates Kodak’s “water” from its “cold water to make”, and it is why no percentage appears on this page.