TF-2 alkaline fixer

Ten grams of Kodalk in a litre of hypo, and four things disappear from the darkroom: the stop bath, the hardener, the hypo clearing agent and most of the wash. That is the claim this formula is built on, and its authors publish it with a caveat you should read before you weigh anything — they would rather you used ammonium thiosulfate.

Ingredient	Quantity	Form the source specifies
Sodium thiosulfate	250 g	no hydrate named; read here as the pentahydrate
Sodium sulfite	15 g	anhydrous
Sodium metaborate	10 g	no hydrate named; Kodalk, read here as the tetrahydrate
Water	to make 1000 mL	750 mL at the head, no temperature given

Purpose

To dissolve the undeveloped silver halide out of a film or a print without the process ever going acid. Every other fixer in this formulary except the plain and printing-out baths is acid on purpose, because acid stops development in the tray and because potassium alum only hardens gelatin in an acid solution. TF-2 gives up both of those and buys three things with them.

The wash gets short. Troop and Anchell’s second edition puts the argument in one line: alkaline fixers allow much shorter washing times and therefore substantial savings in water usage, and removal of hypo is much faster even than when an ordinary fixer plus a hypo clearing agent is used. Film fixed in an alkaline fixer, they write, does not require a hypo clearing agent at all, because hypo is down to archival levels after 40 seconds of washing — a figure they attribute to Haist’s Modern Photographic Processing, volume II, page 203 — although film should still be washed a total of two minutes to remove developer residue. Anchell’s Darkroom Cookbook gives the mechanism in a single clause: keeping the process alkaline or neutral from developer to fixer improves permanence because the thiosulfate will not mordant to the silver image or base.

The thiosulfate stops being attacked. A thiosulfate ion is stable in alkali and unstable in acid. Every acid fixer in this formulary carries sulfite or bisulfite whose main job is to hold back the decomposition its own acid is driving. Remove the acid and that fight is not being fought.

Nothing has to be rinsed out before toning. Anchell’s account of stains in toned prints is that improper fixing is probably their major cause: an exhausted bath leaves insoluble silver compounds that washing cannot remove, and those form a yellow stain when they meet a toner. A non-hardening, non-acid bath removes two of the ways that goes wrong.

!Two books, one formula, and the reason this page can print it

The fixer formulations lesson discusses TF-2 by name and deliberately prints no composition, on the grounds that a formulation documented by specialists rather than by a manufacturer needs a primary source before its quantities can be published, and that the question was not settled.

It is settled here, by the rule the authoring guide records for exactly this case: a formula published by the person who devised it is primary evidence for that formula. TF-2 is printed in The Film Developing Cookbook, which Bill Troop co-wrote, and it is credited to Troop by name in Anchell’s separate Darkroom Cookbook. That is the originator’s own publication plus an independent attribution, which is a stronger position than most of the Kodak formulas in this formulary occupy. The lesson page predates this entry and belongs to another author; it has not been altered.

Recommended uses

Film and paper, undiluted. The Darkroom Cookbook is explicit: use undiluted for either film or paper. There is no stock solution and no working dilution to get wrong.

Materials with little or no silver iodide. This is the authors’ own restriction and it is the most important sentence on the page. TF-2 “would be appropriate to use for negative or print materials that contained little or no silver iodide, such as some hand-coated materials used in alternative processes”. A hand-coated silver chloride or chlorobromide emulsion, a salted paper, a bromide printing paper — these carry no iodide, and the reservation does not apply to them.

Prints you intend to tone. No hardener, no acid, and a bath that leaves less residual thiosulfate in the paper for the toner to react with.

Negatives from a staining developer. The Film Developing Cookbook’s pyro instructions call for an alkaline fixer low in sulfite, because sulfite inhibits the stain, and this bath carries 15 g of it per litre. For scale, the hypo clearing agent printed in the Darkroom Cookbook carries 200 g of sulfite per litre, and a clearing agent is precisely what the pyro instructions tell you to keep away from a stained negative; the course’s own one per cent washing aid, at 10 g per litre, is a third position again. After an alkaline fixer, The Film Developing Cookbook says, the negatives are ready to be washed unless the wash water is acid — Hutchings advises a full 20 to 30 minute wash for PMK anyway, to intensify the stain further. The same reasoning applies to Pyrocat-HD.

Where water is scarce or expensive. The shortened wash is the practical reason most people reach for an alkaline fixer, and it is the one the authors lead with.

When another formula is preferable

• For modern iodide-bearing films, an ammonium thiosulfate bath. This is the authors’ own recommendation, stated in the paragraph that publishes TF-2: they give the formula only for users who are determined to use sodium rather than ammonium thiosulfate. Their own TF-3 puts a 57 to 60 per cent ammonium thiosulfate solution where the sodium thiosulfate stands here, with anhydrous sulfite and metaborate again beneath it at quantities of its own; the course does not print those, because its formulary register does not carry TF-3 as an entry. TF-4 and TF-5 are Photographers’ Formulary products whose compositions are not disclosed.
• Where you want an acid non-hardening bath, F-24, which is the same hypo strength with the alkali replaced by bisulfite — the direct acid counterpart of this formula and a useful comparison.
• Where the emulsion has to be hardened, F-5 or F-6. Sheet film handled wet, tray processing in a busy darkroom, high ambient temperatures: TF-2 offers nothing here, and hardening needs the acid it does not have.
• For a silver printing-out image, Reilly’s alkaline bath, which is the same idea at 15 per cent, alkalised with two grams of carbonate instead of ten of borate, and made fresh for each session.
• To see fixing with nothing else in the tray, plain hypo at 40 per cent, which is this formula with both of its small ingredients removed.
• Where hardening must be avoided but a British-formulary bath is wanted, F-52.

Mixing

Warm water first, then the three solids in the order printed. The formula gives 750 mL of water and no temperature. The temperature comes from the same book’s fixers chapter, and it is a real instruction rather than a convenience: when using the crystalline form of sodium thiosulfate, begin with water of at least 32 °C (90 °F), because dissolving it takes heat out of the water. A quarter of a kilogram of hypo crystals going into 750 mL of water will pull it down several degrees, and a bath mixed at working temperature arrives below it.

Then the sulfite, then the metaborate. Nothing here can precipitate anything else — there is no alum to sludge and no acid to liberate sulfur — so the order is a convenience rather than a hazard. Follow it anyway: dissolving the small ingredients into a solution that is already clear is the only way to see that they have gone.

Expect the metaborate to be slow. The Darkroom Cookbook warns that metaborate may be difficult to dissolve completely at room temperature but that any residual amount will dissolve by itself over a 24-hour period, and that the small residue does not affect the activity. In a bath mixed at 32 °C it is usually gone before you finish stirring.

Then cold water to make one litre. The make-up volume is what fixes the strength, and every figure on this page is computed against it.

🧮Twenty-five per cent, one and a half per cent, one per cent

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

Thiosulfate, read as the pentahydrate

15 g ÷ 126.05 g/mol = 0.119 mol/L, 1.5 % w/v

Sulfite, anhydrous

10 g ÷ 137.86 g/mol = 0.073 mol/L, 1.0 % w/v

Metaborate, read as the tetrahydrate

The hypo is slightly stronger than Kodak’s whole F-family, which puts 240 g of the pentahydrate in a litre of F-5, F-6 and F-24 alike — 1.01 mol/L against 0.97. It is five-eighths of Wall’s 40 per cent plain bath and five-thirds of Reilly’s 15 per cent print fixer.

The sulfite is the interesting one. F-6 carries the same 15 g, and F-24 carries 10 g plus 25 g of bisulfite. In those baths the sulfite is defending the thiosulfate against the formula’s own acid. Here there is no acid, so the same 15 g is doing a smaller job, and the fact that it was not increased is a choice: the bath that strips a pyro stain is a hypo clearing agent, which the Darkroom Cookbook prints at 200 g of sulfite per litre, and a fixer drifting towards that figure would take the stain with it.

Behaviour

It should be odourless. That is Anchell’s own test sentence, and it is diagnostic rather than decorative: this bath contains nothing that can smell. An acid fixer smells of sulfur dioxide, an ammonium bath smells of ammonia. If TF-2 smells of anything, something has gone into it that should not have.

Fixing times are longer than an acid rapid fixer’s, and the authors set them deliberately high. Films get three times the clearing time, or a minimum of five minutes, agitated for a full thirty seconds in each minute. Paper gets ten full minutes with occasional agitation. The three-times rule replaces the traditional twice-the-clearing-time rule for a stated reason: it “will alleviate, though it may not eliminate, concerns about the ability of sodium thiosulfate to fix iodide-containing materials”.

Capacity is twenty 8 × 10 inch sheets per litre, prints or films alike. That is low, and the only comparison the source offers is a product: Photographers’ Formulary TF-4 reaches fifty per litre, which the same page attributes to its greater concentration. Neither book says what sets the limit for TF-2, so the course does not either — capacity is a published number here and not a derived one, and the test below is what you use instead of trusting it.

It tells you when it is finished, twice. The clearing-time test is the primary instrument — clip a scrap of undeveloped film into the bath in room light, time how long it takes to go transparent, and when the clearing time has doubled, mix a fresh bath. The clearing-time test SOP carries the procedure. The secondary sign, which the same chapter gives for fixers generally, is that a bath approaching capacity begins to smell of sulfur; on a formula whose fresh state is odourless, that signal is unusually clear.

No keeping time is published for this formula. The Darkroom Cookbook’s general rule for made-up fixer working solutions is not more than two months, and less above 29 °C (85 °F). No figure for TF-2 in particular was found in either book, so the general rule is what this page records and it is labelled as what it is.

⁇Is a sodium thiosulfate fixer adequate for a modern film? The two books answer differently

Anchell’s Darkroom Cookbook prints TF-2 as a working formula for film and paper, with times, a capacity and no restriction on the material.

Troop and Anchell’s Film Developing Cookbook restricts it. They “only give this formula for users who are determined to use sodium rather than ammonium thiosulfate”, say it “would be appropriate” for materials containing little or no silver iodide such as hand-coated alternative-process materials, and report that preliminary findings were that sodium thiosulfate fixers were not adequate for modern films and papers — that some Kodak researchers went so far as to suggest thiosulfate be replaced altogether, and that layoffs ended the investigation. The second edition adds the reason the problem grew: iodide levels in films and papers increased in the 1980s, when manufacturers refined the ways iodide could be used to improve speed, tone and sharpness.

What the course states. The restriction is the stronger claim because it comes from the formula’s own author and carries a mechanism, so this page leads with it. TF-2 is published here as a fixer for iodide-poor materials — papers, hand-coated emulsions, alternative-process negatives — and as a teaching formula for what one per cent of an alkali does to a fixing bath. For a modern iodide-rich film, fix for three times the clearing time as the authors direct, and run a residual silver test before you trust it with anything you cannot re-shoot. No measurement of residual silver from TF-2 on a named modern film was found in either book, and the course has none of its own.

Image characteristics

No colour, no stain and no signature of its own. A fixer that is working correctly leaves nothing behind. What distinguishes this one is what it fails to leave behind: thiosulfate.

The emulsion comes out soft. There is no hardener, and no acid in which a hardener could work, so the gelatin is fully swollen and easily marked while wet. On roll film in a tank that is a non-issue; on sheet film handled in a tray, or on a fibre print squeegeed carelessly, it is the practical price of the formula. Anchell’s judgement for tray-processed paper is that hardener is unnecessary unless you habitually scratch prints; for sheet film he takes the opposite view.

A pyro stain survives it. The low sulfite is the reason, and it is the reason the same authors send pyro users to an alkaline fixer low in sulfite and away from a hypo clearing agent, whose sulfite concentration would remove the stain.

Prints tone without an intervening acid to chase out. The visible failure this avoids is the yellow stain that appears when a toner meets residual silver compounds left by an exhausted fixer — which is, in Anchell’s account, probably the major cause of stains in toned prints.

What you should never see is a milky bath or a pale yellow deposit. Both mean acid has reached the thiosulfate, and on this formula there is only one way that can happen: it came in from outside.

The mechanism

Fixing itself is the same chemistry in every bath on this shelf. Thiosulfate binds silver far more strongly than the halide lattice does, two ligands to each silver ion, and the resulting argentothiosulfate anion is soluble.

AgBr + 2 S₂O₃²⁻ → [Ag(S₂O₃)₂]³⁻ + Br⁻

Fixing: silver bromide into the soluble bis(thiosulfato) complex

What is different about TF-2 is not that reaction but the pH the reaction is run at, and three consequences follow from it.

Why acid is what a thiosulfate bath is afraid of

Acidify a thiosulfate solution and the ion decomposes, throwing out elemental sulfur and leaving hydrogensulfite behind:

H⁺ + S₂O₃²⁻ → S + HSO₃⁻

What an acid fixer spends its sulfite preventing

This is the reaction that dictates the design of every acid fixer in this formulary. F-24 carries 25 g of bisulfite to make the bath acid and 10 g of sulfite to push this equilibrium back; F-5 and F-6 carry acetic acid and sulfite doing the same two-sided job. TF-2 removes the left-hand side of the equation entirely. The 15 g of sulfite it retains is not fighting the formula’s own acid — there is none — it is guarding against oxidation and against the oxidised developer arriving on every film.

What the metaborate actually does

Sodium metaborate is not simply “an alkali”. Dissolved, it hydrolyses to boric acid and hydroxide, and the pair that results is a buffer:

BO₂⁻ + 2 H₂O ⇌ H₃BO₃ + OH⁻

Metaborate in water: a borate buffer, not a slug of alkali

A buffer is what this formula needs and a strong alkali is not. Every sheet of film brings in a little developer and a little water; a bath held by an equilibrium absorbs those insults and returns to nearly the same pH, while an equivalent dose of hydroxide would move with every one of them. Kodak sold this salt as Kodalk precisely for that property, and The Darkroom Cookbook describes it as more alkaline than borax and more easily soluble but less alkaline than carbonate, containing no free carbonate — so no carbon dioxide is evolved if an acid ever does reach it, and no blisters follow.

⚗What pH is this bath? Nobody in the course's sources measured it

Two numbers exist and neither of them is the answer.

HSDB gives the pH of a metaborate solution against concentration at 20 °C: 10.52 at 0.1 % w/v, 11.0 at 1.0 %, 11.4 at 4.0 %, 12.0 at 15 %. TF-2 carries exactly 1.0 % w/v of the tetrahydrate, so the alkali on its own, in water, would read pH 11.0. Notice how flat that column is — a hundred-and-fifty-fold change in concentration moves it 1.5 units. That flatness is the buffering.

The bath is not that solution. It also holds a mole per litre of thiosulfate and 0.12 mol/L of sulfite, both of which are basic anions with their own equilibria, and the ionic strength is enormous. The Darkroom Cookbook’s own approximate pH scale places an alkaline fixer at 8.5 to 9.5, and The Film Developing Cookbook, discussing how one would design such a bath, says an alkali buffering system should keep the pH “within the desired range, which will probably be between 8.5 and 10” and names metaborate with bisulfite as a combination worth trying.

So the course states this and no more: no pH for TF-2 itself was found in either book, the class it belongs to is put at 8.5 to 9.5 by one of its own authors, and the only measurement anyone reading this page can rely on is their own. That is what the pH experiment at the foot of this page is for.

Why the wash is shorter

Thiosulfate is removed from a material by diffusion, and diffusion out of gelatin is fast. What makes an ordinary wash long is the fraction of thiosulfate that is not simply dissolved in the swollen layer but held — mordanted, in Anchell’s word — to the silver image and to the paper base. That holding is a pH-dependent adsorption, and it is much weaker on the alkaline side. Keep the process alkaline or neutral from developer to fixer, he writes, and permanence improves because the thiosulfate will not mordant to the silver image or base. Troop and Anchell put a figure on the result: hypo down to archival levels after 40 seconds of washing, attributed to Haist, with two minutes recommended anyway to clear developer residue.

There is a second, purely physical contribution, and it is the weaker of the two. An acid hardening bath tans the gelatin; an unhardened layer swells more and lets ions out faster. But Kodak’s 1924 primer denied outright that hardened material washes more slowly, and the fixer formulations lesson records that disagreement rather than settling it, so nothing on this page rests on it.

Why iodide is the limit

Silver iodide is very much less soluble than silver bromide, and the same complex forms far more reluctantly:

AgI + 2 S₂O₃²⁻ → [Ag(S₂O₃)₂]³⁻ + I⁻

The same reaction on the halide that resists it

Ammonium thiosulfate is the more powerful complexing agent — The Darkroom Cookbook records that a 15 to 20 per cent ammonium thiosulfate solution fixes more rapidly than a 35 to 40 per cent sodium thiosulfate solution — which is why the authors’ answer to a modern iodide-rich emulsion is TF-3 or TF-4 rather than TF-2, and why, if you use TF-2 anyway, the fixing time goes to three times the clearing time instead of twice.

Function of every ingredient

Sodium thiosulfate, 250 g, read as the pentahydrate. The fixing agent, and just over ninety per cent of the dissolved solids by weight. It supplies the thiosulfate ions that convert undeveloped silver bromide and silver iodide into the soluble bis(thiosulfato) anion. More than 25 per cent buys very little: the capacity limit here is how much silver the bath can carry as the soluble complex, and a fixer discarded on a twenty-sheet count never reaches a thiosulfate-limited state. Every extra gram is also another gram to wash out, which is the property the formula is designed around. Less moves the bath towards the region where the one-ligand and three-ligand complexes matter and where incompletely complexed silver stays in the layer — the classic under-fixed negative that looks clear and yellows two years later.

The hydrate is not stated, and the course does not pretend otherwise. Both books print “Sodium thiosulfate” with no qualifier, and the Darkroom Cookbook prints “Sodium thiosulfate, pentahydrate” elsewhere in its own pages when it means to say it. Three things decide the reading used here. The course’s own chemical registry maps the unqualified name to the pentahydrate. The Darkroom Cookbook’s printing of Kodak F-24 on a nearby page gives “Sodium thiosulfate, 240.0 g” where Kodak’s own data book gives “Sodium Thiosulfate (Pentahydrated), 240.0 grams” — the same weight, so Anchell’s unqualified line demonstrably means Kodak’s pentahydrate. And the same chapter’s mixing advice concerns “the crystalline form of sodium thiosulfate”, which is the pentahydrate. If the anhydrous salt were meant instead, 250 g would be 1.58 mol/L, equivalent to 392 g of the pentahydrate — a 39 per cent bath, half as strong again as anything else in this formulary, and not something an author would print without comment.

Sodium sulfite, 15 g, anhydrous. The preservative, and the one ingredient whose form the source states outright. It scavenges dissolved oxygen and reduces the oxidised developer that arrives on every sheet, so the bath does not discolour and the material does not carry oxidation products into the wash. In an acid fixer, sulfite has a second and larger job — holding back the acid decomposition of thiosulfate — and here it has none, because there is no acid. More sulfite would be pointless at best and damaging at worst: sulfite is a mild silver halide solvent in its own right, and at high concentration it strips the stain from a pyro negative, which is exactly why the same authors route pyro users away from a hypo clearing agent. Anchell’s own printed clearing agent carries 200 g of sulfite per litre — more than thirteen times what is in this bath, and twenty times the 10 g per litre of the course’s one per cent washing aid. Less, or none, and the bath is plain hypo with an alkali in it, which will discolour as soon as it starts taking developer.

Sodium metaborate, 10 g, Kodalk, read as the tetrahydrate. The alkali, the buffer, and the whole formula. Its job is not to make the bath strongly alkaline but to put it on the alkaline side of neutral and hold it there against everything the process carries in. From that one property come all four of the claims on this page: the thiosulfate is not decomposed, so the bath is odourless and does not throw sulfur; the thiosulfate does not mordant to the image or the base, so the wash is short and no clearing agent is needed; nothing acid is wanted in front of it, so the stop bath goes; and there is no acid for an alum to work in, so the hardener goes too. More metaborate raises the pH slowly — the concentration curve is flat — and mostly buys buffering capacity rather than alkalinity, but it is not what the authors specify and an alkaline ammonium thiosulfate bath treated the same way would liberate ammonia, which is the hazard the ammonium thiosulfate page records. Less, and the reserve runs out sooner; none, and you have Wall’s plain hypo bath, which goes alkaline or acid according to whatever last touched it.

The hydrate is not stated here either. Both books print “Sodium metaborate”. The Darkroom Cookbook records that metaborate is commonly sold in the octahydrate state as the most stable form, and that metaborate octahydrate and Kodak’s Balanced Alkali (Kodalk) are for all practical purposes the same and may be substituted weight for weight. The salt sold under those names is the one this course files as the tetrahydrate: NaBO₂·4H₂O is also written Na₂B₂O₄·8H₂O, the same compound expressed for the dimer rather than the monomer. The reading matters, because 10 g of the tetrahydrate is only 4.77 g of the anhydrous salt; anyone weighing out anhydrous metaborate gram for gram would put twice the alkali in the bath.

Water, to make 1000 mL, warm to start. The 750 mL at the head of the formula is the dissolving volume and the litre at the foot is the strength. The temperature is not printed with the formula and is not invented here; what the same book states, in its fixers chapter, is that crystalline sodium thiosulfate should be started in water of at least 32 °C (90 °F), because dissolving it is endothermic and a bath mixed at working temperature will not be at working temperature when it is finished.

Interactions

With the developer in front of it — a water rinse, not a stop bath. This is the interaction the formula is built around. TF-2’s own directions replace the stop with a 60-second plain water rinse or a minimum of five full changes of water. An acid stop bath would spend the metaborate reserve that the formula exists to provide; Anchell states the rule flatly — in order to preserve the alkalinity of the fixer, acid stop bath should not be used.

If you insist on an acid stop, there is a published way to do it. The second edition allows for the user who wants an acid stop before an alkaline fixer and specifies the price: rinse the film in running water for 30 seconds after the stop bath and before the fixer. That is the whole accommodation, and it is worth noticing that the accommodation is a wash.

Never a potassium stop bath. The Film Developing Cookbook is emphatic and gives a mechanism: developers or stop baths high in potassium salts can partly convert ammonium or sodium thiosulfate into potassium thiosulfate, which is inactive compared with the ammonium and sodium salts. Its first listed precaution is never to use a stop bath based on potassium metabisulfite or another potassium salt. If you want an acid stop in the sequence at all, the citric acid bath this course publishes is citric acid and water and carries no potassium — but it is still an acid, so the 30-second rinse above still applies.

With the wash after it — favourably, and that is the point. No hardening, no acid, an unmordanted thiosulfate, and a 40-second figure for reaching archival levels which the authors nevertheless extend to two minutes for developer residue. This is one of the few baths where the honest advice is that the wash can be shorter, and it is still worth testing rather than trusting: the residual hypo and silver test SOP is how.

With a hypo clearing agent — unnecessary, and with pyro, harmful. Film fixed in an alkaline fixer does not require a clearing agent at all. With a staining developer it is worse than unnecessary: the same book tells you to avoid a clearing agent with pyro developers, because the sulfite concentration of such a bath — 200 g per litre in the formula Anchell prints — removes the stain.

With a hardener — chemically incompatible. Potassium alum hardens gelatin only in an acid solution, and an alum bath whose acid has been spent throws a white gelatinous aluminium sulfite sludge instead of hardening; the fixer formulations lesson carries Kodak’s account of it. There is no hardening variant of this formula and there cannot be one.

With toners — the reason many printers mix it. No hardener means a more receptive emulsion, and no acid means less to rinse out before the toner goes on.

With the silver it accumulates. The bath is the silver stream. Twenty sheets per litre is a comparatively rich solution by the time it is discarded, and it goes to recovery, not down the drain.

Variants

TF-3, by the same author, is the ammonium version and is the one the authors would rather you used. Its ingredient list is a 57 to 60 per cent ammonium thiosulfate solution in place of the sodium thiosulfate, with anhydrous sodium sulfite and sodium metaborate again beneath it — at its own quantities, which are not the quantities on this page and are not printed here, because TF-3 is not an entry in this course’s formulary register. What it buys is speed and the ability to cope with iodide.

TF-4 and TF-5 are Photographers’ Formulary products and their compositions are not published. Troop records in the second edition that he formulated TF-4 for the Formulary with the encouragement and advice of Grant Haist and Harold Russell, and that it was the first alkaline fixer ever offered for sale as such. The Darkroom Cookbook notes that TF-4’s greater concentration raises its capacity to fifty 8 × 10 sheets per litre and that its slightly lower alkalinity reduces the ammonium odour. Those are behaviour statements about a product, not a formula, and this course treats a bought product whose maker does not publish its composition as a different kind of page.

The ammonium route is faster and it is not free. An alkalised ammonium thiosulfate bath gives off ammonia — which is why TF-4’s lower alkalinity is described as an improvement rather than a loss, and why Kodak’s own guidance, recorded on that chemical’s page, says the pH of an ammonium-based fixer should not be raised above 7.8 to 8.0 for that reason. TF-2 is the one member of this family with no such ceiling, because a sodium salt has no ammonium ion to give a proton up from. That is the compensation for its speed and its trouble with iodide, and it is the reason the formula is still worth mixing.

Reilly’s alkaline fixing bath is the same idea from the other end of the subject — 15 per cent hypo alkalised with 2 g of sodium carbonate, for albumen and salted paper. Comparing the two is instructive: Reilly needs alkalinity to stop an acid bath bleaching a printing-out image, and reaches for the smallest possible dose of a carbonate; Troop needs alkalinity to shorten a wash on a developing-out material, and reaches for five times as much of a buffer. Same principle, different problem, different quantity.

F-6 uses the identical alkali for the opposite purpose. Kodak’s odourless hardening bath puts 15 g of Kodalk into an acid fixer, where it neutralises part of the acetic acid and becomes boric acid in the tray. The same salt, five grams more of it, and a bath that hardens, smells less than F-5 and still needs a stop bath in front of it. Set the two formulas side by side and you can read off exactly what an alkali does and does not decide.

No modified version of TF-2 appears in this formulary. The course has found none published by anyone, and a fixer whose entire design is a single buffered alkali is not a formula that invites tinkering: change the metaborate and you have changed the only thing it is.

Safety

Level B, and the reason is the metaborate rather than the fixer. Set that beside plain hypo and F-24, which this course classes A.

• Sodium metaborate tetrahydrate carries the signal word Danger in the aggregated GHS classification, with H319 (causes serious eye irritation) and, in a substantial minority of the notifications, H360 (may damage fertility or the unborn child) or the weaker H361. The evidence base is thin — 149 reports across 7 notifications — and the notifiers disagree, but a suspected reproductive toxicant is not something to weigh out casually. A photographer who is pregnant, breastfeeding or trying to conceive should read the chemical page before handling the dry salt.
• Sodium sulfite is classified Danger, with H314 (causes severe skin burns and eye damage), H319, H315 and H302 across a large and divided notification set.
• Sodium thiosulfate pentahydrate has no agreed GHS classification at all: 98.6 per cent of the reports say it meets no hazard criteria. That is an absence of an agreed classification on a thin sample, not a finding that nothing can go wrong.

The controls. The dry metaborate and the dry sulfite are the hazardous states, so weigh both with the tub at the back of the bench, without raising dust, following the weighing SOP; nitrile gloves, splash goggles rather than spectacles while weighing and while the bath is being made, and an apron. Once mixed, this is a 1 per cent borate solution in a strong salt solution, and the routine handling of it is the routine handling of any tray chemistry. The mixing a fixer SOP carries the sequence.

What is not a hazard here, and why. There is no acid in the formula and none should ever reach it, so the route by which every acid fixer in this formulary can evolve sulfur dioxide does not exist. There is no alum, so no aluminium salt and no sludge. There is no ammonium salt, so there is no ammonia — and this is the one respect in which the sodium formula is genuinely better than its ammonium successors, because an alkaline ammonium thiosulfate bath is the combination that liberates ammonia and is the reason ammonium fixers carry a manufacturer’s ceiling on pH. Nothing here is heated, nothing is volatile, and the ventilation that matters in this part of the darkroom is general room ventilation rather than local extraction. That is a hazard assessment of this bath, not a general statement about fixers.

Storage

The made-up bath. No keeping time for TF-2 was found in either book. The general rule the Darkroom Cookbook gives for working fixer dilutions is not more than two months, and less if the ambient temperature is over 29 °C (85 °F). Keep it in a full, stoppered, labelled bottle rather than a part-full one, and treat the twenty-sheet capacity and the doubled clearing time as the real limits; the calendar is the outer bound, not the working one.

The dry chemicals. Hypo crystals deliquesce slightly in damp air and cake, which does not spoil them but does make a weighing unreliable. Anhydrous sodium sulfite oxidises slowly to sulfate in a part-full tub and is the first ingredient to go stale. Sodium metaborate tetrahydrate melts at 53.5 °C, so a tub left on a radiator or in a car in summer will fuse into a solid lump; store it cool and sealed.

Everything in a container that has never held food, labelled with the substance, the hydrate, the strength and the date, per the labelling SOP.

Incompatibilities

Acids of every kind, and this bath has no acid reserve at all — only a base reserve. A splash of stop bath, an acid-contaminated tray, an acidic tap water: any of them pushes the bath towards the sulfur reaction and destroys the property it was mixed for. See incompatibilities.

Acid stop baths specifically, which are not merely unnecessary in front of TF-2 but are counter-indicated by its author.

Potassium salts, from any direction — a potassium metabisulfite stop bath, a developer heavy in potassium carbonate. Potassium thiosulfate is inactive as a fixing agent, and a bath partly converted to it fixes slowly for no visible reason.

Alum and any hardener, which cannot work at this pH and would precipitate rather than harden.

Oxidising agents. Thiosulfate oxidises to tetrathionate, which attacks a silver image. That is the general reason peroxide, persulfate and hypochlorite stay out of a darkroom, and the particular reason the HE-1 hypo eliminator is not used on material this course cares about.

Silver nitrate and the coating bench. A trace of any fixer on a rod, brush or tray ruins the next sheet before it is exposed. Separate everything, per the silver nitrate handling SOP.

Waste

Spent TF-2 is silver-bearing waste and is the most concentrated waste stream this formula produces. Twenty 8 × 10 sheets per litre means the bath is discarded holding most of the silver those sheets shed — on a film, close to the whole of the undeveloped halide. It goes into the silver-recovery container, not down the drain, and the silver-bearing waste SOP carries the handling. Consult the disposal ruling for the reasoning the course applies.

The borate is the second consideration and it does not go away. Borate is not degraded by a sewage works; it passes through. The metaborate page records Kodak’s J-52 figure of 5.6 to 9.4 as the pH window sewer codes most frequently set, and this bath is alkaline enough to be worth a thought on that count alone.

Do not mix it with acid wastes in the same container. An alkaline thiosulfate solution meeting an acid waste is the sulfur reaction at bucket scale, in a closed drum, unattended.

Local regulation decides, and this course cannot tell you what it says where you are. Collect, label, and use the route your authority provides.

Troubleshooting

A smell of sulfur, or a pale yellow cloudiness, in a fresh bath. Acid has reached it — carried in on film, left in the tray, or present in the water. The bath is finished; discard it, wash the tray, and find the acid before mixing another. Anchell’s odourless test exists for exactly this.

A smell of sulfur in a bath that has done work. Different diagnosis: a bath approaching capacity begins to smell of sulfur. Check it against the twenty-sheet count and the clearing time.

Clearing time has lengthened. When it has doubled, mix a fresh bath — that is the published rule, and it is more reliable than counting sheets because it measures the bath rather than your memory of it. The clearing-time test SOP is the procedure.

Negatives look clear coming out but go yellow or milky later. Under-fixing, and on this formula the first suspect is iodide. Modern films carry more of it than films of the 1970s did, sodium thiosulfate complexes it reluctantly, and the authors’ three-times-clearing-time rule exists to compensate. Refix a recently processed film in a fresh bath and rewash; check with a residual silver test.

Prints yellow at the edges after toning. In Anchell’s account this is the major cause of stains in toned prints: an exhausted bath left insoluble silver compounds that washing could not remove, and the toner found them. Two baths in rotation, per the two-bath fixing SOP, and a stricter discard point.

Undissolved white grains in the bottom of the bottle after mixing. Almost certainly the metaborate, which the Darkroom Cookbook says can be slow at room temperature and will dissolve by itself within 24 hours. Mix warmer next time. If the grains persist beyond a day, they are not metaborate.

Scratches and finger marks on wet film. There is no hardener; that is the trade. Handle by the edges, and if the problem recurs on sheet film, the honest answer is that this formula is the wrong one for your handling and F-6 is the right one.

The bath fixes slowly from the first sheet. Check what came before it: a potassium-based stop bath or a potassium-rich developer carried in will have converted part of the thiosulfate to the inactive potassium salt.

Experiments

Measure the pH — the course cannot tell you what it is. Calibrate a meter with the pH SOP and read three solutions: 10 g/L of sodium metaborate in distilled water, the finished TF-2 bath, and the same bath after ten sheets. HSDB puts the first at 11.0 and the Darkroom Cookbook’s scale puts the class of the second at 8.5 to 9.5. The gap between those two numbers is the effect of a mole of thiosulfate per litre, and no source this course holds has measured it.

Test the wash claim directly. Process two identical films, fix one in TF-2 and one in F-24, then wash both for one, two, five and ten minutes, taking a clip at each interval, and run the residual hypo test on every clip. The authors’ claim is 40 seconds to archival levels; this is the experiment that either supports it in your water at your temperature or does not.

Test the iodide reservation. Fix matched strips of a modern tabular-grain film and of a hand-coated or chloride-rich material for twice and for three times the clearing time, then run a residual silver test on all four. This is the authors’ own hedge turned into a measurement, and it is the single most useful thing a reader of this page can do.

Track the capacity honestly. Fix sheets through a litre one at a time, measuring the clearing time of a film clip every fifth sheet, and plot clearing time against sheets fixed. You will get a curve that is flat and then is not, and the point where it doubles is your capacity rather than Anchell’s. Record it in a batch record so that the next litre can be compared.

Isolate the metaborate. Mix one litre of TF-2 and one litre of the same bath with the metaborate left out — which is 25 per cent plain hypo with a little sulfite in it — and run both through the same sequence with a water rinse in front. Compare clearing time on day one, the smell after a week of use, and residual hypo after a two-minute wash. Ten grams is a small weight to be carrying an entire argument, and this is the test of whether it does.

Test whether the stain survives. For PMK or Pyrocat-HD users: develop two identical negatives, fix one in TF-2 and one in an acid fixer, and read the stain density through a blue filter. The authors’ claim is that a low-sulfite alkaline fixer keeps the stain a high-sulfite bath would remove.