PMK pyro

A developer designed backwards. Every other film developer in this formulary tries to keep its oxidation products out of the negative; PMK is built to put them in, and almost every unusual thing about it — the fifth of a gram of preservative, the water stop bath, the fixer that must not harden, the twenty-minute wash — follows from that one decision.

A Solution — the developing agents and their acid preservative

Ingredient	Quantity	Form the source specifies
Sodium bisulfite	5 g
Metol	2.5 g
Pyrogallol	25 g
Water	to make 250 mL	at 24 °C; The sheet prints "Distilled Water 75°F 200 ml" as the starting volume and "Distilled water to make 250 ml" as the close, so this is a make-up volume at a stated temperature; 75 °F is 24 °C. Rempel and Anchell start their litre-scale version from 750 mL rather than 800, and give no temperature. The starting water differs; the make-up volume, and therefore the strength, does not.
The bisulfite goes in twice and the schema can only list it once. The sheet's order is a small pinch of the sodium bisulfite into the water, then all the metol, then the rest of the bisulfite, then the pyrogallol under ventilation - which is Kodak's 1928 rule for a metol-and-sulfite stock, printed again in the 1990s.

B Solution — the alkali, alone in its bottle

Ingredient	Quantity	Form the source specifies
Sodium metaborate tetrahydrate	150 g	The sheet says only "Sodium Metaborate" and explains that Kodalk is Kodak's proprietary name for it. The course reads that as the hydrate actually sold, which is the tetrahydrate - the hydrate is the one thing about this ingredient a buyer must check.
Water	to make 500 mL	at 24 °C; "Distilled Water 75°F 350 ml", then "Distilled water to Make 500 ml". The sheet says distilled water is a MUST here because the solution is highly concentrated and metaborate may precipitate from impure water, and that any residue will dissolve of itself within 24 hours without affecting activity.

Mixed in the ratio — the working developer, mixed at the tank and used once

1 part A Solution + 2 parts B Solution + 100 parts water

1 Part A + 2 Parts B + 100 Parts of water. Example: 10 ml A + 20 ml B + 1000 ml of water make approximately one liter of working solution. It does not matter whether A or B is added first. When PMK is mixed together, the solution will immediately proceed through color changes from gray-green to pale amber. This is an important visual check of solution activity. If there is no color change, something is wrong. Use immediately.

The 1,030 mL that results carries 0.097 g/L of metol, 0.194 g/L of sodium bisulfite, 0.971 g/L of pyrogallol and 5.83 g/L of sodium metaborate tetrahydrate. Anchell and Troop print the same bath as 0.1, 0.2, 1 and 6 grams per litre.

Purpose

To develop a modern film to a silver image and a coloured image at the same time, and to keep the second one. Pyrogallol’s oxidation product is coloured and is laid down in the gelatin along with the silver it made, in proportion to how much development happened there. BERGGER describes the result precisely: a yellow-green tint surrounds each silver grain and fills the usually empty space between grains, so that the density of a pyro negative is the conjunction of two densities, the silver’s and the colour’s.

That is not new — it is what every nineteenth-century pyro developer did, and what D-167 and Kodak’s A.B.C. pyro still do. What is new in PMK is the balance. Photographers’ Formulary prints the design brief in its own words: the formula “is constituted to achieve the best overall results in consideration of the following technical criteria: sharpness, maximum image stain, minimum general stain, edge effects, film speed, flexibility for zone system Plus and Minus development, stability, consistency, convenience of use and long shelf-life.”

Read that list carefully, because the second and third items are a pair and they pull against each other. Image stain is the colour that tracks the silver and is therefore part of the picture. General stain is the same colour spread over areas that never developed, which is fog with a hue. The staining and tanning developers lesson sets out the difference and how to tell them apart on a light box; this page does not repeat it.

What the name says. PMK is Pyro-Metol-Kodalk. The Formulary’s sheet spells it out and adds the piece that dates it: “Kodak has changed the name KODALK to ‘Balanced Alkali’; this is their proprietary name for sodium metaborate.” The developer is named after its three active ingredients and one of the three is named after a trade name that no longer exists.

Recommended uses

Sheet film for silver printing, which is what it was tested on. Both makers publish times for roll film too, and the Formulary’s minimum-volume rule is written in rolls as well as sheets, but the formula came out of large-format practice and its published Zone System flexibility is a sheet-film idea.

Negatives intended for a variable-contrast paper. A yellow-green stain is itself a filter over the blue-sensitive component of the paper, and that is the case where the second density does the most work. The mechanism, and the reason it behaves quite differently on a graded paper, is in the staining lesson.

Where the highlights of a contrasty subject have to hold detail. BERGGER’s claim is detailed highlights, and the Formulary’s is flexibility for minus development. Neither publishes a curve.

Where the darkroom is warm and cannot be cooled. This is the practical case both makers make most loudly, and it is unusual: PMK publishes a working range rather than a temperature. The Formulary gives a rule — reduce the development time by 4 per cent for each degree Fahrenheit above the standard — and says “do not hesitate to use the higher temperatures”. BERGGER publishes three whole columns, at 21, 24 and 27 °C.

Where a developer has to sit on a shelf for years between uses. Both makers claim an extraordinary keeping life for the concentrates, and the Formulary’s version of the claim is “indefinite”.

When another formula is preferable

• Where a stain is not wanted at all, D-76 or D-23. A hundred grams of sulfite per litre is the opposite end of the same dial, and D-76 is the reference every other developer is described against.
• Where the darkroom cannot handle a Level B agent. Pyrogallol decides this page’s classification, and no amount of care with the rest of the formula changes it. See Safety.
• Where a shorter time, more speed and less toxicity are worth a different stain colour, Pyrocat-HD. Bostick and Sullivan’s kit sheet states the case as Sandy King’s own: against PMK, about a third of a stop more effective film speed, 10 to 15 per cent shorter development times, more consistent staining action, lower toxicity, and no streaking or mottling with reduced agitation. Those are the formulator’s claims, relayed by his supplier, and the course records them as claims. Its entry is planned and not yet written.
• Where the process after the tray cannot be changed. PMK requires a non-acid stop, a non-hardening fixer, no hypo eliminator and a twenty-minute wash. A darkroom already committed to an acid stop and a hardening rapid fixer will strip much of what it has just paid for; that is documented below under Interactions.
• Where agitation has to be minimal or intermittent. BERGGER’s development-errors section attributes uneven density, uneven colouring, edge density and streaks to insufficient or clumsy agitation, and both makers specify agitation every 15 seconds. This is not a stand-development formula, and neither sheet offers one.
• For rapid dish work with a stain, D-167, which develops in two to three minutes where PMK takes nine to sixteen.

Mixing

Two bottles, mixed once, then a working bath mixed at the tank and thrown away.

1. A Solution, 250 mL. Start with 200 mL of distilled water at 75 °F (24 °C). Take a small pinch of the sodium bisulfite and add it to the water. Add all the metol and stir until it has dissolved completely. Add the remaining bisulfite and stir until dissolved. Add the pyrogallol — outside or under a ventilating hood, in the sheet’s own words — and stir until it has dissolved completely. Distilled water to make 250 mL.
2. B Solution, 500 mL. 350 mL of distilled water at 75 °F, then 150 g of sodium metaborate. Distilled water is not a preference here, it is the instruction: the sheet capitalises MUST, on the grounds that the solution is highly concentrated and a considerable quantity of the metaborate may precipitate if the water is not pure. Any residue will dissolve of itself within 24 hours and the small amount left will not affect activity even if the solution is used at once. Distilled water to make 500 mL.
3. The working developer. 1 part A, 2 parts B, 100 parts water — 10 mL, 20 mL and 1,000 mL make about a litre. It does not matter which stock goes in first. Use it immediately.

⚗Why the pinch of bisulfite comes before the metol, and the rest after

This is a 1928 Kodak rule printed again on a 1990s kit sheet, and it is worth understanding rather than obeying.

Kodak’s general rule is that the preservative is dissolved first, because a developing agent dissolved in plain water begins to oxidise at once and the sulfite protects it. Its stated exception is metol — Kodak’s Elon — which is “a combination of an insoluble base with an acid which renders it soluble”. Put the metol into a sulfite solution and the weak alkali neutralises the acid part and the insoluble base drops out as a white precipitate. The primer’s numbers are the useful half: once the metol is dissolved it takes a fairly high concentration of sulfite to bring it out again, but only a low concentration to stop it dissolving in the first place.

So the two rules collide, and the answer both Kodak and the Formulary give is to split the preservative. Kodak: “Some direction sheets recommend that a portion of the sulphite should be dissolved in order to prevent the oxidation of the Elon, then dissolve the Elon, and then the remainder of the sulphite. Many workers add a little of the solid sulphite to the Elon when dissolving the latter.” The Formulary: “Take a small pinch of sodium bisulfite and add it to the water. Add the metol… Add the remaining sodium bisulfite.”

The pyrogallol goes in last because it is the ingredient that oxidises fastest and there is now a preservative waiting for it, and it goes in under ventilation because it is a dusty solid. Kodak’s other rule applies throughout: dissolve each chemical completely before adding the next, because a crystal still sitting in the solution when the next ingredient arrives oxidises at its surface and the result gives fog.

🧮What 1 + 2 + 100 actually puts in the tank

Ten millilitres of A, twenty of B and a thousand of water make 1,030 mL. The two stocks are not diluted by the same factor: A by 103, B by 51.5, which is what taking twice as much of one of them means.

10 g/L in A × (10 mL ÷ 1,030 mL) = 0.097 g per litre of working solution

Metol

20 g/L in A × (10 ÷ 1,030) = 0.194 g per litre

Sodium bisulfite

100 g/L in A × (10 ÷ 1,030) = 0.971 g per litre

Pyrogallol

300 g/L in B × (20 ÷ 1,030) = 5.83 g per litre

Sodium metaborate tetrahydrate

Anchell and Troop print these four numbers, rounded, as the composition of the working bath: metol 0.1 g, sodium sulfite anhydrous 0.2 g, pyrogallol 1 g, sodium metaborate 6 g, water to make 1 litre. That is a fourth source arriving at the same place from the other direction, and it is the best single check that the stocks above have been read correctly. Notice the one word they change: the stock holds bisulfite and they write the diluted bath as sulfite, because by the time the two bottles have met, the alkali has taken the acid proton off it. That is their reading of the chemistry, not a different quantity.

Now put the preservative beside the developers it is supposed to preserve, in moles:

0.971 g/L ÷ 126.11 g/mol = 7.70 mmol/L

Pyrogallol

0.097 g/L ÷ 344.39 g/mol = 0.28 mmol/L

Metol

0.194 g/L ÷ 104.06 g/mol = 1.86 mmol/L

Sodium bisulfite

5.83 g/L ÷ 137.86 g/mol = 42.3 mmol/L

Sodium metaborate tetrahydrate

There are four molecules of pyrogallol for every bisulfite ion, and twenty-seven for every molecule of the metol salt — which is fourteen for every molecule of the p-methylaminophenol that salt carries, since metol is (C₇H₉NO)₂·H₂SO₄ and one formula unit releases two of them.

Set the preservative against D-76’s hundred grams of sodium sulfite per litre — 0.79 mol/L — and PMK’s working bath carries about one four-hundredth of it. Against Kodak’s A.B.C. pyro at 10.5 g/L of sulfite in the tray, already described in this course as a deliberately inadequate preservative, PMK carries about one forty-fifth. This is the arithmetic behind every other statement on the page.

Behaviour

It is dilute, it is slow, and it is used once. Nine to sixteen and a half minutes at 21 °C across the published films, from a bath holding less than a gram of developing agent per litre. The Formulary states it flatly: “PMK is a one-shot developer.”

Both makers publish a minimum quantity of developer, and their two figures do not agree. The Formulary sets a floor — a minimum of 300 mL per 80 square inches of film, which it glosses as one 36-exposure 35 mm roll or four 4 by 5 sheets — and explains why the floor exists: “because it is so dilute”. BERGGER sets a ceiling on film instead: 1,000 cm² per litre, listed as two 8x10 sheets, eight 4x5 sheets, one 220 roll, two 120 rolls or two 135-36 rolls. Converted, the Formulary’s rule is one litre per 1,720 cm². BERGGER therefore asks for about 1.7 times as much developer for the same film. Two makers, two statements, no way to reconcile them from the documents; the course prints both and takes neither as the other’s correction.

The mixed bath announces whether it is alive. The Formulary makes the colour change part of the procedure: on mixing, the solution “will immediately proceed through color changes from gray-green to pale amber. This is an important visual check of solution activity. If there is no color change, something is wrong.” BERGGER says the same in one clause — the working solution should quickly take on an amber colour, and this is a guarantee of its effectiveness. A developer whose activity you can see is unusual, and it is a direct consequence of the design: the colour is the oxidation product, and in this developer nothing is there to destroy it.

Then it dies quickly. BERGGER gives the mixed bath one hour in an open vessel without loss of quality. The Formulary gives it no interval at all and says “Use immediately.”

The stocks, by contrast, keep almost indefinitely. The Formulary: “The shelf life of the stock solution is indefinite. Partially filled and stoppered bottles will last for years.” BERGGER: up to ten years, even in half-filled bottles. Anchell and Troop record that PMK’s stock solutions have, according to their formulator, exceptional shelf life. That is a striking claim for a bottle holding a hundred grams of pyrogallol per litre, and the reason is in the next section.

A pre-soak is specified by one maker and not the other. BERGGER calls a 3 to 5 minute pre-wet in water at the developer’s temperature essential, and says insufficient pre-wetting leads to irregularities in development; it repeats the point under development errors, adding that the first minute of immersion in the pyrogallol is critical and offering a slightly alkaline pre-wet — 2 g of sodium metaborate per litre — to neutralise any acidity in the tap water. The Formulary’s sheet prescribes no pre-soak. The course records the disagreement rather than resolving it, and notes that BERGGER’s pre-wet advice is the more conservative of the two.

Temperature is a control here, not a constant. The Formulary’s rule is arithmetic: for each degree Fahrenheit of increased developer temperature, decrease the development time by 4 per cent, with “no loss of quality in the negative”. BERGGER’s is a warning as well: excellent results from 21 to 27 °C, finer grain at 27 °C, and above 27 to 28 °C a risk of emulsion deterioration — delamination and cross-linking. Anchell records the range as beginning at 65 °F / 18 °C. The upper limit is the one that matters, and only BERGGER states it.

Image characteristics

A stained negative, and the stain is the point. BERGGER’s description is the most exact in the course’s sources: a yellow-green tint surrounding each silver grain and filling the usually empty space between them, so that the negative’s density is the sum of two densities. What that means for a densitometer, for a graded paper and for a variable-contrast paper is worked through in the staining lesson and is not restated here.

A tanned emulsion. Pyrogallol hardens the gelatin it develops. This is why the fixer must not harden as well, and it is a property of the class rather than of this formula; the pyrogallol page records what the course can and cannot say about it, and the course cannot describe the mechanism and does not pretend to here.

Sharpness, claimed by both makers and measured by neither. BERGGER: the definition is more pronounced, the negatives have very sharp outlines. The Formulary: sharpness first and edge effects fourth in its list of design criteria. What the course can add from its own arithmetic is that the working bath contains no silver solvent at all — no sulfite worth the name, no thiocyanate, no carbonate at fine-grain concentrations — and the solvent action and grain lesson explains why a developer without one tends towards acutance rather than fine grain.

Which makes BERGGER’s grain claim the odd one out. “The grain is reduced”, and reduced further at 27 °C. There is no solvent in the bath to reduce it by dissolution, so if the effect is real it is either the stain filling the space between grains — which is BERGGER’s own explanation and is an optical effect rather than a physical one — or a property of the tanning. No measurement is published for either reading and the course does not choose between them.

⁇Does PMK increase film speed? Its own datasheet says both

BERGGER’s opening paragraph states that as a result of the stain “the sensitivity of the film and its printing qualities are increased.” Its time-and-temperature chart, three pages later, carries a column headed ISO which gives 200 for HP5 Plus, 250 for Tri-X 400, 80 for FP4 Plus, 64 for Delta 100 and 32 for Pan F Plus. That is two thirds of a stop below box speed for Tri-X, FP4 Plus, Delta 100 and Pan F Plus, and a full stop below it for HP5 Plus. All nine films in the chart are rated below box speed, by between a third of a stop — Delta 400 at 320 — and a whole one, which is where HP5 Plus, Fomapan 100, Fomapan 200 and BERGGER’s own Pancro 400 sit.

Both statements are BERGGER’s. They can be reconciled — a stain that adds density in the shadows can raise printing speed while the manufacturer still recommends generous exposure for safety, and the sentence does say “sensitivity… and its printing qualities” together — but that reconciliation is the course’s and not the maker’s, and it is offered as a reading, not as a fact.

Photographers’ Formulary’s indices point the same way and slightly less far: FP4 Plus at 80–100, HP5 Plus at 320–400, Tri-X at 260, T-Max 100 at 80–100 and T-Max 400 at its full box speed of 400. T-Max 400 is the only film in either table given a single index equal to its box speed, though the ranges for HP5 Plus and T-Max 100 reach theirs at the top end.

Sandy King, offering Pyrocat-HD as an alternative to PMK, claims about a third of a stop more effective film speed than PMK — which is a competitor’s claim about a competitor’s product, relayed by a supplier, and is recorded here as exactly that.

What the course holds: no measured speed figure for PMK exists in any document it has read. The published exposure indices are what the two makers recommend, and they are below box speed for eight of the nine films in BERGGER’s table.

The mechanism

Two developing agents reduce exposed silver halide to silver, and one of them leaves its oxidation product in the film on purpose.

AgBr + e⁻ → Ag + Br⁻

What both agents are ultimately doing

The course does not write pyrogallol’s oxidation. It cannot name the coloured product, cannot give the equation and cannot describe how the same chemistry tans gelatin. That gap is stated on the pyrogallol page and argued out at length in the staining lesson; nothing on this page quietly fills it in.

What this page can explain is the architecture — why the formula is two bottles, why the preservative is an acid one, why there is so little of it, and what happens in the ten seconds after the two stocks meet.

⚗Why the stocks keep for years and the working bath dies in an hour

Kodak’s 1928 primer gives the rule that governs the whole design: “bisulphite is preferable as a preservative in the case of a two-solution developer, since oxidation progresses less readily in acid than in alkaline solution.”

That single sentence explains the shelf life. A Solution is an acid solution of two developing agents. Sodium bisulfite gives hydrogen sulfite in water, which is acidic, and in that environment pyrogallol — the most readily oxidised agent in this course — is nearly stable. It is not the amount of preservative doing the work; a fifth of the sulfite of D-76’s working bath sits in a bottle carrying about fifteen times D-76’s concentration of developing agent — 0.85 mol/L of pyrogallol and metol together against D-76’s 0.06 mol/L of metol and hydroquinone. It is the pH. The Formulary’s own observation fits: A Solution turns pale yellow over a week or two and then stops, because it has reached an equilibrium.

The moment 20 mL of B goes into the tank, that protection is gone. The alkali deprotonates the developing agents into their active forms and the same aerial oxidation that was creeping now runs. You watch it happen: grey-green to amber in seconds.

Kodak writes the neutralisation for a carbonate developer, and the course prints Kodak’s equation rather than inventing the metaborate one:

NaHSO₃ + Na₂CO₃ → Na₂SO₃ + NaHCO₃

Kodak's 1928 equation, written for carbonate, not for metaborate

“The sodium bisulphite neutralizes or destroys an equivalent quantity of sodium carbonate, thus reducing the proportion of alkali and therefore exerts an apparent restraining action.” The course has read no equation for the same reaction against metaborate and does not write one. What it can do is the stoichiometry, because that needs only the published weights: the working bath holds 1.86 mmol/L of bisulfite against 42.3 mmol/L of metaborate, so whatever the product, at most about 4.4 per cent of the alkali is consumed and the restraining effect Kodak describes is negligible here. In D-76 or a pyro-soda the same term matters; in PMK it does not.

⚗What the alkali is, and why the hydrate on the label decides your development time

Sodium metaborate is the middle alkali — Kodak Limited’s own description is “intermediate in activity between sodium carbonate and borax”. HSDB’s measured pH against concentration for the tetrahydrate is 10.52 at 0.1 per cent w/v and 11.0 at 1.0 per cent, so PMK’s working concentration of 0.58 per cent sits between those, nearer the top. That is the pH of the alkali alone. The bath also carries pyrogallol, which is itself a weak triprotic acid, and a trace of bisulfite, and no source the course has read publishes a pH for PMK’s working solution. None is given here.

The hydrate is the practical trap. The tetrahydrate is 137.86 g/mol and the anhydrous salt is 65.80 — a factor of 2.1. Weigh out 150 g of the anhydrous salt where the formula means the hydrate and B Solution carries twice the alkalinity it should. Anchell notes that Kodalk’s composition is known to be sodium metaborate octahydrate and that the salt is commonly sold in that form; written per two formula units, Na₂B₂O₄·8H₂O is 2 NaBO₂·4H₂O, so the octahydrate of the older literature and the tetrahydrate of a modern supplier’s label are the same salt counted differently. The one that is genuinely different is the anhydrous salt, and the only place its identity appears is the safety data sheet.

Function of every ingredient

Pyrogallol, 25.0 g in A Solution — 100 g per litre of stock, 0.97 g/L in the tank. The developing agent the formula exists for, and the reason its name begins with P. It reduces exposed silver halide like any other agent, and unlike any other agent in this formulary its own oxidation product is deliberately kept: coloured, deposited in the gelatin in proportion to the development that happened there, and adding a second density to the negative. It also tans the gelatin it develops, which is why the fixer must not harden as well. More pyrogallol means more silver density and more stain together and would need the times re-tested; less means less of both, and BERGGER’s own remedy for an overexposed film whose silver outruns its stain is to dilute the whole bath by a further 25 per cent and extend the time. Three practical facts belong to its own page and matter at the bench: it turns grey in light and air, it is a dusty solid that must be weighed under ventilation, and it is the ingredient that sets this page’s safety level.

Metol, 2.5 g in A Solution — 10 g per litre of stock, 0.097 g/L in the tank. The M of PMK, and the smallest ingredient by both weight and moles: a tenth of the pyrogallol by weight, and one molecule of the metol salt to every twenty-seven of pyrogallol. It is the fast, low-alkali agent — first to work, working in the shadows, and the reason the developer starts at all in a bath whose pH would leave a hydroquinone inert. Its presence is also what makes PMK a pyro-metol formula rather than a pyro-soda one: Anchell and Troop print it beside two other pyro-metol developers, BJ Pyro-metol and Wimberly WD2D, and record that pyro-metol is generally considered to work better with contemporary films. Metol carries the formula’s mixing rule, for the reason set out under Mixing: it must go into the water before the bulk of the preservative or it will not dissolve. More metol would give a faster, flatter, less stained negative because more of the development would be done by the agent that leaves nothing behind; less would slow the start of development and push the whole burden onto the pyro. It is also the ingredient most likely to give a person trouble — the Formulary’s own sheet warns that some individuals become sensitised to it and should stop using it.

Sodium bisulfite, 5.0 g in A Solution — 20 g per litre of stock, 0.194 g/L in the tank. The preservative, and the most carefully judged number in the formula. Its job in the bottle is to hold A Solution acid, because Kodak’s rule is that oxidation progresses less readily in acid than in alkaline solution; that, and not its quantity, is what gives the stock a shelf life measured in years. Its job in the tank is very nearly nothing, and that is deliberate. A staining developer cannot carry a normal preservative, because a preservative’s function is to destroy exactly the substance the stain is made of. Kodak’s own graded experiment — no sulfite giving a very yellow negative whose image is part silver and part oxidised pyrogallol, sulfite giving a much less yellow one, a great deal of sulfite giving almost as blue an image as metol alone — is the whole argument, and it is set out in the sulfite and preservation lesson. More bisulfite here would keep the stock a little better and would visibly reduce the stain; less would give a stock that browns on the shelf, and a first-mixing precipitate of metol base. Two further notes: Anchell and Troop record that sodium metabisulfite is sometimes substituted for sodium bisulfite in this formula and that the substitution should not have any observable effect, since metabisulfite becomes bisulfite on dissolving; and Kodak’s chemical notes warn that bisulfite is difficult to prepare free from iron and that iron in the bisulfite produces a dark colour in a pyro solution — the one contaminant whose effect is hardest to diagnose in a developer that is supposed to be coloured.

Sodium metaborate tetrahydrate, 150.0 g in B Solution — 300 g per litre of stock, 5.83 g/L in the tank. The K of PMK, by way of Kodak’s dead trade name Kodalk, and the only thing in the second bottle. It is the accelerator: it deprotonates the developing agents into the anionic forms that actually reduce silver halide, and its concentration in the tank is what sets the development time. Kodak Limited’s note on the same alkali in DK-50 is the clearest statement in this course’s sources of what that buys you — changing the quantity of metaborate either raises or lowers the contrast reached in a fixed time, or shortens or lengthens the time needed to reach a fixed contrast, and which of the two you get depends on whether you hold the clock or the contrast constant. That is exactly the “flexibility for zone system Plus and Minus development” the Formulary’s brief asks for, and it is the knob Anchell says Hutchings turns in the variant he calls PMK+. More metaborate means faster development, more contrast in a given time, and more oxidation of the pyro into general stain; less means longer times and a flatter negative. Two reasons this particular alkali and not carbonate: it raises no carbon dioxide when it meets an acid bath, so a film carried into acid does not blister; and at 41.9 per cent solubility at 20 °C it will hold 300 g in a litre of cold water, which a carbonate would not. It is also the ingredient with the highest hazard classification in the formula after the pyro — see Safety — and it is stored badly by anything warm, since the tetrahydrate melts at 53.5 °C.

Water, 250 mL and 500 mL as make-up volumes, both at 75 °F (24 °C). Distilled in both bottles as the sheet gives it, and required in B: the sheet capitalises MUST, because a 30 per cent metaborate solution is close enough to saturation that impurities throw it out of solution. The other place water is a named ingredient is the working bath, where a hundred parts of it do most of the developer’s work by making it dilute: dilution is what buys the long times, and long times are what the compensating and edge behaviour of this class of developer are usually credited to. BERGGER adds the one water quality note either maker makes about the tank: black spots and foreign matter on the emulsion are attributed to metal salts dissolved in the water, and the remedy is to filter it or use distilled.

Interactions

Between the two bottles, and this is the formula’s defining interaction. The stocks are stable apart and unstable together. Mix at the tank, use at once, discard.

Between the bisulfite and the metaborate. They neutralise, by the reaction Kodak writes for carbonate; the arithmetic above shows it consumes at most about 4.4 per cent of the alkali, so unlike in a pyro-soda formula the preservative does not measurably restrain this developer.

With the stop bath: it must not be acid. The Formulary is explicit — “Use of an acid stop bath will strip the pyro stain” — and prescribes a plain water bath with a large volume and continuous agitation. BERGGER says the same. This puts SB-1 and the citric acid stop bath out of use with this developer, which is a real cost: a water rinse does not stop development as sharply, and it carries alkali into the fixer.

With the fixer: it must not harden, and preferably must not be acid. The Formulary asks for its own non-acidic fixer and states the general rule that “fixers with hardening agent will decrease the image stain, therefore, the use of non-hardening fixers is necessary”. BERGGER calls a non-tanning bath essential for good subsequent colouration and asks for twice the clearing time, determined by a clip test. The formulary’s own non-hardening bath, F-52, is non-hardening but acid; Reilly’s alkaline plain-hypo bath is alkaline but is published for printing-out papers, not film. The course therefore has no published alkaline film fixer of its own to recommend here, and says so rather than improvising one.

With the wash, favourably and for longer than you expect. Both makers require 20 to 30 minutes of running water, and both give the same reason: the image colouring intensifies during washing. The wash is part of the image formation, not just its removal of fixer.

With a hypo eliminator, badly. BERGGER’s instruction is “above all, do not use a hypo-sulphite (hypo-clear) eliminator, which would weaken the colouring of the negative.” That rules out the one per cent sodium sulfite washing aid after this developer — BERGGER’s own parenthesis is “(hypo-clear)”, so it is the clearing bath it means — and it is a rare case where a bath that is good practice everywhere else is contraindicated. The reason is the same sulfite chemistry that keeps sulfite out of the developer, arriving one tray too late.

With the alkali after-bath, deliberately. The Formulary offers a “pyro after bath”: negatives go straight from the fixer into the used developer for two minutes with agitation every 30 seconds, “the alkali after bath induces the formation of stain in the developed negative”, with 5 g of sodium metaborate per litre of water as an alternative. This is a stain intensification step and it is optional; BERGGER does not mention it.

With agitation, sensitively. Every fault in BERGGER’s development-errors list except two is attributed to agitation: uneven densities and olive-to-yellow colour variation from insufficient agitation, denser image edges from turbulence at the edges, transverse and lateral high-density marks from inadequate agitation or from obstruction by the developing equipment.

With hard or acid tap water, at the start. BERGGER’s remedy for irregular circular markings and lines of varying density is a 3 to 5 minute pre-wet about 2 °C warmer than the developer, or a pre-wet made slightly alkaline with 2 g of sodium metaborate per litre “to neutralize any acidity in the tap water”.

Variants

PMK+, named by Hutchings and recorded by Anchell. The Darkroom Cookbook’s note is that the alkali can be altered without altering development times, and that Gordon Hutchings calls the result PMK+. The course has not read the quantities — Anchell’s sentence is all it has — so no entry is written and none is implied. What can be said is that it is the same knob described under the metaborate above, turned the other way: fix the time and let the contrast move.

BERGGER PMK and the Photographers’ Formulary kits are the same formula sold two ways, on the evidence of identical concentrate volumes, an identical 1+2+100 dilution and identical yields, and on BERGGER’s own statement that its product is the pyrogallol developer “adapted to modern films by Gordon Hutchings in the 1980s”. That is an inference from two datasheets, not a statement either maker makes, and their published development times differ by up to two minutes on the same film, which is what you would expect of two makers testing independently and is also what you would expect if the products were not identical.

Pyrocat-HD and 510-Pyro are the other modern staining developers and this course prints no composition for either. Pyrocat-HD’s kit sheet names no ingredient at all; 510-Pyro’s document is a development-time chart credited to a community database. Both entries are planned. The staining lesson sets out exactly how much each sheet does and does not give.

The historical pyro formulas this one descends from: Kodak’s A.B.C. pyro D-1, whose quantities the staining lesson prints, and Kodak Limited’s D-167 and D-177. The comparison that matters is dilution. D-1’s tray bath holds 6 g of pyro per litre and D-167’s 7.5 g; PMK’s holds 0.97 g. PMK is the same idea run six to eight times more dilute and six times longer, which is the change that separates a nineteenth-century tray developer from a modern one.

No course variant is offered. The obvious safening move is to cut the pyrogallol, and cutting the pyrogallol produces a different developer rather than a safer version of this one.

Safety

Level B, and pyrogallol alone decides it.

Read the pyrogallol page before the jar is opened. Its aggregated GHS classification carries “harmful in contact with skin”, “harmful if inhaled” and “suspected of causing genetic defects” at 100 per cent of notifiers, plus harmful if swallowed and harmful to aquatic life with long-lasting effects. There is no workplace exposure limit for it in HSE’s EH40 list, which means there is no airborne concentration to measure yourself against — the control is not to make dust at all.

Both makers publish their own warnings and they agree. BERGGER: pyrogallol is toxic by inhalation, skin contact and ingestion, causes kidney, liver and circulatory disorders or even death; it is a phenol and can cause burns; brief skin contact may cause a dark, non-scalding stain and prolonged contact a chemical burn very similar to a heat burn; use gloves and clean all equipment with soap and water. Photographers’ Formulary: pyro “is quite toxic and is readily absorbed through the lungs, skin and mouth”, is a phenol with the potential to cause skin burns, and “is also very dusty. Work in a well ventilated area. Do not inhale its dust.” Rempel’s hazard handbook heads its entry “PYROGALLOL (PYRO) (Use With Extreme Caution)”.

Weighing 25 grams of a dusty phenol is the hazardous operation on this page, and it happens once per batch of stock. Do it in moving air or an enclosure, with gloves, eye protection and a dust mask — the Formulary asks for gloves and a dust mask by name — and the Formulary’s own mixing order helps here too, since the pyro goes in last, “outside or under a ventilating hood”.

Metol is the sensitiser. It carries “may cause an allergic skin reaction” and “very toxic to aquatic life with long lasting effects”. The Formulary’s sheet gives the practical version: some individuals develop allergic symptoms or rashes, and anyone who does should stop using it and see a doctor.

Sodium metaborate is the reproductive-toxicity entry in this formula, notified as “may damage fertility or the unborn child” by nearly half of its notifiers and as the weaker “suspected of” by a quarter, and as a serious eye irritant by more than four fifths. B Solution is 30 per cent w/v, which is alkaline enough to sting badly. Eye protection is not optional while it is being made.

Sodium bisulfite is the mildest ingredient here and is the one that gives sulfur dioxide if a strong acid reaches it. A Solution is already acid, so keep acids away from it and from its waste.

The working bath is far more dilute than the stocks and is not the dangerous part of this process. Under a gram of pyrogallol per litre, and alkaline — gloves and no skin contact, as for any developer, and a tray that stains is a tray to keep tongs in. The stock bottles are where the hazard lives, and both makers say the same thing about them: keep them tightly closed, keep them out of light, and keep them away from children.

Storage

Two bottles, both stoppered, both dark, both labelled with the word pyrogallol. The Formulary prefers glass and accepts plastic, allows clear bottles provided A Solution is kept out of strong light, and adds one specific prohibition: avoid metallic lids or lid liners on the bottle used for solution A.

A Solution will turn pale yellow over a week or two and then stop. That is the equilibrium the Formulary describes and not a fault. A stock that goes on darkening past it is a stock that has been opened too often or has met something it should not have.

Partly filled bottles are explicitly allowed, which is unusual and is the strongest evidence of how well an acid pyro stock keeps: the Formulary says partially filled stoppered bottles will last for years, and BERGGER puts ten years on half-filled ones. Compare that with the developers whose keeping tables in this formulary halve when the bottle is half empty.

The mixed working solution is not stored. One hour in an open vessel by BERGGER’s account, and “use immediately” by the Formulary’s.

Cool, and away from anything warm. The metaborate tetrahydrate melts at 53.5 °C, and its dry tub also picks up carbon dioxide from the air to become carbonate and borax over time, so a tub left open slowly turns into a different alkali.

Label both bottles with the formula, the letter, the strength and the date, per the labelling SOP, and record the batch on the formula version record. Write “pyrogallol — toxic, do not inhale dust” on A Solution in words a person who has never read this page would understand.

Incompatibilities

Oxidising agents of every kind. Pyrogallol is the most readily oxidised developing agent in this course.

Acids with A Solution, which will drive sulfur dioxide off the bisulfite, and acids with B Solution, which will simply convert the metaborate to boric acid and destroy the alkali. Carry-back from an acid stop bath or fixer is the darkroom’s ordinary version of the second.

Iron, from a clip, a tray, a metal lid or a contaminated bisulfite tub. Kodak’s note is specific: iron in the bisulfite produces a dark colour in a pyro solution.

Light and air for A Solution, which is a storage matter and a practical incompatibility.

Fixer, in either direction, and more so than usual with a developer whose whole product is a colour. One set of tongs per tray.

Sulfite, after the tray — the hypo eliminator that BERGGER forbids, for the same chemical reason that keeps sulfite out of the developer.

Anything the incompatibilities page lists against a reducing agent, a phenol or an alkali, which is the page to read rather than this paragraph.

Waste

Developer waste, alkaline, carrying pyrogallol, metol and their oxidation products, plus dissolved silver from the film. It is not the fixer’s silver stream, but it is not clean water either.

Three of the four ingredients carry an environmental classification. Pyrogallol is “harmful to aquatic life with long lasting effects”; metol is “very toxic to aquatic life with long lasting effects”; borate does not degrade and the related borax is recorded as harmful to aquatic organisms. Spent PMK does not go on the garden.

pH is the other question a disposal route has to answer. Even a 0.1 per cent metaborate solution reads about pH 10.5, and sewer codes commonly set a window around 5.6 to 9.4.

Keep it out of the acid stream, both because developer and fixer wastes are collected separately and because A Solution’s bisulfite gives sulfur dioxide with acid.

Collect it, label it, and follow the general chemical waste SOP and the disposal ruling. The Formulary’s own sheet says the same thing in one line: “Please consult with local sewer and water authorities regarding the proper disposal of darkroom chemicals in your area.” Local regulation governs and this course cannot tell you what it says where you are.

Troubleshooting

No colour change when A and B meet. The Formulary treats this as a diagnostic and so should you: the mixed solution must move from grey-green to pale amber within seconds. If it does not, “something is wrong. Recheck your stock solution for correct formulation.” The commonest formulation error is the alkali — 150 g of the anhydrous metaborate where the formula means the hydrate gives a B Solution of twice the intended alkalinity, and the tetrahydrate weighed as though it were anhydrous gives half.

A white precipitate while mixing A Solution. The bisulfite went in before the metol, or too much of it did. It is the insoluble metol base, and there is no alkali in that bottle to redissolve it. Kodak’s rule is that only a low concentration of sulfite is needed to stop metol dissolving; the sheet’s “small pinch” is meant literally. Re-make the stock.

Undissolved crystals in B Solution. Expected if the water was not distilled, and the sheet says so: the solution is highly concentrated, and any residue will dissolve of itself within 24 hours without affecting activity even if the developer is used at once.

Uneven density, or colour varying from olive green to yellow across the frame. BERGGER attributes this to insufficient agitation and prescribes more force and more frequency, especially where the negatives are thin and lack colouration.

Denser edges, or transverse and lateral bands of high density. Turbulence at the edges of the negative, or physical obstruction from the developing equipment. Review the agitation and check the reel or hanger for anything that induces flow.

Irregular circular markings and lines of varying width. BERGGER’s answer is the pre-wet: 3 to 5 minutes in water about 2 °C warmer than the developer, because the first minute of immersion in the pyrogallol is critical; or a pre-wet made slightly alkaline with 2 g of sodium metaborate per litre to neutralise acid tap water.

Black spots or foreign matter on the emulsion. Metal salts dissolved in the water, per BERGGER. Filter the water or use distilled.

Plenty of silver and very little stain. BERGGER calls this rare and attributes it to overexposure on some films: review the exposure index, dilute the developer by adding 25 per cent more water, and increase the development time by 15 to 25 per cent.

A weak stain after an otherwise normal process. Look at what came after the tray before you look at the developer. An acid stop strips the stain; a hardening fixer decreases it; a short wash never lets it come up, because the colour intensifies during washing; and a hypo eliminator weakens it. Four separate opportunities to lose the thing you mixed the developer for.

Fuzzy or degraded negatives with no agitation explanation. BERGGER’s other cause is contamination — “verify that the developing equipment is free of traces of chemicals that may contaminate pyrogallol.”

The emulsion is soft, frilled or lifting. Check the temperature first. BERGGER’s limit is categorical: above 27 to 28 °C there is a risk of delamination and cross-linking. This is the one number on the page that is a hard stop rather than a starting point.

Thin negatives across a whole session. Check the volume of developer before anything else. The two makers’ minimum-quantity figures differ by a factor of 1.7, and the Formulary’s own comment is that inconsistencies result from varying the ratio of film to developer.

Experiments

Read the stain as a density in two channels. Develop a step wedge in PMK and read it visually or through green, then through blue. The gap between the two curves is the stain, and whether it widens with exposure tells you whether you have image stain or general stain. Neither maker publishes a curve of any kind for this developer, so any curve you plot is more than either of them has given you.

Test the two capacity figures against each other. Develop the same film in the Formulary’s minimum volume — 300 mL per 80 square inches — and in BERGGER’s — one litre per 1,000 cm² — and compare density and stain. One of these makers is being 1.7 times more generous with developer than the other and the documents cannot say which is right.

Calibrate the temperature rule. The Formulary claims 4 per cent less time per degree Fahrenheit, with no loss of quality. Develop identical strips at 21, 24 and 27 °C using that rule and compare them for density, stain and grain. BERGGER’s chart is itself a test of the same claim: its own 21 °C and 27 °C times for HP5 Plus, 13 and 8 minutes, span 10.8 °F. Compounded, the Formulary’s 4 per cent a degree predicts 13 × 0.96¹⁰·⁸ = 8.4 minutes, against the 8 BERGGER prints — close, and not identical. Do the same sum for every row of that chart before you trust either.

Turn the alkali knob and see which of the two effects you get. Make B Solution at 200, 300 and 400 g/L, keep the time fixed, and read the contrast; then keep the contrast fixed and read the time. Kodak Limited’s claim for the same alkali is that you can have either. Nobody has published the plot for PMK.

Test the pre-soak disagreement. One maker calls a 3 to 5 minute pre-wet essential and the other does not mention it. Same film, same everything, half the sheets pre-soaked. Look for the specific faults BERGGER predicts — irregular circular markings, uneven colour — rather than for a general impression.

Establish your own exposure index rather than borrowing one. BERGGER’s sentence says sensitivity is increased and BERGGER’s chart recommends a third to a full stop less exposure. Expose one film at box speed and at each of the recommended indices, develop identically, and print. This is the experiment that resolves the contradiction for your film and your meter, and it resolves it for nobody else.

Try the alkali after-bath and measure it. Two minutes in the used developer after fixing, against a control that skips it. The Formulary says it induces stain; the size of the effect is not published.

Race it against a non-staining developer on the same negative. Half a roll in PMK, half in D-76, printed to the same shadow value on the same variable-contrast paper. The comparison people report — that a stained negative prints with more highlight separation than its silver density alone would predict — is an experiential claim throughout the literature the course has read, and it has never been given a number in any document on this page.