Borax kallitype developer

There is one substance in this bottle and it cannot develop anything. It is not a developing agent, it is not a ligand for iron in any sense the course can source, and on its own it will not turn an exposed kallitype into a picture. Borax is here to set a pH, and everything this page is about follows from the fact that the pH it sets — about 9.5 — is high enough to change the colour of the metallic silver as it forms, and high enough to leave the unexposed iron in the paper in a form that no clearing bath afterwards will take out.

The kit that supplies it never uses it alone, and neither does any other source read for this page. It is one of a pair. The other bottle is the Rochelle salt stock, which does the developing; this one decides what colour the developing comes out.

Ingredient	Quantity	Form the source specifies
Borax (sodium tetraborate decahydrate)	75 g	The sheet writes "Borax" and names no hydrate. The encyclopaedia's entry is the decahydrate, Na2B4O7·10H2O, formula weight 381.4, which is what a photographic formula means by borax; the pentahydrate at 291.4 and the anhydrous salt at 201.2 are sold beside it and carry 31 and 90 per cent more borate per gram
Water	400 mL, added	at 52 °C; Distilled water at 52 °C/125 °F, and an added volume rather than a make-up one: the sheet's table gives the water and the solid and states no final volume. Unlike the tartrate stock, this one is at or beyond saturation when it cools, and the sheet says so — the borax dissolves slowly and residual solid commonly remains. The heat here buys capacity, not merely rate.

Purpose

To raise the pH of a kallitype developer far enough that the image silver comes out neutral black instead of brown, and to hold it there while the print develops.

Photographers’ Formulary states the working rule in its own words, and it is a rule about proportion rather than about quantity: “if you increase the amount or proportion of Stock Developer Solution A (Rochelle salts) in the developer, you will increase the sepia-tone of the print. If you increase the amount or proportion of Stock Developer Solution B (borax), you will increase the blackness of the print.”

Two duties belong to every siderotype developer — dissolving the iron(II) that light made, and carrying the unexposed iron(III) out of the paper — and neither of them is this bottle’s. Both are set out in full on the Rochelle salt and sodium citrate pages. What the borax adds is a third thing that is not a developing action at all, and Mike Ware states it exactly:

“nitrate is an oxidising anion, and tends to dissolve the colloidal image silver during wet processing, especially under acidic conditions. To minimise this loss of image the Kallitype process employs alkaline-buffered developers of high pH, e.g. Borax.”

That sentence is the whole justification for this bottle’s existence, and the sentence that immediately follows it in the same paragraph is the whole case against it:

“Alas, these create a new problem, because they cause hydrolysis of the excess iron(III) in the sensitizer and the deposition of insoluble ferric hydroxide in the image, which ultimately causes it to fade.”

A page about a borax developer that gives the first quotation and not the second is selling something. Both are under The mechanism.

Recommended uses

A kallitype that must be neutral black out of the tray. This is the only route the traditional kit offers to a cold image without a toner, and it reaches it with one extra bottle rather than with a metal salt. If the print is going to be judged as it comes off the wash line, this is the developer that puts the colour where a printer coming from silver-gelatin expects it.

The cold end of a deliberate colour range. The reason to own both stocks is that the pair spans a range no single bottle covers: sepia with no borax, brown at 64 mL, black at 128 mL. Three published mixtures is enough to interpolate between, and the first experiment at the foot of this page is how to map the range on one negative instead of guessing at it.

Where the print will be toned in platinum or palladium anyway. Sandy King’s argument for choosing a developer on grounds other than colour is that toning will overrule it: a kallitype toned in a noble metal is, in his words, “in every way an exact equivalent, both visually and in terms of image permanence, of a Pt/Pd print”. If the colour is going to be decided in the toner, the developer’s job narrows to protecting the image while it is wet, which is the job Ware says the borax bath is for.

As the one bath in this formulary where an alkali is the whole formula. Every other developer in the course uses alkali to drive a reducing agent: 67.5 g of sodium carbonate per litre behind the Metol and hydroquinone of D-72, 2 g of this same borax behind the same two agents in D-76. Here there is no reducing agent for it to drive, the working bath carries somewhere between six and twenty-four times D-76’s two grams per litre depending on how much of the stock is really in solution, and the pH acts on the metal as it forms rather than on the molecule that makes it. It is the clearest demonstration in the formulary that pH is not only a rate control.

When another formula is preferable

• When you want a warm print and no borax at all. Use the Rochelle salt developer. It is the same kit’s sepia bath, it needs no heat, and it is a Level A material where this one is Level B.
• When permanence is the whole point. Use the sodium citrate developer. It is what the trade moved to: Photographers’ Formulary’s own later kallitype kit carries no borax at all and replaces all three tartrate-and-borax developers with a single 20 per cent citrate bath, and King reduces the developer question to one bath on the grounds that colour should be decided later, in the toner, “when it is fairly obvious if the print is a keeper or not”. The argument under The mechanism — that a bath at pH 9.5 hydrolyses iron(III) into the paper rather than complexing it out of it — is the chemical reason that move makes sense.
• When the image metal is platinum or palladium. Use Willis’s potassium oxalate developer. Ware’s table of potentials says why: the weakly reducing complexed-iron couples reduce silver(I) and gold(III) and do not reduce platinum(II), and an alkali does not change that.
• When there is to be no developer at all. The Van Dyke Brown sensitiser and Ware’s argyrotype print out in the frame. The argyrotype is in fact Ware’s own answer to the dilemma quoted under Purpose: instead of adding an alkali to stop nitrate etching the image, he removed the nitrate.
• When you are reconstructing the process as Nicol first published it. In Nicol’s kallitype the silver is in the developer rather than in the paper, which is a different formula and not a variant of this one.

Mixing

Seventy-five grams of borax into four hundred millilitres of distilled water at 52 °C/125 °F. The sheet says to mix it “in the same manner as Stock Solution A” — hot water into the vessel first, solid added to it, stirred — and then adds the sentence that makes this bottle different from its neighbour: “The borax will dissolve slowly, and it is not uncommon for residual solid to remain in the container.”

That is not a warning about impatience. It is a statement that the stock is at or past the limit of what the water will hold, and it has a consequence for every bath drawn from it.

🧮The stock is saturated, and that is why its strength cannot be quoted

Take the sheet’s own numbers. 75 g of borax into 400 mL of water is 18.75 g per 100 mL if the solid all dissolves and the volume does not change. Now put that against the published solubilities of borax, which disagree with one another by about a factor of two and agree completely on the shape of the curve:

Source	Solubility	Temperature
Chemical Safety Card 0567	5.1 g per 100 mL	20 °C
HSDB, on PubChem	5.93 g per 100 mL	25 °C
HSDB, second entry	3.17 g per 100 g of water	25 °C
HSDB	1 g in 16 mL cold; 1 g in 0.6 mL boiling	cold; 100 °C
NIOSH	6 per cent	not stated
Wall’s 1912 dictionary	6 per cent cold; 200 per cent hot	cold; hot

A cold bottle of this stock can hold about a third of what the sheet puts into it. The 1 g in 0.6 mL of boiling water is about 167 g per 100 mL, so at 100 °C the 18.75 would dissolve nine times over; at 52 °C it is somewhere on the way between, which is exactly why the sheet warns that dissolution is slow and that solid may remain. The 52 °C here is buying capacity, not just rate — the opposite of the tartrate stock next door, where the same temperature buys only patience and the solution is at a third of saturation even cold.

So what is the black-tone working developer’s borax strength? It has an upper bound and a lower one, and no number.

• Upper. If every gram dissolved and the stock’s volume were still 400 mL, 128 mL of it carries 24 g of borax into a bath made to 500 mL: 4.8 per cent w/v. The true figure is lower, because 75 g of solid occupies real space and the stock’s volume is therefore greater than 400 mL — the sheet states no final volume, so by how much is not published.
• Lower. If the bottle has stood at 20 °C and thrown its excess, the stock is a saturated solution at about 5.1 g per 100 mL, so 128 mL carries 6.5 g and the bath is about 1.3 per cent w/v.

Between those two readings lies a factor of nearly four, and the only thing that decides which one you are working with is the temperature of the bottle when you draw from it. That is the single most practically important fact on this page, and the sheet does not draw the conclusion: warm the stock and stir it back into solution before measuring, or the black-tone developer you mix is a fraction of the one the sheet designed, and the print comes out browner than it should.

⚗A century-old check on the upper bound

The 4.8 per cent upper bound is worth testing against the two independent printings the course has read, because it is the only way to tell whether the sheet intends a fully dissolved stock.

Thomson’s developer, in Wall’s 1924 collection, is equal parts of a 5.2 per cent Rochelle salts solution and a 9.4 per cent borax solution — so 4.7 per cent borax in the bath as used. That is within a tenth of a per cent of the black-tone bath’s upper bound, and it is a different formulator, a different country and sixty years earlier.

Wall’s 1912 developer No. 1, “for pure black tones”, is borax 1 oz and Rochelle salt ¾ oz in 10 fluid ounces of distilled water. Taking the avoirdupois ounce of 437.5 grains and the imperial fluid ounce, that is 9.98 g per 100 mL of borax and 7.48 of tartrate; on the apothecaries’ ounce of 480 grains the borax reads 10.95, and the ambiguity does not matter at this precision. His No. 4, for purple, is borax 120 grains and Rochelle salt 450 grains in the same ten ounces: 2.74 per cent borax and 10.26 per cent tartrate.

Two things fall out. First, the modern black-tone bath at its upper bound sits between Wall’s purple and his black, and Thomson’s sits with it — three sources across a century put a cold-toned kallitype developer between roughly 2.7 and 10 per cent borax. A bath at the 1.3 per cent lower bound is outside that band entirely, which is evidence that the sheet means the stock to be fully in solution and that a cold, half-dissolved bottle is a fault rather than a variant.

Second, Wall’s own black-tone bath is impossible cold. Ten per cent borax is nearly twice the cold-water solubility his own dictionary gives under Borax — 6 per cent cold, 200 per cent hot. Either he mixed it warm or it was never all in solution, and he does not say which. The same is true of Thomson’s 9.4 per cent stock. Every published borax kallitype developer is a hot mix, and the modern sheet is the only one that says so.

Use distilled water, as the sheet requires in capitals. The reason on the tartrate page is calcium, and it applies here too — Ware gives the reaction in which calcium precipitates as insoluble calcium oxalate and pushes the iron down the aquation chain towards iron(III) hydroxide. In an alkaline bath that chain runs faster, so the borax developer has more to lose from hard water than the tartrate one does, not less.

Making the working bath. For black tone, put 200 mL of distilled water in the mixing bowl or the tray, add 72 mL of the Rochelle salt stock and 128 mL of this one, then a further 100 mL of water to bring the bath to 500 mL, and stir. For brown tone, 96 mL and 64 mL of the two stocks, and 140 mL of water to finish. The sheet prints the starting water temperature as “20°F/68°F”, which is a slip for 20 °C — 20 °F is well below freezing, and the same sheet gives 20 °C/68 °F correctly for the clearing bath three tables earlier.

Working developer	Rochelle salt stock	Borax stock	Water	Time and temperature
Black tone	72 mL	128 mL	to make 500 mL	5 minutes, around 38 °C or higher
Brown tone	96 mL	64 mL	to make 500 mL	5 minutes, warm
Sepia tone	48 mL	none	to make 500 mL	10 minutes at room temperature

The third row is the Rochelle salt developer and is on its own page. This page is about the middle column and the first two rows.

Behaviour

Five minutes, warm, against ten minutes cold in the bath without borax. That is the trade the sheet makes visible by publishing all three developers together, and it is the most concrete piece of evidence anywhere in the sources that the borax is doing something and not merely sitting there. The same print, the same sensitiser and the same exposure develop in half the time when the alkali is present, and the sheet asks for 38 °C on top of that.

Why an alkali should speed a bath that contains no reducing agent is not settled by anything read. The course will not assert a mechanism it cannot source. What can be said is that the step the tray performs is a redox reaction between complexed iron(II) and silver(I), and that the potential of a complexed-iron couple depends on the ligand and on the pH, so a change of pH changing the rate is unsurprising. Nobody read has measured the rate, or the potential of the tartrato couple at either pH. The bracket the course does have is on the tartrate page: Ware’s potentials for the oxalato and citrato couples differ by more than a third of a volt purely through the choice of ligand, and both still reduce silver(I) comfortably.

The image arrives long before the five minutes are up. No source read times the appearance of the image in this bath specifically; Photographers’ Formulary’s later citrate sheet describes an image that appears “almost immediately” and directs the printer to develop the full time anyway “to allow the developer to react with all available iron and silver in the sensitizer”, and Bostick and Sullivan say the image “will appear immediately so this must be done quickly, or else watermarks may appear”. The clock is for the iron, not for the picture. Wall put it best in 1912, for all four of his developers: the print “must be left in the developer for about ten or fifteen minutes. This is necessary in order to ensure that the iron salts shall be all dissolved. The presence of the iron salts is a most prolific cause of failure.”

The developer has to reach the whole sheet in one movement. With five minutes rather than ten and a bath that wants to be at 38 °C, there is less margin for a two-stage immersion than in the cool tartrate bath, and a tide-line does not come out afterwards. Wall’s method for a large print is to immerse it face downwards and turn it over at once, breaking any air bubbles with a fingertip; Photographers’ Formulary’s later sheet describes the tilted-tray pour, in which the developer is pooled at one end of the tray and released across the paper in a single wave.

A dark residue collects in the bath. The same manufacturer describes it for its citrate developer — “a residual black substance forming from and next to dark tones” — and directs the printer to agitate so it does not settle on the highlights, and to filter it out of the stored bath through a coffee filter. No source read describes it for this bath specifically and no source read says what it is. The course’s reading, offered as a reading: a tray holding reduced iron and dissolved silver nitrate that has diffused off the sheet is a place for silver to be reduced in the liquid rather than in the paper, and finely divided silver is black.

Exhaustion shows up in the clearing bath, not in this one. The borate is not consumed by developing; what accumulates is iron, and the symptom is prints that take longer and longer to clear. This sheet publishes no replenishment rate and no discard point, which is a real gap and not something the course can fill by arithmetic — the citrate kits that replaced it both publish one.

The print is not finished when it leaves the developer. It goes to a clearing bath — potassium oxalate in this kit, 60 g in 500 mL for five minutes at 20 °C — and then to a fixer for not more than five minutes, because “a longer soak will cause the print to fade”. Bostick and Sullivan put the same warning the other way round: “Kallitype prints will bleach in the fix, so either tone before fixing or overprint by a stop or two.” Judge the developer at the end of the line.

Image characteristics

Colour: the cold end of the kit’s range, and the sheet’s own three mixtures show which variable carries it.

Working developer	Borax stock	Rochelle salt stock	Borax as a share of the two stocks	Colour
Sepia tone	0 mL	48 mL	0 per cent	warmest
Brown tone	64 mL	96 mL	40 per cent	middle
Black tone	128 mL	72 mL	64 per cent	coldest

Read down the borax column and it climbs 0, 64, 128 as the print goes sepia, brown, black. Read down the tartrate column and it goes 48, 96, 72, which is not an order at all: the brown-tone bath carries more tartrate than the black-tone one and is warmer. The manufacturer states its rule in terms of proportion, and its own table is why.

⚗Wall's four developers of 1912 order themselves the same way

The same test on a source seventy years earlier gives the same answer. Wall’s four kallitype developers, each in ten fluid ounces of distilled water, carry:

• Sepia — Rochelle salt ½ oz, no borax.
• Purple — Rochelle salt 450 grains, borax 120 grains.
• Pure black — Rochelle salt ¾ oz, borax 1 oz.
• Warm maroon — sodium tungstate 1 oz, and neither of the other two salts.

Laid out warm to cold, the borax climbs from nothing to 120 grains to a full ounce — 0, 2.74, 9.98 per cent — and the tartrate goes 219, 450, 328 grains, which is no order at all. Two independent sources, seventy years apart and in different unit systems, both put borax in charge of the colour and neither puts tartrate in charge of it. That is an observation about two published tables, not a mechanism; the mechanism the course can offer is below and is marked as a reading.

Wall’s fourth developer is the reminder not to over-generalise. Sodium tungstate contains no tartrate and no borate and gives a fourth colour again. The chemical encyclopaedia has no entry for sodium tungstate, so the course can do no more with it than record that Wall printed it.

Why a kallitype is brown in the first place is particle size, not chemistry. Ware’s measurements on plain-paper silver prints put the image particles at colloidal dimensions, around 20 nm — far smaller than the 500 nm wavelengths of visible light — and their colour comes from an absorption that depends on the particles’ “shape, size, state of aggregation and chemical environment” rather than on anything about silver as an element. The same metal in the micron-sized filaments of a developed silver-gelatin print reads as neutral black. Ware reproduces Wiegel’s calculated and experimentally confirmed table for silver hydrosols: particles of 10 to 20 nm transmit yellow, 25 to 35 nm red, 35 to 45 nm purplish-red, 50 to 60 nm violet. Departure from a spherical shape shifts the absorption again, and so does the refractive index of the matrix the particles sit in.

Why the alkaline bath should give the colder print is the course’s reading, and it rests on a statement Ware makes about a different system. Discussing Talbot’s ammonia-buffered paper, Ware writes that “the more neutral image colour is also consistent with a larger particle size for the silver colloid formed in such a sensitizer” — a buffered alkali, a larger particle, a colder colour. Borax is a buffer at about pH 9.5; a Rochelle salt solution is not buffered in any useful sense. If alkalinity pushes the reduction towards fewer and larger particles, then the borate bath gives the colder print, which is what both Wall and Photographers’ Formulary report. That is a hypothesis consistent with the evidence and not a measurement. Nobody read has measured the particle size any kallitype developer produces, so this page gives the principle and no number.

The sizing is part of the colour and is easy to forget. The same sheet says that prints on paper sized with arrowroot starch “will have a brown color while those sized with gelatin will have a blue tone”. If you are comparing the two stocks, size every sheet the same way or you are comparing two variables at once.

Contrast: none is offered here, and that is a policy rather than an omission. The only contrast control this sheet publishes is 5 to 20 drops of a 10 per cent potassium dichromate solution per 500 mL of mixed developer, and it is emphatic in bold type that the dichromate goes into the developer and not the sensitiser. The course does not use chromium(VI) at any level; the chromium policy sets out the rule. What is left is the negative, and the sheet’s own claim is that a negative with a density range up to 1.85 can be printed.

The mechanism

Four steps make a kallitype, and this bottle takes part in none of them directly. It changes the conditions under which three of them happen.

Step one, in the printing frame: light makes an insoluble solid. Ultraviolet light decomposes iron(III) oxalate, reducing the iron at the expense of an oxalate ligand that leaves as carbon dioxide — the reaction Döbereiner reported in 1831, decades before anyone printed with it.

Fe₂(C₂O₄)₃ + UV → 2 FeC₂O₄ + 2 CO₂

Döbereiner's photolysis, after Ware

The product is iron(II) oxalate, whose solubility Ware gives as 0.022 g per 100 cc: for practical purposes it stays exactly where the photon left it.

Step two, in this tray: the tartrate dissolves it. That is the other bottle’s work and is set out on its page. Borax is not a ligand for iron in any source read, and the course makes no claim that it is one.

Step three, still in this tray: the dissolved iron(II) reduces silver(I) to metal.

Fe²⁺ + Ag⁺ → Fe³⁺ + Ag

The image-forming step, stripped of its ligands

Wall states the same thing in 1924 without the notation: “the ferrous salts dissolve in the developer, and reduce silver nitrate to the metallic state at the points where the ferric salt has been reduced by light.”

Step four, over the following minutes: the developer is supposed to carry the unexposed iron(III) out of the paper. This is where the borax stops being a bystander and starts working against the bath it is in, and it is the argument of this page.

Deeper: what the alkali buys

Ware’s case for the high pH is about the silver, and it turns on the anion that comes with it. The sensitiser is silver nitrate, and

“nitrate is an oxidising anion, and tends to dissolve the colloidal image silver during wet processing, especially under acidic conditions.”

The image is made of 20 nm particles. A particle that small is nearly all surface, and Ware notes that such particles “are inevitably more vulnerable to chemical attack: they present a relatively large surface area and are rapidly dissolved by reagents that ‘etch’ or ‘bleach’ (i.e. oxidise) silver.” Take the acid away and the etching slows. That is what borax is for, and it is a real benefit — the same reasoning is behind the sheet’s instruction never to use a standard acid photographic fixing bath, which would take the image away outright.

⚗Why borax and not a stronger alkali

Borax is the sodium salt of a very weak boron oxyacid, so it hydrolyses in water and the solution is alkaline: HSDB records an aqueous borax solution as alkaline to litmus and to phenolphthalein at about pH 9.5, and Chemical Safety Card 0567 calls it a weak base. That figure sits very close to the ionisation constant OpenStax gives for boric acid, 5.4 × 10⁻¹⁰, a pK_a of 9.27:

B(OH)₃ + H₂O ⇌ B(OH)₄⁻ + H⁺

The conjugate acid–base pair a borax solution sits on

A solution holding comparable amounts of an acid and its conjugate base is the textbook definition of a buffer, and OpenStax’s buffer section gives the consequence: such a pair holds the pH near the pK_a and moves only slowly as acid is added. That matters here because development generates acid. Every silver ion reduced leaves a nitrate behind, the paper carries free oxalic acid from the sensitiser, and a tray takes print after print. An unbuffered alkali would be neutralised by the first sheet; a buffer has buffer capacity and walks down the plateau instead of falling off it.

This is the same property that put borax in D-76 at 2 g per litre. Kodak’s 1928 primer introduces it as the alkali for a developer that must not be hurried, and says plainly that “adding carbonate to such a developer speeds development and accentuates the graininess of the resulting negative”. A photographic formula reaches for borax when it wants an alkali that holds a modest pH rather than one that maximises it — and pH 9.5 is modest next to the pH 11 and above a carbonate or a hydroxide would give.

Deeper: what the alkali costs, which is the iron

Ware’s next sentence is the one this page exists to put beside the last:

“Alas, these create a new problem, because they cause hydrolysis of the excess iron(III) in the sensitizer and the deposition of insoluble ferric hydroxide in the image, which ultimately causes it to fade.”

The number that makes it concrete is in his platinum monograph: “at pH values above 4, iron(III) tends to hydrolyse … forming polymeric colloidal iron(III) hydroxide, which could lodge in the paper fibres and eventually impart a yellow stain.” A borax developer runs five and a half pH units above that threshold.

And hydrolysed iron does not wait for you. Ware sets out the sequence in four stages: mono- and dimers form reversibly in a rapid equilibrium; then, over minutes, a “red cationic polymer” of 2 to 4 nm particles; then over days to weeks, larger polymers of 20 to 50 nm that agglomerate irreversibly into chains and sheets; and finally the crystalline oxide-hydroxides. His conclusion for the printer is blunt: “While freshly-formed iron(III) hydroxide can be redissolved in dilute acids initially, if it is not soon removed it slowly transforms irreversibly … into a highly insoluble polymeric form, iron(III) oxyhydroxide, FeO(OH) – the mineral called Goethite – which is quite insoluble in dilute acids. It is therefore essential to remove all the iron(III) at the wet processing stage before the print dries.”

The most direct evidence that this is not a theoretical objection is Ware’s own instruction about a different bath entirely. Discussing the clearing sequence for platinum prints, he warns against using tetrasodium EDTA as the first bath, “in spite of the fact that it has been recommended by Bostick & Sullivan”, because “it has a high pH ~10 at which the iron(III) is not effectively complexed, but rather hydrolysed, with the eventual result of yellow or brown staining.”

A borax kallitype developer is a bath at pH 9.5 with which the print’s first and longest wet contact is made. By Ware’s criterion, applied to a chemistry he applies it to elsewhere, it is close to the worst pH at which to be asking iron(III) to leave paper.

!What the manufacturer said next

The strongest corroboration of the argument above is not from a chemist. It is from the same company, in the sheet for the kit that replaced this one.

Photographers’ Formulary’s later kallitype kit carries no borax at all. It replaces the three tartrate-and-borax developers with a single 20 per cent sodium citrate bath, clears in 3 per cent citric acid, and prints this instruction about the rinse between the two: “The water must have a neutral or slightly acidic ph. Water with a base ph will make the print difficult to clear.”

Sandy King’s published method says the same thing about the same minute, in more detail: “it is very important that this first rinse be done in water that is either neutral or slightly acidic. If the first rinse is alkaline, ferrous hydroxide compounds may be formed in the paper, making complete clearing difficult or impossible.”

Both are talking about water that touches the print for one or two minutes. This developer touches it for five, at 38 °C, at pH 9.5.

⁇Which oxidation state kills the print — Ware says iron(III), King says iron(II)

The two specialists who write most clearly about kallitype permanence name different culprits, and the course states both rather than choosing.

Ware: “the inherent problem of the iron-based silver processes lies in the danger of leaving residual ferric iron in the print — to its ultimate undoing, because iron(III) will oxidise silver with consequent degradation of the image.”

King: “The major danger to long-term permanence of a kallitype image is residual ferrous iron, Fe(2+). If left in the paper, even very small quantities of residual ferrous iron will eventually oxidize the silver, and the image will fade.”

They are not necessarily in conflict, and the course’s reading — offered as a reading — is that they describe the two ends of one sequence. Iron(II) is not itself an oxidant for silver; it is the reductant that made the image. But Ware’s own monograph records that molecular oxygen re-oxidises it, and records the pH dependence in a parenthesis that matters enormously here — “slowly in acidic and rapidly in basic solution”:

4 Fe²⁺ + O₂ + 4 H⁺ → 4 Fe³⁺ + 2 H₂O

Air re-oxidation of iron(II), after Ware

So iron(II) left in the paper becomes iron(III), and iron(III) attacks the silver. King names what you leave behind; Ware names what it turns into. If that reading is right, an alkaline developer is doubly exposed: it hydrolyses iron(III) into the fibres where no clearing bath can reach it, and it accelerates the conversion of any iron(II) left there into more of the same. Neither author states that conclusion, and no source read tests it.

Ware adds a further reason to want the iron out whatever its oxidation state: iron(II) in paper with traces of peroxide drives the Fenton reaction, whose hydroxyl radicals cut cellulose chains and cost the sheet its strength.

Deeper: what the trade did with the dilemma

There are only three honest ways out of the bind Ware describes, and the history of the process is the history of all three being tried.

1. Keep the alkali and clear harder. This is the traditional kallitype, and it is what this page documents. Ware’s verdict on how well it worked is severe: kallitype “as practised at the time, was unreliable”, and Dick Stevens, surveying many major American collections, found in total one historic kallitype. Ware records that as “the strongest indication we have” that the prints were short-lived. The Getty’s platinotype atlas notes that even the best clearing procedures leave iron detectable by XRF, so this is a matter of degree rather than of success and failure.
2. Drop the alkali and use a near-neutral chelating developer. This is where the trade went. Citrate both develops and clears, and works at a pH where iron(III) is complexed instead of hydrolysed; see the sodium citrate developer.
3. Remove the reason the alkali was needed. This is Ware’s own answer. Since the problem was nitrate etching colloidal silver in acid, he replaced silver nitrate with silver sulphamate, whose anion does not oxidise, and got a sensitiser that works at pH 2 to 3 and “will wash out of the paper cleanly, without hydrolysis of the excess ferric iron, and without any tendency to dissolve the colloidal silver image”. That is the argyrotype.

The one thing this page will not do is pretend the choice is only about colour.

Function of every ingredient

Borax decahydrate, 75 g — the entire solution, and an alkali rather than a developer.

What it is. Sodium tetraborate decahydrate, Na₂B₄O₇·10H₂O, formula weight 381.4, CAS 1303-96-4: white odourless crystals, relative density 1.7. Its encyclopaedia entry records that it effloresces slightly in warm dry air. The sheet writes “Borax” and names no hydrate; photographic formulas mean the decahydrate by that word, and the pentahydrate at 291.4 and the anhydrous salt at 201.2 are sold beside it.

Why it is here. To make the developing bath alkaline and keep it alkaline. Ware’s account is that the kallitype “employs alkaline-buffered developers of high pH, e.g. Borax” specifically to stop the nitrate anion dissolving the colloidal image silver while the print is wet. The manufacturer’s account is about colour — more of this stock, blacker print — and the two accounts are compatible if the reason the print is blacker is that the silver particles formed in an alkaline bath are larger, which is the reading given under Image characteristics.

What it does chemically. One thing, and it does it well. It supplies a boric acid / borate conjugate pair in roughly equal measure, which holds the solution near pH 9.5 and resists the acid that development, the paper and the sensitiser bring into the tray. It is not oxidised, it is not reduced, and no source read gives it any coordinating role towards iron. It is not a chelating agent, and a bath of borax alone would not develop a kallitype at all — which is exactly why no published kallitype developer is borax alone.

What the photographic consequence is. A neutral-black image instead of a brown one; development in five minutes instead of ten; a bath that wants to be at 38 °C; better protection of the image silver while it is wet; and more iron(III) hydrolysed into the paper for the clearing bath to fail to remove.

What happens with more of it. A colder print, up to a point nobody read has established, and a worse iron problem. The sheet’s own two mixtures move the borax by a factor of two between brown and black. Wall’s 1912 pair moves it by a factor of 3.6 between purple and pure black. Beyond that the sources stop and the course stops with them: no source read gives an upper limit, a maximum useful proportion, or a composition in which more borax stops making the print colder.

What happens with less of it. A warmer print, and — below the point where the two stocks meet in the sepia bath — no borax at all and the process reverts to the tartrate developer. The practical route to “less of it” is not a change of formula but a cold stock bottle, which is the failure described under Mixing: a saturated stock at 20 °C carries about a quarter of the borax the recipe assumes, and the printer who draws from it gets a bath they did not intend and no visible sign that anything is wrong until the print is dry.

What it interacts with. Acids, which destroy it: NIOSH lists strong acids among its incompatibilities, and the reaction liberates boric acid and removes the alkalinity the developer exists to supply. The Rochelle salt stock, which it is always mixed with and never chemically reacted with in any source read. Iron(III), which it hydrolyses rather than binds. And the clearing bath and the rinse that follow it, which are where its cost is paid.

Distilled water, 400 mL at 52 °C — not an inert ingredient here. The temperature is doing real work: at 18.75 g per 100 mL the stock is roughly three times what cold water will hold, so the heat is what gets the solid in at all, and the sheet’s own warning that residual solid commonly remains is the evidence that it is close to the limit even at 52 °C. Distilled water is required in capitals throughout the kit, and the reason is calcium: Ware’s reaction in which calcium precipitates as insoluble calcium oxalate and drives the iron down the aquation chain runs faster in an alkaline tray, not slower.

What is deliberately absent. There is no developing agent, because the reducing agent was manufactured by light in the paper hours ago. There is no sodium sulfite or other preservative, because there is no easily oxidised organic reducer to preserve. There is no restrainer, because there is no fog reaction to restrain — unexposed silver nitrate simply stays as silver nitrate until the fixer takes it. And there is no ligand in this bottle at all, which is why it is half a developer and not a developer.

Interactions

Borax and the tartrate stock — the interaction the formula is built on. The two are miscible in any proportion and the sheet publishes two of those proportions. Adding this stock to the other shortens the development time, raises the temperature the bath wants, and moves the image colour towards neutral. Whether borate and tartrate interact chemically with one another when the two stocks meet is not established by anything read for this page, and the course will not assert that they do or that they do not. What is established is that the mixture behaves differently from either alone, and that the sources describe that difference entirely in terms of pH and colour.

Borax and iron(III) — the interaction that decides the print’s future. Not a complexation. Above pH 4, Ware records, iron(III) hydrolyses to polymeric colloidal hydroxide; this bath is at about pH 9.5 and holds it there by design. The iron that should be leaving the paper is instead being converted into a form that will not leave it. See The mechanism.

Borax and the image silver — the interaction that justifies it. Alkalinity suppresses the etching of colloidal silver by nitrate, which is acid-favoured. This is the benefit, and it is real.

Borax and acid, anywhere in the process. The one chemical incompatibility that matters day to day. An acid stop bath, an acid fixer, an acid-rinsed graduate or a tray still wet from the citric acid clearing bath of another process will neutralise the borate and, at the concentrations here, will do it quietly. The bath does not change colour and does not fizz. It simply stops being alkaline, and the print comes out brown.

The developer and the first rinse, where two published rules pull in opposite directions. King’s instruction after his citrate developer is unambiguous: rinse in neutral or slightly acidic water, because “if the first rinse is alkaline, ferrous hydroxide compounds may be formed in the paper, making complete clearing difficult or impossible”. Ware’s argument is equally unambiguous in the other direction: nitrate dissolves colloidal image silver “especially under acidic conditions”. Both concern the same wet print in the same minute. The course states both and picks neither, because nothing read tests them against each other; what it will say is that “not alkaline” and “not strongly acidic” leave a window between them, and that a print coming out of this developer arrives at that rinse carrying more alkali than a print from either of the other two baths.

The developer and the clearing bath. In this kit the clearing bath is potassium oxalate, 60 g in 500 mL, five minutes at 20 °C. Carrying a well-buffered alkaline developer into it on a poorly drained print both dilutes it and works against it. Drain, rinse quickly, and move on.

The developer and the fixer. The kit’s fixer is 50 g of sodium thiosulfate pentahydrate and 12 mL of 28 per cent ammonia in a litre, used for not more than five minutes, and the sheet’s reason for the limit is that “a longer soak will cause the print to fade. Do not use a standard photographic fixing bath; the finely divided, unprotected silver metal will be etched from the print.” That is the same mechanism this developer’s alkalinity exists to suppress, met at a point where alkalinity cannot help.

The developer and chromium(VI). The one interaction this course declines. See Safety.

Variants

Wall’s four developers of 1912 — the historical record, not a procedure. Wall’s ninth edition prints four kallitype developers, each in ten fluid ounces of distilled water, and says that “on the salt used the tone of the finished print will depend”. Two of the four contain borax and both carry a dichromate:

Wall’s formula	Tone	Borax	Rochelle salt	1 per cent potassium bichromate
No. 1	pure black	1 oz	¾ oz	7 to 9 drams
No. 2	sepia	none	½ oz	4 to 5 drams
No. 3	warm maroon	none	none — sodium tungstate 1 oz	none
No. 4	purple	120 grains	450 grains	10 drams

Formula No. 1 is the direct ancestor of the black-tone bath on this page, at about twice its borax strength, and the difference between them is the chromium. The course prints Wall’s composition as history and does not offer it as an instruction.

Thomson’s developer, 1924. Wall’s later collection gives it as equal parts of a 5.2 per cent Rochelle salts solution and a 9.4 per cent borax solution “with the addition of 0.02 to 0.8 per cent potassium bichromate, which keeps the whites pure and acts as a restrainer”, and directs thirty minutes in it. Three things are worth taking from it. The borax strength as used, 4.7 per cent, is the closest independent check the course has on the modern bath. The thirty minutes is six times the modern figure and shows how unsettled the development time was. And the description of the dichromate as a restrainer rather than a contrast agent is a different account of the same additive from the one the modern sheets give, and is recorded here as the source’s wording.

Hall’s formulas, 1924. Wall prints a kallitype developer of an entirely different construction — sodium acetate 125 g and tartaric acid in a litre, with a dichromate solution — whose clearing bath is sodium citrate with citric acid. It is worth a line here because it is an acid kallitype developer, the opposite choice from this page’s, from the same decade.

What the trade did next. Photographers’ Formulary’s own later kallitype kit carries no borax and no Rochelle salt: one 20 per cent sodium citrate bath, and a citric acid clearing sequence. Bostick and Sullivan supply a proprietary “black tone developer” whose composition is not published, so the course cannot say whether it is a borax bath. King recommends one developer and states the reason: “there is really no reason to use any other developer unless you want an unusual color that cannot be rendered through toning with gold, platinum or palladium.”

No course variant of these quantities is offered. There is a real temptation to publish a “safer” version — borax is the only Level B material in the developer chain — but a borax developer with less borax in it is just the brown-tone bath, which the sheet already publishes, and a borax developer with something else in it is a formula no source supports. The hazard here is a dust and reproductive-toxicity hazard of the dry solid, answered by handling rather than by reformulation.

☠The dichromate contrast control, which this page refuses

Every source read that gives a contrast control for a borax kallitype developer gives a chromium(VI) salt. Photographers’ Formulary supplies 5 g of potassium dichromate for a 10 per cent solution and directs 5 to 20 drops per 500 mL of mixed developer, in bold type, into the developer and not the sensitiser. Wall’s 1912 developers each carry a 1 per cent bichromate solution. Thomson’s 1924 formula carries 0.02 to 0.8 per cent. Bostick and Sullivan supply ammonium dichromate at 5 per cent as a “contrast booster”. The Getty atlas records the same practice for the platinotype, with potassium chlorate as the other historical oxidant.

The chromium ruling is that this course uses chromium(VI) nowhere and at no concentration, and the classification behind it is not marginal. The notified GHS entries for potassium dichromate carry H350 for cancer, H340 for genetic defects, H360 for reproductive toxicity, H330 for fatal by inhalation and H410 for long-lasting aquatic toxicity; its encyclopaedia entry is safety level D, historical study only. Photographers’ Formulary’s own sheet does not disguise this — it states that “all chromium compounds are potential carcinogens” and that a skin spillage “will cause a chemical burn, which will appear as ulceration” — and then tells the reader to wash the excess down a drain with copious water, which is the one instruction on that sheet this course flatly declines to reproduce.

So this page publishes no contrast control. What is left is the negative. No chromium-free substitute is invented here, because no source read establishes one.

Safety

Safety level B, and this is the one page in the kallitype developer family where the classification is driven by the developer itself rather than by the baths on either side of it.

The Rochelle salt developer is Level A because its only ingredient comes back with no hazard classification anywhere. Borax does not. The chemical page sets out the assessment; the short version is:

• Signal word Danger. The aggregated ECHA C&L Inventory notifications for disodium tetraborate decahydrate carry H360, may damage fertility or the unborn child, in 93.2 per cent of the 2,865 company reports that classify it, and H319, causes serious eye irritation, in 12.6 per cent. ILO-WHO Chemical Safety Card 0567 carries the same two statements.
• It has a workplace exposure limit, which the tartrate does not: HSE’s EH40 gives 5 mg/m³ long-term for the decahydrate and 1 mg/m³ for the anhydrous and pentahydrate forms. The limits are set for the dust.
• Chemical Safety Card 0567 records irritation of eyes, skin and respiratory tract, possible effects on the central nervous system, kidneys and testes, and that a harmful airborne concentration is reached quickly, especially if the material is powdered.

Why Level B rather than A or C. The course’s classification rubric caps Level A at a classification “at most irritant, harmful if swallowed, or corrosive at the concentrations actually handled”, and reproductive toxicity is outside that ceiling. It does not reach Level C, whose reproductive-toxin criterion applies where a fume cupboard or specialist disposal is the recognised control; here the controls are dust suppression, gloves, eye protection and hygiene.

Where the hazard actually is: the seventy-five grams of dry crystals, not the tray. The whole of the exposure risk on this page is concentrated in the thirty seconds it takes to weigh the solid and tip it into the water. Once it is in 400 mL of water and then diluted into a 500 mL working bath, it is a dilute weak alkali. Weigh it over a tray, do not tip it from a height, and do not brush spilled powder off a bench dry.

Who should be especially careful. The classification driving all of this is reproductive toxicity. A photographer who is pregnant, breastfeeding or trying to conceive should read the supplier’s safety data sheet for the actual product and take the specific risk assessment ILFORD’s general guidance describes. Familiarity from the laundry aisle is not a hazard assessment: the classification above is filed against this substance by the companies that sell it.

The other hazards of this session, which are not the borax.

• Hot water. The stock is mixed at 52 °C/125 °F. That is a scald temperature for a slow spill. Mix in a sink, in a vessel you can hold.
• The sheet in the tray is not clean. It arrives carrying silver nitrate and ferric oxalate, and the developer becomes a solution containing both once a few prints have been through it. Silver nitrate stains skin brown-black, and the stain is silver bound to protein that does not wash off. Handle prints with tongs.
• The baths on either side. The kit’s clearing bath is potassium oxalate, which the sheet itself calls “rather toxic” and an anticoagulant, and its fixer is made with 28 per cent ammonia, which the sheet says must be mixed in a well-ventilated area and never sniffed.
• Chromium(VI) is not used. If your kit contains the dichromate packet, it still has to be labelled, stored away from anything reducing, and disposed of through a licensed route rather than down a drain.

Personal protective equipment. Nitrile gloves — HSE’s COSHH essentials sheet P1 takes single-use nitrile gloves 0.2 mm thick as splash protection where the safety data sheet gives no more specific advice — and eye protection, which Chemical Safety Card 0567 specifies for this substance rather than the full splash goggles a caustic alkali would need. Splash goggles while the hot stock is being mixed, for the water rather than for the borate.

Ventilation. Nothing in the tray produces a vapour. The ventilation requirement of this session belongs to the ammonia in the fixer and to dust control while the solid is being weighed.

Storage

The dry solid. Well closed and dry, in a labelled container never used for food. HSDB records that borax effloresces slightly in warm dry air, and the direction of that drift matters: a tub kept somewhere warm loses water of crystallisation and becomes richer in borate per gram than the label assumes. For a bath measured in tens of grams the effect is small, and it runs towards a colder print rather than a warmer one.

✕Which borax did you weigh? A 90 per cent error waiting to happen

Borax is sold as the decahydrate, the pentahydrate and the anhydrous salt, and a formula that says “borax” means the decahydrate. The molar masses set the conversions: 381.4 for the decahydrate, 291.4 for the pentahydrate and 201.2 for the anhydrous salt.

The sheet’s 75 g of decahydrate is 75 ÷ 381.4 = 0.197 mol of borate. The same amount of borate is 57.3 g of the pentahydrate or 39.6 g of the anhydrous salt. Put the other way round: weigh out 75 g of the anhydrous salt by mistake and you have put 90 per cent more borate into the bottle than the formula asks for.

On most pages a hydrate mix-up is a nuisance. Here it is a direct hit on the one variable that decides the image colour, and the print will come out colder for a reason you will not be able to see. Read the tub, and write the hydrate in the notebook rather than adjusting the weight, because no source read publishes a conversion for this formula and the course will not invent one.

The stock solution. In any closed, labelled bottle, and no source read publishes a keeping time. What this bottle does have is a diagnostic problem the tartrate stock does not: crystals in the bottom are the normal state here, not a warning sign, because the sheet says residual solid is expected. So the usual test does not apply, and the useful discipline is different — warm the bottle and stir it back into solution before you measure from it, every time, for the reason set out under Mixing. A stock drawn cold is a stock at perhaps a quarter strength.

The working developer. The sheet says to store it in any convenient container and gives no life for it. It is not the borate that ages; it is the iron and silver the bath accumulates, and the symptom is a clearing problem rather than a development one.

Incompatibilities

• Acids of every kind. NIOSH lists strong acids among borax’s incompatibilities. In this darkroom the realistic sources are an acid stop bath from another process, an acid hardening fixer, a citric acid clearing bath, and glassware rinsed in either. Neutralising the borate does not announce itself.
• Chromium(VI) in any form. Refused under the chromium policy, and separately a poor chemical neighbour to a bath whose purpose is to carry a reducing iron(II) complex.
• Metallic salts, which NIOSH lists generally, and — specifically for this darkroom — silver salts in the bottle. A splash of sensitiser into an alkaline stock is a place for silver oxide to appear.
• Hard water. Calcium precipitates as calcium oxalate in the presence of the oxalate coming off the sheet and drives the iron towards hydrolysis, which is the failure this bath is already most exposed to. Distilled water throughout, as the sheet requires.
• An alkaline first rinse after development, which King warns forms ferrous hydroxide compounds in the paper and makes complete clearing “difficult or impossible”, and which the manufacturer’s later sheet repeats. The developer itself is that alkaline; the rinse must not be.
• The tartrate stock, when you did not intend it. Not a hazard, but the contamination that will silently change what the page is about. Keep a dedicated funnel, graduate and bottle for each stock.

Waste

The borate is the part of this bath the course has the clearest published guidance on, and it is not negligible. Chemical Safety Card 0567 records that the substance is harmful to aquatic organisms, and PubChem’s use list records borax as a registered herbicide for total vegetation control on non-crop land — so a spent borax developer does not go on the garden, and it is not the mild household substance its reputation suggests.

Kodak’s J-52 publication gives 5.6 to 9.4 as the pH window sewer codes most frequently set, and a borax solution at about pH 9.5 sits just outside it — the only developer in this family for which pH is a disposal consideration at all. The working bath is diluted well below the stock, so the practical answer for the small volumes a home darkroom produces is dilution; the practical answer for the stock bottle is not to pour it away concentrated.

What makes the spent developer a waste stream beyond that is what it has taken out of the print — iron from the sensitiser, silver that has diffused off the sheet, and the black residue that settles out of a used bath, which is very likely silver-bearing. Bottle the used developer, label it and hold it with the other iron- and silver-bearing baths from the same session, which in this kit means the clearing bath and the fixer as well. ILFORD’s guidance for domestic users is to bottle wastes separately, label them and take them to a household waste and recycling centre. Photographers’ Formulary’s own sheet tells the reader to “consult with local sewer and water authorities regarding proper disposal of darkroom chemicals in your area”, which is the right instruction. Local regulation governs, and this page does not give a jurisdiction-specific rule.

The dichromate packet, if your kit has one, is not part of this. It is a chromium(VI) waste and goes through a licensed route.

Troubleshooting

The black-tone developer gives a brown print. The first suspect is the stock bottle, not the formula. A stock that has stood cold has thrown its excess borax and is a saturated solution at perhaps a quarter of the intended strength; the arithmetic is under Mixing. Warm it, stir it until the solid is gone, and mix a fresh working bath. The second suspect is contamination by acid — a graduate that held citric acid, a tray that held an acid stop. The third is the sizing: the sheet says gelatin sizing gives a blue tone where arrowroot gives brown, so a change of paper can look exactly like a change of developer.

The print is colder than expected and you cannot account for it. Check the hydrate on the tub. Seventy-five grams of the anhydrous salt is 90 per cent more borate than 75 g of the decahydrate.

A yellow or brown stain in the areas the negative masked. Residual iron, and this is the developer most exposed to it. Develop the full five minutes rather than pulling the print when the image looks complete; make sure the bath is actually warm, since the sheet ties the time to the temperature; keep the first rinse neutral or slightly acidic, as both King and the manufacturer’s later sheet require; and check the clearing bath, which is the step designed to finish the job. Ware’s warning is that the window for fixing this is short — freshly formed iron(III) hydroxide redissolves in dilute acid, and the same material after it has dried and aged does not.

Prints take longer and longer to clear as the session goes on. Iron is accumulating in the tray, and in this bath a good deal of it is arriving already hydrolysed. No published replenishment rate or discard point exists for this developer, so the conservative course is the only defensible one: mix a fresh 500 mL rather than nursing a tired bath, and write down how many sheets each tray took before the masked border began to stain. Both citrate kits publish a replenishment figure and this one does not, so the number you record is genuinely missing from the literature rather than merely missing from your notebook.

A tide-line or a band of different density across the print. The sheet went into the developer in two stages, and with a five-minute bath there is less time to even it out than with the ten-minute tartrate one. Wall’s method for a large print is face down and turned over at once, breaking bubbles with a fingertip; the manufacturer’s later sheet describes the tilted-tray pour.

The bath has thrown a dark deposit. Expected, and described under Behaviour. Agitate so it does not settle on the highlights. Solid in the stock bottle is also expected and means something quite different: it is undissolved borax and it means the bath you are about to mix will be weak.

The image is weak and got weaker after the fixer. Two faults with one symptom. Underexposure is the first candidate, because a kallitype’s density is fixed by how much iron the light reduced and no amount of development will add to it. The second is bleaching in the fixer: Bostick and Sullivan warn that kallitype prints bleach in the fix, and Photographers’ Formulary caps fixing at five minutes for the same reason.

Experiments

Every one of these moves a single variable. Two controls matter more here than on most pages: everything downstream of the tray must be identical, because the clearing bath and the fixer alter this print at least as much as the developer does; and every sheet must come from one sensitiser batch on one paper with one sizing, because the sheet’s own note that gelatin sizing gives a blue tone will otherwise imitate exactly the effect you are trying to measure.

1. The colour ladder, and whether it is proportion or amount. Hypothesis: image colour is set by the proportion of borax to tartrate, not by the amount of either. Control: the black-tone bath as published, 72 mL of A and 128 mL of B in 500 mL. Variable: the A-to-B proportion. Make up five working developers at 500 mL each — the three the sheet publishes, plus one at 48 mL of A with 32 mL of B and one at 48 mL of A with 96 mL of B. Develop for a matched time, clear, fix and wash identically, and judge the prints dry and side by side under one named light. The brown-tone bath, which has more tartrate than the black-tone one and is warmer, is the case that separates proportion from amount.

2. The one this page most needs: does the cold stock really cost you the black? Hypothesis: a stock bottle drawn at 20 °C without re-warming yields a working bath substantially weaker in borax, and a visibly warmer print. Control: black-tone developer mixed from stock warmed to 52 °C and stirred until clear. Variable: the state of the stock. Mix a second black-tone bath from the same bottle after it has stood at room temperature long enough to throw solid, drawing the supernatant without disturbing the sediment. Develop matched sheets, and record the colour of both dry. If the arithmetic under Mixing is right, the second print should sit somewhere between the published black and brown. This is the experiment whose result the course would most like to have, because the whole factor-of-four uncertainty in this page’s strength turns on it.

3. The pH of the three baths. Hypothesis: the borax baths are strongly buffered near pH 9.5 and the tartrate bath is mildly alkaline and very poorly buffered. Control: freshly mixed black-tone developer. Variable: added acid. Measure the pH of all three fresh working developers, then add successive small measured volumes of a dilute acid to each and plot pH against acid added. The three curves are the buffer argument made visible, and the starting values are numbers no source read publishes for this formula.

4. Does the alkali really shorten the development? Hypothesis: the five minutes against ten is the borax and not the temperature. Control: the black-tone bath at 38 °C for 5 minutes. Variable: separate the two. Run four sheets — black-tone at 38 °C and at room temperature, tartrate-only at 38 °C and at room temperature — all for the same time, and compare density and colour. The sheet confounds alkali with heat by warming one bath and not the other; this untangles them.

5. What the borax costs in iron. Hypothesis: prints developed in the borax bath are harder to clear than prints developed in the tartrate bath, all else equal. Control: a sheet developed in the sepia bath. Variable: the developer. Mask a strip of each sheet during exposure so every print has a border that saw no light. Develop one in each of the three baths, clear all three in the same fresh bath, and time each to visually clean; then compare the borders after drying, and again after a month in the light. Ware’s argument predicts the borax prints clear more slowly and yellow sooner. A negative result would be worth recording just as loudly, because the argument on this page is a chemical inference and nobody read has tested it on kallitypes.

📓What to record

Paper and its sizing. Sensitiser batch and coating date. Exposure source and time. The hydrate printed on the borax tub. Which stock bottles, mixed on which date, and — for this bottle above all — whether there was undissolved solid in it and whether you warmed it before drawing. The working bath’s composition in millilitres of each stock. The actual temperature of the tray, measured, not assumed. Development time. Clearing time to visually clean, which is the number that carries this page’s argument. Fixing time. The wet colour and the dry colour, judged under a named light. And the number of prints this tray had already taken — because that is the figure no published source for this bath supplies.