Lab: Printing a Kallitype

Change one ligand and the process changes character. The Van Dyke’s iron was held by citrate; the kallitype’s is held by oxalate, and the photoproduct that oxalate makes — iron(II) oxalate — is almost insoluble, so it cannot move to the silver sitting a molecular distance away. Nothing much happens under the light. Then the sheet goes into a tray of sodium citrate and the picture arrives in fifteen seconds.

That is what you are here to see, and the interesting part is what follows from it. Because the second step now happens in a bath rather than in the coating, the bath is a lever, and a printer who has one negative and three developers has three prints. It is also where the iron leaves, which is why development runs for five to ten minutes when the image has been finished for nine and a half of them.

Purpose

To coat a two-solution kallitype sensitiser mixed drop by drop for the sheet in hand, expose it to a faint print-out image that is a guide rather than a picture, develop three prints from one negative in the three classical developers — sodium citrate, Rochelle salt and borax — and measure the tonal scale and image colour each one gives, so that the part’s main craft claim is settled on your paper rather than quoted.

This page does not restate the formulas. The sensitiser’s strengths, provenance and ingredient functions are on its formulary entry, the three developers have one page each, and the chemistry is the siderotype lesson’s.

!This lab does not finish the print either

As with the Van Dyke, what comes off the line tonight is developed, fixed and washed but not properly cleared, and an uncleared kallitype is the textbook example of a print that looks right and fails within a few years. Sandy King’s position is blunt: all untoned kallitypes will eventually fade, because “it is impossible to remove all residual ferrous iron from the paper”.

The clearing and toning lab finishes them, tests them and tones them. Until then: flat, dark, labelled uncleared, not mounted.

Learning objectives

By the end of the session you will be able to:

• Say what changes when citrate is replaced by oxalate, in terms of the redox potential and the solubility of the photoproduct.
• Judge the quality of a ferric oxalate solution with the ferricyanide spot test the suppliers publish, before you mix it with silver.
• Mix a two-solution sensitiser drop by drop for one sheet, and say why it is not made up in advance.
• Read a faint print-out image as a guide and not as a picture.
• Explain what the developer is doing, and say what it is not doing.
• Compare three developers on one negative and report colour and tonal scale as measurements.
• Recognise an exhausted developer from the print rather than from a count.

Prerequisites

• Lab: printing a Van Dyke Brown — the coating technique, the fixer discipline and the record format are assumed here.
• The siderotype principle, for the potentials, the solubility argument and what a developer means in this family.
• Negatives and papers for the alternative processes — unbuffered cotton, and the clearing test for paper below is the process-specific extension of it.
• Chemical waste and silver waste, because this session generates more silver-bearing and iron-bearing solution than any before it.
• A negative of long density range: Photographers’ Formulary give up to 1.85, King recommends about log 1.8 and reaches it by developing film about 50 per cent longer than normal for a grade 2 paper.

Safety classification

Level B, set by two substances rather than one.

Silver nitrate, as in the previous lab. Signal word Danger across 803 ECHA reports, H272 as an oxidising solid, H314 for severe skin burns and eye damage, and H400 and H410 for aquatic toxicity. Incompatible with ammonia, reducing agents and metals; permanently staining; present in every tray tonight.

The oxalates, which are a step up in toxicity from anything this cluster has used. Ferric oxalate’s ECHA entry, under the name diiron trioxalate, gives H302 and H312 — harmful if swallowed and harmful in contact with skin — at 100 per cent of a single notification’s reports. Oxalic acid, which every commercial ferric oxalate solution carries as a deliberate excess, is classified Danger across 1,282 reports with H302 at 99.8 per cent, H312 at 99.7 and H318 at 31.1. And potassium oxalate, the clearing bath of the traditional kit, is H302 and H312 at 100 per cent of the reports carrying those codes, with H319 at 36.4.

The distinction that matters is between an irritant and a systemic toxin. Photographers’ Formulary say it about potassium oxalate in plainer language than most safety sheets manage: it “is an anticoagulant (prevents blood clotting) and a poison. Since this chemical is used as the clearing bath, it can easily come into contact with your skin. It is strongly advised that you use tongs to clear Kallitype prints or wear rubber gloves.” The International Chemical Safety Card for oxalic acid names the kidney as the target organ for both short-term and repeated exposure. Nothing about this session justifies bare hands, and the reason is not a splash on the skin but what a soluble oxalate does once it is inside somebody.

One raised step, declared here. If you are weighing solid ferric oxalate or solid potassium oxalate rather than buying a solution, that weighing is the highest-hazard operation of the session and carries its own controls under the raised-step rule: a mask rated for fine particulates in addition to goggles and gloves, no sweeping motions, the jar opened and closed rather than left open, and the balance on a tray in still air. Both suppliers sell ferric oxalate as a 20 per cent solution precisely so that this step can be avoided, and the rubric prefers the bought solution.

⚠What is not a hazard here, and one thing that would be if the kit sheet were followed

No dichromate is used in this session. Photographers’ Formulary’s traditional kit ships 5 g of potassium dichromate and Bostick & Sullivan’s ships 25 mL of a 5 per cent ammonium dichromate “contrast booster”; their New Kallitype kit ships none and says so. The course uses none of them, at any level, under the chromium ruling — the aggregated classifications carry H340 for genetic defects and H350 for cancer at essentially every report. If your kit contains one, leave it sealed, do not follow the kit’s drain-disposal instruction, and read the contrast lesson for what the reagent was doing and what is available instead.

No ammonia is used either. The traditional kit’s fixing bath adds 12 mL of 28 per cent ammonia per litre, and the sheet’s own warning is that the concentrated liquid “releases extremely choking ammonia gas when opened”. This lab reaches an alkaline fixer through King’s carbonate and sulfite instead — same purpose, no vapour, and no concentrated ammonia in a room that also contains silver nitrate, which is an incompatibility rather than a preference.

No vapour and no heat source above 50 °C. Nothing here is volatile at room temperature. The one temperature limit that matters is Photographers’ Formulary’s ceiling for ferric oxalate: do not heat the solution, or the sensitised paper while drying it, above 50 °C.

And the ultraviolet is the hazard nothing in the room announces, which is why this page declares requiresUV.

Hazards

Hazard	Where it arises	Control
Systemic oxalate toxicity, by skin absorption or ingestion	Ferric oxalate solution, the coating, the developer, the clearing bath	Nitrile gloves at every step, tongs for the clearing bath on the supplier’s own instruction, nothing eaten or drunk at the bench, hands washed before leaving it
Fine oxalate dust, if a solid is weighed	Weighing ferric oxalate or potassium oxalate powder	The raised step above: particulate mask, goggles, still air, no sweeping. Better, buy the solution
Corrosive silver nitrate, to skin and eye	Solution A, the mixed sensitiser, the coating pool	Splash goggles for mixing, spectacles for the trays, gloves throughout
Permanent staining	Any contact with the sensitiser	Metallic silver bound to skin protein; gloves, apron, blotting paper under everything
Explosive silver oxalate	Oxalic acid or an oxalate solution left in contact with silver compounds and allowed to dry	The safety card names it explicitly. Nothing is left to dry; trays are rinsed at once; oxalates are stored away from silver salts
Incompatible mixing	Silver nitrate meeting ammonia, a reducing agent or a metal	Nothing ammoniacal in the room; no metal spatula, tongs, clips or trays
Ultraviolet, to eye and skin	Every minute the source is on	Part XVI’s enclosure and interlock, or outdoors shade and covered skin
Silver and iron in every bath	Developer, clearing bath, fixer, both washes	Collect all of it. Silver-bearing waste SOP

Required PPE

Nitrile gloves throughout, and this is the page where they stop being about splash protection. HSE’s COSHH essentials sheet takes single-use nitrile at 0.2 mm where a safety data sheet gives no more specific advice; the reason to keep them on for the whole session here is the oxalate, which is a systemic toxin absorbed through skin rather than an irritant you would notice.

Tongs for the clearing bath, on Photographers’ Formulary’s own instruction — and non-metal tongs, because silver.

Chemical splash goggles at the balance and while making up solution A; safety spectacles for the trays.

A particulate mask if, and only if, you are weighing an oxalate as a dry powder. The specification comes from the raised-step declaration above and not from a general rule.

An apron. The stain is silver and it is permanent.

Ventilation

The controls here are dust management if a solid is weighed, and keeping incompatible substances apart. Airflow is not among them, because nothing in this session produces a vapour — provided the ammonia route is not taken. That is the one exception, and it is the reason this lab does not take it: Photographers’ Formulary’s own instruction for their ammonia-alkalised fixer is to “mix this bath in a well-ventilated area”, and their description of the concentrated liquid is that it “releases extremely choking ammonia gas when opened”.

Work in a room with the ordinary through draught HSE ask for wet photographic work, on a lipped, wipeable surface. If you do weigh a solid, shut the window while you weigh and open it afterwards, because a draught at the balance lifts powder.

Materials

• Eight sheets of unbuffered 100 per cent cotton paper, hot-pressed, cut to 8 × 10 in: three for the developer comparison, one for the clearing test below, two for dose strips, two spare.
• A negative the same size as the print, of long density range — the standard negative, and the same one your Van Dyke was made from.
• Two brown dropper bottles, one for each solution, and a shot glass or small cup for the mixture.
• Red or ultraviolet-opaque masking material, so that every sheet carries a coated-but-unexposed border. On this process it is not optional: the masked border is how you know when clearing is finished, and both King and Photographers’ Formulary define the end point by it.
• Blotting paper, tape, a soft pencil, non-metal tongs.
• Distilled water, about 4 L. Photographers’ Formulary print the instruction in capitals on both kit sheets: use distilled water for all solutions.
• A step wedge from Part XIII, which this session needs more than the Van Dyke did, because three developers have to be compared on the same scale.
• A thermometer. Two of the three developers are specified warm and one at room temperature, so temperature is a variable you are controlling rather than observing.

Chemicals

The formulas are not restated here. What follows is what the session consumes.

Chemical	Quantity	Form
Ferric oxalate	about 6 mL of a 20 % w/v solution	Buy the solution. See the callout below for why, and for the test that tells you whether the bottle is any good
Silver nitrate	about 6 mL of a 10 % w/v solution	0.6 g of silver nitrate. Made up separately and kept separate
Sodium citrate	100 g	For 500 mL of the 20 % developer
Potassium sodium tartrate	100 g	Rochelle salt, for stock A of the two-stock developer system
Borax	75 g	For stock B. Read its own hazard note below
Citric acid	60 g	For two litres of 3 % clearing bath
Sodium thiosulfate pentahydrate	25 g	For 500 mL of 5 % fixer
Sodium carbonate and sodium sulfite	5 g and 1 g	The alkaline additions to the fixer, plus 5 g of sulfite for the hypo clear

!Borax is the surprise on this list

Of the eight substances above, the one whose classification is most likely to catch a reader out is not the silver or the oxalate. Borax — disodium tetraborate decahydrate — carries H360 for reproductive toxicity in 93.2 per cent of 2,865 aggregated ECHA reports, with signal word Danger. It is sold in supermarkets and in Part VIII it appears at 2 g per litre in D-76 without much ceremony; here it is 75 g in 400 mL of stock solution and the working bath is one of three you are comparing.

The course does not exclude it — that is a judgement for the individual and it is the developer that gives the coldest image colour the process can reach — but a reader who is or may become pregnant should read the borax page before choosing which of the three developers to make, and should not be finding this out from a supermarket box.

⚗Buy the ferric oxalate, and test the bottle before you trust it

Why the course says buy rather than make. Ware reviews four chemically distinct preparation routes — dissolving freshly precipitated iron(III) hydroxide in oxalic acid; precipitating iron(II) oxalate and oxidising it with hydrogen peroxide; reacting solid iron(III) nitrate with solid oxalic acid; and double decomposition of barium oxalate with iron(III) sulphate — and prefaces all four with the sentence that decides the question: “Because ferric oxalate is an ill-defined polymeric substance, the properties of the solutions and solids resulting from the methods of preparation described below will vary considerably.” A home preparation adds an uncontrolled variable to the one part of this process that is already uncontrolled, and every route works with oxalic acid in quantity. Photographers’ Formulary add the commercial half of the argument: they will not sell the green tripotassium salt for this purpose, because “its photo-activity is low and it is difficult to convert to the more active form”, and what they supply is a 20 per cent solution of the tri-hydrogen form made by the iron alum and oxalic acid route with a slight excess of oxalic acid left in.

Why the bottle still needs testing. Ferric oxalate solutions decompose. Ware records six to nine months in the dark as the figure some give, and notes that at least one well-respected platinum printer makes up a fresh solution the night before every session; King’s rule is to mix no more than will be used in two to three months, because the solution degrades “with a resulting increase in print fog”. What degrades is that iron(III) becomes iron(II) in the bottle, and iron(II) in the bottle makes silver in the coating everywhere rather than where the light fell.

The test the suppliers publish, and it costs two crystals. Put about two crystals of potassium ferricyanide in about 2 mL of water in a shot glass. Under a red safelight add one drop of the ferric oxalate. Then read it three ways:

1. Under the safelight. A slight darkening means the solution is good. Very dark or black means it already contains iron(II).
2. Step into room light. Yellow-brown to orange is good. Green means a trace of iron(II); a blue cast condemns it, and “the deeper the blue, the poorer the quality”.
3. Hold it beside a 100 W frosted bulb. Within a minute a deep blue should form on the side nearest the lamp. That blue is the evidence that photosensitive iron(III) is present, and it is Prussian blue — the same reaction as Part XXI’s, used here as an assay instead of as a picture.

Photographers’ Formulary print this test on both kit sheets and give the reason for it in one line: with a little practice “you will be able to gauge the quality of the ferric oxalate before you mix it with an expensive metal salt.”

Equipment

Two calibrated droppers or 2 mL syringes, one per solution, never interchanged, and a small non-metal cup for the mixture. A balance reading to 0.01 g for the developer salts, checked by the balance and thermometer check. Graduates and a stirring rod, verified under the glassware SOP.

A coating rod or a soft brush with no metal ferrule, and — for a kallitype specifically — the option of Tween 20 as a spreading agent, one drop of a 10 per cent solution per sheet’s worth of sensitiser on Bostick & Sullivan’s figure.

Six trays, which is more than any previous session in this cluster: three developers, a rinse, a clearing bath and a fixer. A contact frame with a split back, a UVA source from Part XVI or the sun, a timer, and a thermometer that reads to 40 °C.

Nothing metal touches anything, for the silver’s sake, and nothing that has held another alternative process without being properly washed. By this point in the cluster, cross-contamination is the commonest cause of an inexplicable result.

A dim working light. Both Photographers’ Formulary sheets ask for a red safelight or very subdued incandescent light for the ferric oxalate; Bostick & Sullivan say to coat “in a dimly lit room”. This is a darker session than the Van Dyke was, and the reason is the iron rather than the silver.

Estimated cost

Band £££, and it is the most expensive session in the part. The silver is the same as the Van Dyke’s; what is added is ferric oxalate — a substance Ware notes is listed by very few fine chemical houses and typically priced at about a hundred times ferrous oxalate — and three developers rather than none.

The capital is the same as the previous lab’s, with the addition of trays. Both suppliers sell complete kits, and both publish their yields: Photographers’ Formulary’s traditional kit makes “up to 30 4-by-5 prints (or about seven 8-by-10)” from 30 mL of ferric oxalate, and their New Kallitype kit “about twenty five to thirty 4x5 or seven to ten 8x10 prints”. Seven 8 × 10 prints from a kit is the figure to plan against, and it is a good deal fewer than a beginner expects.

Estimated consumables cost

Every price with a number is the planner’s own dated UK figure and every quantity comes from the Materials and Chemicals sections. Four of the ten rows have no sourced price at all.

Consumed	This session	Sourced price	Cost this session
Nitrile gloves	4 pairs	£6.64 to £14.99 per box of 50 to 100	£0.53 to £1.20
Ferric oxalate, 20 % solution	about 6 mL	Not priced. A gap the file names, and it explains why: the bottle is sold at 20, 25 and 27 per cent under one name, so a price with no strength beside it is not a cost per sheet	—
Silver nitrate, as 6 mL of 10 % solution	0.6 g	£59.95 per 25 g, or £112.90 per 10 g	£1.44 to £6.77
Sodium citrate	100 g	Not priced	—
Rochelle salt (potassium sodium tartrate)	100 g	Not priced	—
Borax	75 g	£9.98 per 200 g, decahydrate	£3.74
Citric acid	60 g	£10.00 per 250 g of the monohydrate	£2.40
Sodium thiosulfate pentahydrate	25 g	£14.70 per 1 kg of the raw salt	£0.37
Sodium carbonate and sodium sulfite	5 g and 6 g	£7.20 per 500 g; £13.68 to £19.98 per kg	£0.15 to £0.19
Unbuffered cotton paper, 8 × 10 in	8 sheets	Not priced. A gap the file already names	—

The priced rows come to about £8.63 to £14.67, and that is a floor rather than a total. Two things about it are worth reading rather than skimming. The borax, the citric acid and the developer salts are bought in quantities that last many sessions, so the figure above overstates a single evening’s share of them by a large factor — but it does not overstate the silver, which really is spent tonight. And the single biggest unpriced item is the ferric oxalate, which on Ware’s remark about its price relative to ferrous oxalate is likely to be the most expensive gram in the room after the silver.

Equipment is deliberately absent, because trays and droppers are not consumed.

Waste streams

Five streams, and this session produces more volume than any before it. The developer carries iron(II), iron(III), citrate or tartrate or borate, and the black residue the New Kallitype sheet describes. The first rinse carries the same, dilute. The clearing bath carries iron chelated or dissolved, and — if you used the traditional kit’s route — potassium oxalate, which is the most toxic solution on the bench. The fixer carries silver as thiosulfate complexes. The final wash carries thiosulfate.

Collect all of it, label each container with contents and date under the labelling SOP, and follow the silver-bearing waste SOP and the general chemical waste SOP. Oxalate waste is kept away from silver waste: the International Chemical Safety Card for oxalic acid names contact with silver compounds as forming explosive silver oxalate, and a mixed bottle that dries out is the case it is warning about. Check your local regulations; they govern.

Alternative route

Without an ultraviolet unit, print in the sun — and this is the page where that costs you most. The Van Dyke prints out and can be judged by inspection under any sky. The kallitype cannot: Bostick & Sullivan state that “there will be little print out image so timing will have to be done by trial and error or test strip”, which means the exposure has to be repeatable, and a sky is not. The honest substitute is to expose the whole comparison — all three sheets and the strips — in one session under an unchanging sky, so that the comparison between developers is valid even though the absolute dose is unknown, and to record conditions rather than a dose under the daylight exposure SOP. Say so in the analysis. A measurement whose limits are stated is a measurement.

Without three trays’ worth of developer chemistry, the comparison can be run on one developer and two temperatures instead, since Photographers’ Formulary specify the black and brown developers warm at around 38 °C and the sepia one at room temperature. You lose the colour comparison and keep the temperature one.

Without a densitometer, the developer comparison still works: three prints from one negative under one light, side by side, described in words with a step wedge visible in each. You lose the number and keep the finding.

One thing has no alternative. There is no version of this session without ultraviolet light and none without running water — Photographers’ Formulary give 40 minutes of final washing, or a shorter wash plus a hypo-clearing bath plus 15 to 20 minutes more; Bostick & Sullivan give 15 to 20 minutes. If you cannot wash, this page cannot be run, and the honest thing is to say so rather than offer a substitute that makes a print which fades.

Preparation

The day before, at least. Make up solution B if you are dissolving powder: King’s instruction is that ferric oxalate “takes a long time to go into solution and should be mixed about 24 hours before use”. Make up solution A. Make up the developers — Rochelle salt dissolves endothermically, so the solution cools as it goes and Photographers’ Formulary warn that the bowl may need warming, and borax dissolves slowly with residual solid commonly left over.

Run the ferricyanide test on the ferric oxalate, before it meets any silver. Record the result.

Test the paper before you commit a picture to it. This is the process-specific check that Part XXI’s paper lesson does not carry. Coat one sheet with sensitiser, dry it, and take it straight through development and clearing without exposing it. King’s criterion: “Papers that will not clear completely in about 4-5 minutes should not be used.” Photographers’ Formulary’s New Kallitype sheet gives the same test with a longer limit and a different diagnosis: “If the print is taking longer than 10 minutes to clear your paper is probably too absorbent and it will be necessary to size it before applying the sensitizer.” Take King’s four to five minutes as the working figure and the Formulary’s ten as the point at which the paper is disqualified rather than merely awkward.

The bench. Six trays in sequence, thermometer in the first developer, tongs by the clearing bath, blotting paper under the coating station, nothing metal, nothing ammoniacal.

Procedure

Nine stages, about three and a half hours of attended time plus drying and a long final wash.

The kallitype sequence, and what leaves the sheet at each step

1. 11. Mix the sensitiser for one sheetEqual drops of 20 % ferric oxalate and 10 % silver nitrate in a shot glass. Nothing is made up in advance, and the two bottles are stored apart
2. 22. Coat and dryRod or brush, then 15 to 30 minutes hanging. A fan is allowed; forced heat is not, because King records that it may fog
3. 33. Expose to a faint print-out imageA guide, not the picture. Bostick & Sullivan: about one to two stops faster than traditional palladium, and the timing has to come from a test strip
4. 44. Develop — and the image arrives in secondsIron(II) oxalate dissolves, reaches the silver, and reduces it. Out goes most of the residual iron, which is why the bath runs for minutes after the picture has stopped changing
5. 55. First rinse, 1 to 2 minutes, neutral or slightly acidKing: an alkaline rinse here forms iron(II) hydroxide compounds that make complete clearing difficult or impossible
6. 66. Clear, until the masked border is white3 per cent citric acid on King and the New Kallitype kit; tetrasodium EDTA on Bostick & Sullivan; potassium oxalate on the traditional kit. The bath differs; the end point does not
7. 77. Fix, 5 per cent, two to five minutes, never acidAnd the print bleaches while you watch, unless it has been toned first
8. 88. Hypo clear and wash15 to 40 minutes depending on whose sheet you follow
9. 99. What is still in the sheetIron bound to the cellulose, and an untoned image. Both are the next lab

Nine steps, of which two are clearing steps and one is a rinse whose pH matters. Times and reagents from the four kallitype sources; the disagreements between them are set out in the text.

Stage 1 — Mix the sensitiser for the sheet in hand (5 minutes)

Equal parts, in a shot glass, immediately before coating. All four sources agree on the ratio and on the timing. Bostick & Sullivan give a starting point of about 20 drops of each per 8 × 10 print and 12 of each per 5 × 7; Photographers’ Formulary give 12 to 20 drops of each for an 8 × 10 on Arches 140 lb hot press, and 1 to 2 mL of each; King gives about 2 mL of combined solution for an 8 × 10.

Why the two bottles are stored apart, and this is not the Van Dyke’s reason. In the Van Dyke, the acid holds a single mixed bottle stable for months. Here, mixing silver nitrate with a solution containing free oxalate precipitates silver oxalate — Photographers’ Formulary say it is “very common” and does no harm provided you do not transfer it to the paper — and the mixture has no published keeping time at all. Mix what one sheet needs.

📓Two disagreements in the sources, both worth recording rather than resolving

The ratio. Photographers’ Formulary’s New Kallitype sheet gives the one qualification anybody makes to equal parts: “Most research shows that the best print density will result from our recommendation of equal proportions. Some studies show that slightly better densities can be achieved with slightly more silver nitrate solution.” They name no such proportion, so this course gives none, and a reader who wants to test it should vary it in known steps and measure rather than guess.

Ripening. Photographers’ Formulary’s traditional kit has the silver dissolved directly into the ferric oxalate and then states that “the sensitizer must ripen for a few (2-3) days before use”, stirred occasionally. Their New Kallitype kit keeps the two apart and mixes drop by drop with no ripening at all. King and Bostick & Sullivan both mix drop by drop. The two Formulary sheets describe two different sensitisers, and this lab teaches the two-bottle one because three of the four sources do and because a bottle that must ripen is a bottle you cannot make on the evening.

Stage 2 — Coat and dry (40 minutes, mostly waiting)

The coating technique is the Van Dyke lab’s and is not repeated. Four things differ.

Work dimmer. A red safelight or very subdued incandescent light, on both Formulary sheets; “a dimly lit room” on Bostick & Sullivan’s.

Coat liberally but not running wet, which is Bostick & Sullivan’s phrase, and let the sheet rest one to two minutes before drying, which is theirs too — a Tween addition, if you use one, evens the coating out during that rest.

Mask every sheet. On this process the coated-but-unexposed border is not a diagnostic luxury, it is the end-point indicator for clearing, and both King and Photographers’ Formulary define completion by it.

Dry with a fan or in still air, and not with heat. King is explicit: “A fan may be used to accelerate drying, but DO NOT force dry with heat, which may cause fogging”, and his time is 15 to 30 minutes. Photographers’ Formulary permit a hair dryer but cap the temperature at 50 °C. Bostick & Sullivan allow “gentle heat”.

⁇Humidity: what this lab was asked to teach, and what the sources actually support

The course manifest for this page asks for coating and drying “with humidity controlled and recorded, since this process is more humidity sensitive than the two before it”. No kallitype source read for this course supports that claim, and this page will not make it.

What the four kallitype sources say about humidity, in full. King: drying “will take about 15-30 minutes, depending on temperature and humidity” — a statement about drying time. Bostick & Sullivan: air dry naturally “if you are not in an extremely moist climate”. Photographers’ Formulary, on both sheets: nothing at all. That is the whole of it. Not one of them treats humidity as a variable that changes the print.

Where the humidity evidence actually comes from, and why it does not transfer. Ware’s Platinomicon tabulates exposure scale against relative humidity for the print-out platinum and palladium sensitisers, and his argyrotype notes make humidity a deliberate colour control, because humidifying a coated sheet to 100 per cent RH before exposure shifts the print-out image to a purplish-grey. Both of those are print-out processes in which the reduction happens in the coating, and the water in the fibres is what lets the ions move and the particles grow. A kallitype is a developing-out process: the reaction that makes the picture happens in a tray with as much water as it could want. There is no mechanism by which the sheet’s moisture content at exposure would govern the particle size in the same way, and no source read for this course claims that it does.

What the course therefore asks. Record the relative humidity and temperature at coating, drying and exposure, because they cost nothing to write down and because a claim you can test later needs a record made now. Do not control humidity, do not buy a humidity box for this process, and do not transfer the platinum figures. If your own comparison shows a humidity effect on a kallitype, that would be a new finding and it should be reported as one.

Stage 3 — Exposure, to an image that is a guide and not a picture (45 minutes)

Expect very little. Wall’s 1912 dictionary describes what you should see as “a faint brown image on a yellow ground”, and Bostick & Sullivan say plainly that “there will be little print out image so timing will have to be done by trial and error or test strip”.

The reason is the solubility argument from the siderotype lesson: iron(II) oxalate is sparingly soluble — Ware gives 0.022 g per 100 cc — so in a dry sheet the ions are immobile and cannot meet the silver. Some do meet, because the coating is not perfectly dry and the sensitiser carries free oxalate; that is the faint brown image. Most of what light did is still waiting.

!The bracket, and the one comparative figure worth having

Two sourced figures exist for this process and both are somebody else’s lamp:

• 10 to 20 minutes under a 275 or 300 W sunlamp at 12 to 18 inches, or 4 to 6 minutes in a ultraviolet light box — Photographers’ Formulary, on both kit sheets.
• About one to two stops faster than traditional palladium — Bostick & Sullivan, who publish no absolute time at all.

That last is the more useful of the two if you have ever printed palladium, and it is the only cross-process speed statement in the corpus for this family.

The bracket this page publishes is the course’s own derivation from those figures: a stepped series of 2, 4, 8 and 16 minutes in a UV box, or 5, 10, 20 and 40 under a sunlamp. Run it, and then recalibrate when anything changes — the paper, the ferric oxalate bottle, the array height, the lamp hours.

Judge the exposure from the developed strips, not from the frame. That is the structural difference from the Van Dyke and it is worth stating as an instruction: with a printing-out process you look; with this one you develop and then look. Bostick & Sullivan add the practical consequence — because the print bleaches in the fix, “either tone before fixing or overprint by a stop or two”.

Stage 4 — Development, which is where a kallitype becomes a photograph (10 minutes per print)

Get the developer onto the whole sheet at once. Every source warns about this and the reason is that the image appears immediately: Bostick & Sullivan say development “must be done quickly, or else watermarks may appear”; King pours the developer over a face-up print “as quickly as possible”; Photographers’ Formulary describe tilting the tray so the developer pools at one end, holding the sheet clear, and lowering the tray so the solution runs across in one movement. Any part of the sheet that starts developing a second late will show it, and the fault is blotchy development.

Then wait, long after nothing is changing. King: development is “visually complete in about 15-30 seconds, but a development time of 5-10 minutes is important for archival purposes: much of the residual ferric iron, which if left in the print could cause loss of permanence, is removed at this stage.” Bostick & Sullivan: at least five minutes, standard 8 to 10. Photographers’ Formulary’s New Kallitype sheet is the outlier at two to three minutes with constant agitation, and gives its own reason — to let the developer “react with all available iron and silver”.

What the developer does, at the scale of a paper fibre

1. 1Dry coating: iron(III) oxalate and silver nitrate, side by side and immobile — the ions cannot encounter one another, so nothing happens in the dark
2. 2After exposure: iron(II) oxalate where the light fell — insoluble, 0.022 g per 100 cc, so it stays put and the print-out image is faint
3. 3In the developer: the iron(II) dissolves as a complex, moves, and reduces the silver — and the iron that leaves in this bath is iron nobody has to clear afterwards

Drawn to show the sequence, not the scale. The solubility figure and the mechanism are Ware's; the statement that the ferrous salts dissolve in the developer and reduce the silver nitrate where light reduced the ferric salt is Wall's, from 1924.

The three developers, compared as the sources compare them. This is the part’s main craft claim and it needs to be reported precisely, because the sources are much clearer about colour than about contrast.

Developer	The source’s own words	Time and temperature	What the sources say it does
Sodium citrate 20 %	King’s single recommended developer; the New Kallitype kit’s only one	5 to 10 minutes (King); 2 to 3 minutes (Formulary) at room temperature	King: after development the print has “a rather unpleasant brown color”, changed dramatically by the processing that follows. He recommends it as the one developer to learn on
Rochelle salt, stock A alone diluted	Formulary’s sepia-tone developer, 48 mL of stock A to 500 mL	10 minutes at room temperature	“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”
Borax with Rochelle salt	Formulary’s black-tone developer, 72 mL A plus 128 mL B to 500 mL	5 minutes, and “works best if it is warm, (around 38 °C/100 °F or higher)”	“If you increase the amount or proportion of Stock Developer Solution B (borax), you will increase the blackness of the print”
The two mixed the other way	Formulary’s brown-tone developer, 96 mL A plus 64 mL B to 500 mL	5 minutes, likewise best warm	The intermediate, and the sheet invites the reader to try further intermediate mixtures

=What the sources establish about the developers, and what they do not

Colour is well established and it is a proportion rather than a switch. Photographers’ Formulary give a single rule that covers all three of their developers — more Rochelle salt for sepia, more borax for black — and invite intermediate mixtures. Wall’s 1912 dictionary records four developers giving “black, sepia, warm maroon and purple”, which is a wider range than the modern kits offer and is a reason to think the intermediate mixtures are worth exploring. Bostick & Sullivan say only that “different developers will change the color tone of the print”.

Temperature is established as part of the formula rather than as a variable. The black and brown developers are specified warm at around 38 °C or higher; the sepia one is specified at room temperature and given twice the time. Warming is not a general control: it is written into two of the three recipes, and the sepia developer is not simply the same bath run cold.

Contrast and maximum density are the weak part of the claim, and this page says so. Not one of the four sources attributes a contrast difference to the choice among these three developers. Where the sources do discuss kallitype contrast, they attribute it to a dichromate added to the developer — King gives 1 to 16 mL of a 5 per cent solution per litre and says it takes the printable density range from about 1.2 to about 2.2 — which is a reagent this course does not use. King’s claim that the process as a whole reaches a higher maximum density than a Van Dyke rests on “well-made comparison prints side by side”, which is a practitioner’s comparison rather than a measurement, and he adds that the difference “is not huge”.

Which is precisely why this lab measures it. Three prints, one negative, one step wedge, three developers, read on a densitometer. If the developers differ in exposure scale and maximum density as well as in colour, your numbers will show it and no source the course has read will have told you.

Warmth, in practice. The two warm developers need a tray sitting in a larger tray of warm water, and a thermometer in the working solution rather than in the water bath. A developer that has drifted from 38 °C to 26 °C over three prints is a fourth variable in a three-variable experiment.

Stage 5 — Stopping, and the rinse whose pH decides the clearing (2 minutes)

This is the step most likely to be treated as a rinse and is not one. King’s instruction and his reason: “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.”

Read that against what has just happened. If you developed in borax, the sheet has come out of an alkaline bath carrying dissolved iron; if the rinse water is also alkaline, the iron hydrolyses in the fibres instead of leaving. Ware makes the same point about the whole family from the other end: the kallitype’s alkaline developers protect the image silver from the nitrate anion, and in doing so “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”.

So: one to two minutes in running water that you have checked, and if your supply is above pH 7, acidify it slightly or use distilled. Photographers’ Formulary say the same in their own words — water with a base pH “will make the print difficult to clear”.

Stage 6 — Clearing, to the end point rather than the clock (5 to 10 minutes)

Tonight’s clearing is the short version; the full sequence and its chemistry is the lab after next. Use 3 per cent citric acid, two or three baths rotated so the freshest is last, which is King’s method and the New Kallitype kit’s.

The end point is the masked border going white, and it is defined by every source the same way: King, “until there is absolutely no stain left in the sensitized but unexposed areas”; Photographers’ Formulary, “until the whites appear free of a yellow or grey fog”. Not a time.

And the print will look worse. King’s warning is worth having before it happens: “The image will lighten considerably during clearing, but don’t worry because all the lost density will return during toning and fixing.”

Stage 7 — Fixing (2 to 5 minutes)

Five per cent, alkaline, short, and it bleaches while you watch. The strength is the Van Dyke’s and the reasoning is identical, so it is not repeated. Three things are specific to this process.

The bleaching is worse here, and the sources are unanimous about it. Bostick & Sullivan: “Kallitype prints will bleach in the fix, so either tone before fixing or overprint by a stop or two. These are the only effective solutions to the bleaching problem.” Photographers’ Formulary’s New Kallitype sheet: the fix “tends to bleach highlights so you will likely want to compensate by over exposing the print prior to development”.

Temperature is a control on the bleaching. Bostick & Sullivan specify about 20 °C “because if the water is too warm, it’ll accelerate the bleaching”.

And the fixing itself is fast. Bostick & Sullivan’s own footnote is the clearest statement in the corpus of why this bath is unlike a Part XI fixer: “Unlike silver bromide prints, the Kallitype’s silver is not enmeshed in a gelatin colloid and fixes much faster. I believe that even more dilute fix and shorter times may be equally as effective.” Two minutes on their sheet, two to five on the New Kallitype sheet, not more than five on the traditional one, four minutes or two-plus-two on King’s.

Stage 8 — Hypo clear and wash

Hypo clear, 1 per cent sodium sulfite for two minutes on King’s figure, then final wash: 15 to 20 minutes on Bostick & Sullivan’s, 20 to 30 on King’s with the hypo-clear step or a full hour without it, 40 minutes on Photographers’ Formulary’s or a shorter wash plus their hypo-clear plus 15 to 20 more. Take the longest you can manage; the wash is the cheapest archival step in the process.

Stage 9 — Dry, and read

Air-dry on a screen or hanging. Read the prints the next morning, dry, in one light, side by side with the step wedge visible on each.

Expected observations

On the dry coated sheet. Yellow to yellow-green — the colour Photographers’ Formulary give for the ferric oxalate solution itself. Not green, and not blue: a blue or green cast means iron(II) is already present, and the test on this page is how you find that out before you have coated eight sheets.

During the exposure. Very little. A faint brown image on a yellow ground, on Wall’s description, and on some papers barely that.

In the developer. The image appears within seconds. Photographers’ Formulary describe a further detail worth knowing about before you see it: “Note a residual black substance forming from and next to dark tones. Actively agitate the print so this substance does not stick to the highlights. The black residual accumulates in your developer and may be filtered out through coffee filters if necessary.” That black material is image substance that did not stay in the paper, and a developer that has gone grey and turbid is a developer that has been used.

In the clearing bath. The print lightens, sometimes alarmingly, and the masked border goes from yellow to white. If the border will not go white in about five minutes, the paper is the problem.

In the fixer. Further lightening — this is the bleaching every source warns about — and a shift in colour. If the print has been toned first, it does not happen.

On drying. More density again, and a warmer colour than the wet print showed.

And one observation that is a fault rather than a stage. King records that untoned kallitypes “frequently see tone reversal in heavily exposed areas, that is, with increasing exposure the shadow areas actually get lighter”, and calls the look unpleasant. It is solarisation, it belongs to this process rather than to your technique, and King’s remedy is toning: gold, platinum or palladium “counteracts tone reversal and restores normal tonal values to the heavily exposed shadow areas”.

What is happening chemically

Under the light, the same photoreduction as everywhere in this family, with the oxalate paying for the electron:

Fe₂(C₂O₄)₃ + UV → 2 FeC₂O₄ + 2 CO₂

Light: iron(III) oxalate to iron(II) oxalate, with carbon dioxide evolved

And then almost nothing, because the product is insoluble and the ions cannot move. Ware gives iron(II) oxalate’s solubility as 0.022 g per 100 cc and states the consequence for the platinum case in terms that apply here: the photoproduct “cannot reduce platinum(II) or palladium(II) salts in aqueous solution to the metal unless it is solubilised by complexation”.

In the developer, the ligand does the solubilising:

FeC₂O₄ + 2 C₆H₅O₇³⁻ → [Fe(C₆H₅O₇)₂]⁴⁻ + C₂O₄²⁻

Citrate displaces oxalate and the iron(II) goes into solution as a citrato-complex

and the reaction that was always thermodynamically allowed finally has mobile reagents:

Fe²⁺ + Ag⁺ → Fe³⁺ + Ag

One electron, one silver atom, and the iron leaves into the bath as iron(III)

Wall’s 1924 statement of the whole sequence has not been improved on: “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.”

⚗Why the developer exhausts, and why exhaustion shows up as a clearing problem rather than a weak print

Look at the right-hand side of the last two equations. Every silver atom made puts one iron(III) into the developer, and every unexposed region gives up its unused iron(III) too. The developer is accumulating exactly the substance the rest of the process is trying to remove.

King’s replenishment rule and his reason: about 200 mL of fresh developer per 500 square inches of print, decanting from the top and discarding the sediment, because “if the developer is not replenished, the accumulation of ferrous iron will make it increasingly difficult to clear the print. This will not only result in an unpleasant stain in the masked areas of the print, but may also decrease permanence, because the stain consists in large part of residual ferrous iron.”

So an exhausted kallitype developer does not announce itself as a thin print. It announces itself as a print that takes longer and longer to clear, and then as a print whose masked border stays yellow — which is why the clearing end point is the measurement that tells you the state of the bath. The New Kallitype kit’s replenishment schedule is 100 mL after about four 8 × 10 prints and 100 mL after each further two, and its alternative is blunter: pour some out and top it up as it clouds.

Data to record

Use the lab notebook and the batch record SOP.

The batch record, for each of the two sensitiser bottles and each developer: strength, make-up volume, supplier and lot of the solid, date mixed, and — for the ferric oxalate — the result of the ferricyanide test, in the three readings the test gives.

The session log. Date, room temperature, relative humidity at coating, drying and exposure. Paper: maker, product, weight, surface, and its clearing time from the unexposed test sheet. Sensitiser: drops of each per sheet, whether Tween was added. Drying: method, time, temperature. Source, distance, warm-up, lamp hours, or the sky. Exposure per sheet. Developer: which, its strength, its temperature at the start and end of each print, and how many prints had been through it. Rinse water pH. Clearing: bath, number of baths, and the time to a white border. Fixer: strength, temperature, time. Wash.

The measurement table, which is the product of this session:

Column	What goes in it
Print	1 sodium citrate, 2 Rochelle salt, 3 borax-and-Rochelle
Developer temperature	Start and end, in °C
Development time	Minutes
Step wedge: first step above base	The step number, and the density difference
Step wedge: first step at maximum	The step number
Exposure scale	Computed from the two, in log exposure units
Maximum density	Measured dry, next morning
Image colour	In words, in daylight, dry — and a hue reading if your instrument gives one
Clearing time	To a white border, in minutes
Notes	Reversal in the shadows, black residue on the highlights, evenness

Analysis

First, what you may claim. One print per developer supports a comparison, not a measurement of the developer. Say so.

Second, the comparison this session exists for. Put the three prints side by side, dry, under one light, and answer three questions in this order:

• Do the colours differ, and in the direction the sources predict? More Rochelle salt should give more sepia and more borax more blackness. If your prints do not show that, the interesting question is which of the two variables in your version — the developer or its temperature — is responsible.
• Do the exposure scales differ? Read the step wedge on all three. No source read for this course claims they do, so this is a measurement rather than a confirmation.
• Do the maximum densities differ? Same caveat. And if you have last week’s Van Dyke from the same negative, read its Dmax too, because that puts King’s “more Dmax with kallitype, but the difference is not huge” to a test with a number attached.

🧮Reading an exposure scale off a step wedge, worked on constructed figures

The step numbers below are invented to show the arithmetic. Your wedge and your prints supply the real ones.

A Stouffer 21-step wedge has 0.15 density between steps. Suppose on the citrate-developed print the first step distinguishable from paper white is step 3, and the first step that has reached maximum density is step 14:

(14 − 3) × 0.15 = 1.65

Exposure scale

and suppose the borax-developed print from the same negative reads steps 4 to 14:

(14 − 4) × 0.15 = 1.50

And for the second developer

What that would mean. A 0.15 difference is one step, which is at the edge of what a single pair of prints can support — so the honest report is “no difference I can distinguish”, not “the borax developer is a stop shorter”. Two steps would be a finding. This is the discipline Part XIII teaches, applied to a process where nobody has published the numbers.

Third, read the clearing times as data about the developer, not about the paper. If print 3 cleared in four minutes and print 1 in nine, and both were on the same paper, the difference is what was in the bath. That is the exhaustion signal from the callout above, arriving as a measurement.

Fourth, decide what to do next. The most useful single output of this session is a sentence in your notebook naming which developer you will use for the rest of the part and why — because the clearing and toning lab needs prints, and comparing toners across three different developers would be comparing four things at once.

Troubleshooting

The image appeared instantly and completely on immersion, with no separation in the shadows. Over-exposure. In a developing-out process the developer has a fixed amount of iron(II) to work with, and if every part of the sheet has enough to reduce all the silver available to it, every part goes to maximum density at once. Halve the exposure and repeat. The same appearance from a very short development is the opposite fault and is distinguished by the clearing time: an over-exposed print clears normally, an under-developed one does not.

Blotchy or streaked development, with hard-edged pale patches. Almost always the pour: see the atlas entry, and re-read Photographers’ Formulary’s tilted-tray method. A cold developer where a warm one was specified produces the same appearance more slowly.

The masked border will not clear. Take the candidates in cost order: the developer is exhausted (cheapest to test — mix fresh and repeat one print); the first rinse was alkaline; the paper is too absorbent, which the unexposed test sheet in Preparation would have caught; or the clearing bath is spent. See the atlas entry.

A grey or brown veil over everything, including the masked border. Fog. On this process the first suspect is the ferric oxalate bottle, and the ferricyanide test settles it in two minutes. Then the working light, then forced heat during drying, which King names specifically.

The print bleached badly in the fixer. Expected to some degree — every source says so — and excessive if the bath was warm, strong, acid or long. The two remedies the sources give are the ones to adopt: tone before fixing, or overprint by a stop or two.

Black specks or smears on the highlights. The residual black substance the New Kallitype sheet describes, stuck to the sheet during development. Agitate more actively, and filter or replace the developer.

A print that was fine last week and is not this week, with nothing changed. Check the ferric oxalate first. It is the least stable thing on the bench, its solutions degrade in months, and King’s consequence is exactly this — fog that increases with the age of the bottle.

Clean-up

Rinse everything at once, and the reason on this bench is chemical rather than tidy: an oxalate solution left to dry in a tray that has also held silver is the condition the oxalic acid safety card names for forming explosive silver oxalate. Nothing dries with both in it.

Wipe the bench, bin the blotting paper into the solid waste, and rinse graduates into the silver-bearing waste container. Gloves off last, under the PPE removal SOP, and hands washed before you touch anything else — this session’s controlling hazard is absorption, not splash.

Storage

The two sensitiser solutions: dark brown bottles, apart, cool, labelled and dated. Photographers’ Formulary’s instruction on both sheets, and their reason is that both are light-sensitive.

Ferric oxalate has the shortest life of anything in this part. As a powder it “lasts indefinitely”, in King’s words; in solution it does not. Ware’s figure from the literature is six to nine months in the dark, with the note that at least one platinum printer makes it fresh the night before every session; King’s rule is to mix no more than will be used in two to three months. Date the bottle, and re-run the ferricyanide test before any session that matters.

The mixed sensitiser is not stored at all. No source gives it a keeping time, and silver oxalate comes out of it.

Developers keep, and they change while they keep. The two-stock system stores as stocks; the mixed developers are reused and replenished rather than kept indefinitely, and the New Kallitype sheet’s instruction is to save the developer between sessions and discard it when the kit is used up.

Coated paper: use it within an hour or two of drying, which is Photographers’ Formulary’s own figure and much shorter than the Van Dyke’s.

Finished prints, once cleared and toned: unbuffered mounts, for the same reason as the rest of the cluster.

Disposal considerations

The chemistry. The waste carries iron(II) and iron(III) complexes, free oxalate, citrate, tartrate or borate, silver as nitrate and as thiosulfate complexes, and thiosulfate. Three of those govern.

Silver, whose aggregated classification carries H400 and H410 in over 99 per cent of ECHA reports, and which is worth recovering — Part XII owns that argument.

The oxalates, which are the new thing in this part. Ferric oxalate is H302 and H312; oxalic acid is Danger with H302, H312 and H318; potassium oxalate is H302 and H312 with H319 in a third of reports. They are collected, kept away from silver waste, and not poured away on the assumption that dilute means resolved.

Borate, if you made the borax developer. Borax’s classification is dominated by H360, and the quantity here — 75 g in a stock solution — is not trivial.

The general practice. Bottle each stream, label it, never top up an unlabelled container, follow the silver-bearing waste SOP and the general chemical waste SOP, and read the disposal ruling. Both Photographers’ Formulary kit sheets tell the reader to wash solids and solutions down a drain with copious water; this course does not repeat that instruction, and their own sheets tell you to consult the local sewer and water authority in the same section. Check your local regulations; they govern.

Questions

1. Why does a kallitype barely print out when a Van Dyke does? Answer with the solubility figure and say what it implies about where the reaction happens.
2. What is in a sodium citrate developer that reduces silver? If the answer is “nothing”, say what the bath is for instead, in two functions.
3. Your masked borders took four minutes to clear on the first print of the evening and nine on the sixth. What has happened, and what does it predict about the permanence of print six?
4. Why must the first rinse be neutral or slightly acid, and why does that matter more after a borax developer than after a citrate one?
5. Bostick & Sullivan say the only two effective answers to fixer bleaching are to tone before fixing or to overprint. Why is “fix for a shorter time” not on their list?
6. You are told a kallitype has a longer tonal scale than a Van Dyke. What evidence would settle that, and what evidence do the sources actually offer?
7. Your ferric oxalate gives a distinct green cast in the room-light stage of the ferricyanide test. What does that mean, what will it do to your prints, and can the bottle be used?

Further experiments

The intermediate developers. Photographers’ Formulary invite it explicitly: mix stocks A and B in proportions between their three published ones and see whether the colour moves continuously or in steps. Wall’s 1912 dictionary records four period developers giving “black, sepia, warm maroon and purple”, which is a wider range than the modern kits reach, so there is somewhere to go.

Temperature against developer, separated. Run the black-tone developer at 38 °C and at 20 °C on two halves of one exposed sheet. The sheets specify warmth for two of the three baths and nobody says what happens without it.

The exhaustion curve. Develop ten prints in one unreplenished bath, and record the clearing time of each. Two things should come out: the number of prints your bath will take, and whether the clearing time rises smoothly or falls off a cliff.

The ratio. Photographers’ Formulary say some studies get slightly better density with slightly more silver, and name no figure. Coat three sheets at 1:1, 1.2:1 and 1.5:1 silver to iron, expose and develop them together, and read the maximum densities.

And the one that connects forward. Keep one uncleared, untoned print from tonight in the dark and one on a windowsill, both labelled and dated, and look at them when you have finished Part XXV. That is the only permanence experiment in this course that costs nothing but patience.

Recap

Change the ligand and you change where the reaction happens. Oxalate makes an insoluble photoproduct, so almost nothing happens under the light and the picture waits for a bath that can dissolve it.

The developer supplies a ligand and a solvent, not a reducing agent. Wall said it in 1924 and nothing since has improved on it; the redox reaction is the same one the Van Dyke does in the coating.

Development runs for minutes after the image has stopped changing, because that is when the residual iron leaves — which makes development the first clearing bath and makes an exhausted developer show up as a clearing failure rather than a weak print.

The three classical developers are well documented for colour and poorly documented for contrast. More Rochelle salt is sepia, more borax is black, and the temperature is written into the recipe. Nobody publishes their exposure scales, which is why you measure them.

The first rinse decides whether the print can be cleared at all, because an alkaline rinse precipitates iron hydroxides in the fibres.

The fixer bleaches, and the only two documented answers are to tone first or to overprint.

And the humidity requirement this page was asked to teach is not in the kallitype literature. It belongs to the print-out platinum and palladium processes. Record humidity; do not control it; and do not transfer a requirement between processes without evidence.

Check your understanding

Question 1. Why does a kallitype show almost no print-out image where a Van Dyke shows about half its final density?

• Ferric oxalate is much less light-sensitive than ferric ammonium citrate
• The photoproduct, iron(II) oxalate, is only sparingly soluble - 0.022 g per 100 cc - so in a dry coating the ions cannot move to meet the silver, and the reaction waits for a bath that dissolves them
• Silver nitrate is present at a lower concentration in a kallitype sensitiser
• The exposure is shorter, so less silver is reduced

Show the answer and why

Answer: The photoproduct, iron(II) oxalate, is only sparingly soluble - 0.022 g per 100 cc - so in a dry coating the ions cannot move to meet the silver, and the reaction waits for a bath that dissolves them

The opposite of the first option is true: ferric oxalate is the faster of the two ligands, with a quantum yield of about 1.2 against the citrate system's 0.45 maximum, and Bostick & Sullivan put kallitype print times about one to two stops faster than traditional palladium. What differs is mobility, not sensitivity. Ware states the consequence for the platinum case in terms that apply here: the iron(II) oxalate photoproduct cannot reduce a noble-metal salt in aqueous solution unless it is solubilised by complexation.

Question 2. Development is visually complete in 15 to 30 seconds. Why does King develop for 5 to 10 minutes?

• To let the image reach its full maximum density, which happens slowly
• Because much of the residual iron leaves the sheet at that stage, so the developer is also the first clearing bath
• To let the developer neutralise the acid in the sensitiser
• Because a short development leaves unreduced silver that the fixer cannot remove

Show the answer and why

Answer: Because much of the residual iron leaves the sheet at that stage, so the developer is also the first clearing bath

King gives the reason directly: development for five to ten minutes "is important for archival purposes: much of the residual ferric iron, which if left in the print could cause loss of permanence, is removed at this stage". That also explains why an exhausted developer shows itself as a clearing problem rather than a thin print - the bath has accumulated the very iron it is supposed to be carrying away, and King's replenishment rule exists for exactly that reason.

Question 3. You develop in borax and rinse in tap water at pH 8. What have you done?

• Nothing much; the clearing bath that follows is acid and will correct it
• Formed iron(II) hydroxide compounds in the paper, which King says make complete clearing difficult or impossible
• Neutralised the developer, which is what the rinse is for
• Bleached the highlights, because alkali dissolves colloidal silver

Show the answer and why

Answer: Formed iron(II) hydroxide compounds in the paper, which King says make complete clearing difficult or impossible

King's instruction is that the first rinse must be neutral or slightly acidic, and his reason is that an alkaline rinse forms ferrous hydroxide compounds in the paper. Ware makes the same point about the family: the alkaline developers that protect the image silver from the oxidising nitrate anion do so at the cost of hydrolysing the excess iron into the image. A later acid bath does not reliably undo it, because iron hydroxide left in a sheet converts irreversibly to an oxyhydroxide that dilute acids will not touch. And alkali does not bleach silver - that is what the thiosulfate does.

Question 4. Which of these does the published literature actually establish about the three classical kallitype developers? (Select all that apply.)

• More Rochelle salt gives a more sepia image and more borax a blacker one
• The black and brown developers work best warm, around 38 °C, and the sepia one is used at room temperature for twice as long
• The three developers give measurably different exposure scales
• The three developers give measurably different maximum densities

Show the answer and why

Answer: More Rochelle salt gives a more sepia image and more borax a blacker one, The black and brown developers work best warm, around 38 °C, and the sepia one is used at room temperature for twice as long

The first two are Photographers' Formulary's own statements, printed as part of the formulas. The last two are not established by any of the four kallitype sources read for this course: where the sources discuss kallitype contrast they attribute it to a dichromate added to the developer, which this course does not use, and King's claim that the process reaches a higher maximum density than a Van Dyke rests on side-by-side comparison prints rather than measurement. That gap is why this lab asks for a step wedge in all three prints.

Question 5. A drop of your ferric oxalate solution in a ferricyanide test appears distinctly green in room light. What does it mean?

• The solution is fresh and photosensitive; green is the expected colour
• A trace of iron(II) is already present in the bottle, which will raise print fog; a blue cast would be worse still, and the deeper the blue the poorer the material
• The ferricyanide has decomposed and the test is invalid
• The solution has been contaminated with silver

Show the answer and why

Answer: A trace of iron(II) is already present in the bottle, which will raise print fog; a blue cast would be worse still, and the deeper the blue the poorer the material

Photographers' Formulary give the three readings: yellow-brown to orange in room light is good, green shows a trace of iron(II), and a blue cast condemns it in proportion to its depth. The blue is Prussian blue - iron(II) reacting with ferricyanide - which is why the third step of the test, holding the vessel beside a lamp and watching blue form on the lit side, is the positive control that shows photosensitive iron(III) is present. Iron(II) in the bottle makes silver everywhere rather than where the light fell, which is fog.

Question 6. The manifest for this lab asked for coating and drying with humidity controlled. Why does the page decline?

• Because humidity control is impractical in a home darkroom
• Because no kallitype source read for this course treats humidity as a variable that changes the print - the published humidity evidence is for print-out platinum, palladium and argyrotype, where the reduction happens in the coating rather than in a tray
• Because the kallitype developer washes out any humidity effect
• Because humidity affects only the drying time and never the image

Show the answer and why

Answer: Because no kallitype source read for this course treats humidity as a variable that changes the print - the published humidity evidence is for print-out platinum, palladium and argyrotype, where the reduction happens in the coating rather than in a tray

The four kallitype sources mention humidity three times between them, and all three are about drying: King notes that drying time depends on it, Bostick & Sullivan qualify air drying with "if you are not in an extremely moist climate", and Photographers' Formulary say nothing at all. Ware's humidity tables and his argyrotype colour control are for printing-out processes, where the water in the fibres governs how large the metal particles can grow during the exposure. A kallitype makes its image in a tray. The last option overstates the other way - the course records humidity precisely so the claim can be tested rather than assumed either true or false.

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