Kallitype

The kallitype is the process in which the printer’s decisions are furthest from the coating and closest to the tray. Light reduces the iron; a developer then lets the iron(II) reduce the silver to metal; and because the developer is chosen rather than given, one sensitised sheet can yield several different prints. That is the difference from Van Dyke Brown, which prints out, and it is the whole reason both entries exist.

The chemistry

The first half is the siderotype’s and is shared with every iron process in this atlas: ultraviolet reduces iron(III) to iron(II) and takes the organic acid off as carbon dioxide. The silver is not light-sensitive, and forgetting that leads to the wrong diagnosis every time, because a fault that looks like a speed problem is an iron problem and a fault that looks like a fixing problem is a clearing one.

The second half is what the developer is for. Where the sensitiser uses ferric oxalate, the photoproduct is ferrous oxalate, which is insoluble: it stays exactly where it was made and cannot go and find the silver. A developer that supplies a chelating anion takes the iron(II) into solution as a mobile complex, and only then can it reduce the silver where it stands.

⚗Three developers, three colours, and one gap the course leaves open

Photographers’ Formulary’s kit makes Stock A from 100 g of Rochelle salt — potassium sodium tartrate — in 200 mL of distilled water at 52 °C, and Stock B from 75 g of borax in 400 mL at the same temperature. The three published working developers, each made to 500 mL, are:

• Black tone — 72 mL of A with 128 mL of B; develop 5 minutes, and the bath works best warm, around 38 °C or higher.
• Brown tone — 96 mL of A with 64 mL of B; 5 minutes, likewise warm.
• Sepia tone — 48 mL of A and no borax at all; 10 minutes at room temperature.

The rule of thumb is that more of the tartrate stock increases the sepia. The New Kallitype kit uses a different anion again — a 20 per cent sodium citrate developer — and the palladiotype uses a citrate developer too, so the family is really one photochemistry with a choice of chelating bath at the end.

Why a tartrate bath gives sepia and a borate bath gives black is not explained by any source read for this course. The observation is well attested; the explanation is not given, and this page does not supply one. What can be said is the shape of it: the three anions differ in how strongly and how fast they hold the iron, and image colour in a silver print is a particle-size effect, so a developer that releases iron(II) faster is building silver faster and coarser.

One practical note that reads like superstition and is not. Rochelle salt dissolves with absorption of heat, so the solution cools as it goes and may need the bowl warmed; the mixture turns cloudy on stirring and clears in time. That is why the stock is specified at 52 °C — not because the salt needs heat, but because dissolving it takes heat out of the water. A cold-water stock looks like a failure long before it becomes a solution.

Historical workflow

Coat, dry, expose under ultraviolet to a faint image, develop in the chosen bath, clear, fix, wash. The exposure is carried much further by the developer than by the light, which is the practical meaning of developing out and the reason a kallitype is faster than a Van Dyke from the same sheet.

The clearing sequence is not an afterthought here. Iron left in the paper is the family’s characteristic fault, and the kits supply a clearing agent as a named component: disodium EDTA’s page records that Bostick & Sullivan’s kallitype sheet names EDTA tetrasodium for its clearing bath while their platinum and Ziatype kits list “250 g EDTA clearing agent” without naming the salt at all, and that a printer who reads both and assumes one product is making an assumption the sheets do not support. Where the course cannot establish which salt a published formula meant, it says so rather than choosing quietly.

The image

Colour is a developer decision, which is unique in this atlas. Everywhere else the colour is set by the sensitiser, by the metal or by a toner applied afterwards; here the same exposed sheet gives sepia or black according to which bath it goes into. That is what makes the kallitype the best place in the course to learn what a developer choice actually costs and buys.

Surface is the family’s: silver among the fibres, no binder, matte.

Contrast is put in by the developer and by any oxidant in the sensitiser, not by grade. Part XXIV plans a lesson on contrast control in iron-based printing for exactly that reason.

Permanence

The kallitype’s bad reputation is the most interesting permanence question in the iron-silver family, and the course’s position is that the failures are procedural, and every one of them happens after the exposure.

Residual iron is the first and the commonest. It stains the paper yellow and goes on reacting, and it is a clearing failure rather than a fixing one — which means that lengthening the fixer does not touch it.

Residual thiosulfate is the second, and it is the salt print’s problem arriving in a different process: hypo left in the paper converts image silver to silver sulfide over years.

Untoned colloidal silver is the third. A printed or developed silver image of very small particle size has an enormous surface area relative to its mass, which chloroauric acid’s page identifies as what makes it a conspicuous target for hydrogen sulfide and sulfur dioxide from the air — and for the sulfur-bearing amino acids in any protein near it. That is the argument for toning a kallitype, and it is a chemical argument rather than an aesthetic one.

Ware’s redesign of the neighbouring print-out process is the fourth strand and it is a criticism of the sensitiser rather than of the printer. He objects that the kallitype’s usual answer to contrast — an alkaline developer — causes excess iron(III) to hydrolyse and deposit ferric hydroxide in the image, which is why his argyrotype runs the whole process acid instead.

Hazards

Silver nitrate, named explicitly in the rubric under Level B.

Ferric oxalate, Level B: soluble oxalates are systemic toxins, and the standard sensitiser is a 25 per cent solution stirred in the dark for about twenty hours.

Rochelle salt is one of the few reagents in the encyclopaedia that three separate ECHA entries agree meets no GHS hazard criterion at all, and borax and sodium citrate are mild. The developer is not the hazard on this page; the sensitiser is.

Two operational points. The developer is worked warm, around 38 °C or higher for the black and brown baths, which is a scald risk rather than a chemical one. And the spent developer carries dissolved iron and silver from the sheet, so it is collected rather than poured away; Kodak’s J-52 publication gives 5.6 to 9.4 as the pH window sewer codes most often set, and a tartrate developer sits inside it, which is not the same as saying it may be discharged.

!A photoproduct is not a reagent

Ferrous oxalate’s page makes a distinction worth carrying into every iron process. The one operation that takes the compound out of Level B is the one this course actually performs: in a platinum, palladium or kallitype print it is never weighed, never poured and never concentrated — it is made by light, in micrograms, inside a sheet of paper, and dissolved away in the next tray. Handled that way it sits at Level A, and the level belongs to the developer rather than to the photoproduct. The same substance, two situations, and not the same hazard.

Where the course teaches it

Part XXIV, in Lab: Printing a Kallitype at Level B — one negative, one coating and three trays of developer, because in this process the developer is where the image colour and much of the contrast are decided, and comparing three is the only way to see that rather than be told it.

It sits between the Van Dyke lab and Contrast Control in Iron-Based Printing, which ranks the controls and is explicit that the developer is a real lever here in a way it is not in the printed-out sibling. The Siderotype Principle: Iron Reduces Silver supplies the chemistry — including the observation this entry depends on, that a developer here is doing something when nothing in it is a developing agent — and puts print-out and develop-out in one family separated by a tray.

The part closes on the two pages that decide whether a kallitype is still there in ten years: Lab: Clearing, Toning and Making an Iron-Silver Print Last, which asks you to prove the iron has gone rather than assume it, and Break/Fix: The Iron-Silver Print That Would Not Clear. The part’s overview states the clearing problem before you start, which is the right order for a process whose reputation was made by people who skipped it.

It also has a role outside its own part. Part XXV names the palladium-toned kallitype as a legitimate substitute for a palladium print for anyone who cannot afford the metal, and argues the accessibility route in full rather than mentioning it — the cheaper routes are compared honestly there, beside the cost arithmetic for the metal itself. That makes this process the cheapest entry to noble-metal printing in the course, and toned kallitype is where that route is described.

And it is one of the processes the cluster’s closing assignment asks you to print. The Process Comparison Atlas takes one negative through every process you can reach, measured the same way each time — which is the comparison this reference atlas is organised around and that nobody in the published literature has actually made.