Iron-silver highlights that will not clear

Owned by Break/Fix — the iron-silver print that would not clear, whose first case is this fault and which separates its four candidates by when they appear: a first-print failure is the paper or the water, and a failure that gets worse through a session is the clearing bath or the developer. It also records what neither the course nor its sources can do — distinguish a residual-iron yellow from a residual-silver yellow by any published test — and offers a ferricyanide and sulfide spot pair on one sacrificial strip as its own combination. The clearing and toning lab owns the baths. This entry was written earlier from the encyclopaedia entries for the reagents.

What you see

Highlights that stay yellow-brown on a Van Dyke, kallitype or argyrotype, however long the print is washed. On a Van Dyke the first wash normally lifts a visible yellow stain out of the sheet; when it does not lift completely, the whites carry a tone that the dried print keeps.

Two residues, one appearance, and that is why this fault resists the obvious remedy of more water.

Likely causes

1. Unreduced silver in the highlights. Water does not remove a silver salt; a fixing bath does, and on these processes it is a weak, brief one.
2. Iron bound to the cellulose. Ware’s account of the siderotypes makes iron(III) the chief problem for effective clearing, some of it chemisorbed to the hydroxyl groups of the cellulose, and water is not a chelating agent.
3. A wash that was too short, too cold or too hard. Warm water shortens the wash; hard water lengthens it and does worse than that.
4. Sensitiser on the surface rather than in the fibres, so there was more of it to shift in the first place — see blotchy and streaked hand coating.

What is happening: the chemistry and physics

The two residues need two different chemistries, and washing supplies neither.

The iron hydrolyses above pH 4 to a polymeric colloidal iron(III) hydroxide that lodges in the fibres and imparts a yellow stain. Ware’s warning applies to every iron process, not only to platinum: if that hydroxide is not removed while the print is wet, it transforms irreversibly into iron(III) oxyhydroxide — goethite — which is quite insoluble in dilute acids. A chelating bath removes it; water does not. And calcium in hard water or in a chalk-buffered paper actively promotes the hydrolysis, so the hardest water gives the most stubborn stain.

The silver is a different problem with an opposite pH preference, and Ware states the tension exactly for the argyrotype. Making a clearing bath distinctly alkaline at pH 9–10 with a little ammonia inhibits the dissolution of silver — which preserves delicate highlight detail — but may raise the level of residual iron in the image. Clear hard and you lose highlights; clear gently and you leave iron. The two residues pull in opposite directions, and the practitioner is choosing between them rather than eliminating both.

He also names a structural reason for one of them. Silver nitrate carries an oxidising anion, which tends to dissolve the colloidal image silver during wet processing; his argyrotype replaces it with silver sulfamate made in situ for that reason. So a classic Van Dyke’s highlight behaviour is partly built into its formula.

!The confirming test: clear a strip three ways

Cut one exposed, developed print into four and treat the pieces differently.

Piece	Treatment	What it tells you
1	Water only, extended	Whether washing alone was ever going to work
2	Chelating clearing bath, then water	Whether the residue is iron
3	Weak thiosulfate fixer, then water	Whether the residue is silver
4	Full sequence, in the process’s own order	The control

Whichever piece clears is the diagnosis, and the answer is often that pieces 2 and 3 each clear part of it — which is the finding, not a failure of the test.

Then look at where the clearing is needed at all. Photographers’ Formulary make the point that it depends on the developer: some kallitype developers clear instantly in the developing tray, and the black kallitype developer supplied with their kit does require clearing — three to five minutes in tetrasodium EDTA at two tablespoons to a litre, reusable until about twenty 8 × 10 prints have been through it.

Diagnostic questions

• Which developer? On the kallitype it decides whether a clearing bath is needed at all.
• Was there a clearing bath, and how old is it? Twenty prints per litre is the Formulary’s figure.
• How hard is the water? Calcium is on the reaction path to the stain.
• Did the print dry between processing steps? Once the hydroxide has aged to goethite, dilute acid will not touch it.
• Was the print toned, and when? The Formulary’s order is to tone between the clearing bath and the fixing bath, and a print toned out of order carries different residues into each.
• Is the highlight tone yellow-brown or grey? Yellow is the iron; a grey veil is more likely fog or unreduced silver reduced by something it should not have met.
• Which print in the session was the first to fail? This is the question the owning page adds, and it costs nothing because the answer is already in the clearing times you recorded. A first-print failure is the paper or the water, both of which were wrong before any bath had done any work. A failure that arrives part way through and gets worse is the clearing bath or the developer, because both accumulate iron as the afternoon goes on. Record the clearing time of every print and the differential resolves itself without an experiment.

Corrective action

Re-wet and clear again before the print has been dry for long. That is the only window Ware’s chemistry leaves open, and it closes.

Add the bath the residue calls for, from the test above — a chelating bath for iron, a brief weak fixer for silver — rather than lengthening the wash, which addresses neither.

Accept the trade and record which side you chose. Ware’s alkaline-clearing note is explicit that protecting the highlights costs residual iron and that removing the iron costs highlight silver. Write down which you did, because the print’s permanence depends on it and a print that faded within weeks is the bill for the wrong choice.

Prevention

Get the sensitiser into the fibres so that less of it has to be washed off the surface.

Clear in the order the process specifies, and never let the sheet dry mid-sequence.

Finish in soft or distilled water.

Aim at Ware’s own standard for a stable print: the residual iron and silver in the unexposed areas should be very low. That is the criterion, and it is testable — the residual hypo and silver tests are the course’s procedures for the silver half.