The iron-silver print that faded within weeks

Owned by Break/Fix — the iron-silver print that would not clear, whose second case calls this the fault the whole part is arranged around and the one that cannot be diagnosed on the day it is suspected, and which states the mechanism as King and Ware do: residual iron, in very small quantities, oxidises the image silver, and an iron-silver image is colloidal silver of about 20 nm with no binder over it. The clearing and toning lab owns the prevention. This entry was written earlier from Part XII’s permanence lesson.

What you see

A print that has visibly lost density in weeks or months, not decades. The shadows go first and go furthest; the image colour shifts; and there is often a yellow-brown tone in the highlights at the same time, which is the same residue seen from the other side.

The timescale is what makes this its own entry. Silver images deteriorate over decades as a rule. This one does not, and the reason is a specific contaminant.

Likely causes

1. Residual iron in the image. Ware’s statement about the argyrotype names the mechanism directly: alkaline-buffered developers of high pH cause hydrolysis of the excess iron(III) in the sensitiser and the deposition of insoluble ferric hydroxide in the image, which ultimately causes it to fade.
2. Residual thiosulfate and silver-thiosulfate complexes. Reilly names these as the principal internal causes of generalised image fading for every silver print.
3. An untoned colloidal silver image on plain paper. Ware: like any colloidal silver image, and especially one on plain paper unprotected by a colloid binder layer, it is inevitably rather susceptible to attack by oxidising acids and sulphur-containing substances.
4. The environment. Reilly’s external causes are sulfiding from atmospheric sulfur compounds and oxidation fading from oxidising gases such as ozone and organic solvents.

What is happening: the chemistry and physics

The image is very finely divided silver with nothing over it. A silver gelatin print has a binder; a Van Dyke, kallitype or argyrotype has silver sitting in the paper fibres, with the largest possible surface area exposed to whatever the air brings. That alone makes it a faster material than a gelatin print, and Ware says so plainly.

Then add iron, and it is worse than a bystander. Ware’s mechanism is deposition of insoluble ferric hydroxide in the image — not merely a stain in the whites — and his verdict on the consequence is unambiguous: it ultimately causes the image to fade. The same substance that is a cosmetic fault in the highlights is a destructive one in the shadows.

The processing choices that leave it there are the ones that protect something else. Ware’s own account of the clearing bath is a trade: alkaline conditions inhibit the dissolution of image silver, preserving delicate highlight detail, but may raise the level of residual iron. And silver nitrate itself carries an oxidising anion which tends to dissolve the colloidal image silver during processing, which is why his argyrotype uses silver sulfamate instead.

Ware’s own criterion for a good outcome is a number of a sort, and it is the one to aim at: with the residual iron and silver in the unexposed areas very low, image stability and lightfastness are good. The fault is the failure of that condition, not an inherent property of the process.

!The confirming test: a control print, a dark drawer and a residual test

Make two prints, treat them identically, and put one in a dark drawer in a neutral enclosure while the other is displayed. Compare them after a month.

• Both faded: the cause is internal — residual iron, residual thiosulfate, or residual silver — and the processing is the suspect.
• Only the displayed one faded: the cause is external, and the answer is toning, mounting and display.

Then test the residues rather than guessing them. The residual hypo and silver tests address Reilly’s internal causes directly. The iron does not have a comparable test in this course’s corpus, and the course says so rather than inventing one: what it has instead is the coated, unexposed margin, where residual iron shows as a yellow stain first — see iron-silver highlights that will not clear.

The discriminator against silver mirroring is that mirroring is a bluish metallic sheen seen by reflected light and starting at the edges, whereas this is a loss of density seen by ordinary viewing, over the whole image, worst in the shadows.

Diagnostic questions

• What developer, and at what pH? Ware’s objection is specifically to alkaline-buffered developers of high pH.
• Was the print cleared, and with what? A clearing bath that protects highlights may be the bath that left the iron.
• Was it toned? Photographers’ Formulary state it plainly for the kallitype: toning will also increase the permanence of the print — and their order is to tone between clearing and fixing.
• How was it fixed and washed? Reilly’s internal causes are the same for these processes as for any silver print.
• What is it mounted on and framed with? IPI’s framing guidance describes oxidation reactions from poor framing materials and pollution causing fading, and edge fading from mount and adhesive is the entry for that pattern.

Corrective action

A faded print cannot be restored in this course. There is no assessed treatment here, and Reilly’s finding for the related processes is discouraging — the bleach-and-redevelop methods that work on gelatin materials do not transfer, partly because residual silver in the highlights redevelops along with the image.

Re-print, and change the processing rather than the storage. Clearing, fixing, washing and toning are where this fault is decided.

Tone the re-print. Ware notes the image is receptive to the usual toning treatments if improved permanence is desired, and the Formulary say toning increases permanence in as many words. The course has gold, selenium and sulfide routes in its formulary already.

Prevention

Get the iron out while the print is wet, per the clearing entry, and do not let a print dry mid-sequence.

Fix, wash and test, following Part XII’s archival sequence.

Tone. On these processes it is not a matter of colour.

Mount and store on materials that have been tested, and keep the print out of strong light and away from oxidising gases.