Silver mirroring and sulfiding in an untoned printed-out print

Owned by Break/Fix — the printed-out image that faded, whose sixth case names this entry and puts three numbers behind its argument: about 3 mg of silver in a whole-plate salt print, particles perhaps a hundredth the size of a modern print’s, and a maximum density that falls by a factor of about thirty on complete conversion to silver sulfide. It also answers the question this entry raises and does not settle — why the result reads yellow rather than the black of bulk silver sulfide — from Ware’s account of nanoparticle absorption. This entry was written earlier from Part XII.

What you see

Two faults, and they are told apart by how you hold the print.

Mirroring is a metallic, often bluish sheen, seen by reflected light and not by transmission, typically beginning at the edges. IPI define it as an oxidation in which the image silver migrates to the surface, creating a mirror-like appearance.

Sulfiding is a general loss and shift of the image seen by ordinary viewing — density gone, colour moved towards a flat yellow-brown, highlight detail lost.

They often occur together, because the conditions that cause one favour the other.

Likely causes

1. The print was never toned. A printing-out paper is stabilised through toning and fixing, in the AIC’s own description of the process. An untoned print has skipped half of that.
2. Residual thiosulfate and silver-thiosulfate complexes. Reilly names these as the principal internal causes of generalised image fading.
3. Oxidising gases — ozone, organic solvents, and whatever the framing materials give off.
4. Sulfur compounds, from the atmosphere, from the mount, or from residual fixer decomposing in the paper.

What is happening: the chemistry and physics

A printed-out image is colloidal silver with an enormous surface area. That is why it is a warm purple-brown rather than the neutral black of a developed image, and it is why it is vulnerable: everything that attacks silver attacks it faster.

Ware states the general case for an unprotected print: 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. A gelatin POP has a binder and is therefore better placed than a salt print, but not by much.

Mirroring is an oxidation followed by a reduction, in two different places. IPI’s framing guidance gives the sequence: the reactions caused by poor framing materials, like those from air pollution, are often oxidation reactions that result in image fading — and the faded silver can migrate to the surface and be converted back into metallic silver by other pollutants, forming the mirror-like sheen. So the sheen is the same silver that left the image, deposited somewhere it does no good.

Sulfiding is a conversion in place. Reilly’s account of albumen highlight yellowing is the clearest in the corpus and it applies to the image as well as the whites: silver reacts with labile sulfur supplied by residual fixer or atmospheric pollution to give silver sulfide. Silver sulfide is more stable than the colloidal silver of the image — which is precisely why deliberate sulfide toning is a permanence treatment — but uncontrolled sulfiding converts the image on the atmosphere’s terms rather than yours, and the result is a loss.

That is the whole argument for toning, and it is worth stating as an argument rather than a habit. Toning does deliberately, evenly and completely what the atmosphere will otherwise do slowly, unevenly and partially.

!The confirming test: look at it, then look through it, then test the residues

Hold the print to a lamp and look at the surface; then hold it up and look through it.

• A metallic sheen by reflection that is not there by transmission: mirroring.
• Loss of density and a colour shift seen by ordinary viewing: sulfiding or oxidation fading.
• Yellow or brown stains in transmitted light on a plate or negative: improperly washed processing chemistry rather than mirroring — the same discriminator the silver mirroring entry uses.

Then test the residues with the residual hypo and silver tests, which address Reilly’s internal causes directly, and inspect the mount and frame, which address the external ones.

And handle a mirrored area carefully, because on a dry plate the AIC record that areas with silver mirroring are extremely susceptible to abrasion, and there is no reason to think an unprotected print is tougher.

Diagnostic questions

• Was the print toned, and with what? Gold, selenium and sulfide routes are all in the formulary.
• How was it fixed and washed? These processes take a brief, weak fixer and a long wash, and both edges of that window matter — see the print that bleached in the fixer.
• What is it mounted on and framed with? IPI’s guidance is that the frame is part of the chemistry.
• Where is the damage worst? Edges point at the atmosphere and the enclosure; uniform loss points at what is inside the paper.
• Is there yellowing in the highlights as well? Then residual silver is implicated too, and that has its own entry.

Corrective action

There is no treatment in this course, and Reilly’s finding for the closest-studied case is discouraging: albumen prints do not respond to the bleach-and-redevelopment methods that have restored sulfided gelatin-based develop-out materials, because the residual silver in the highlights redevelops along with the image, the redevelopment does not give sufficient density, and the restored colour is out of character with the original.

Get it away from what is attacking it. Remove it from a poor frame or mount, and store it in a tested enclosure.

Re-print and tone, if the negative survives.

Prevention

Tone. On an unprotected silver image it is a permanence operation before it is an aesthetic one, and Ware notes the image is receptive to the usual toning treatments if improved permanence is desired.

Fix briefly and wash thoroughly, and test rather than assume — Reilly’s internal causes are the ones you control completely.

Choose enclosures that have passed the Photographic Activity Test, and remember IPI’s warning that acid-free, archival, museum-quality and conservation board are marketing terms rather than standardised ones.

Keep it out of pollution and out of the light, which are the two external causes and the two you can act on by where you hang it.