Yellow-brown highlight stain from residual silver

Owned by The Albumen Print as an Object, and How It Decays, which treats the highlight yellowing as inherent to the binder rather than as a processing failure, and by Break/Fix — the printed-out image that faded, whose second case names this entry and supplies the test pair that separates retained silver from retained thiosulfate — ST-1 first because it needs no acid, then HT-2 — with the caveat that both were devised for gelatin-coated papers, so a comparison between two of your own strips means something and an absolute reading against a printed patch does not. This entry was written earlier from Part XII’s work on retained silver.

What you see

Yellow or yellow-brown in the highlights, with the image itself apparently unchanged. Reilly records how common it is: approximately 85 per cent of surviving albumen prints made after 1860 show what he calls moderate to severe yellowing, and for the 1850s the figure is probably nearer 95 per cent.

And it hides itself. Reilly points out a property of vision that keeps the problem from being noticed: the human visual system automatically seeks out the lightest area in a print and pegs it as a reference white, so highlights look brighter than they are unless a side-by-side comparison is made with a true white. Put a fresh sheet of the same paper next to the print. That is the test, and it is uncomfortable.

Likely causes

1. Silver bound to the binder itself. Reilly’s account is that silver bonds to sulfur-containing side groups on the albumen protein, some of which have a very high affinity for it, and that the bond is so tight that treatment in hypo is not sufficient to remove it.
2. Residual fixer decomposing, supplying labile sulfur to that bound silver.
3. Atmospheric sulfur doing the same thing from outside.
4. An exhausted fixing bath. Kodak state the general case: an exhausted bath contains insoluble silver compounds that remain in prints, cannot be removed completely by washing, and form a dark yellow stain on contact with a toner, especially in borders and highlights.

What is happening: the chemistry and physics

There is silver in the whites, and it was put there on purpose. Reilly’s chapter is a nineteenth-century detective story with a modern conclusion, and the evidence is worth having.

1859. Davanne and Girard report to the French Photographic Society that a 2 per cent potassium cyanide solution removes all traces of silver from albumen prints while strong solutions of hypo do not — and note two drawbacks that ruled cyanide out as a practical technique: it severely bleached the image, and it was highly poisonous.

1868. John Spiller reports that the metal is retained in the whites, and indeed throughout the coating, as a colourless argentic organic compound, unalterable by light and comparatively insoluble in hyposulphites. He detected it by moistening the white surface with ammonium sulphide and watching a brown stain appear.

The 1890s. Haddon and Grundy measure it. A sheet sensitised, thoroughly fixed and washed but never exposed — a sheet that should contain no silver at all — still held nearly 5 per cent of the silver present after sensitisation. To show what that meant, they converted the residual silver to silver chloride with chlorine water, applied potassium nitrite as a chlorine acceptor, and printed out an image on it that was nearly as intense as one printed in the usual way.

So the whites of an albumen print are a light-sensitive material in their own right. The immediate cause of the yellowing is the conversion of that bound silver to silver sulfide by labile sulfur, from residual fixer or from the air.

!The confirming test, and the honest limit of what follows from it

Compare against a true white. Lay a fresh, unsensitised sheet of the same paper beside the print. Reilly’s point about reference white means this comparison finds staining that direct inspection will not.

Then separate the two histories. Both this fault and a bleached cyanotype present as yellow-brown, and both incomplete clearing and this one present as yellow highlights. The discriminators are the process and the location: iron stains are in iron processes and follow the coating; silver-sulfide stains are in silver processes and are worst where the fixer sat longest.

And test the residues you can still control with the residual hypo and silver tests, because Reilly is explicit that a print that was inadequately fixed or washed will yellow in addition to fading — and that the same kind of yellow staining occurs in gelatin and collodion prints too, not only in albumen.

Diagnostic questions

• Which process? The bound-silver mechanism is specific to a protein binder, and albumen is the extreme case — Reilly notes that highlight yellowing is so prevalent in albumen prints that it serves as an identification clue, and does not occur in quite the same way in otherwise similar gelatin and collodion papers.
• How was it fixed, and in what? Kodak’s warning about both directions applies: an exhausted bath leaves insoluble silver, and prolonged fixing expands the paper and traps fixer in the base, which later turns toned prints yellow.
• How was it washed? Residual fixer is the internal sulfur supply.
• Where has it been stored? Reilly’s own view is that the onset is affected primarily by the moisture level and temperature of the storage and the amount of residual thiosulfate and silver-thiosulfate complexes.
• Is the image faded as well? Severe highlight yellowing is accompanied in most cases by a colour shift and density loss in the image itself.

Corrective action

There is none, and the source says so plainly. Reilly: no presently known treatment can remove the highlight yellowing without completely altering the character of the print, because the silver sulfide that forms the stain is much more chemically stable than the colloidal silver of the image. Anything that attacks the stain attacks the picture first.

So the actions are preventive for the next print and custodial for this one: stable, cool, dry storage, and an enclosure that is not adding sulfur.

Do not attempt cyanide. Davanne and Girard’s 1859 result is recorded here as history. Potassium cyanide is a Level D substance in this course, it bleaches the image, and the course has no circumstance in which it would put that procedure in a reader’s hands.

Prevention

Fix in a fresh bath, briefly, and wash thoroughly. Two-bath fixing is Kodak’s recommendation and the course already teaches the rotation.

Do not over-fix. Kodak’s mechanism is specific — prolonged fixing expands the paper and lets solution into the base, where it is difficult to remove.

Tone, which converts the image silver deliberately and improves its odds against the same sulfur that attacks the highlights.

Store cool, dry and away from sulfur, following Part XII, and keep a fresh sheet of the paper with the print so that the comparison remains possible in twenty years.