> I was fortunate to have enough time to visit the Museum of
> Modern Art in San Francisco last week. They have an excellent
> exhibit that features a number of Edward Weston's prints.
>
> I noticed that there was a shiny metalic silver colored deposit
> on the surface of Weston's "Pepper #38" in the areas of the
> print having the deepest blacks.
>
> The print is a silver-gelatin with deep rich warm black tones. The
> deposit was very thin, on the surface of the print, and only in
> the deepest black areas. I don't know if the print was toned or not
> (probably not). You need to look at the print on an angle to notice
> it clearly.
>
> I've noticed this same effect on some (but not all) silver prints
> that I bought that were made in the 1920's as well. I'm also
> assuming that they didn't look that way when they were originally
> printed but I wasn't around then so I don't know for sure.
>
> Some questions:
>
> Is this caused by a reaction with pollutants in the atmosphere
> or by some other mechanism?
>
> Given enough time will this affect the entire print?
>
> Are current silverprinting materials prone to this effect as well?
>
> Is this deposit metalic Silver or something else?
>
You bring up a form of deterioration that is widely seen and rarely discussed.
The shiny metallic deposits are caused by metallic silver on the surface of
the paper. How it gets there is a more difficult process to explain.
It is usually called mirroring out or silvering out. What happens is
that over time imaging silver can begin to oxidize and break down, when
this breakdown occurs silver ions break free from the silver imaging
particles in the print. These silver ions are both invisible and
migratory and can actually move through the gelatin. This movement
is halted when these ions run into a reducing agent (such as sulfur)
and is reduced back to metallic silver (usually silver sulfide).
This occurs most often in the maximum density areas, simply because
that is where the most silver is.
The reason that it appears on the surface of the print is that that is the
most opportune location for these migrating silver ions to come into
contact with reducing agents (sulfur in the atmosphere).
There is no known cure for this problem. Some conservators have
tried farmers reducer, physical abrasion and even thiourea. These
"cures" usually cause more problems than they solve.
Thiourea, by the way has been eliminated from any use by conservators
working with silver images, as it complexes with the silver and cannot
be washed out. The residue that remains can reek havoc in years to
come.
To try to avoid this happening to your prints (it may happen anyway):
Keep them away from oxidizing agentsP strong UV light (sun light,
florescent bulbs), oil paint fumes, ozone (from copying machines), other
fumes from paints, shellacs, varnishes etc.
The best view to take is to learn to enjoy the "aesthetics of
deterioration." I have found these mirrored out prints often have an
added beauty to them, just as a nicely tarnished daguerreotype is often
enhanced by the patina.
Hope this information is useful. If this all seems greek to you, let me
know and I will try a fuller explanation.
Roger Watson
Conservation Department
George Eastman House
900 East Avenue
Rochester, NY 14607
(716) 271-3361
e-mail RWATSON @ geh.org