[pure-silver] Re: Silver Mirroring and Care of Old Photographs...
----- Original Message ----- From: "Ray Rogers" <earthsoda@xxxxxxxxx> 
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, May 22, 2008 6:36 PM
Subject: [pure-silver] Silver Mirroring and Care of Old Photographs...
Does someone remember (or know of) an active conservation list? or some person active in the field that likes to talk about conservation and true (analog) 
restoration?
There may be someone on this list... I am not sure, (perhaps Roger K? is with us?)
Anyway, I have a few questions I would like to direct to people who have seen a lot of examples of 
print deterioation such as silver mirroring.
(Of course GEH and IPI come imeadiately to mind, but that should be later I think.) 


Alternativly,
Anyone here have any photographs damaged by silver mirroring? 
If so, you may respond off list, if you prefer.
(If there is not a suitable list for conservation questions, 
perhaps I will post them here....)

Ray
A great deal of research about "mirroring" or "silvering" has been published in the last several years. Its a common problem curiously enough for materials that were processed according to the best practices for image longevity as understood up to about 1960. Silvering comes from oxidation of the image silver by peroxides in the atomosphere. These peroxides are much more common now than, say, sixty years ago so the problem has become much more apparant. The oxides consist of very fine particles which can migrate through the emulsion. Some wind up on the surface where they are reduced again to metallic silver forming the black to yellow coating. There have been several methods of removing this film but none can repair the damge to the image because some of the original silver has been lose. 
   A good source for research papers is:
http://palimpsest.stanford.edu/
the Conservation On Line site. There is now a search engine there and a search for silvering will get several hits. For new images the best method of preventing image oxidation is toning. The toners which are effective are: sulfide, selenium, and gold. However, not all toners of a given type are equal because some tone different densities unequally. Selenium in high dilutions, which for many years was the recommended toner, was found about fifteen years ago, to be ineffective for microfilm. However, it _is_ effective when used in stronger dilutions. Gold toning is a standard method for microfilm but is somewhat expensive. The best sulfiding toner is a polysulfide type like Kodak Brown Toner or Agfa Viradon. These tone uniformly and will provide protection to all parts of an image with relatively little toning. Toning to completion with any of these toners provides excellent protection but will modify the appearance and structure of the image. Silvering can be removed in several ways. See the references available from the COOL site for some. Kodak recommends using film strength acid rapid fixer with about 15 grams per liter of citric acid added. This forms a mild silver solvent but can also bleach the image if allowed to continue too long. 

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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