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Marco B
06-30-2011, 03:56 AM
Hi all,

No, this is not that kind of coating book... It is a book about coatings or lacquers/varnishes applied to photographic images, often for conservation and protective purposes, for example to prevent silver corrosion of daguerreotypes. This is a practice that seems to have had far wider application than I knew before. I had seen the video (http://www.apug.org/forums/media.php?do=details&mid=58) by Quinn Jacobson showing the application of a varnish to a collodion image, but I didn't know even salt prints and platinum prints on paper were sometimes treated in such ways.

The book can be bought here:
Coatings on Photographs: Materials, Techniques, and Conservation (http://cool.conservation-us.org/coolaic/sg/pmg/coatings.html)
The American Institute of for Conservation of Historic & Artistic Works

You can get a sneak preview here (http://www.albertina.at/jart/prj3/albertina/data/uploads/Forschung/restaurierung/CoatingsEderAlbertina.pdf). It is one chapter of the book available as PDF on the website of the Austrian Albertina Museum. It is reproduced with permission as the Albertina museum is actually the original author of the article included in the book, and did the conservation research discussed in the chapter regarding coatings on daguerreotypes.

In case of daguerreotypes, one of the most applied materials seems to have been nitrated cellulose, the same stuff that constitutes collodion, gun cotton and some explosives, as it seems to provide some real protection and impenetrability against oxidizing gasses like H2S.

One advantage of cellulose nitrate lacquer seems to be that it can be applied in such thin layers, so as to not even change the appearance of the original photo or coated material, as it doesn't seem to impart a gloss of its own if applied properly and thinly. Disadvantage seem the deterioration and discolouration of cellulose nitrate with time.

Another interesting notion I hadn't been aware of, but mentioned in the above linked article by the Albertina Museum, is the surprisingly quick corrosion of (some) glass types. They mention glass corrosion products being detectable on some of the daguerreotypes. I had been aware glass can deteriorate with time and under specific conditions, like ancient glass buried in soil, but I hadn't expected cover / glazing glass to possibly show signs of deterioration after just a century or so (except of course those caused by mishandling like scratches and abrasion marks). Maybe that is partly due to their age, being of the notorious "Victorian" times, when large scale coal combustion caused wide spread aerial pollution with oxidizing and acid gasses in heavily industrialized areas. In addition, the type of glass (e.g. soda lime, lead glass, borosilicate), may play a minor role...

From what I read, this is another book going on my list of "books to buy".

Marco