Early photography on glass deterioration question

From: John F. Ptak ^lt;[email protected]>
Date: 04/07/04-01:09:00 PM Z
Message-id: <200404071509.AA39125144@thesciencebookstore.com>

Hello group. I have a question about an object that I have that is, or seems to be, a very early photographic portrait made on glass. Given all of the data it seems to be of the late 1840's or very early 1850's, which makes it quite early for what (in its limited scope) it is--also the portrait is of a very good-looking man (also not terribly common among these things).

The question concerns its state--under the best possible viewing circumstances the dark coat-covered outer arms and most of the shoulders of the fellow have now blended into the blackness of the background of the image. The rest the features of the portrait are in sharp relief--knuckles, eyes, eyebrows, hair part, etc are very clear. There are even bags under the sitter's eye. It is not so precise an image (being a half-length portrait) that you can see hand veins, but the detail in general is pretty good.

The question concerns the deterioration--what process is it that takes place to cause this blending of the darknesss of the sitter's coat with th edark background of the studio setting? I apologize if this is terribly rudimentary--I just don't know what is going on/what went on with the physical process of the aging of the photograph.

Many thanks.

John Ptak

John Ptak
Antiquarian Maps and Prints
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JF Ptak Science Books
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Specializing in iconic and obscure works in the history of science, as well as unusual and uncommon antique maps and prints.
Received on Wed Apr 7 13:12:48 2004

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