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  1. #1
    M Carter's Avatar
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    decayed daguerreotypes/

    Found this oddly beautiful and spooky...

    http://publicdomainreview.org/2013/0...aguerreotypes/

  2. #2

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    Very interesting. Thanks for sharing that find with us!

  3. #3
    AgX
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    the glass itself can also deteriorate and bubbles of solvent explode upon the image
    Well...
    But I admit deterioration other than caused by rubbing of any kind has been reported and is researched on in Rochester.

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    There are several good (academic) books on dag deterioration and restoration. If anyone is interested I can give citations later. IDK about glass deterioration and solvent bubbles... never heard of that. Most of my dags (and those in the link) show silver oxidation (tarnish) more than anything else. I have one that someone tried polishing with silver polish... it's a complete mess.

  5. #5
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    There is a very extensive project at George Eastman House investigating this deterioration. The phenomena involved are not well understood.

    PE

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    Daguerreotypes had a metal base, typically copper, which had a silver coating on top, if I remember correctly. The silver was immersed in halide fumes, typically iodine, forming light-sensitive silver halide crystals on the surface of the photograph. This was next placed in the camera and exposed to the image produced by the lens. This exposure could be as long as 15 minutes.

    To develop the daguerreotype the exposed plate was placed in a dark box over a dish of liquid mercury which was heated by an alcohol lamp or a candle. Heated mercury fumes would bombard the plate. Wherever the plate was exposed to light the silver halide was converted to pure silver metal. The mercury atoms would stick to the pure silver metal and form an amalgam, (this process was known since the Middle Ages). The amalgam was lighter in color than the unexposed silver halide, so wherever light struck the plate it would appear lighter in color than the unexposed parts. Therefore daguerreotypes were a direct positive process which usually produced a mirror image.

    Considering that the image layer of a daguerreotype contains silver, silver halide, mercury, mercury silver amalgam and copper it's a wonder that more daguerreotypes do NOT tarnish. There are so many chemically reactive metals touching each other it is hard to see how the system could be stable.

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    IDK about the chemistry and associated stability, but the better sealed they are the less they tend to tarnish.

  8. #8
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    At GEH they are making glass frames that can contain a Daguerreotype under an inert atmosphere so as to preserve them. It does appear that air and air pollutants are involved, but again, no one seems to know the mechanism and no one knows how to restore one AFAIK.

    PE

  9. #9
    AgX
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    Quote Originally Posted by falotico View Post
    The amalgam was lighter in color than the unexposed silver halide, so wherever light struck the plate it would appear lighter in color than the unexposed parts. Therefore daguerreotypes were a direct positive process which usually produced a mirror image.
    The silver halide is fixed out. The amalgam thus has to compete with still polished silver in the end. Something only possible if there is no specular reflection from the silver but diffuse reflecttion from the amalgam. Thus the process is a lighting dependant direct-positive process.
    Last edited by AgX; 05-08-2013 at 07:16 PM. Click to view previous post history.

  10. #10

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    Did they use thiosulfate or cyanide compounds to fix daguerreotypes? Or was some other method used to remove the silver halides?

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