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  1. #1
    gandolfi's Avatar
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    emulsion making confusion...

    I was looking in the book Silver gelatin and ran across a very simple recipie for an unwashed emulsion.

    It contains of
    A:
    Gelatine
    destilled water
    salt

    B:
    destilled water
    silver nitrate

    this recipie looks so familiar to salt print so my question would be:

    Is this for an emulsion used in a darkroom - and if so with a normal developer (salt prints doesn't require developer)?
    Or is it for contacting technique using UV light?

    The book doesn't mention anything except the recipie....

    Anyone knows?

  2. #2
    Photo Engineer's Avatar
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    A salt print has an excess of Silver, but a true modern emulsion has an excess of salt (within reason). The emulsion you show, if used with NaCl (Sodium Chloride), will make an emulsion that is primarily sensitive to UV with some visible light sensitivity. It will be similar to Azo paper. It will be about 5 stops slower than a modern enlarging emulsion. It will develop nicely with either Dektol or an Amidol developer.

    If made, the coating should be carried out in about 5 - 10% gelatin with a surfactant and a hardener. The emulsion should keep for 6+ months in a refrigerator, and the coatings should keep for at least one year.

    Not all of the emulsions in that book have been tested, but I do recommend it. It is a very good introductory book on the subject.

    PE

  3. #3
    gandolfi's Avatar
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    Quote Originally Posted by Photo Engineer View Post
    A salt print has an excess of Silver, but a true modern emulsion has an excess of salt (within reason). The emulsion you show, if used with NaCl (Sodium Chloride), will make an emulsion that is primarily sensitive to UV with some visible light sensitivity. It will be similar to Azo paper. It will be about 5 stops slower than a modern enlarging emulsion. It will develop nicely with either Dektol or an Amidol developer.

    If made, the coating should be carried out in about 5 - 10% gelatin with a surfactant and a hardener. The emulsion should keep for 6+ months in a refrigerator, and the coatings should keep for at least one year.

    Not all of the emulsions in that book have been tested, but I do recommend it. It is a very good introductory book on the subject.

    PE
    thanks - I'll give it a try.

    What does surfactant mean? never heard that word before...

  4. #4
    Photo Engineer's Avatar
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    Wetting agent or spreading agent = surfactant (surface active agent). Photo Flo 200 is a very good one.

    Soap is one, but should not be sued due to additives and pH.

    They come in 3 forms: Neutral (no charge in the molecule at all), Anionic (negative charge in molecule) and Cationic (positive charge in Molecule). The first two are best as they have no activity against emulsions but the last one can cause fog and stain. Photo Flo is neutral.

    PE



 

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