What extra sensitizer do commercial film have?

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by Hans2008, Mar 3, 2009.

  1. Hans2008

    Hans2008 Member

    Sep 27, 2008
    Medium Format
    When making my holographic film I have to sensitize it with a slightly alkaline dilute developer before use. Otherwise there is hardly any sensitivity. I noticed that when I leave a undeveloped piece of film in the light, it will print-out (become dark) in a relatively short time due to the dip in the very dilute developer.

    If I don't do this sensitizing the film is about 100 times less sensitive and there will be no print-out whatsoever if left in the light without developing. Even virgin gold sensitized emulsion does not print-out if not sensitized with a reducer before use.

    I noticed that COMMERCIAL film also prints-out when left in the light. So that leads me to conclude that there is likely a reducer present in it as well.

    Does anyone know what is used in commercial film? I have been using hydroquinone, but I am looking for a better product.
  2. Photo Engineer

    Photo Engineer Subscriber

    Apr 19, 2005
    Rochester, NY
    Multi Format
    Commercial films use a combination of Sodium Thiosulfate and Gold Chloride in a ration of 3/1 and a heat treatment before coating that places sensitivity centers on the film.

    Even so, the film is only sensitive to Blue and UV light or out to about 450 nm. To reach better sensitivity, Green and Red sensitizers are added, right after the Sulfur + Gold treatment.

    Since these are both surface effects, the amount used and the time+temperature profile are governed by the surface area.

  3. Kirk Keyes

    Kirk Keyes Member

    Jun 17, 2004
    Portland, OR
    4x5 Format
    Hans - I think your conclusion is incorrect.

    I believe that any film will "print out" when exposed to enough light. It's simply that silver halides decompose upon exposure to light to form metallic silver which it what causes any film to become darker.
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