fogging problem

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by narigas2006, Feb 14, 2007.

  1. narigas2006

    narigas2006 Member

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    Hi all,

    after getting relatively nice results on my first try, my second batch of emulsion (just the normal basic emulsion + Na tiosulfate gave very low contrast and lot's of gray were it should not be, including unexposed sections. Don't think the fogging happen at the sensitising phase as i tried the gelatin in a piece of paper and there was some considerable grays in unexposed gel. I did 3 different things this time compared to the 1st time, the AgNO3 was older (but it did not appear darker than the other one I used), it was added slower and I use the Na tiosulfate. My developer is D19, normal concentration for films (and ilford Hypan fixer). any suggestions in how to improve the contrast? Many many thanks!
     
  2. Photo Engineer

    Photo Engineer Subscriber

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    Sodium thiosulfate can increase speed, fog and contrast. It must be added after the emulsion is precipiated and digested. The hypo solution is added and the emulsion is heated to 60 degrees C for a specific time, determined in advance on samples of this emulsion. The quantity and time vary for each grain size emulsion and halide type and must be determined by experiment.

    I have described this elsewhere in more detail.

    PE
     
  3. narigas2006

    narigas2006 Member

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    Thanks! but do you think the old AgNO3 can be a problem? Also, is it a problem to use d19 in normal concentration? Thanks!
     
  4. Photo Engineer

    Photo Engineer Subscriber

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    No, and no, everything else considered.

    PE