Kodacolor continued

Discussion in 'Color: Film, Paper, and Chemistry' started by Michael Talbert, Dec 29, 2005.

  1. Michael Talbert

    Michael Talbert Member

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    But how does a B/W silver emulsion survive intact through the bleach and fixer of a colour negative process? It was not a dye forming layer. In some references to the film the B/W emulsion mask layer is stated to have been a slow blue sensitive emulsion, (Progress in Photography 1940-50 p80)
    My theory is:- Say the B/W mask layer was twice the sped of Kodacolor film, then 25 ASA. Mask layer is 50ASA. The bleach and fixer would remove all the silver from the three dye forming layers, but leave enough silver in the mask layer to make a weak positive image when exposed to white light. The chemicals would leave enough silver in the B/W mask layer because it takes longer to fix a fast emulsion (mask layer) than a slow one (dye forming layers). As the mask was blue sensitive, it would have been unlikely to have been affected by camera exposure on account of the yellow filter.After C-22 processing, the film might have been handled in a Bromide safelight (Wratten No. OA, in those days) until exposed and B/W developed. If anyone can confirm that my theories are correct, (or maybe the film was processed in a different way) I would be very grateful.
     
  2. Photo Engineer

    Photo Engineer Subscriber

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    By use of a non-rehalogenizing bleach, much as used in reversal B&W processes today, the silver negative image would be bleached and inactivated. The positive silver image remaining would be exposed properly to form the mask image and then would be developed.

    Care would have to be taken to prevent re-exposure of the silver halide in the imaging layers. This could be done in a manner similar to that used in Kodachrome today.

    Fixation would clear out any silver salts remaining and leave just the final positive silver mask.

    This silver mask corrrected only for brightness errors, but not for color errors in the magenta and cyan dyes.

    Remember that there was a Kodacolor reversal motion picture film that used the lenticular process for color imaging. This is a totally different product which was long discontinued when the Kodacolor negative film was introduced. They are not related in any way in spite of having the same product names.

    PE
     
  3. Aggie

    Aggie Member

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    This is just a continuation of the orginal thread, where the poster wanted to ask a question that was answered. Should it not be merged into the orginal thread instead of starting a new thread?