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  1. #31

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    Just answering my own question...

    PE,

    I don't mind searching for answers, but this forum thread is now so big sometimes it takes a lot of digging to find the nuggets! No doubt this problem will be eased when your book comes out

    I found this in one of your earlier posts:

    "The only way to get speed is by chemical sensitization, or finishing. This involves the addition of any one of a variety of ingredients. The original was allyl thiourea, another was thiourea, and then finally they added sodium thiocyanate. Modern emulsions use either sodium thiosulfate or sodium thiosulfate plus a gold salt. It is done after the wash step, as excess halide represses this sensitization. This finishing step varies for every emulsion and sometimes for every batch..."

    So, that answers my what to use question. Any good reason for choosing one over the other?
    I have sodium thiocyanate and sodium thiosulphate (thiosulfate) in my darkroom.

    I could still do with a hint about concentrations and how to add them.

    Steve
    Steve

  2. #32
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    Use sodium thiosulfate pentahydrate as a 0.1% solution in water.

    The amount to use is dependant on grain size and can only say that the amount goes DOWN as grain size goes up. It can only be determined for a given emulsion by trial and error or by knowing average grain size.

    The mid point on this scale is about 50 milligrams of hypo per mole of silver. I'm assuming you can figure this out. I use 100 mg / mole for my emulsion as it is quite finer in grain. I finish at 60 degrees for 60 minutes.

    It took me about 10 experiments to arrive at this figure.

    PE

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