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  1. #1

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    Kodak ST-1 Test for residual silver

    Hello there,

    A couple of quick questions with regards to the ST-1 test process:

    Once the paper has been fixed, is the paper given a full wash and then tested, or does the test take place directly after fixing?

    If there is a wash inbetween fixing and testing, would a hypo clearing bath interfere with results?

    Thanks!

  2. #2
    ic-racer's Avatar
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    I just give a quick rinse, but someone may have a better answer.

  3. #3

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    Quote Originally Posted by Marco Buonocore View Post
    Hello there,
    A couple of quick questions with regards to the ST-1 test process:

    Once the paper has been fixed, is the paper given a full wash and
    then tested, or does the test take place directly after fixing?

    If there is a wash inbetween fixing and testing, would a hypo
    clearing bath interfere with results? Thanks!
    The ST-1 test uses sodium sulfide as a test for silver. If silver
    is present a silver sulfide stain will be produced. Fixers work by
    forming soluble complexes with the other wise insoluble
    undeveloped silver halides in the emulsion. So the
    fixer carries silver.

    The test's sulfide will combine with that attached silver and
    give a false reading. Give the paper a thorough cleaning. Hypo
    clear after fixing only assists in the removal of the fixer. Dan

  4. #4
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    Wash only, for the prescribed time and method for your paper and fixer. Then apply the test.

    PE

  5. #5

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    Thanks! Exactly the information I needed.

  6. #6

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    A correction.

    Quote Originally Posted by dancqu View Post
    Fixers work by forming soluble complexes with the other wise
    insoluble undeveloped silver halides in the emulsion.
    That within quotes is incorrect. The fixer's action is to form
    soluble silver compounds. The halide be it chlorine, bromine,
    or iodine, is not a part of the complexes formed twixt the
    fixer and silver.

    The thiosulfate ion is the primary agent in removing the
    silver and in the presence of iodine the only agent with
    the necessary affinity. The ammonium ion's affinity
    for silver is much less. So, with films containing
    extremely insoluble iodized silver rapid fixers
    become slow fixers. Dan

  7. #7

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    Dan:

    Am I wrong in thinking that today's film emulsions increasingly use silver iodide? If so, does that mean that sodium thiosulphate is a better fixer for modern emulsions?

    Bob H
    "Why is there always a better way?"

  8. #8

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    Quote Originally Posted by BobNewYork View Post
    Dan:

    Am I wrong in thinking that today's film emulsions increasingly use silver iodide? If so, does that mean that sodium thiosulphate is a better fixer for modern emulsions?

    Bob H
    IDK, but according to Anchell/Anchell & Troop, he/they speculate that sod. thio is inferior to ammon. thio with newer emulsions. I'll have to look up the exact quote/phrase.

  9. #9

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    Maybe I've got it wrong about increased use of iodide in modern emulsions - I just seem to recall reading it somewhere. I know that Bill Troop and Steve Anchell concluded that ammonium thio was better for modern emulsions, that's why I was surprised when Dan pointed out that ammonium doesn't fix well in the presence of iodides. I tend to overfix (8 minutes) anyway as ammonium doesn't reduce density like sodium in extended fixes. The only reason I do it though is because I limit my 1.5l of fixer to twenty films and use the three times clearing rule based upon the last batch. That way my fixing time is standard each time. My brain hurts a little less that way!!

    Bob H
    "Why is there always a better way?"

  10. #10
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    Modern emulsions use up to 10% iodide, but emulsions from about 75 years ago were typically maxed out at about 3%. Fixing with Ammonium Thiosulfate is always faster regardless of emulsion type, so in a difficult situation the Ammonium salt is the way to go. Since Iodide represents only a max of about 10% of the halide present, the effect is not huge, but can be seen, particularly in exhaustion of a fix used with high iodide films.

    PE

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