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  1. #1

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    Sodium carbonate as a swelling salt for re-washing dirty negatives/slides

    Can plain sodium carbonate solution help re-washing a dirty negative/slide by swelling the emulsion, opening up the gelatin matrix and let any grit embedded in it go away?

    A putative processing would be this:

    1- souping the emulsion in a tank filled up with a solution of sodium carbonate, agitating the tank to let any grit go away from the swollen negative;

    2- washing with distilled water as per Ilford washing method;

    3- hardening the emulsion;

    4- rewashing (Ilford method);

    5- photoflo;

    6- hang to dry.


    Since I've not tried this method, is there anyone who can shed light on this?
    Thanks.

  2. #2
    Maine-iac's Avatar
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    I've not tried it either, but theoretically the carbonate should not harm your negative. I'd leave out step 3, however. I don't think there's a need to harden the emulsion, and hardening only makes washing take longer.

    Larry

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    Quote Originally Posted by Maine-iac
    I've not tried it either, but theoretically the carbonate should not harm your negative. I'd leave out step 3, however. I don't think there's a need to harden the emulsion, and hardening only makes washing take longer.

    Larry
    My concern is that, after having souped the negative in an alkaline medium, the emulsion would become too fragile and prone to scratches.
    Hence the hardening...

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    "My concern is that, after having souped the negative in an alkaline medium, the emulsion would become too fragile and prone to scratches.
    Hence the hardening..."

    Not so, in my experience. I agree with Larry, hardening is not needed.

    Having said that, I am skeptical that a sodium carbonate solution soak will be of any help.

    If the problem is embedded dirt, nothing is going to be of much help.

    If the problem is calcium scum on the surface of the film, soaking the film in a solution of sodium citrate or sodium hexametaphosphate followed by a distilled water wash might help.
    Tom Hoskinson
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  5. #5
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    Quote Originally Posted by Tom Hoskinson

    If the problem is calcium scum on the surface of the film, soaking the film in a solution of sodium citrate or sodium hexametaphosphate followed by a distilled water wash might help.
    I'm not sure what sodium hexametaphosphate is, but in Paris where calcium scum and particles were a constant problem, I solved it by giving the film a final dunking in plain tap water softened with some water softening crystals of the sort we all had to use in our dishwashers and washing machines. I used about a teaspoon per liter, and it could be re-used many, many times, since it was only providing a final rinse after washing. Worked for me.

    Larry

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    Larry, sodium hexametaphosphate is a calcium chelating agent and was the principal ingredient in the original Calgon water softening crystals.

    Sodium hexametaphosphate has been largely replaced by one form or another of sodium citrate, which is also a calcium chelating agent. The primary reason for the replacement was environmental concerns about phosphates.
    Tom Hoskinson
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  7. #7

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    I've some 120 strips which need cleaning. A test done placed a strip in
    a shallow tray with soapy water. A cheap 1'' paint brush was then used
    to gently scrub the surface. That strip of Efke should be flat enough
    by now to evaluate.

    If I could, I'd hang the strips and do as above but add a forcefull spray
    to the procedure. Too little margin on many ends to clamp and hang. Dan

  8. #8

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    I looked up in a book "fotographische chemie", the highest degree of swelling will be either at pH 11 (Carbonate) or pH 2.5 (citric acid). So citric acid would give swelling as well as complexing ions. In this book they do not give any special advise to clean films, except Tetrachloroform for removing finger prints.
    No warranty can be given on these informations as this book has been printed in the GDR and we all know what happened to them...( 1989:As Praktica was not able to present a good AF camera Erich decided to call it a day - 2005: As Leica was not able to present a good digital camera ....)

    Wolfram
    Colour? We can always use an airbrush later...

  9. #9

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    That would seem to be still the case. Acid or alkali, the
    emulsion will swell. Ph 5 is the point of least swell. Hardened
    emulsions swell much less. Dan

  10. #10
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    Quote Originally Posted by Tom Hoskinson
    Larry, sodium hexametaphosphate is a calcium chelating agent and was the principal ingredient in the original Calgon water softening crystals.

    Sodium hexametaphosphate has been largely replaced by one form or another of sodium citrate, which is also a calcium chelating agent. The primary reason for the replacement was environmental concerns about phosphates.
    So the stuff I was using in Paris probably was sodium hexametaphosphate. I suspect one water softener is much like another. At any rate, whatever it was, it sure worked for killing the calcium particles.

    L.



 

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