Emulsion Ractionization Durring Washing?

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by wildbillbugman, Sep 20, 2008.

  1. wildbillbugman

    wildbillbugman Member

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    Hello,
    I am mostly adressing this question to Photo Engineer, but anyone with an answere may chime in.
    Assuming that mixing has been thurough, is the mass of emulsion being washed by water only,or by iso-washing, fairly homoginous? O r do differences in M.W. or other factors cause the mass to have differnt compositions from one area to another, or from the "core" to the outer areas. Intuitively, it seams like there would be differences in the composition of the mass, depending on how fast it solidified.
    The reson that I ask is that I always loose some of the emulsion durring cold water washing,and I wonder exactly what I am loosing.
    I also wonder if "finishing" might be better acomplished befor washing. At that point one knows axactly what is in the emulsion.
    If,on the other hand, the loss durring washing is not homogenous,one dose not realy know what is realy in the beaker.
    Just a thought to pnder.
    Bill
     
  2. Photo Engineer

    Photo Engineer Subscriber

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    Nominally, washing is uniform with noodle or ISO washing. UF washing is localized to what is going through the filter, but as it returns to the starting vessel it is mixed in and becomes uniform.

    You can make a noodle wash non-uniform if you wish, by letting it settle out with slow cooling in a tall narrow container before you noodle it. You can't with ISO washing.

    Forgot to add.... Finsihing can be done before or after washing, but the excess salt retards the finish and changes the rate of fog formation so you do get different results.

    PE
     
  3. Kirk Keyes

    Kirk Keyes Member

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    Bill - I guess you can think of the only important parts of the emulsion at the point of washing as the silver halide and the gelatin. The halide is "emulsified" by the gelatin - it's actually physically bound to the gelatin.

    There is a difference in MW, but then the silver halide is the light stuff when you consider the MW of gelatin is on the order of 5000 to 250,000 MW. The rest of the stuff in the pot at that point, the excess bromide, potassium, nitrate, and ammonia if you used it, are in there too. But they are not bound to the gelatin like the silver halide is.

    So the stuff you are washing out should be all those unreacted reagents or byproducts of reaction (Br-, NO3-, K+, NH4+), and little bits of gelatin, which yes, does have some silver halide bound to it. So as long as you retain a large part of the gelatin, you should not be losing anything important.
     
  4. AgX

    AgX Member

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    Bill,

    would you be so kind and explain the term `Ractionization┬┤.

    Or could it be that you mean `fractionization┬┤?
    (For a non-native speaker Apug is hard enough even without some rarely used technical terms.)
     
  5. wildbillbugman

    wildbillbugman Member

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  6. Photo Engineer

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    I understood it, thus the answer above.

    Melted, unstirred emulsion will fractionate as described above leaving large grains on the bottom and small grains at the top. This is usually only seen with a huge grain size differential and a long settle time in a large container. At the scale we are working, it can be dismissed.

    PE
     
    Last edited by a moderator: Sep 21, 2008
  7. wildbillbugman

    wildbillbugman Member

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    Thank you Ron and Kirk,
    So, the reason we are told to be carful to not lose any "pieces" of emulsion durring washing is a matter of preserving maximum quantity? It has nothing to do with the "quality" of the emulsion? This question has been bothering me all along, since I took Ron's Workshop.
    Thanks,
    Bill
     
  8. Photo Engineer

    Photo Engineer Subscriber

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    Bill;

    You do not want to lose any pieces of the emulsion because the emulsion will change weight while being washed, and you want to know, as closely as possible, the exact silver content in the emulsion in order to figure out how to prepare it for the sulfur or sulfur+gold finish and how to prepare it for coating.

    If you don't do this, you can suffer speed and contrast changes from batch to batch because of errors in finish and coating strength.

    PE
     
  9. AgX

    AgX Member

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  10. wildbillbugman

    wildbillbugman Member

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    AgX,
    I assure you; your English is far,far superior to my Deutsh !
    Regards,
    Bill
     
  11. Kirk Keyes

    Kirk Keyes Member

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    What the heck was that? Canned is something that is put into a can, but I have no clue what that means...
     
  12. Photo Engineer

    Photo Engineer Subscriber

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    In that context, it means something or someone is cancelled, fired or dismissed. Context gives it more exact meaning. If you were canned, you would no longer have a job. Of course, this is not going to happen, right?

    PE