[Jewelry making - Article 00047] - Re: [Orchid] Casting sheet silver

[jesse brennan]

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    I brushed over rather lightly yesterday what probably is the biggest
    problem you  face.  That is porosity.  Molten silver  can adsorb  a
    tremendous quantity of oxygen - about 20 times its volume. as the
    metal freezes it can no longer hold this and  the gas escapes.  This
    will create a very porous  surface particularly on the top or where
    the metal freezes last.  This problem would be alleviated by using a
    material other than  standard copper based sterling and or handling
    in an oxygen free atmosphere.  There is a  germanium -silver alloy
    that is supposed to be  deoxidized enough by the germanium so that is
    free of this porosity. I haven't used it and haven't handled nearly
    as much silver in one pour as this piece (20cm by 30 cm) would take.
    A flux cover and  maybe a graphite mold would be needed . Copper has
    some of the same problem to a lesser extent-  in this case the
    silicon bronze alloys handle the problem quite well. The preferred
    one being Everdure  bronze which is copper with 4% silicon as a
    deoxidizer and property improver. This would be a preferred alloy to
    cast. You may want to consider silver plating a bronze casting  if
    you don't mind not being a purist. Someone casting bronze 
    plaques could  do this  for you quite easily from your pattern. jesse


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