[Jewelry making - Article 00190] - Re: [Orchid] Instead of talc?

[David L. Huffman]

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Hello Martin;

    You can use corn starch instead of talc. Talc will not burn cleanly
    away in the investment, but corn starch will.  But as for your
    problem of degraded surfaces from the talc, here's my advice, for
    what it's worth. You shouldn't really need to have any talc (or corn
    starch) on the surfaces of the mold which come in direct contact
    with the wax in order to get details to fill properlly. The secret is
    in cutting vents in the mold for air to escape. This takes a little
    more instruction that I can give here, but in short, here's what I
    mean. 

    Suppose there's an area on a mold that is not filling. If you make a
    cut in the rubber leading from the point at which the wax is not
    filling the mold, not too deep, and lead this cut out a ways,
    sometimes to the edge of the mold, that's a vent.  Pry open this
    cut, dust it with talc, then let it close, trapping the talc in the
    cut. Now brush away the talc that's on the surfaces where the wax
    will be. What has happened is that the cut in the rubber is filled
    now with a slight bit of talc, which is permeable to air. The air
    trapped in the mold can escape into the talc/vent, allowing the wax
    to more completely fill the cavity.  Hope this helps.  What would be
    best would be for you to watch an expert cut a mold.  All kinds of
    factors are involved, including the selection of injection wax, the
    mold rubber, the spruing, wax/air pressure, wax temperature, etc.
    Takes a little experimentation. 

David L. Huffman

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