[Jewelry making - Article 00496] - Re: [Orchid] RTV Mold compounds

[Andrew Werby]

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    I've done quite a bit of work with organic specimens and RTV.
    "Ditto" is one brand marketed mostly to jewelers which is used
    pretty much like a vulcanized rubber; its major advantage is that
    it's clear, so one can see any bubbles that form on the surface of
    the part, assuming one uses transparent mold plates. It allows a
    jeweler to deal with specimens that won't stand the heat and/or
    pressure of normal vulcanization, and to produce a mold that can be
    treated similarly to a regular injection mold. 

    I usually use less-expensive general-purpose 2-part silicone mold
    rubber, painting the liquid rubber onto the the specimen first,
    letting that set, and then applying successive coats of thickened
    rubber. (There are various compounds one can add to it to make it
    less runny.) While these molds can't be used with a wax injector,
    they use a lot less rubber and are hence cheaper to make. I melt wax
    in a deep-fat fryer and pour it in and out to get contoured
    castings. Most places that sell sculptor's supplies will have a
    range of RTV rubbers you can try. I prefer the silicones, because
    they release well from models and castings; the urethanes are
    cheaper, but tend to stick. 2-part silicones come in two basic
    types: tin soap catalyzed and platinum catalyzed. The tin soap type
    is less expensive but isn't as tough or long-lasting as the platinum
    type. But the platinum-cure silicones are very touchy about what
    they will set up on - many substances - oils, clays, rubbers,
    sulphur - will inhibit them, so they remain a sticky mess instead of
    a mold. 

    I've got more information on silicone and other rubber mold
    compounds on my art site, in the alt.sculpture FAQs. 

Andrew Werby
www.unitedartworks.com

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