Q: I'm making models in clay that have lots of undercuts, and would like
to take molds of them so I can make permanent sculptures in plaster or polyester
resin. What is the cheapest thing I can use that won't tear up the originals
A: You don't mention what you mean by "clay" Would that be potter's
clay (waterbase) or plasticine (oilbase)? Mold materials work differently
depending on what they are applied to. Silicone compounds, in particular,
are sensitive to the sulphur found in most plasticine. Urethane rubber is
cheaper, and works quite well for most applications. Natural latex is the
cheapest, but is very tedious to apply, does not last well, and undercuts
are a particular problem due to its thinness. Generally one doen't expect
to preserve an unfired clay model used as a pattern for mold-making.
Offhand, I would say that moulage is the best bet for what you propose.
This is a compound that melts in a double-boiler and is applied warm (which
can be a problem if your model is plasticine). But it is gentle to most
patterns, and can be melted down and reused, so it is fairly economical.
While it is reasonably firm, its toughness can be enhanced by embedding
gauze in the mold wall, though this makes recycling a bit harder. You can
make quick shells using melted wax and cloth that will help support the
somewhat floppy moulage once it is stripped off your pattern. There are
other compounds that work the same way, such as hide glue and polyvinyl
acetate, but moulage smells the best, and goes on the coolest. I know it
works well with plaster. In any case, I would advise a small-scale experiment
to test the reactions between the mold compound you decide on and the clay
you used, and between the mold and the polyester resin (which is really
nasty stuff, but that's another issue).
Andrew Werby - United Artworks
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