RTV Mold compounds

I am interested in making molds of organic specimens. I have never
worked with Ditto or any of the other RTV compounds. If you have
any advice on these type compounds, would appreciate hearing from

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 on silicone and other rubber mold
compounds on my art site, in the alt.sculpture FAQs.

Andrew Werby

Dear Ms. Koslow,

Attached is a link to our product page, which shows a casting I did
of a fresh STRAWBERRY ! If I could do a strawberry, you can do
anything that doesn’t move or crawl away. There’s also a link to our
instruction page.


Our LiquaCast is NOT a silicone rubber and as a result is much
cheaper, tougher and easier to use than Ditto and similar compounds.

Please give me your shipping address and I’d be happy to send you a
small free sample to try out. Not a P.O. box, please.

Anyone else out there want a free sample??

Michael Knight

& F.E. Knight Inc.
120 Constitution Blvd.
Franklin, MA 02038 U.S.A.