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Mold Making Materials

I need to purchase some liquid mold making supplies and request
practical on the properties of the various products

I have used clear urethane mold compound but found it very difficult
to control. I have used Rio Grande Ditto silicone and found it
excellent, but expensive.

I am looking at Ferris See-Thru Flexible mold compound. This
material is a lot less expensive than silicone and thus desirable.
The catalogue description indicates it is transparent when baked at
350 degrees F and is good for beginners.

The Question is, if I am molding a pattern carved from wax, what
prevents the wax part from melting during the baking operation? It
would appear this material is limited to reproducing original parts
produced from metal?

Keeping an open mind,are there other molding compounds I am missing
that might be better?

Ben A Harris

Hello Ben;

    I have used clear urethane mold compound but found it very
difficult to control. 

Your wax model will never withstand the temperatures required to
cure the Ferris See-Thru compound. In addition, while you don’t need
to weight out and mix 2 parts, you do need to vacume the living
daylights out of the stuff, and you’d better make sure there is no
moisture on your model or you’ll get serious problems with bubbles.
Silver is perticularly prone to this, since its somewhat porous
surface can retain moisture. I understand your price concerns with
regards to the RTV liquid mold compounds. You can usually get
smaller quantities. Here’s my suggestion. If you don’t have a
vulcanizer, get the ABC vulcanizer (around $75) from Rio Grande.
Then, invest in some of Stuller’s economy silicone mold compound.
It’s wonderfully simple to use (don’t forget to get the locator
buttons for it). It’s around $37 per 5 lbs, if I remember correctly.
That will suffice for general mold making. If you want to save more
money, learn to cut molds and go with the Castaldo rubber compounds.
You could still use the ABC vulcanizer for that. For situations
where you want to take a mold directly from the wax model, you could
try their Belicold compound (also with the ABC unit) if the wax would
withstand the pressure, but you can also look at their “Ditto” mold
compounds, which, while they are still expensive and require the
appropriate mold frame with glass plates (and probably need vacuming
too), look a little cheaper than the Silastic brand. Good Luck.

David L. Huffman

Try a company called Polytek in Easton PA. They have a great
variety of different RTV materials. Call them for a catalog and you
can purchase their sample book. 800-858-5990. You really need a
vaccum system or a pressure pot to make good RTV molds. Good luck.

Also try Smooth-on. They too have a number of mold making
materials. Some RTV’s are much less prone to bubbles than others.
Some self “release” bubbles (to a degree). I really do not know why
so many in the jewelry (especially) industry are still so hung up on
vulcanized molds verses RTV’s! Contact any of the bigger suppliers
and ask what materials they recommend for your project and lack of
equipment. You can make bubble free molds without vacuum or
pressure, but either makes bubble free pieces easier.

MidLife Crisis Enterprises
Cynthia Thomas Designs
Cynthia’s sculptures are at:
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