If it has to go through a vulcanized rubber mould proces, yes. Here is some info from the 1listsculpting FAQ:
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3.3 -What materials should I not use?
If a miniature is not going to be vulcanized, then you are pretty much free in your choices of materials. Otherwise, vulcanization usually subjects a miniature to high temperature (about 350 Fahrenheit/ 177 degrees Centigrade) and pressure (about 50PSI/ 3.45 bar). This means that some materials can cause problems like:
Plastic They can melt.
Wax This melts.
Superglue This liquefies which can affect the mold. It can work if covered with putty. Check this with the mold-maker as some do not seem to be troubled by it. See 3.14.
Resin This should also be checked with the caster. If you use a resin, you have to be careful about enclosed air bubbles. These would collapse during vulcanization of the mold. See 5.14.
Metal Tubing These can collapse under the pressure and if they are enclosed on both sides, the seals on the ends can pop off. If tubes are used, then they should be totally filled with putty for support and to avoid enclosed air spaces.
Lead This can be too soft. It's better to use brass.
Malleable Materials They can deform.
Aluminium This can sometimes be a problem. Check with the mold maker.
Brittle Materials Like certain clays, can crumble or explode from impurities overheating.
Ren Shape It's porous and will fill up with rubber, which makes cleaning the mold a problem.
Wood Saps and resins in the wood can damage the rubber or boil off, causing deformations and possible ruptures.
Low-Melt Alloys Make sure that, whatever metal you use for parts, the melting temperature is above the vulcanization temperature.
When in doubt, always check with the mold-maker. This does not mean that a mold can not be made if parts are made of these materials. There are different techniques for this, such making a cast of it first, using a room temperature vulcanizing rubber mould or using a vulcanization process at lower temperatures -but not all mold-makers are willing to or can go to this extra effort.
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One remark to be added in the future: polymer clay masters are not accepted by all casters either. They stand less chance of surviving. Nevertheless, excellent figures have been made with it.
The FAQ is found at the 1listsculpting group
http://groups.yahoo.com/group/1listsculpting/ and here:
http://www.lyonstudio.com/Sculpting/1lists...g_FAQ_v2-4a.pdf
Bye, Ming-Hua