6 years ago#1
Merrill571
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Perhaps a plaster cast could be used after all - if it was first given a couple of coats of shellac or some other sealant to minimise moisture absorbtion. I haven't tried it, just thinking.

Best of luck,

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6 years ago#2
Linda2
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Silicon molds last a pretty long time, but I assume that they degrade over time if not preserved properly. Was wondering if anyone knows a good method to preserve the mold from shrinkage. Have heard that keeping a plaster cast inside is bad because it absorbs the moisture... but what material is good?

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6 years ago#3
garyncurtis
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[I never heard that about plaster- I use plaster shells on silicone rubber molds and have never noticed that they degrade any faster than molds without them. Silicone rubber is fairly inert when set up; I doubt that anything would be absorbed from them in any case. But if you're worried about it, try filling your molds with wax before storing them.]

Andrew Werby

UNITED ARTWORKS- Sculpture, Jewelry, and other art stuff http://unitedartworks.com http://www.computersculpture.com for 3d design tools

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5 years ago#4
pabrad
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I know this is an old thread, but just wanted to chime in incase anyone else is seeking this info.
There are two different silicone rubbers used to make molds: TIN (Condensation) Silicone & PLATINUM (Addition) Silicone.

Looking at shelf life, you can either view it as the mold sitting there un-used or being-used (# of castings). Let's focus on the mold unused, just sitting on the shelf.

TIN silicones exude acetic acid, alcohol and water as by-products after they are cured. This exudation also affects dimensional stability - typically resulting in slight shrinkage. Their shelf life can be 3 - 5 years in a moderate environment, less in a dry environment. As these ingredients leave the rubber, the material looses it's pliability and will typically rip. You can extend the shelf life of a tin mold by putting the mold in a zip lock bag, which will help it to maintain it's moisture content & extend the shelf life.

PLATINUM silicones do not exude any by products and thus are totally dimensionally stable. Their shelf life can literally be 25 years or more if stored in a moderate environment. No zip lock bag necessary. The main drawback with platinums is that they contain expensive metal which adds to the cost....

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5 years ago#5
copper
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Pabrad, thanks That indeed is valuable information. I think it is one of those things that should be categorized so when people are looking for this kind of information they can find it easily. Perhaps a "wikipedia" - like "materials" forum section would fit here?

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5 years ago#6
pabrad
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Sure;
There is a lot of information about materials that could be posted; unfortunately people do not think to seek info until it is too late.

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5 years ago#7
copper
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Perhaps if we start up such informational section on this forum people will see it before it is too late?

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