Silicone Rubber for Molds
Silicone molds may be the best medium for custom molds since man first realized that muddy footprints were negative imprints of feet in prehistoric times. The properties of silicones that make it outstanding for molds are its inert nature which makes it superior at high temperatures, its ability to accurately capture fine detail, its elasticity, and durability. Silicone elastomers can actually transfer submicron surface details, accurately rendering details as intricate as those of velvet, wood or fingerprints.
The first recorded reference to a silicone mold appeared in the 1950’s; a composite made of mica or paper and a binder was shaped around an electrical coil using a silicone mold. However, the earliest application of silicones where the details of an original surface was transferred via a mold appears to have been with dental molds. Commercial products for these dental molds were available from 1955 on, with fast-curing compositions appearing later.
Silicone molds come in a variety of formulations and are available ready-made for purchase, or you can buy a silicone rubber kit and make your own custom mold. Silicone is actually a mold-making elastomer—a fancy title for a product which is usually composed of two liquid parts, a base and a curing agent (sometimes improperly called catalyst), which are easily cast around an original artifact after being mixed. Once hardened, elastomers are a flexible material which can be stretched (which eases demolding), even around deep undercuts, yet return to their original shape—a detailed negative impression of the original, and also feature easy release at demolding even without mold release.
Newer formulations of silicone rubber make creating custom silicone molds easier than ever before. Now you can make your own finely detailed molds with all the advantages silicone offers, PLUS lower viscosity (thinner) to help prevent bubbles forming, and a 1:1 by volume mix ratio. No more weighing or degassing the liquid after mixing! Check the manufacturer’s instructions to be sure that the rubber has the characteristics you are looking for.
When casting resin in a silicone mold, Alumilite recommends heating silicone molds for 30 minutes in an oven set on “Warm” and then sprinkling the mold with baby powder or talc powder until all area of the mold are covered. Then blow or gently knock out any loose powder. This allows the resin to flow into the mold more easily and reduces the likelihood of air bubbles. You can also stretch your silicone mold while adding your resin to increase your pour space without damaging or stretching the mold. Although mold release is not required, it is still a good idea as it makes clean up easier and prolongs the life of the mold.
Silicone molds are wonderful tools for resin crafters and well worth learning the knack to be able to take advantage of their many benefits.
ResinObsession.com offers several ready-made silicone molds for sale, as well as a full line of silicone mold rubber and putty for all of your mold-making projects. Cindy, the ResinLady, is always eager to help you with any questions or problems that you may have.
This article was published on Saturday 02 October, 2010.
