1. INTRODUCTION 

Vulcanized rubber molds are used to produce wax masters in quantity for investment casting of metal parts such as jewelry, small industrial components, and gaming miniatures. During the chemical process of vulcanization, rubber, which is stringy and weak in its natural state, becomes firmer and tear-resistant. Both natural rubber and silicone can be vulcanized. 

Natural rubber and most silicone molding materials vulcanize when exposed to high temperature and pressure. This method, traditionally used by professional jewelers, requires an investment in specialized heat vulcanizing equipment. A wide variety of materials with different hardnesses is available. Some silicone molding rubbers cure at room temperature with the addition of a chemical catalyst; this is called room temperature vulcanization (RTV) or cold molding. 

This technique requires a much lower upfront investment, but ongoing material costs may be higher. RTV molds can require anywhere from one hour to eighteen hours  to cure. Molds are generally a little firmer than natural rubber or  heat-vulcanized silicone. Masters for moldmaking are traditionally machined out of metal (which is expensive and cost prohibitive for small-scale production) or hand-crafted (which may not be precise enough for some applications). 

3D printing presents a low-cost method for producing precise CAM master models for vulcanized rubber molds. 

Note: RTV can be an attractive technique for small scale  production, requiring less initial investment than a heat vulcanizing setup. For a small shop, this makes moldmaking a very reasonablypriced addition to your workflow. There are a wide range of mold materials available. Products such as Castaldo ICE RTV cure within 60 – 90 minutes or less, which can be very quick and convenient.