There are several ways to do this. Below you'll find links that will give you a brief grounding in these moldmaking materials and information on how to cast with them.

Latex

Instamold

Silicone


My book on accessories contains pictures and information on my forays into two-part moldmaking, (and notes on the kind of things you want to avoid doing when attempting it yourself.) Be sure to check out this tutorial's Links Page for access to additional information on the subject.

Don't forget to visit my bonus section on the Casting of Resin Gemstones.