Mythbusters' Adam Savage teaches you how the pros replicate objects.In principle, moldmaking is a simple process, but with every object you want to replicate comes a new series of pitfalls, innovations, and solutions. This article explains how to make a two-part, underpoured block mold, which is a versatile and beginner-friendly type that's great for small, detailed objects such as jewelry, game pieces, masks, picture frames, and figurines. Savage learned this technique by apprenticing under some of the great moldmaking masters in the specialeffects industry, and this article reveals their unpublished tricks.We'll make our mold out of silicone rubber, an excellent casting material, but it costs about $100 per gallon. This process uses as little of it as necessary, and it's important to follow all of these instructions, because a mistake can be costly. Then we'll cast our duplicates in opaque urethane resin (clear resin requires a more difficult process).This primer first appeared in Make: Technology on Your Time Volume 08, which is sold out and no longer available.