PMC stands for Precious Metal Clay. Developed in the early 90's at Mitsubushi, it consists of very finely ground silver or gold mixed with water and some sort of organic binder to form a clay-like substance which can be molded into shapes that would be difficult to achieve with traditional metal fabrication techniques.

When the clay is formed and then fired, usually in a small kiln, the binder burns away and the metal particles fuse together and you're left with a pure metal object approximately 30 percent smaller than the object you started with. After firing, PMC can be treated like fine silver or 24K yellow gold (because that's what it is). It has a tendency to be porous, though, so burnishing it before you attempt any soldering is a good idea.