Since I decided to mold and cast my female turian mask using resin, rather than using latex like I did with Garrus, I wanted to do a quick write-up to show some of the differences.
Casting with latex (a soft material) is done with a hard, porous mold, usually made from plaster of some kind. Casting resin (a hard material) requires a soft, non-porous mold, in this case made from silicone.
Clays made with a base of oil or wax (or a combination of both) are a type of sculpting medium that will never cure or harden completely. This makes them ideal for sculpting a large project that you may need to work on over a period of days or weeks. When the sculpture is complete, you make a mold from it, and then cast it to get your final piece.