Acrylic can be used for relief carving projects. Translucent (opaque) cast acrylic is a consistent material. Ivory-colored, 3/16″-thick acrylic makes particularly nice pieces. (Thinner sheets of acrylic can warp under the high heat of the carving process.) I use it a lot to test graphics before committing to carving on a special piece of wood.
-Jim Puentes, COOLaserCraft