Forms on which a piece (often a slab) of plastic material such as clay, wax, or glass can be shaped. Types of drape molds are hump, slump and press molds. The example shown to the right is a hemispheric hump mold made of plaster. square slumpThe example to the left is a square plaster slump mold. A clay bowl, for instance, might be formed either by draping a slab of clay onto a hump mold or into a slump mold. In order to better separate the surface of the mold from that of the material shaped, you may need to employ a release agent. This might be a powder, an oil, a sheet of cellophane or tissue paper.