These techniques rely upon the use of molds to shape or form clay material while in a plastic (pliable) or liquid state. CNC technologies can be employed to directly carve molds (of plaster or other materials) or to produce contra molds (negatives of negatives) or models (positives) from which molds can then be cast. Mold parts must be designed to interlock tightly during casting or shaping processes while being easily removed from the resulting piece without damaging it.