In sculpture / mould-making / casting terms, the core is the solid internal portion of an investment mould for casting a hollow piece of sculpture (such as a portrait). The amount of space left between the core and the mould (occupied by wax before it is "lost), determines the thickness of the cast metal. The core is made of foundry sand (can also be same as investment material) in sand casting and in the lost-wax process.<br><br>A hollow wax sculpture to be cast in metal is filled with clay or plaster with grog (refractory material). The wax can be modeled directly over a preformed core, and after the sculpture is cast, the core is generally removed in order to make the sculpture less heavy. A core might be either an original model pared down, or it might be poured into a hollow wax cast. A core may contain an armature, and it may hold chaplets.Also see direct casting, indirect casting, and lost-wax casting.