The material of patterns in the case of investing casting is.

Explanation:

Investment casting

• The investment casting process also called lost wax process begins with the production of wax replicas or patterns of the desired shape of the castings
• A pattern is needed for every casting to be produced
• The patterns are prepared by injecting wax or polystyrene in a metal die
• A number of patterns are attached to a central wax sprue to form an assembly
• The mould is prepared by surrounding the pattern with the refractory slurry that can set at room temperature
• The mould is then heated so that pattern melts and flows out, leaving a clean cavity behind
• The mould is further hardened by heating and the molten metal is poured while it is still hot
• When the casting is solidified, the mould is broken and the casting is taken out