Abstract: In a method for forming castings made from a polymerizable hydrophobic monomeric material wherein a liquid hydrophobic polymerizable plastic monomer material is pumped into a cavity, which is defined by a pair of spaced apart smooth surfaced plates that are sealed about the outer perimeter, and polymerized therein to a solid, self-supporting casting, the improvement comprising the preliminary step of applying the relatively thin thermoplastic sheet across at least a portion of at least one of the spaced apart smooth surfaces, said thermoplastic sheet stretching when in contact with the liquid polymerizable monomer material during polymerization of said material and during cooling of said polymerized material, the sheet shrinking and distorting in random fashion so as to produce a randomly textured surface on at least the corresponding adjacent portion of the polymerized casting.