a material such as individual glass beads coated with anV epoxy resin to bind the .beads together into the mold shape'.v A description of a preferred form of mold material and the method ofmaking `such material is provided in copend-Y ing patent application `of Modersohn and Hornbostel, entitled Moldf U.S. Serial No. 89,451, led February 15, The individual resin particles, being substantially inso