A method of investment casting utilizes a pattern produced by stereolithography in which a three-dimensional specimen is provided by light cure of ethylenically unsaturated liquid material. The stereolithography composition is constituted by the ethylenically unsaturated liquid material in admixture with an inert low thermoplastic material which weakens the pattern when heated within the mold used in the investment casting process to prevent the thermal expansion of the pattern from cracking the mold.