In an investment casting procedure using microwave energy as the heat source virgin wax models are attached to a spree of wax-type pattern material incorporating a susceptor, the spree having a pour cup also of a wax-type pattern material, the pour cup material having a higher percentage of the susceptor than the material of the spree. In use the pour cup will melt first and the spree second, unblocking the path of the virgin wax so that its expansion will not crack ceramic with which it has been coated.