Abstract: A method of making an investment shell mold in such a way that the shell is protected from cracking on simultaneous firing and removal of the pattern. The method includes application of conventional molding materials in the first slurry and stucco coats. By conventional molding materials is meant molding materials that are transparent to microwaves and microwave energy. In the second slurry and/or stucco coats, and in later coats if necessary, a certain amount of microwave susceptible material, such as graphite or certain metal oxides including Fe.sub.2 O.sub.4, MnO.sub.2, NiO and cobalt oxide, is added. Then, if necessary to achieve sufficient mold strength, additional coats of conventional molding materials are applied. After drying is complete, the pattern and mold are exposed to microwave radiation. This radiation interacts with the microwave susceptible material to heat the pattern adjacent to the mold surface, while avoiding generalized heating of the pattern.