Multiple part cores for investment casting

A composite core for a hollow gas turbine engine blade is constructed by forming a first core part determinative of the cavity size of the trailing edge blade portion from a first ceramic material and joined to a second core part determinative of the blade cavity for the blade body portion which is formed from a second ceramic material. The first and second ceramic materials can be chosen to have appropriate characteristics grain sizes, flowability, leachability, and/or reactivity characteristics taking into consideration the different dimensional restrictions imposed by the desired blade product. A tongue is formed on the adjoining edge surface of the trailing edge core part, and the trailing edge core part is then inserted into a second die and the body core part is formed, including a complementary groove member which is formed around the tongue member on the trailing edge core part. The joined trailing edge and body core parts can then be sintered to form a composite casting core.