Sacrificial lost casting cores of green or fired ceramic, which include at least one tension spring as a metallic reinforcing element, wherein at least one end of this reinforcing element lies near one of the surfaces of the casting core or extends therethrough, and wherein the melting point of all metallic reinforcing elements lie above the melting point of the casting metal, as well as processes for production of such casting cores, including the steps of preparing a principal mold, seating therein at least one reinforcing element, filling the principal mold with ceramic slip, drying the slip for formation of a green ceramic and releasing the casting core from the principal mold. The principal mold is preferably lined with a flexible internal mold or liner. The reinforcing element in the form a tension spring can be used following casting for breaking up the ceramic casting core.