Abstract: A ceramic core that includes, prior to core sintering, erbia filler material alone or admixed with a second ceramic filler material, such as alumina, and a binder to provide a core that is relatively non-reactive with superalloys used in the manufacture of turbine blades, dimensionally stable during directional solidification (DS) for extended times, removable by chemcial leaching techniques, and having enhanced X-ray detectable during post-cast inspection operations. After core sintering, the ceramic core has a microstructure comprising an erbia-alumina garnet phase and an unreacted ceramic filler phase (e.g. alumina).