A blackbody high temperature probe is formed by thermally fusing a coating of composite ceramic material on the tip of a high temperature lightpipe or fiber. The ceramic coating replaces conventional sputtered metallic thin films to form a blackbody optical cavity. The ingredients of the composite ceramic material include a mixture of refractory metal oxides forming the bulk of the material, various pigments and/or refractory metal powders, and binding agents. A firing process is used to thermally fuse the coating onto the lightpipe. Embodiments of the firing process include using a flame or furnace technique, or alternatively using various flame- or plasma- spraying techniques. A thermally fused coating of from 10 to a few hundred micrometers provides a durable blackbody temperature sensor suitable for use in a wide range of applications including measurements in high temperature, high flow rate and abrasive environments such as that encountered in an internal combustion engine, gas turbine or rocket exhaust stream.