A support for optical elements is described. The support includes a base substrate with high specific stiffness and a finishing layer. The base substrate is a non-oxide ceramic material, preferably a carbide, such as boron carbide or silicon carbide. The finishing layer is preferably Ge or an alloy of Al and Si. The finishing layer is or is capable of being processed to provide a surface with low finish. Low finish is achieved by diamond turning or polishing the finishing material. The finishing layer has a coefficient of thermal expansion similar to the coefficient of thermal expansion of the base substrate. The optical element optionally includes a reflective stack on the finishing layer.