Thermal treatment of ceramics composed of two or more oxides under controlled reducing conditions selectively volatilizes the less stable components, leaving microstructured surfaces consisting of the most stable of the original oxides. Volatility diagrams showing equilibrium partial pressures allow interpretation of this process and the calculation of equilibrium conditions for the different reactions involved. In this communication we present results for ceramics composed of mullite (3Al(2)O(3)center dot 2SiO(2)), zircon (SiO2 center dot ZrO2) and cordierite (2Al(2)O(3)center dot 2MgO center dot 5SiO(2)).