Contrast enhancement with interference layers

For ceramic materials that are not extremely hard (e.g., stabilized zirconium oxide or multiphase materials), surface relief can be created within a few minutes by means of final polishing with colloidal silica on a chemicaUy resistant, short-napped fiber cloth. Because removal is dependent on the grain orientation and the type of phase, it is possible to distinguish between grains of a single phase and between different phases during microscopic examination. Application of the DIC method makes it possible to use even poorly defined reUef to display microstructure under the optical microscope. A brief final polishing step with very fine alumina (0.05 pm) will help reveal the spinel phase in aluminum oxide materials, for example. 

In ceramic-metal composites, the application of nonmetallic interference layers to polished or etched sections can also be used for purposes of brightness matching. This involves reducing the reflectivity of the phases of the metal component while increasing the reflectivity of the ceramic material. 

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