Sometimes it is beneficial to examine the specimen in the as polished condition. The as polished condition is useful for examining the microstructures of materials whose constituents exhibit large differences in light reflectivity after polishing. Porosity and inclusions are examples of features that are easily observed in the as polished condition. But most materials are etched to reveal the microstructure. Etching is a controlled corrosion process resulting form electrolytic action between surface areas of different potential.
Etching reveals the microstructure of a material by selective dissolution of the structure.
Specimens are then examined using optical and electron microscopes. There are also many other techniques used to characterize the structure of metals, but this article will concentrate on microstructural characterization.