The purpose of etching is to optically enhance the microstructural features such as grain size, phase
identification and other microstructural features. Etching selectively alters these microstructural features
based on composition, stress, or crystal structure. The most common technique for etching is selective
chemical etching, and numerous formulations have been used over the years. Other techniques such as
molten salt, electrolytic, thermal, plasma and magnetic etching have also found specialized applications.