After sectioning and grinding several cycles of etching and polishing remove
disturbed metal layers from the surface of the sample. For the chemical etching acidic or basic chemicals in an aqueous or alcoholic solution can be used. When a surface is treated with an etchant metal ions at the boundary between two grains are dissolved. Microstructures become clearly visible. 2% Nital and 4 % Picral are the most common etchants. There are hundreds of different etchants available to reveal information about microstructures of ferrous and nonferrous alloys.