A Surface View of Etching
Chemical etching has been practiced since at least the late Middle Ages. In its early form, it involved coating an object, such as a metal plate, with wax, carefully patterning the hardened wax by cutting down through it with a sharpened tool to expose but not penetrate the object's surface and then exposing the object to an etching solution, typically an acid. With time, the etchant molecules in the solution would react with atoms of the exposed surface to form reaction products that would dissolve, thereby removing material from the surface.