Metal finishing operations involve preparing and finishing metal parts for final use. Metal finishing operations can include cleaning, degreasing, pickling, electroplating and electroless metal plating, etching, and conversion coating. Nickel, cadmium, and zinc are also used for plating parts to provide a corrosion protection finish. These coatings are significantly thinner than hard-chrome plates and are applied in minutes, rather than the hours or days required for hard-chrome plating. Production of printed circuit boards involves the plating and selective etching of flat circuits of copper supported on a nonconductive sheet of plastic. Production begins with a sheet of plastic laminated with a thin layer of copper foil. Holes are drilled through the board using an automated drilling machine. The holes are used to mount electronic components on the board and to provide a conductive circuit from one layer of the board to another.