Nickel can be plated mat, Simi-bright, or fully bright: hard or comparatively soft; with or without internal stress; ductile or brittle; quite corrosion-resistant or having only decorative properties. Nickel is plated as an undercoat for many plating finishes including decorative chrome, silver, and gold. Under gold it is used as a barrier coating between the gold and the substrate. By itself, the corrosion protection of nickel is limited and is a function of the thickness and the substrate. Very thin coatings will protect copper easily but thicker coatings must be used for iron or steel.