Patina ( or ) is a thin layer that variously forms (a small amount of surface rust, without pitting) on the surface of stone; on copper, bronze and similar metals (such as any ferrous metals, i.e. steels and irons) (tarnish produced by oxidation (rust) or other chemical processes); on wooden furniture (sheen produced by age, wear, and polishing); or any such acquired change of a surface through age and exposure. Patinas can provide a protective covering to materials that would otherwise be damaged by corrosion or weathering. They may also be aesthetically appealing.