Patina

Patina (/ˈpætᵻnə/ or /pəˈtiːnə/) is a thin layer that variously forms on the surface of stone; on copper, bronze and similar metals (tarnish produced by oxidation 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.