what is a patina

A patina is a thin layer that forms on the surface of copper, brass, bronze, and similar metals and metal alloys, or certain stones and wooden furniture, or any similar acquired change of a surface through age and exposure. It can also refer to accumulated changes in surface texture and color that result from normal use of an object such as a coin or a piece of furniture over time. In geology and geomorphology, the term patina is used to refer to discolored film or thin outer layer produced either on or within the surface of a rock or other material by either the development of a weathering rind within the surface of a rock, the formation of desert varnish on the surface of a rock, or combination of both. The word patina comes from the Italian patina (shallow layer of deposit on a surface), derived from the Latin patĭna (pan, shallow dish) . Figuratively, patina can refer to any fading, darkening, or other signs of age, which are felt to be natural or unavoidable (or both) .