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. Here are some key points about patina:

• Usage: On metal, patina is a coating of various chemical compounds such as oxides, carbonates, sulfides, or sulfates formed on the surface during exposure to atmospheric elements such as oxygen, rain, acid rain, carbon dioxide, and sulfur-bearing compounds.

• Appearance: Patina refers 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. It can also refer to the natural color that a metal will take on over time.

• Etymology: 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).

• Preservation: A little wax or lacquer can go a long way in preserving the patina of an antique object. For metal, a coat of lacquer can prevent corrosion and also seal in the patina. For patina on wood, a protective layer of wax is a handy non-invasive way to keep your pieces safe without making them look new.

• Development: Leather, wood, waxed canvas, metal, and even stone can develop patina through use and exposure. In order to get a nice patina on an item, it needs to be used. Much like the ongoing debate on whether people should actively be trying to get quicker fades on their denim or just simply wear them, those looking for a patina on their items should use them.

In summary, patina is a natural or acquired change of a surface through age and exposure, and it can refer to accumulated changes in surface texture and color that result from normal use of an object. It can develop on various materials such as metal, wood, leather, and stone, and it can be preserved with a protective layer of wax or lacquer.