Patina

Patina (/pəˈtiːnə/ pə-TEE-nə or /ˈpætɪnə/ PAT-ih-nə) is a thin layer that variously forms on the surface of copper, brass, bronze, and similar metals and metal alloys (tarnish produced by oxidation or other chemical processes), or certain stones[1] and wooden furniture (sheen produced by age, wear, and polishing), or any similar acquired change of a surface through age and exposure.

[2] Patina also 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.

[3] Archaeologists also use the term patina to refer to a corticated layer that develops over time that is due to a range of complex factors on flint tools and ancient stone monuments.

It also refers to development as the result of weathering of a case-hardened layer, called cortex by geologists, within the surface of either a flint or chert nodule.

Figuratively, patina can refer to any fading, darkening, or other signs of age, which are felt to be natural or unavoidable (or both).

Buildings in damp coastal or marine environments will develop patina layers faster than ones in dry inland areas.

Antique and well-used firearms will often develop a layer of rust on the action, barrel, or other steel parts after the original finish has worn.

Artists and metalworkers often deliberately add patinas as a part of the original design and decoration of art and furniture, or to simulate antiquity in newly made objects.

Colors range from matte sandstone yellow to deep blues, greens, whites, reds, and various blacks.

More simply, the French sculptor Auguste Rodin used to instruct assistants at his studio to urinate over bronzes stored in the outside yard[citation needed].