"Patina (/pəˈtiːnə/or /ˈpætɪnə/) is a thin layer that variously forms on the surface of copper, brass, bronze and similar metals (tarnish produced by oxidation or other ...
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chemical processes), or certain stones, and wooden furniture (sheen produced by age, wear, and polishing), or any similar acquired change of a surface through age and exposure.
Additionally, the term is used to describe the aging of high-quality leather. The patinas on leather goods are unique to the type of leather, frequency of use, 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." - (en.wikipedia.org 18.12.2020)