patina

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. See paten.
2. n. A thin greenish layer, usually basic copper sulfate, that forms on copper or copper alloys, such as bronze, as a result of corrosion.
3. n. The sheen on any surface, produced by age and use.
4. n. A change in appearance produced by long-standing behavior, practice, or use: a face etched with a patina of fine lines and tiny wrinkles.

Century Dictionary and Cyclopedia

1. n. A bowl; a patella.
2. n. An incrustation which forms on bronze after a certain amount of exposure to the weather, or after burial beneath the ground. It is, when, perfectly developed, of a dark-green color, and has nearly the composition of the mineral malachite (hydrated carbonate of copper). Such an incrustation, although very thin, is considered to add greatly to the beauty of an antique object, especially of a bust or statue, and is of importance as protecting it from further oxidation. Artificial and evanescent patinas are produced by forgers of antiquities by the application of heat or of acids, and in various other ways. Some modern bronzes acquire a dark colored patina, which is a disfigurement rather than an ornament. Elaborate investigation on the part of various chemists has failed to explain this ill-colored patina very satisfactorily. It is believed, however, that coal-smoke in large cities may be a cause of its formation, as under such circumstances it contains particles of carbonaceous matter; and, also, that the present almost universal practice of putting considerable zinc into the bronze, to facilitate its casting, is one of the causes of this defect. The dark color of the patina of Japanese bronze has been shown, in a considerable number of cases at least, to be in all probability due to the presence of lead in the alloy. Also patine.
3. n. By extension, the surface-texture or -color which other works of decorative art, as a wooden cabinet or the like, gain through the action of time.
4. n. The surface, produced partly by accretion, partly by discoloration and the effects of acid in the soil, given to marble by long inhumation.
5. n. [capitalized] [NL.] In conch., a genus of gastropods.

Wiktionary

1. n. originally A paten, flat type of dish
2. n. The color or incrustation which age and wear give to (mainly metallic) objects; especially, the green rust which covers works of art such as ancient bronzes, coins and medals.
3. n. A green colour, tinted with grey, like that of bronze patina.
4. n. figuratively A gloss or superficial layer.
5. adj. Of a green colour, tinted with grey, like that of bronze patina.

GNU Webster's 1913

1. n. A dish or plate of metal or earthenware; a patella.
2. n. (Fine Arts) The color or incrustation which age gives to works of art; especially, the green rust which covers ancient bronzes, coins, and medals.

WordNet 3.0

1. n. a fine coating of oxide on the surface of a metal