Patina is a thin layer that variously 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.
Copper roof on the Minneapolis City Hall, coated with patina
The Dresden Frauenkirche. The church was destroyed during the bombing of Dresden in 1945 and then rebuilt from 1993 to 2005 with new material; the stones with the black patina are the parts that survived the firebombing from the original 18th-century church.
Pre-colonial copper coin formerly used in the Copper Belt (Democratic Republic of the Congo and Zambia). The external layer has been weathered by moisture and rain, leading to the oxidation of copper.
Copper weather vane with verdigris patina
Copper is a chemical element; it has symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.
Copper
A copper disc (99.95% pure) made by continuous casting; etched to reveal crystallites
Unoxidized copper wire (left) and oxidized copper wire (right)
The East Tower of the Royal Observatory, Edinburgh, showing the contrast between the refurbished copper installed in 2010 and the green color of the original 1894 copper
