is a layer of
corrosion that develops over copper,
brass, silver, aluminum as well as a degree of semi-reactive metals as
they undergo
oxidation.
It is analogous to rust, but with a slower rate of occurrence. It is mainly
caused by chemicals in the air such as
sulfur. It typically appears as a gray or black film over ferrous
metals. Other metals and elements result in various colorations.
Also see ductile,
luster, malleable,
patina.
Application
Notes:
