Verdigris

Etymology

From Old French "vert-de-Grice," literally "green of Greece" (vert de Grèce) — why Greece was invoked is unclear. The pigment was once made by exposing copper to vinegar fumes, and painters used it for centuries despite its tendency to darken.

noun · /VUR-dih-grees/
The blue-green crust that forms on copper, brass, or bronze as it weathers.
What it names
A single word for that oxidized patina — the color of old statues and church roofs, prized as beautiful and dreaded as corrosion.
Example
A century of rain had turned the bronze general and his horse a soft verdigris.
Related idea
Verdigris is a specific green on copper; patina is the broader term for any surface film that age lends to metal, wood, or leather.