Tarnish

Tarnish is a film that forms on the exposed surface of a metal and is usually a metallic oxide. When silver tarnishes the coating that forms is silver sulfide.
This Circa 1900 Compact Shows a Dark Gray Tarnish in the Recessed Areas. This Can Also be Termed Patina.

This Circa 1900 Compact Shows a Dark Gray Tarnish in the Recessed Areas. This Can Also be Termed Patina.