Missouri Basic Skills Practice Test

Discoloration on a surface caused by a chemical change is called tarnish. When metals are exposed to air or chemicals, a thin layer forms that alters the color or dulls the shine. Tarnish is the general term for this surface change on metals like silver, copper, or brass. Rust is a specific kind of tarnish that happens to iron and steel, turning reddish-brown. A stain is any discoloration caused by substances being absorbed or left on the surface, while patina refers to an aging layer that can develop over time and is often considered desirable. So tarnish best fits the idea of a discoloration on a surface.