What is tarnish

Tarnish is a dulling or discoloration that can occur on metals or other materials.

It can also be used as a verb to mean to make something dull or discolored. 

A thin layer of corrosion that forms on the surface of a metal

A dull layer of chemically changed material on the surface of a metal

Examples

Silver tarnishes when it reacts with sulfur-containing gases in the air 

Tarnish can appear as a dull, gray or black film or coating over metal

How to remove tarnish 

Polishing or other techniques can remove tarnish, but this cleaning can be labor intensive

Each time an object tarnishes and is cleaned, some material is lost

How to prevent tarnish 

Store jewelry away from materials that can expedite tarnish development