Tarnishing p. pr. & vb. n. : of Tarnish

Example:
How can I stop my prom tiara from Tarnishing?

Taxonomy
free encyclopedia, product, thin coat, search, reactive metals, metal, Unsourced, layer, occurrence, chemicals, Prevention, using steel, rub, dull surface, physical chemistry, Personal tools, Interaction, Toolbox.

Defination from the web:
Tarnish is a product of a chemical reaction between a metal and a nonmetal or compound, especially oxygen and sulfur dioxide. ... Using a thin coat of polish can prevent tarnish from forming over semi-reactive metals. ...