Tarnish

Webster's Dictionary of the English Language

·noun The quality or state of being tarnished; stain; soil; blemish.

II. Tarnish ·vi To lose luster; to become dull; as, gilding will tarnish in a foul air.

III. Tarnish ·noun A thin film on the surface of a metal, usually due to a slight alteration of the original color; as, the steel tarnish in columbite.

IV. Tarnish ·adj To soil, or change the appearance of, especially by an alternation induced by the air, or by dust, or the like; to diminish, dull, or destroy the luster of; to Sully; as, to tarnish a metal; to tarnish gilding; to tarnish the purity of color.