Sterling silver jewelry has a pronounced tendency to tarnish. The tarnish is always due to the contact with sulphur compounds. The main cause of tarnishing of silver is a trace of hydrogen sulfide gas in the air. This gas is particularly present in smoke from burnt raw fuel, such as coal or oil; in some strong smelling foodstuffs, such as eggs and onions; in some fish or shellfish; and in polluted air.
The tarnish may turn the jewelry black and may also be rubbed off on the skin or clothing. A few people with especially moist skin may find that the sterling silver stains their skin green. This is due to the copper component of the silver alloy. When this occurs you should polish your jewelry frequently and use an absorbent powder on those moist skin areas which come into contact with your jewelry.
Metallic Abrasion
Corrosion