Tarnish is created by warm air, dust, and sunlight. Heated air contains a small amount of carbon and sulfide (a mixture similar to smog), which chemically react with the surface of silver and cause tarnish to develop. In air, a silver object can tarnish owing to the reaction of silver with hydrogen sulfide naturally present in the air .
Silver and silver-plated objects naturally react with sulfur and sulfur compounds to produce silver sulfide (Ag2S), or tarnish. Contact of silver and silver-plated items with materials which contain sulfur compounds, such as hardboiled eggs, mayonnaise, mustard, and rubber bands will also cause tarnish.
The chemical reaction of silver with hydrogen sulfide to form tarnish is shown below: