Silver does not oxidize, or rust, on exposure to air.
In fact, compared with most other elements, it is not particularly reactive.
It does, however, react with sulfur or sulfur compounds, like hydrogen sulfide in the air, forming tarnish, a compound that is chiefly silver sulfide.
Silver sulfide, A025, also called argentous sulfide, is 87.06 percent silver and 12.94 percent sulfur.
It is a grayish-black heavy powder that is completely insoluble in water. It occurs in nature as argentite, an important ore of silver.
Silver is also tarnished by many sulfur-containing organic compounds, including proteins like albumin, or egg white, which is why eggs tarnish silver spoons so readily.
Another threat to the family silverware is posed by common rubber bands, which are vulcanized with sulfur compounds. Low-grade cardboard may also emit tarnishing fumes.
Common silver polishes remove tarnish with elbow grease and a mild abrasive, along with a thin layer of the silver.
Tarnish may be removed chemically by heating the article in a dilute solution of sodium chloride (table salt) and sodium hydrogen carbonate (baking soda).
It can also be removed by placing the item in contact with a more active metal, like aluminum, which reacts with the sulfur and eventually leaves the silver clean.
This may be done with a wad of aluminum foil in a dishpan of soapy water.