The tarnish on sterling silver jewelry is the result of oxidative reactions with sulfur, such as Hydrogen Sulfide, in the air and environment (the nickel or copper alloy in most sterling silver also undergoes its own oxidative reactions). The corrosion of silver combined with sulfur creates the darkening referred to as tarnish. Therefore, you must insure your Tiffany & Co jewelry is clean and dry before storage; since any moisture, dirt, oils or other residual chemicals will accelerate the tarnishing.