Just to clarify for everyone on this post - Copper oxidizes very rapidly but Silver does not.
A clean Copper surface prepared in vacuum forms a monolayer of Copper Oxide within minutes of exposure to air. A clean Silver surface prepared in vacuum forms a fraction of a monolayer of Silver Sulfide within minutes of exposure to air but no oxide within that timeframe. The tarnish observed on Silver is primarily Silver Sulfide.
A clean Copper surface prepared in vacuum forms a monolayer of Copper Oxide within minutes of exposure to air. A clean Silver surface prepared in vacuum forms a fraction of a monolayer of Silver Sulfide within minutes of exposure to air but no oxide within that timeframe. The tarnish observed on Silver is primarily Silver Sulfide.