to increase the hardness of silver for jewelry, silver is often alloyed with copper. the most popular alloy is "sterling silver", which is 92.5% silver and 7.5% copper. this is just enough copper to add toughness without dimishing silver's alluring glow
in the US silver jewelry must be at least 92.5% pure to be deemed "silver," earning the stamp 925 or 0.925
is 99.9% silver or better with no additional alloys. fine silver does not tarnish and does not oxidize when heated with a torch to its melting point of 1640°F