Why the comparison with a Mercury Dime??
First of all, the Mercury Dime (or Winged Liberty Head dime) was produced by the United States government from 1916 to 1945. The coin weighs 2.5 grams and is composed of 90% silver and 10% copper. Today's current Roosevelt dime for example is composed of 0% silver.
When I believe a Silver medal or charm has some age to it, using a Mercury Dime from 1943 (almost 70 years old and 90% real silver) in a picture together with the charm or medal can be an invaluable aid in judging age. The comparison shows you what the standard patina and wear really look like on a 70 year old coin and you can judge for yourself whether the charm/medal has more or less wear/patina than the coin and is, therefore, more or less old than the coin.