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. For example,
today's current Roosevelt dime is composed of 0% silver.
So, when I believe a Silver medal or charm has some age to it, I'll use a
Mercury Dime from 1943 (almost 70 years old and 90% real silver) in a
picture together with it. This can be an invaluable aid in judging
age. In fact, the comparison shows you not only the size, but what the
standard patina and wear really look like on a 70 year old coin. You
can then judge for yourself whether the charm/medal has more or less
wear or patina than the coin and is, therefore,
more or less old than the coin. And, if the item isn't silver, then the
dime is just for size comparison.