Rowland- The short answer is… It depends. If the coin is in "mint"
condition or is very rare and has some numismatic value, then you
should understand that as soon as it’s scratched in any way it looses
it’s value. These coins are best left alone or placed in a pendant.
If you want to make a ring I’d recommend that you make a bezel with a
1mm thick top pre made so that the coin is set from below and there
is a 1mm rim on the top to protect it from the worst of every day
wear. I set from the back, not with tabs but with a circle of pure
silver or gold and that is held in place with beads that I raise on
the inside of the bezel from the back. Like nice cameos are set. When
ever I have to handle a fine coin I ALWAYS cover it with nail polish
or tape until the job is completely done, polishing and all.
Have fun and make lots of jewelry.