Andy, you will have to remove the stones from the ring, and then heat
the ring to the point that the mercury vaporizes. This step will
need to be done with very good ventilation as the fumes are quite
toxic. Also, you want to carry the vapor away from the gold, else
when it cools, it will condense back onto the ring, or any other gold
that it comes in contact with. Solder joints will be a problem also
as they will harden and might crack. I hope it wasn’t an inlay ring,
as you may loose the opal when removing it. If it is an inlay, soak
it in a jar of Attack to break down the epoxy and carefully remove
the opal. Hopefully, the opal will be thick enough to withstand the
pressure of the expanding epoxy and to allow for a final finish when
it is reset. When resetting the opal, you will need to blacken the
bottom of the opal before setting it. Sometimes you can use a black
permanent marker, or black India ink. Set the opal with clear epoxy.
Good luck and keep in mind the ventilation issue.