You could try "Heat Shield" but it actually sounds like you are
trying this with too small of a tip on your torch. You need a
greater total number of BTU's but not a hotter flame. Silver is a
great heat "grabber" so you need a greater number of BTU's per time
period (bigger flame) but not a hotter one.
Yes, Ann, you need more heat, and fast. If it takes more than five or
ten seconds, you will be messed up. You can practice by suspending a
similar wire, without the pendant attached. Try to keep very little
of the wire in the water, just enough to submerge the pendant. Heat
Shield instead of water can help with this aspect, because you can
mold it around the work and keep it off of more of the ring. But then
you can’t see what is happening under there! I’d say, more heat,
fast, and practice. If you do not have the torch for this job, don’t
attempt it unless you are prepared to replace the stone if necessary.
Perhaps you can jam some insulating material, like a piece from a
coiled soldering pad, between the wire ring and the top of the hole
in the piece, if there is any room there. That might help.