In this here newsgroup called rec.crafts.jewelry on Wed, 11 Feb 2009
23:49:58 -0800 we all dun see'd a message a-written by Peter W. Rowe
which dun sed:

On Wed, 11 Feb 2009 23:42:02 -0800, in rec.crafts.jewelry Gantzi
wrote:

In addition, you might want to cover the stone and some of the ring
with cooling paste so it won't be damaged when soldering the
additional piece of silver.

As a general rule, in my experience I've found those paste products to be only
marginally useful with silver (or with gold too, often enough). While they have
uses in cases where you need to protect some smaller detail, they suffer from
the problem that as a paste or gel, they aren't able to flow towards the metal.
What happens is that the metal gets hot, the gel absorbs the heat for a while
till it dries out at the surface of the metal. When that happens (and it
doesn't take long), then a slight air gap develops between the remaining gel and
the metal, so although the metal under the gel is not subject to the direct
flame, it's also not heat sinked by the gel. Silver is the finest thermal
conductor of all the metals, and transmits heat very quickly. If you need to
heat sink a heat sensative stone while sizing anything but the thinnest of
shanks, you need a more effective heat sink. Plain water does the trick nicely.
Immerse the top half of the ring (the stone set part) under water in a container
(I use an old tuna fish can). Now, as the silver transmits heat to the water,
the water can continue to wet the surface. It will sizzle, the water may even
boil, but the stone will get no hotter than boiling water. If the sizzling and
spitting of the water boiling where it contact the silver is a problem, or if
you have trouble holding the ring in position, you can also use coarse sand, or
carborundum soldering grain, in that container and then saturated with water.
The grain or sand hold the ring in position. But with less water, there's a
little less heat sinking capacity. Still, this is often a useful method. The
other big advantage to the use of plain water or wet sand is that not only does
it work better than those paste products, but it's a lot less expensive, and not
so messy to use.

Peter

I agree, yet...
I use powdered asbestos mixed with water. It doesn't pull away from
the silver, in fact it almost bonds with it, and doesn't pull away so
much.
And before everyone jumps all over my sh!t, no, I don't put the
asbestos into a paper sack and huff it.