However I am curious to hear how well vigor shield works. and on
what type of stones.
I don't trust most of those products for much of anything. ever.
The paste types will look like they're remaining moist, but right at
the metal surface, they'll have dried out as the metal heats, and
their heat sinking ability is then gone, along with the protection
beyond just deflecting contact with the flame itself. The types made
of a fiber matting to hold water, similar to using tissue or cotton
wrapped around the item then soaked with water, works a bit better,
as the liquid water can flow towards the metal, replenishing what's
lost to heating. But it's still often less effective than the
manufacturers represent, if one is working with anything that's
actually heat sensative, because again, the amount of water is
limited, and as you heat, it's too easy for a bit of sizzling to move
the protection away from the metal.
What does work, almost all the time, is to actually immerse the
stone under water. Position a container (something like a tuna fish,
cat food, or similar low round tin can) with water so your third hand
tweezers can hold the item with the whole stone under water, and at
least a small margin of metal next to the stone also under water. Now
the stone cannot get hotter than 212 degrees, and to do that, you'd
have to pump enough heat into the water to actually boil it. The
limits to this is that working with silver, it's such an amazingly
good heat conductor, that the size of the torch flame you'll need to
get solder to flow on the silver may be much bigger than you expect.
I've had silver rings to size, with the top half of the ring under
water, the exposed bottom half of the shank with seam to be soldered,
above, and find the flame I have to use to get the silver solder to
flow is hot enough that I could have melted a half ounce of platinum
with that flame. But with that water cooling it, the solder just
barely flows. Accompanied with the whole can of water sizzling and
boiling, and occasionally spitting and trying to blow the flame out.
Takes a little practice to get use to this. But it works. I can think
of only a few things I'd not trust this to, and those simply are
things that won't even take the heat of boiling water. Amber, and
anything glued with epoxies (including opal doublets and triplets),
especially if the glue is getting old. There may be others too.
But in most cases, stones will be just fine with this, especially
since the heating is gradual as the water heats up.