It’s an old technique. Back in the day…
Ok, back in the stone age…
We used to have to make or repair men’s rings that had an onyx with
a diamond set in a small plate set in the center. They were always
getting loose and we’d have to tighten them or replace the worn
The diamond set plate would have a tube of FINE silver, not
sterling, soldered on the back. The onyx, or whatever, would have a
hole drilled through with two small notches at the end of the hole on
the bottom of the stone. The tube was tightened by using a small
burnisher to flare the tubing underneath the main stone. The two
notches helped keep it from turning. Don’t see too many gents rings
these days with that old technique.
We also used fine silver for under bezels to set uneven and fragile
cameos from behind. The fine silver was so soft that you could shape
it to the uneven back side of a fragile shell cameo and then raise
beads under it to keep it in place.
It was considered ok to used fine sliver on a piece that was gold.
I’m guessing because it was never soldered to the actual piece. But
then in those days folks played pretty fast and loose with metal
karat stamping. Now these days, I’m betting that lasers are called
into service for this.