I use sawdust to put under a stone to cushion it. Someone once
told me they used silicone caulking compound and I tried it.
Although it was strange to work with, it worked, plus it is
waterproof. Of course, if the bezel is properly turned over the
stone, it should be waterproof. That may be the white "stuff
"behind the ring you have. Old timers used to use cut-up pieces
of credit cards, etc. which never made any sense to me.
Iris in Baltimore