Silver soldering and acids.... and stones

Hi Sabine

 And what about stones? If you've done a repair on a piece of
jewelry with the stones in place, is it possible to pickle the
piece in alum without damaging the stones? 

I use alum for everything inc gold… and diamonds . I havent
repaired anything yet with other stones! So far all the earring
studs etc have stayed on!! Perhaps Hanuman might know? Felicity
from very wet west Oz