I believe that glycerin was added to water as well.
Please never use glycerin with opals! It is hygroscopic, which means
it attracts water to itself. This is fine for hand creams where
glycerin pulls water from the air and helps hold it in skin, but
when an opal is immersed in glycerin, it pulls water out of the opal
structure and will make crazing worse or cause it.
I was unable to find the reference to restoration of a damaged
Czechoslovakian opal collection, and it is possible a process was
used involving an epoxy and a vacuum, but such a treatment would
have been done by skilled conservators.
Crazing is cracking. It’s like safety glass breaking but not coming
Filling the cracks with an epoxy material to hold it together may be
possible, but it usually requires repolishing afterwards. Years ago,
Opticon used to be recommended for this purpose, but it yellowed
over time. I haven’t seen any treated this way in many years so this
may no longer be true. Opticon may have been changed since then, and
it may need a vacuum system to get it deep into the cracked areas. I
believe it also needs heat which can worsen your original situation,
so you risk losing your opal altogether. There may be other products
on the market now that work in a similar way.
If it’s a valuable or treasured stone, it might be worth exploring a
professional restoration. The only person I know who can restore
some broken opals is Stan McCall, but I do not know if his process
works on crazing. And since I’ve been out of the loop concerning
opals for some time, again, there may be others now.
Sorry not to be more encouraging,