While I am not an opal specialist, I am a professional cutter. I
handle opal maybe once a week on average (most of my work is custom
faceting and repair to the trade). I'm in my 32nd year of this. I
passed the 1000 piece mark with opal long ago.
Apparently, your experience is somehow different, but I have NEVER
seen an opal damaged by soaking in a solvent, unless that opal has
been filled with an epoxy like Opticon to "heal" the cracks.
I HAVE seen opal break when a 2-part epoxy (not a cyanoacrylate) is
is used to glue an opal to a small dop in preparation for working on
the stone. The shrinkage of the excess epoxy around the dop pulls on
the unsupported opal hard enough to fracture it, but only if the
epoxy is allowed to cure for an extended period. Amber and other
softer materials are prone to the same thing.
For this reason, cyanoacrylate (SuperGlue) is a preferred adhesive
for opal, and acetone will break the bond with no damage to the
opal. Often, freezing will as well, but a quick return from the
freezer to room temperature is scary with larger opal. I don't
really recommend it with someone else's opal.
Would you please give us an example of a solvent damaging an opal,
and why that could take place? This is not about me being right and
you being wrong (I think you are), but about disseminating
that may be misleading to those who are in earlier parts
of their journey here.
Oh, I've been wrong before, but............