I am unfamiliar with the warning you speak of but "
crazing " in an opal refers to small cracks that can develop on
the face of the cab usually due to losing moisture in the
stone, a bath in glycerin once in a while will prevent that .
I beg to differ, please.
While the opal won’t craze while it’ kept in plain water, since
drying won’t continue, this won’t heal anything that’s already
happened, and with the opals prone to craze, won’t replace any
lost hydrate content, nor will it slow it down again when the
opals are removed from the water. A good polish on the stone
will slow it down, but won’t prevent it, and coatings like oil,
or occasional soaks in anything, won’t prevent crazing when the
stones are then removed. Cutting the opal in the form of a
triplet, a thin slice sandwiched between upper clear and lower
(whatever) layers can protect that thin layer from crazing in
many cases, but with solid stones, that’s not an option. The
simple truth of opals is that some of them are going to craze,
and some will not, given normal care. The incidence varies a
great deal from of deposit/location to another. Mexican stones
are far more prone to it than are Australian stones. Idaho
opals too, are very frequently prone to craze. You simply need
to get them from someone who’s kept them around long enough that
the ones prone to crazing will have already started to do so, and
you don’t buy those…
Also, though I know that opal rough is sometimes packaged in
vials of glycerine, I recall being told by one gent who’s
knowledge of both opals and chemistry greatly exceeds my own,
that glycerine actually can draw moisture OUT of a material,
including opal. That would be the exact opposite effect from
what one would wish to occur. I’d suggest not using glycerine as
a bath for your opals. Plain water, if you wish something, is
going to be the best.
Hope this helps.