I love opal. It was my first stone to cut and still the one I go
back to to get refreshed.
It seems that opals from many locations are quite stable whereas
others can be notoriously unstable. I’ve never had a problem with
spontaneous cracking in Australian opal. Although I’ve heard that
the stone from a small remote field called Lambina, which can produce
extraordinary stones, can be a problem. (for a photo of an amazing
lambina opal go to my web page gemmaker.com and look at the carved
flower I use for logo.)
I have talked to other cutters and jewelry makers who have
experienced problems with unstable opals as well. I believe the
tendency towards crazing is directly connected with the degree of
translucency of the stone. What’s known as crystal opal, the very
clear material, can have a greater problem with stability than would
white opal, for instance.
Like Hans, I’ve had some problems with Mexican opal. I cut a
beautiful highly translucent red cab that when I looked at it 6
months later had cracked. Even some of the while Mexican has cracked
on me. Ethiopian opal is well known for instability to as much as
50% of loss and even the Ethiopian dealers I’ve spoken with will
readily admit this.
I’ve had Honduran opal rough that I bought when it was in water. The
stone was all clear when I bought it and about half of it went
cloudy once it was out of water for a month or so.
Chemically opal, of course, is SIO2 H20. Some people say that the
crazing, if it’s going to be unstable, comes from the evaporation of
water from the stone. I don’t know if this is true, but I’ve
certainly seen opal crack. I do know absolutely that it does not
take well to heat. It’s especially fun and terribly easy to crack
them with overheating. Opal also does not like to be frozen and
might well crack if it is. Again water content would make sense.
By the way, for Helen who enquired about polishing the old stone,
actually older stones, mined roughly more than around 50 years
previous, whether opal or even other species can be particularly
susceptible to crazing when repolished. All the scratching on the
surface should tell us that it’s had some rough treatment and been
seriously abraded. So that might affect the internal structure and
there may be cracks in there that you can’t see.
I’m told that older stones can also be more susceptible to changes
in internal stresses when changes are made on the surface. Don’t
know the truth of that, but I do know that there’s a greater chance
of instability in older stones. Let’s face it stones can change a
lot due to outside changes in environment. Many stones can fade in
long exposure to sunlight, I believe people talked here about
kunzite color-fading. Some topazes can fade as well, especially the
redder colors. Amethyst can fade, too etc.
I’ve experienced the problem of recutting very old stones myself and
spoken with other people who’ve also had the problem and those
weren’t even opal. But older opal can be worse. Furthermore the
approach you were asking about for polish, using a metal polish,
would be particularly dangerous for the stone because you’d be far
more likely to generate heat that way. If you want to take the risk
of polishing it, it really should be done wet with cerium or
aluminum oxide on damp leather. But it would also need to be
prepolished first.
And yes, Fred Ward has gone through a terrible time with that
lawsuit. So that’s a cautionary tale. I guess in the final analysis
the conclusion has to be that stones do lots of different things
that change them. It’s why we love them isn’t it?
Finally, just for general please folks be aware that at
the moment, because of fuel prices and other factors, mining for
Australian opal has significantly shrunk so sooner or later the
supply will be very much affected. This is also true for many other
products of mining, especially in the gem stone categories. Mining
after all is a very energy intensive activity. Metal supplies on the
other hand might increase since old mines are being reopened as the
cost of metal has escalated so much. But in stones, and certainly in
Australian opal, some things may get ever more scarce. I mentioned
the Lambina opal field earlier. I understand that it is such a
remote and forbidding location that they have to bring absolutely
everything in to operate there, all food, water, fuel, etc. So that
field has at least for the time being been all but abandoned.
This having all been said, I hope people incorporate opal into their
jewelry all the time. I can’t get enough of the stuff.
Derek Levin
www.gemmaker.com
