[Jewelry making - Article 00152] - Re: [Orchid] Incorporating opal

[Hans Durstling]

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Kevin,

    I too have been cutting opal for quite a few years, and yes, I have
    had them spontaneously craze. One memorable one was a Mexican fire
    opal that I had faceted to a roughly 2 carat emerald cut. I had put
    it in a gem case immediately after finishing it, where it stayed,
    untouched, for I don't know how many months, probably more than six
    and less than a year.

    Next time I did look at it there was a pronounced sickle shaped
    crack in the pavilion that had not been there before, and, even more
    singular, in the cusp of the sickle was a milky white cloud. One
    could argue that the crack might have already been there, too minute
    to see, but certainly that white cloud was NOT in the stone to begin
    with. 

    I have also seen Ethiopian opal spontaneously crack. At Tucson last
    year I met up with two Ethiopian dealers & did quite a bit of cutting
    & instruction for them, say about forty or fifty stones. Of these,
    several crystal opals (the glass-transparent type) developed
    spontaneous cracks within a day or two after finishing. Again, one
    could argue that the cracks had been there already, too small to see. 


    Two personal observations may be of interest for anyone working
    Ethiopian opal. One, of the stones I cut, the transparent ones were
    by far more susceptible to spontaneous cracking; the dark base,
    chocolate colored ones stayed sound. Second, hot wax dopping the
    transparent ones infallibly cracked them; the chocolate base stones
    remained unaffected. 

    These are special cases; Australian opal (generally) is much more
    reliable. But some from the Mintabie field contains minute interior
    cracks which may not be immediately apparent and may grow. Further,
    as far as I know there have been no significant new opal discoveries
    in Australia in about the past decade (Christine Roussel, correct me
    if I am wrong???) - so it seems quite likely we'll be seeing more and
    more of the Ethiopian material in the next few years. 

Cheers,
Hans Durstling
Moncton, Canada
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