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Opal Cracking Study


Anyone, Just yet another opal question.

Why doesn’t anyone put to rest all of the inconsistencies with opal
cracking and crazing by doing a detailed scientific study on it. I
am a research chemist in the fiberglass industry. We use a
semi-quantitative rating method for determining the performance in a
fiberglass panel. You could polish stones from several places that
supposedly have a growing tendency to crack and simply count the
number and size of cracks in the stones after they have been cut and
polished. You could reduce inconsistency by taking an average of
several samples until you have something statiscally valid. You
could then specify 90% confidence ranges using a “Minitab” type
statiscal program. You could try this on many cheaper samples as
well as possibly smaller high quality samples. You could assign
grades on opal giving a simple letter grade for a range of crack
number and size “A” would be 0 cracks, “B” could be 1 -5 cracks of a
certain size. Or you could just change the testing conditions unt il
cracking initiated and rate the opal on a similar scale, but time
and temperature based. You could even couple this study with a
chemical analysis vs. water content, Selenium content, etc.

I know that material from a given area has a broad range of cracking
tendencies, but why not at least attempt to quantify what those
expectations would be? Why don’t we value more the most stable
material, and give it the attention it deserves?

There seems to be alot of guesswork with opal, maybe even more so
than alot of other material. I think these beautiful stones are
worth putting forth the extra effort to understand their durability
or fragility.