Jeweler’s Tears, Chapter One

November 15th, 2008 by James L. Sweaney, CGA, FGA. GG

While photographing gems for our website, I was working with a really beautiful Australian opal, a “picture” stone with lots of bright red rolling flash. We shoot with a 100 mm f/2.8 macro lens mated to a Canon Rebel XT in our ImageDome, and can really get great close-ups.  Looking through the camera, I noticed some fine lines in the face of the opal that I hadn’t seen before.  My first thought was “Oh no!”

I have seen these telltale lines in other opals. On closer examination in the microscope, the fine lines proved to be “crazing”.

Crazing is the presence of fine cracks in an opal, usually starting from the surface and penetrating into the stone.  There can be one or many, they can be shallow or deep and it can be a progressive condition where more cracks develop.  The theory is that since opals are basically a hydrated silica gel, having approximately 4 – 6 % water within their makeup; they can dry out and loose structural integrity.

For the most part, opal miners allow their rough material to rest for an extended period, perhaps 6 months, before they cut the stone for this very reason.  The material that is prone to crazing will do so in this drying-out period.  Most reputable opal dealers will exchange a crazed stone – it just goes with the territory.

Certain opal mines within an opal field can be “cracky”, and certain locales produce material that tends to craze.  The “black” opals from Indonesia are notoriously unstable.  On the other hand, I’ve appraised many estate opal pieces that were made in the late 19th and early 20th century that showed no signs of crazing, even after over a century of wear.

I’ve spoken with numerous experts about valuing crazed opals.  It’s a difficult subject because of the unknown factor – will it get worse?  The general consensus is that the value of the opal is reduced by 30 to 100%, depending on the severity and history of the material.

In this case, we have other stones from the same field, same dealer, same age, which show no indication of the problem.  This particular stone is relatively thin for its overall size so that may have something to do with it.   Even though the stone is still quite beautiful and probably won’t get worse, we won’t sell it.  We’ll make it into something for personal use.  It’s just a shame – and that’s why we call it “Jeweler’s Tears.”

Tags: , ,

Other Posts

Comments are closed.

Member - American Gem Society Member - American Gem Trade Association Polygon - The Jewelers Information Highway Harmony Recycled Precious Metals Firemark Diamonds