An Opinion on Opals Gerry Manning, Manning International    Share    How to correct long misrepresented "facts" about opal? Even highly respected labs often misstate information regarding opal characteristics and treatments. Here are some observations from my personal experience: • Opal is NOT sensitive to solvents, not unless you're talking about the same acids that are used to etch glass. • Opal is NOT sensitive to or vulnerable to ultrasound. I've used ultrasound with opal for more than 35 years with no adverse effects. • Gem opal is NOT — as some have claimed — up to 12 percent WATER. That, if true, would mean that one could literally shake water from the stone! In fact, there are infinitesimal amounts — or, no water — left in any gem opal. Often, water vapor has remained trapped in the silica lattice. This is where an experienced buyer has a distinct an advantage in providing the market with reliably "cured" opal. I am speaking of Australian, Brazilian and Mexican opal, not some of the less stable varieties that are so porous as to soak up water through their open lattice gaps. Regarding dying, infilling, or impregnating? Sure there are categories where these treatments do apply. oolitic opal, or "Sugar Cured" opal is in-filled (infused) with a sugary solution, then placed in sulfuric acid, the sugar blackened or "carbonized" to imitate the appearance of natural black opal. Some oolitic materials and hydrophanes can be "stabilized" with resin compounds, dyed to resemble black opal. But these are the minority of opal varieties. They are NOT the norm. But how does one correct popular misconceptions regarding gem opal? I've tried over the years, but generally accepted "facts" about opal continue to prevail. (This is not to mention the superstition surrounding opal as a "bad luck" stone. There's a wealth of information to disprove this misnomer, but that's the stuff of another article.) Regarding the "new" Ethiopian opal: Before you think that I have a vested interest in detracting from the "legitimacy" of this new market participant; let me disavow such a notion. I truly hope that this new find will become a reliable staple in the marketplace. I've purchased rough material and will continue to experiment with it, learning of its do's and dont's. Having said this, let me continue with my own personal experience to date. For one thing, Ethiopian opal is still untested by time and exposure to normal wear. I've cut a score of material and observed many characteristics that are, I think, worth discussing with you. This material is more susceptible to heat (in my experience) than Australian or Brazilian opal. It absorbs moisture through capillary action. And, unlike Brazilian hydrophane that turns "crystal" when water is absorbed into the lattice, this Ethiopian material behaves in an opposite manner. A good percentage will lose color, becoming nearly transparent during the cutting process due to water absorption. As a cutter must actually SEE the material he/she is cutting, this phenomenal characteristic can present quite a challenge. Where did the color go? Can one actually define the perimeter? Can one really see the surface anomalies during this "wet" stage? I've had stones actually "explode" off the dopstick when I've removed them to turn top to bottom or bottom to top. With so much moisture absorbed into the lattice, even the heat of the alcohol lamp to remove the green low heat wax can cause the moisture to seek a fast escape route from front, back or sides of the stone on the dop. This can result in a quick and unexpected exit from the stick. (Note: I observed no cracking in spite of this unexpected escape route.) Sadly, after finishing several really lovely stones with unusually fine "crystal" color display, a not insignificant percentage has cracked — or crazed — in the final polishing stage. This is decidedly NOT a characteristic of Australian, Brazilian or Mexican opal. It MAY be something similar to the Idaho materials and the less stable materials from other parts of the world. Finally, with the lattice of Ethiopian material being so accepting of moisture, even a humid environment will allow moisture to penetrate the stone. Washing dishes or doing other daily chores — may expose it to undue challenges, possibly absorbing unwanted low viscosity oils, detergents or other liquid-borne materials into the spaces between the silica lattice. And the notion that merely polishing the material "seals it?" Not so. While some stones seem to hold up very well, others do not — even in the earliest stages of processing. And, because the hydrophane-like nature of the lattice is so welcoming to impregnation, we shall necessarily be on guard for (undisclosed) impregnated stones ("stabilized" with resins or other hardeners). The jury is still out on Ethiopian opal, in my opinion. With almost 50 years as an opal cutter, rough buyer, etc, I tend to take a long view on any newcomer to the market. And in this case, the frenzy over Ethiopian opal is one to take a step back from and be cautiously optimistic, with a dash of circumspection. It is not to say, however, that Ethiopian opal will not prove itself in the long term. We have more data to gather, more stones to cut, more experience to report. Please see the photo examples for some of the cutter's challenges in bringing this opal to life as a finished gemstone. Do you have an interesting story like this one that you would like to submit to ePRISM? Please send your story to adam@agta.org for consideration.