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OPAL : Yea, the people who have the safety deposit box immediately below yourswould be extremely unhappy to find their stock and bond certificates turnedinto an ink-smeared mush.This is a common question regarding opal. It is true that some opal cracks andcrazes and no one can tell you which opal will or wont. Some opal fromparticular fields is prone to this. I have heard various explanations as to whyopal crazes and as all opal contains water (look at the chemical formula) thereis something to be said for storing opal out of the heat and in water. Icant say that this will definitely stop the opal crazing but I can tell you for sure that it will not hurt it! I have been told that if opal contains a certain amount of water (in th echemical formula) then it will craze no matter what you do. Thus it wouldappearthat you are not in control of whether or not the opal will craze. I have beencutting and collecting opal for a number of years and have not had too many problems.
OPAL : Actually it's a little more correct to refer to the water as being part ofthe physical structure, rather than the chemical formula, as no realchemical bonding is present. Opal is a hydrated silica gel, with varyingamounts of water and silica filling the space between the gel spheres. That water, not being chemically bound, can literally dry out, if it is astructure coarse enough that surface tension/capilary attraction, etc arenot sufficient to keep it there. It's not so much the chemistry, but thecoarseness of this non crystaline structure, how tightly the spheres arepacked and intergrown, and the like. The looser structures, having more water filling the spaces (think of asort of highly ordered, microscopic sponge, soaked in water) are moreprone to this drying. As the opal dries, loss of the water causesshrinkage. Since it dries from the outside in, the surface is shrinkingaround an inner mass that is not. That's why it cracks. If the structurehas less water and is denser, then not only is less water available to dryout, but it dries slower, and more uniformly through the stone. And whatdrying takes place causes less shrinkage and less stresses, so less or nocracking.
OPAL : Storing opals in water, or a humid environment, forstalls any possibledrying, and prevents cracking from occuring while the stone is in water. But it cannot repair cracks once formed, and for most opal, does notreverse the process of dehydration that has already occurred (if any) (There are a couple notable exceptions to that statement. Hydrophaneopal, for example, can absorb water again, and changes it's appearance asa result of drying or rehydrating)And storing opal in water is no prevention for later cracking occuringwhen the stone is removed. It only forstalls the process if it is goingto occur.Most reputable opal dealers and cutters will keep their cut opals around,loose and dry, long enough to allow most of those stones which are goingto dry and craze, to do so while still in their inventory. If an opal hassurvived for a time without problems, the chances are better that it willcontinue to do so. And many dealers will offer some warranty againsttheir stones crazing.
OPAL : Usually, cracking/crazing problems are typical of certain locations. Idaho opal, for example, is notorious for it, which is why most of it iscut as triplets or doublets. The very thin seams of opal used this wayare either protected from drying in the triplets, or are so thin in thedoublets that uneven shrinkage doesn't occur. Mexican stones as well areoften a problem, while Australian opals from most fields are typicallypretty stableThere is some, as yet unproven, thought that the process of polishingtends to flow and seal the surface of the opal, preventing or slowing thedehydration or crazing process. I don't know if this is true. But propercare of opals includes treating them gently, keeping them away from suddengreat changes or extremes in temperature (Don't freeze them or allowthem to sit in the hot sun, for example, and don't drop cold opals in aboiling hot cleaning solution either). With care, most of them can havenice long crack free lives.
OPAL : Has anyone tried lab opal made with resin instead of the quartz? I knowGilson uses the quartz but in the USA there is some lab opal made withresin. I was just wondering how the difference would be in cutting,polishing, and looks in jewelry.\On Mon, 24 Jul 2000 21:26:28 -1000, in rec.crafts.jewelry Charles Flanagan wrote:Lets just clarify something here. Gilson, and similar products, are a truesynthetic opal, which by the definition of "synthetic", means it must duplicateexactly the chemical and physical structure and formulas for the naturalcounterpart. The only differences between a synthetic and the natural, then arethose various "artifacts" of the growth environment and processes, such asinclusions, flaws, trace elements which are not part of the essential definitionof a mineral, and the like.
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