Opal is a precious gem composed of silica minerals and can be found is a rainbow of colours. Due to their limited mining sources and availability, synthetic or composite opals abound on the gem market. A composite opal, called a doublet or triplet, has a thin layer of opal sandwiched between one or more other materials to give the appearance of a larger stone, while synthetics are not genuine opals at all. If you have an opal or want to purchase one, there are few simple techniques to tell whether one is real or not.
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Look carefully at the overall body of the opal for clarity, consistency and lightness with a loupe. Even a dark-coloured opal will appear bright and light throughout its body, while a doublet or triplet will look dark and dull because of the backing materials used. The colouring should not be blotchy or excessive as this does not occur in nature.
Check the colouring pattern within the body of the stone. Unlike the overall colour tone of a real stone, which is very natural and consistent, the actual pattern of brightness will be spontaneous and random. Look for recurring, snakeskin-like or uniform patterns for signs of synthetic gems.
Turn the opal to its side and inspect the sides carefully. If you see obvious and uniform layering lines, the gem is a doublet or triplet. The lines show where the opal layer is bonded to the backing or capping layers.
Check for striations, which are commonly found on natural stones. These marks are subtle and show the pattern of colouring that is visible inside the stone. If the striations are very straight, evenly spaced or predictable your opal is likely synthetic.
Look through the rounded top of the opal while holding the stone on its side. If the opal is real, you will not be able to see all the way through. A triplet has a glass dome on top, so if your stone has one, your view through the top will be unimpeded.
Turn the opal over to inspect the back. If you feel a plastic material on the back of the stone or the gem is very flat and even, you have a doublet or triplet. A real opal will have a smooth back that is slightly irregular in level instead of being flat. You should also be able to see the light of the stone clearly through the backside.
Tips and warnings
- Always check your opals before your seller sets them in jewellery so you will be able to inspect them from all sides.
- Never buy an opal without having it tested by a gemologist first or without seeing gemological certification from the seller.
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