Opal Doublets and Opal Triplets
1. Opal Doublets
Doublets consist of two layers adhered together with glue:
* A black backing which is made of either black industrial glass, black potch (colourless opal), hard plastic, brown ironstone or sometimes vitrolite.
* A thin slice of opal (normally crystal opal or white opal). The thickness of the opal in a doublet can vary, however it is generally thicker than the opal found in a triplet. The edges of the slice of opal are generally rounded off (if there is enough opal) to give the stone a cabochon (domed top).
Doublets can usually be identified by looking at the side of the opal – if the stone has been adhered together you will notice that the line where the coloured opal and the black backing meet is perfectly straight. This is necessary for the two layers to be adhered together. If a doublet is set into jewellery with the sides covered, it is extremely difficult, even for an expert, to tell whether it is a doublet or a solid opal. Since the top of the stone consists of pure opal, it therefore appears exactly like a black opal, and doublets thus have a much more natural appearance than triplets.
2. Opal Triplets
Triplets consist of three layers:
* A black backing as above
* A paper-thin slice of opal in the middle
* A clear glass, quartz, or plastic capping in the shape of a dome. The slice of opal in a triplet is usually extremely thin (paper-thin) so the clear capping serves to give the stone a nice cabochon on top. The clear capping may also magnify the colour of the opal slightly, and also serve to protect the opal.
Because triplet opals have a clear non-opal capping on top, it is easy for an experienced person to identify a triplet immediately by the appearance of the stone. Triplets usually have a ‘glassy’ appearance and the light reflects differently from the top of the stone. You can look at the side of the stone to identify a straight line where all the layers meet, and also look at the back of the stone. If the back of the stone appears to be black plastic then you are not looking at a solid stone. Be aware however that it is also very common for a backing to be made of black potch (exactly the same stone which forms the backing of a natural black opal) or brown ironstone (which is also the natural backing for Queensland boulder opals).
Triplets are normally cheaper than doublets because they contain less real opal. Because the top of the stone can be made from synthetic material, triplets can be a lot more resistant to impact than solid or doublet opal stones. (Opal by its nature is a fragile gemstone).
