Composite gemstones are exactly what the term implies; stones composed of more than one part, Composites come in two basic types. Doublets are composite stones consisting of two parts, sometimes held together by a colored bonding agent. Triplets are composite stones consisting of three parts, usually glued together to a colored middle part.
Doublets are especially important to know about because, while widely used in antique jewelry before the development of synthetics, today they are making a comeback and reappearing throughout the jewelry market.
In antique pieces, the most commonly encountered doublet, often referred to as false doublet, consisted of a red garnet top fused to an appropriately colored glass bottom. With the right combination, any colored gem could be simulated by this method. Garnets were used for the top portion of these false doublets because they possessed nice luster and excellent durability and were readily available in great quantity, which made them very inexpensive.
Another form of the doublet is made from two parts of a colorless material, fused together with an appropriately colored binding agent. An "emerald" (sometimes sold as "soude" emerald) can be made, for example, using a colorless synthetic spinel top and bottom, held together in the middle (at the girdle) by green glue. Red glue or blue glue could be used to simulate ruby or sapphire.
True doublets are created by using two genuine stone parts, fusing them together with an appropriately colored glue to create a "larger" gem of better color than the original components. For example, we sometimes see emerald doublets composed of two parts of genuine pale green emerald, fused with deep green glue to create a large, deep green "gem" emerald.
A clever version of a true doublet which we sometimes still encounter is a "sapphire" doublet composed of two pieces of genuine sapphire, but pale yellow sapphire fused together with blue glue. This creates an especially convincing "fine blue sapphire." The same techniques are used to make ruby doublets, although they don't look as convincing. And the same basic procedures can produce emerald doublets, using beryl instead sapphire.
Opal doublets also occur, usually consisting of a thin top layer of genuine opal cemented to a base that can be either a poorer grade of opal or some other substance altogether. The most commonly encountered opal doublets are those made to look like the precious black opal. This doublet is usually composed of a translucent or transparent top that is cemented by black cement to a bottom portion of cheaper opal or other material that acts as a support. Please not that the tops of these "black opal" doublets are usually not genuine black opal, tough they certainly look like it.
Opal doublets are also made by cementing a thin piece of fine opal to a larger piece of less fine opal to create a larger overall appearance. The doublets can be identified by observing the join of the two pieces at the girdle; you can see the dark line of the cement between the two pieces.
Many of the doublets now appearing in jewelry sold by reputable firms were originally slipped in with genuine stones shipped to buyers around the world. Since doublets are difficult to spot and will even pass four gemological tests providing positive identification, it is easy to pass one on to a customer unknowingly, especially when set in sleek, modern "bezel" settings.
Jewelry manufacturers offer true doublets as affordable alternative to natural gems.
On the other hand, we are also seeing the legitimate marketing by manufacturers of doublets as an affordable and desirable alternative to natural gemstones. One company is producing an emerald doublet that, like those described earlier, consists of two parts of colorless beryl (the mineral called emerald when green, aquamarine when blue) fused together with green glue to produce a composite being sold as the "Lannyte Emerald Doublet."
There is nothing wrong with buying a doublet as long as you know what you are buying, and pay a fair price. Just be careful not to buy a doublet unknowingly. Be sure to verify all facts.
Triplets are frequently encountered in opal market and have substantially replaced the doublet there. The triplet is exactly like the opal doublet except that it has a cabochon shaped colorless quartz cap (the third part) that covers the entire doublet, giving the delicate doublet greater protection from breakage and providing greater luminescence (brightness) to the stone.
With careful examination a competent jeweler or gemologist should be able to easily differentiate a doublet or triplet from a natural. We should note, however, that detection of an opal doublet may be very difficult if it is set in a mounting with a rim (bezel set) covering the seam where the two pieces are cemented together. It might be necessary to remove the stone from its setting for positive identification. Because of opal's fragile nature, removal must be performed only by a very competent bench jeweler (a jeweler who actually makes or repairs jewelry), and he may agree to do so only at your risk, not wanting to assume responsibility for any breakage. In the case of a black opal worth several thousand dollars, it is well worth the additional cost and inconvenience to be sure it is not a doublet worth only a few hundred dollars. Always be apprehensive when buying a "flat topped opal" that is bezel set.
Another form of misrepresentation occurs when colored stone are called by names that lead the buyer to believe they are something they are not. This practice is frequently encountered, especially outside the United States. When the stone is described with a qualifier as in "Rio Topaz" or "Zambian emerald," be sure to ask whether the stone is a genuine, natural gemstone. Ask why there is a qualifier.
Let's examine two examples: "Japanese amethyst" and "Ceylon Sapphire." In the case of Japanese amethyst, the stone is not genuine, but synthetics and the name, therefore, is clearly misleading. However, in the case of the Ceylon sapphire, "Ceylon" refers to the location from which that gem was mined, and most Ceylon sapphires are always a particular tone of blue (a lighter shade, and very lively). Furthermore, because of their particular color, Ceylon sapphires sell for more per carat than certain other varieties, such as Australian or Thai. Therefore, in this case, "Ceylon" is very important to the gemstone's complete description.
Let's look at one more example, Ceylon-colored sapphire. In this case, the qualifier is the word "colored." In most cases the presence of this word implies some type of color alteration or treatment. A Ceylon-colored sapphire is not a Ceylon sapphire but a sapphire that has been treated to obtain the Ceylon color.
There is nothing wrong with selling "Japanese amethyst" or "Ceylon-colored sapphire," or other similarly named stones, as long as they are properly represented and priced. Then the decision becomes yours; either you like it or you don't; it meets your emotional need for an amethyst or Ceylon sapphire or it doesn't; and the price is right or it isn't.
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