What is an assembled gemstone?
An assembled stone is one that is constructed out of two or more combined materials. Assembled stones are therefore not naturally occurring, although their component parts may be.
Varieties of assembled stones include such creations as:
- doublets and triplets
- intarsias and inlays
- Mabe pearls
There are four common reasons why gemstones like this are assembled:
- To make use of otherwise unsuitable or fragile gem material
- To create an entirely new category of gem product or gemstone
- To provide an inexpensive simulant for an expensive natural gem
- To deceive a buyer into thinking a piece is something more valuable
What are Doublets and Triplets?
Most gem lovers are familiar with doublets and triplets, especially the opal variety. Opal frequently occurs as thin seams of material within a host or matrix rock. Although beautifully colored, some deposits are so thin and fragile as to be useless for jewelry. A doublet or triplet is created by cementing one of these thin layers to a strong backing, such as black onyx, black opal, or something similar.
By combining these materials, two goals can be achieved. First, the strong backing provides the thickness and strength needed for setting. This keeps the finished jewelry piece stable enough to survive actual wear. Second, the dark color behind a somewhat transparent gem like opal makes the usually translucent opal layer look like black or dark grey opal. The color play in the gem material is then displayed in high contrast against this dark background. An opal doublet must still be set and worn with care, as the exposed surface is relatively soft. Well-executed pieces look wonderful, and make affordable, reasonably durable, opal jewelry.
Doublets can also be faceted, as seen below. First, the material is combined into a “rough” state, and then faceted to exhibit a specific optical effect.
Boulder and matrix opals have sometimes been referred to as “natural doublets” although, in my view, this term is an oxymoron. These natural materials are fashioned with their thin opal seams showing on the surface of the natural matrix in which they formed and are not assembled stones.
Opal triplets have a colorless, usually somewhat domed, cap cemented to the doublet. Such caps are made of scratch resistant, tough materials, like rock crystal quartz, synthetic colorless spinel or even synthetic colorless sapphire. Although such products are quite durable, they lack the natural appearance of well made doublets.
Since ammolite has gained in popularity and recognition as a gem material, another type of doublet and triplet have become common. Ammolite is the trade name for the fossilized shell of an extinct ammonite mollusc, (related to today’s Nautilus.) The iridescent layer, that is so highly valued, is quite thin and extremely fragile and lays over a relatively soft matrix. For this reason, virtually all ammolite gems have been, as a minimum, stabilized with resin impregnated into it by a proprietary vacuum process. Even these pieces, called “solid ammolites” are quite fragile and must be given highly protective settings or worn infrequently. By making doublets or triplets from ammolite, it becomes a much more durable material, which can be used in many more jewelry applications.
What are Gemstone Intarsias and Inlays?
When small, flat pieces of gem material are set within a recess in a stone tablet to create a pattern or picture, the result is called an intarsia. Some of these creations are reminiscent of miniature mosaics and are executed with superb precision and skill. If, instead, such pieces are set into channels within metal, the term inlay is used. Intarsias and inlays illustrate both reasons #1 and #2 for making assembled stones, in that they allow use of small or thin pieces which might otherwise be discarded, and they also provide a unique and lovely gem product not found in nature.
What are Mabe Pearls?
Another example of a beautiful man-made creation is the Mabe pearl. These constructions are made from a usually hollow, blister “pearl” harvested from the shell of the Mabe, or butterfly shell mollusc. It is not technically a pearl, since it is formed from the shell of the animal, rather than within its body. The mother-of-pearl blister is cut from the shell, filled with a special cement and a mother-of-pearl bead, then cemented to a mother-of-pearl back. These products come in a variety of sizes and styles, and with their flat backs are easily settable. Compared to cultured pearls of the same size, Mabe pearls are quite inexpensive.
What are Foilbacks? Are they the same as Rhinestones?
Rhinestones are a type of foilback. Since the advent of reasonably priced synthetics, the number and variety of assembled stones produced for reason #3, (to provide an inexpensive simulant for an expensive natural gem,) has diminished. Historically, a foilback, called the “Rhinestone” was an important product of this type. Applying a metal foil or metallic paint backing to a gem, allows it to simulate a much more brilliant material. Rock crystal quartz stones from the Rhine Valley were the first widely used product to receive this treatment, and where the term “Rhinestone” got its name. They were once a common choice as diamond simulants. One of my most cherished mementos from my mother, is her, circa 1940, Rhinestone necklace and earring set. Cubic zirconia is presently the most common diamond simulant on the market, but to my mind lacks the charm of those Rhinestones.
Even though synthetic emerald is widely available, as synthetics go, it is quite expensive. This creates a need for a good looking, less expensive substitute. As it turns out, the inexpensive flame fusion process which is used to make synthetic corundum and synthetic spinel in a great variety of colors, cannot yet create a convincing emerald green color. That job is most often filled, at present, by the synthetic spinel triplet. This creation is sold by the thousands, if not millions, as the imitation May birthstone and in high school and college class rings. This clever, and actually, pretty decent looking assemblage, consists of a colorless synthetic spinel crown cemented to a colorless synthetic spinel pavilion with a layer of green glue.
Fakes and Frauds
Although assembled stones had their hey day as deliberate fakes in earlier times, before cheap synthetics made them all but obsolete, there are still some around today to watch out for — especially if you are purchasing antique jewelry. The most famous example is the garnet and glass doublet. This piece of trickery, if done well, is extremely convincing. I can attest to this personally, as I misidentified one early in my GIA coursework. The pavilion and most of the crown is glass, which can be of almost any color. Red for ruby, blue for sapphire, green for emerald, etc. A thin slice of natural garnet, (usually red,) is fused by heat and pressure, (or sometimes less convincingly, glued,) to the center of the crown. Although it sounds like you should be able to pick these out a mile away, well-done pieces show no red color, face up, and no eye-visible demarkation between the glass and the garnet. The garnet provides durability, high luster and brilliance and even some natural looking inclusions when magnified. Once placed in a setting, they are excellent forgeries and would pass all but the most thorough examinations. A doublet, foilback, or any other assembled stone, can be a fake if it is misrepresented as a natural or solid gem, and when set in a closed bezel may look completely convincing. Unset gems are much more difficult to pass off as something they aren’t. To illustrate, if you look at a solid opal from the side, it is obvious that you are seeing a single, uniform material. Look at an opal doublet from the side, and you’ll see a sharp demarcation in a straight line between the opal and the base. Natural boulder or matrix opals have irregularities and undulations between their opal layer and the matrix which makes them easy to distinguish from either a solid piece or a doublet. Triplets are the easiest of all to identify, even when set, as their colorless crown is obvious from just about any angle. It would take many pages to catalog the multitude of assembled fakes that have been, and are still, occasionally, being used. There certainly has been no shortage of human ingenuity in this department. Deceivers will try just about anything, and sad to say, they still sometimes find willing buyers. Reputable dealers fully disclose the nature of the materials they sell. The current AGTA standards for labeling assembled gems for sale, specify the following gem enhancement code: [Gec: ASMBL].
Caring for Assembled Gemstones
The care and wearing recommendations for assembled stones vary with the materials involved and method of assembly, but certainly ultrasonic and steam cleaning should be avoided. It would also be prudent to have such stones removed when jewelry containing them is repaired or sized. In general, erring on the side of caution is be a good idea.
For the most part, even though they have been used to deceive, assembled stones have brought increased variety, beauty, practicality and affordability to the gem marketplace.
Special thanks for the text and photos to Barbara Smigel at Artistic Colored Stones.