Gemstone Doublets, Triplets, and Other Assembled Stones


gemstone doublets - faceted doublet
“New World P,” faceted doublet. Designed and faceted by Mark Oros. Photographed by Sarah Oros. © Hashnu Stones & Gems. Used with permission.

What is an Assembled Gemstone?

An assembled gemstone is one constructed from two or more combined materials. While these component parts may occur naturally, assembled stones themselves don’t occur naturally. For example, a gem cutter may cement a thin layer of natural opal onto a layer of natural onyx. The components are natural, of course, but the combined piece isn’t. (Read more about natural, synthetic, and imitation gems here).

Varieties of assembled stones include creations such as gemstone doublets and triplets, intarsias and inlays, mabe pearls, and foil backs. We’ll discuss these all below.

Why do people create assembled gemstones? Some common reasons are:

  • Making use of otherwise unsuitable or fragile gem material.
  • Creating an entirely new category of gem product.
  • Providing an inexpensive simulant for an expensive natural gem.
  • (Unfortunately) deceiving a buyer into thinking a piece is something more valuable.

Gemstone Doublets and Triplets

Most gem enthusiasts will recognize doublets and triplets, especially the opal varieties. Opal frequently occurs as thin seams of material within a host or matrix rock. Although beautifully colored, some deposits are too thin and fragile to be used for jewelry. However, cementing one of these thin layers onto a strong backing, such as black onyx, black opal, or something similar, creates a doublet or triplet. A doublet is a thin layer of opal glued to a black base. A triplet adds a transparent cap layer.

gemstone doublets - opal pendant
“Opal Doublet” by Opalcutters23. Licensed under CC By-SA 3.0.

Combining these materials achieves two goals. 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. As a result, the play of color in the gem material appears in high contrast against this dark background.

The exposed surface of an opal doublet is still relatively soft. Therefore, jewelry wearers must treat these pieces carefully. All opal jewelry requires special care and cleaning methods. Nevertheless, well-executed and cared for doublets look wonderful and make affordable, reasonably durable jewelry pieces.

gemstone doublets - unset and set opals
Left, opal doublet ready for setting. Right, opal doublet jewelry. Photos courtesy of Barbara Smigel, Artistic Colored Stones.

Faceted Gemstone Doublets

Gemstone doublets can also be faceted, as you can see below. First, the gem cutter combines the material into a “rough” state. Then, the material is faceted to exhibit a specific optical effect.

gemstone doublets - Orion's Belt
“Orion’s Belt C,” faceted doublet. Designed and faceted by Mark Oros. Photographed by Sara Oros. © Hashnu Stones & Gems. Used with permission.

Are Boulder Opals “Natural Gemstone Doublets”?

Boulder opals form on brown ironstone matrix and can show dazzling fire. Matrix opals consist of specks of precious opals that form in a rock matrix, usually sandstone. You may find both boulder and matrix opals sometimes referred to as “natural doublets” by some vendors. In my opinion, this usage is an oxymoron. Gem cutters fashion these natural materials to show their thin opal seams on the surface of their natural matrix. They aren’t assembled stones.

gemstone doublets - natural boulder opal
“Boulder Opal,” Carisbrooke Station near Winton, Queensland, Australia, by JJ Harison. Licensed under CC By-SA 3.0.

Opal Triplets

Opal triplets have a colorless, usually somewhat domed, cap cemented to the doublet. Typically, such caps consist of tough, scratch resistant materials, like rock crystal quartz, synthetic colorless spinel, or even synthetic colorless sapphire. Although quite durable, triplets usually lack the natural appearance of well-made doublets.

gemstone doublets - triplet layers
“Opal Triplet with the Three Layers Visible,” a clear quartz cap, a thin opal layer, and a dark background, by LZ6387. Licensed under CC By-SA 4.0.

Assembled Ammolite Gemstones

As the popularity of ammolite jewelry has grown, doublets and triplets made from this material have entered the market. This term refers to gem-quality, iridescent layers of the fossilized shells of ammonites, extinct mollusks related to today’s nautilus.

gemstone doublets - ammolites
“Ammolite” by Sandra Cohen-Rose and Colin Rose. Licensed under CC By 2.0.

While highly valued, these thin and extremely fragile layers occur on a relatively soft matrix. Due to this, virtually all ammolites receive, at a minimum, resin impregnation treatment for stability through a proprietary vacuum process. Even these pieces, called “solid ammolites,” remain fragile and must receive highly protective jewelry settings or infrequent wear. Still, doublets and triplets make ammolite more durable better suited for many jewelry applications.

gemstone doublets - ammolite jewelry
Left, ammolite doublet jewelry. Right, ammolite triplet jewelry. Photos courtesy of Barbara Smigel, Artistic Colored Stones.

Gemstone Intarsias and Inlays

Intarsias are pictures or patterns created by small, flat pieces of gem material set within recesses in stone tablets. Some of these creations may resemble miniature mosaics when executed with precision and skill.

If the pieces are instead set into channels within metal, the results are called inlays.

gemstone doublets - coprolite inlays
Fossilized excrement, coprolites consist mostly of calcium carbonates and silicates. They can make very unusual gem materials. “Coprolite Inlay Cufflinks,” by Jessa and Mark Anderson. Licensed under CC By 2.0.

Intarsias and inlays both illustrate why people make assembled stones. They utilize small or thin pieces of gem material that may otherwise see no use. They also provide gem enthusiasts with unique, lovely products not found in nature.

gemstone doublets - intarsia and inlay
Left, gemstone intarsia. Right, gemstone inlay. Photos courtesy of Barbara Smigel, Artistic Colored Stones.

Mabe Pearls

Although not technically a pearl, the mabe pearl serves as another example of a beautiful assembled stone. Pearl farmers make mabe pearls from usually hollow blister “pearls” harvested from the shells of various mollusks. Abalone mollusks yield particularly prized pieces. Since it forms from the shell of the animal rather than within the body, it’s not considered a true pearl. 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. Their flat backs make them easily settable. Compared to cultured true pearls of the same size, mabe pearls make inexpensive alternatives.

gemstone doublets - mabe pearls
“Mabe Pearl Earrings” by Christina Rutz. Licensed under CC By 2.0.

Foil Backs and Rhinestones

Since the advent of reasonably priced synthetics, producing assembled stones as inexpensive simulants of natural gems has diminished. However, historically, the rhinestone famously fulfilled this need. This was a type of foil back. By applying a metal foil or metallic paint backing to a gem, jewelers could simulate greater brilliance. The first widely used “foil backs,” gems that received this treatment, were rock crystal quartz stones from the Rhine Valley. (Hence, the name “rhinestone”). Due to their enhanced brilliance, they were once common diamond simulants.

One of my most cherished mementos from my mother is her circa-1940 rhinestone necklace and earring set. Although cubic zirconia currently reigns as the most common diamond simulant for jewelry, to my mind it lacks rhinestone’s charm.

gemstone doublets - rhinestones
“Rhinestone Spiral” by Sue Corbisez. Licensed under CC By 2.0.

Assembled Stones for Birthstones and Class Rings

Although widely available, synthetic emerald remains expensive, as synthetics go. This creates a need for a good looking but less expensive substitute, especially for all those people with May birthdays. As it turns out, the inexpensive flame fusion process used to synthesize corundum and spinel can produce many colors. However, it can’t yet create a convincing emerald green color.

At present, that task falls most often to the synthetic spinel triplet. Jewelers sell these by the thousands, if not millions, as imitation emeralds for May birthstones as well as 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

For the most part, assembled stones have brought increased variety, beauty, practicality, and affordability to the gem marketplace. However, buyer beware. Although the heyday of assembled stones as deliberate gemstone fakes has passed, you might still encounter some pretenders. To be clear, gemstone doublets, foil backs, or any other assembled stones aren’t inherently deceptive. However, if a vendor offers these as natural or whole, “solid” gems, that would constitute misrepresentation.

The Garnet-and-Glass Doublet Trick

If you’re purchasing antique jewelry, watch out for the infamous garnet-and-glass gemstone doublets. If done well, this piece of trickery 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 consists of glass. This glass can have almost any color: red for ruby, blue for sapphires, green for emerald, etc. A thin slice of natural garnet, usually red, is fused by heat, pressure, or (less convincingly) glue to the crown’s center. Sounds like you could pick these out a mile away, right? Actually, well-done pieces show no red color, face up, and no eye-visible demarkation between the glass and the garnet. Furthermore, the garnet provides durability, high luster, brilliance, and even some natural-looking inclusions when magnified. Once placed in a setting, these excellent forgeries could pass all but the most thorough examinations.

Set and Unset Assembled Gems

When set in closed bezel settings, gemstone doublets make very convincing fakes. On the other hand, trying to pass off unset gems as something they aren’t proves more difficult. For example, if you look at a solid opal from the side, you can easily see it’s a uniform material. Now, look at an unset opal doublet from the side. 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. These characteristics make them easy to distinguish from either a solid piece or a doublet.

Of all assembled gems, triplets are the easiest to identify. Even when set, their colorless crowns appear obvious from just about any angle.

AGTA Assembled Stone Code

Cataloging the multitude of assembled stone fakes you might encounter would take many pages. This sad chapter has seen no shortage of human ingenuity. Deceivers will try just about anything and, unfortunately, still continue to find willing buyers. However, reputable dealers will fully disclose the nature of the materials they sell.

The American Gem Trade Association (AGTA) has proposed standards for labeling gemstone treatments. For assembled stones, it specifies the following gem enhancement code: [Gec: ASBL].

Caring for Assembled Gemstones

The care and wearing recommendations for assembled stones will vary with the materials involved and method of assembly. However, as a general rule, avoid ultrasonic and steam cleaning. Also, have these stones removed from their jewelry settings, if possible, before repairs or resizing. Err on the side of caution. For more recommendations, consult our gemstone jewelry cleaning guide.

gemstone doublets - New World
“New World C,” faceted doublet. Designed and faceted by Mark Oros. Photographed by Sara Oros. © Hashnu Stones & Gems. Used with permission.

About the author
Barbara Smigel, PhD. GG
Barbara Smigel is a GIA certified gemologist, facetor, jewelry designer, gem dealer, gemology instructor and creator of the well-regarded educational websites acstones.com and bwsmigel.info.
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