It’s Beautiful, But Is It Natural?

Gem treatments and synthesis have made many popular types of stones more readily available to the average consumer. Treatment can turn once unsalable material into attractive, affordable goods. And synthesis can bring clean, beautifully colored stones within the reach of consumers who otherwise couldn’t dream of owning quality emeralds, rubies or other gems.

While some jewelers balk at selling synthetics and others have banned certain types of treated stones from their stores, many retailers and consumers readily accept both. Generally speaking, there’s nothing intrinsically wrong with either type of gemstone – as long as buyers know exactly what they are getting.

Disclosure thus remains the key to selling treated and synthetic stones ethically. (Some sellers, of course, fully intend to deceive; by pretending their goods are natural and/or untreated, they stand to reap a substantial, albeit dishonest profit.) To disclose, however, jewelers first need to know whether stones are treated or synthetic. And they can’t always depend on their suppliers to provide that information.

The following stories are designed to help. First is a roundup of treatments used on colored stones, along with information on the types most often treated and quick tips on detection. Next comes an article on diamond treatments, with some brief remarks on synthetic diamonds. Then there’s a more detailed look at recent synthetic diamond developments, with pointers on how to spot them. Last is a report on the many synthetics now emerging from China.


Some treatments that enhance gem colors are centuries old, others are state-of-the-art. Here’s a primer.

Treating colored stones to enhance their color is nothing new. Emeralds have been oiled for centuries. Colorless topaz has been turned striking blue by heat treatment and irradiation for decades. Now these processes have been joined by epoxy resin filling, diffusion and other state-of-the-art treatments.

In theory there’s nothing wrong with gem treatments, as long as they’re disclosed all along the distribution chain. But in actual practice, it’s not always that simple. Treatments raise questions – including durability, value and detectability – that aren’t always easy to answer. In fact, some treatments are so cleverly disguised that even the most practiced gemologist has trouble distinguishing them. And too often, this kind of treatment is meant only to deceive.

The adage that “if it looks too good to be true, it probably is” holds true for most gems. But treatments still can be perceived as a good thing – an enhancement – as long as everyone who buys the gem understands the treatment and as long as it doesn’t unduly elevate the price.

The following list is designed to help jewelers understand some of today’s most prevalent treatments so they can be on the lookout. The entries are in alphabetical order and are followed by notes on gemstones likely to be treated this way, the prevalence of the treatment and how to identify the treatment.


Bleaching. Many gemstones are often bleached as a prelude to dyeing (see separate entry), among them pearls, coral and jadeite. Bleaching is quite prevalent and difficult to detect; look instead for evidence of dyeing. Common bleaches include acids, peroxides and chlorine.

Coating. Gems can be coated or “backed” with a metallic paint to enhance refraction and reflection. They also may be coated with dye to enhance overall body-color. Gems that are often coated include pearls, turquoise, opal and coral. Any transparent gemstone may be “backed” on the pavilion, though backings are more commonly seen on inexpensive gems or simulants (such as glass). Using a microscope and reflected light, look at the gem’s pavilion for uneven distribution of coating.

Diffusion. In this process, coloring agents are diffused by extreme heat into the upper thin surfaces of gemstones (the gem surface actually liquifies). Iron, titanium and manganese compounds have been used this way to turn colorless corundum into blues and reds. Look for color concentrations at facet junctions under magnification and particularly when the gem is immersed in heavy liquids.

Dyeing. Any porous gem material that accepts color can be dyed. (Ivory, for example, can be dyed with tea to make it look older.) Dyeing is prevalent in turquoise, lapis lazuli, malachite, chalcedony, howlite, amber, jadeite and quench-crackled quartz. Use a microscope to look for color concentrations in surface-reaching cracks or look for unusual spectroscopic patterns. Sometimes you can detect dyeing by gently rubbing the gem with cotton dipped in alcohol or nail polish remover. If the cotton appears even slightly stained, the gem was dyed.

Faceting. Some in the trade consider faceting a treatment because it enhances the look of a gem. The process involves grinding and polishing gem material. The boundaries between what traditionally is faceted and what is cabochoned to a smooth and rounded surface are becoming blurred.

Fracture filling. As with diamonds, fracture filling of colored gems involves filling surface-reaching fractures or laser drill holes with another substance, resulting in a more uniform appearance. Among colored gems treated this way are emerald and corundum. The substances used to fill the holes have a refractive index similar to the gem’s and include various oils, resins, epoxy resins and glass. While some forms of fracture filling have been done for decades, the use of colored fillings is frowned upon. To detect the fillings, use a microscope and look for differences in relief within a gem. With reflected lighting, you may see an area of different reflection.

Heating. Many gems are enhanced with some form of heat treatment. Sustained, moderate heating can change greenish beryl toward blue. Heat will turn zoisite tanzanite from brown to violet blue and colorless topaz to bright blue. It will dissolve silk inclusions in corundum and induce the yellow of citrine in quartz. Regarding detection, it’s safe to assume most tanzanites have been heated to accentuate or change the color. Some other gems acquire stress fractures during heat treatment, and these can be seen under magnification. However, it’s difficult to identify the treatment in gems that don’t exhibit heat-related fractures. Citrine and aquamarine are examples of gems in which heat treatment is difficult to detect.

Irradiating. Gem colors can be enhanced through irradiation via radium salts (no longer used because of residual radioactivity), gamma rays and state-of-the-art linear accelerators. Topaz, amethyst, corundum and beryl, in addition to diamond, are irradiated. There is no standard gemological test for radiation. Residual radioactivity can be detected by a radiation counter, but the U.S. requires gems sold here to have no detectable radioactivity. Indications of an irradiated gem are unnatural colors (untreated topaz is very rarely blue) and unusual, bright colors in diamond.

Laser drilling. Diamonds are sometimes drilled by laser to reach and vaporize dark inclusions. The holes can be filled with a glass-like substance to conceal the presence of the drill hole. Laser drilling is prevalent and best detected through magnification.

Oiling. Oiling of gems – especially emeralds – has been practiced for centuries. To be effectively oiled, gems must be porous. Olive oil, baby oil, palm oil, cedarwood oil and Canada balsam are among the oils used. Under magnification, look for small gas bubbles to indicate oiling.

Quench crackling. Gems that are heated and then plunged in a cold liquid tend to develop a maze of cracks that can be filled with dye to change their appearance. Some very convincing emerald and ruby imitations have been created this way. Under magnification, look for dye concentrations along the cracks.

Reconstitution. Some gems – such as low-grade turquoise or lapis lazuli – are crushed, reconstituted with a combination of dye and bonding agent, and then shaped into the form of a traditional gem or bead. Look for glued particles of gemstones and for dye concentrations under magnification.