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Good Stuff to Know when Shopping for Gemstone Jewelry: A Friendly Primer on Gemstone Treatments, Synthetics, and Imitations.

Above image from Article by Robert Weldon titled "An Introduction to Gem Treatments" published on the Gemological Institute of America (GIA) official website.

In the above image, the sparkly bright blue faceted gemstones to the far right started out looking like the unattractive pale rough to the far left. 

Gem treatments make many stones suitable for jewelry use that otherwise would be practically worthless. Many colored gems are treated to enhance their appearance, such as to improve color and/or clarity. Some gems are also treated to enhance durability.

The worldwide jewelry markets demand the ready availability of popular gemstones, and as a result, many gemstone treatments have become routine. For example, it is estimated that up to 95% of all corundum (ruby and sapphire), emerald, and tanzanite have been treated.

While acceptable treatments can be very important to bringing many popular gemstones to market, it is just as important that consumers have knowledge about treatments, not just for the purpose of knowing what they are buying, but also to understand treatment stability as it relates to jewelry wear, repair, and care.

Information of gemstone treatment should be conveyed at time of sale. However, not all retailers have sufficient knowledge and some simply do not disclose.

Therefore, it is my hope that this Newsletter might offer a little guidance when shopping for gemstone jewelry. For those truly interested in this topic, a more in-depth and very readable online article by guru gemologist Robert Weldon is at: http://www.gia.edu/gem-treatment.

A "natural" gem has been altered only by cutting and polishing.

A "natural" gemstone has not been altered by human intervention other than by fashioning, which involves cutting and polishing the rough into an attractive finished gem for use in jewelry.

Typically, natural gems cost more than untreated gems because they are more rare, and hence, more valuable.

While natural gems can be found at all market levels, very rare natural gems are often sold to collectors at exclusive high-end auctions. Conversely, while treated gems may be found in all market levels, they are especially important in the commercial jewelry markets to meet the demand of mass production.

A "treated" gem is different than "synthetic" or "imitation."

Basically, a "treated" gem refers to a genuine gemstone that was altered beyond cutting and polishing to improve appearance and make it more marketable.  Some common treatments are heating, irradiation, fracture filling, bleaching, dyeing, impregnation, and surface modification.

A "synthetic" gem is the lab-created version of a natural gemstone. Synthetics have essentially the same chemical composition, crystal structure, and physical and optical properties as their natural counterparts. For example, a synthetic diamond has the same crystal structure, hardness, toughness, and optical properties (refraction, reflection, brilliance, and fire, etc.), as a natural diamond. As a result, synthetic diamonds look like natural diamonds. However, natural diamonds are much rarer than synthetic diamonds, and therefore, are more expensive.

Synthetics cannot be detected by the unaided eye. Identification can sometimes be made using standard gemological equipment, but identification of some modern diamond and quartz synthetics requires advanced testing by a gem lab like GIA. Other synthetic gems like spinel and corundum (ruby and sapphire) can often be detected by standard gemologic equipment.

"Imitations," referred to as "simulants" in the trade, are merely look alikes for the natural gem. Imitations can be other natural gems or manmade stones (synthetics, plastic, glass) that only look like the gems they are trying to replace - their chemical compositions and properties are usually very different from those of the materials they imitate.

For example, manmade red glass can imitate natural ruby. Also, natural or synthetic red spinel can imitate natural ruby, and in fact, red spinel was mistaken for ruby until it was scientifically identified as a separate gem species in the 1800s. Therefore, red spinel is not only an imitation for ruby, but also a gem in its own right. Synthetic ruby is not technically a ruby imitation because both synthetic ruby and natural ruby share essentially the same chemical composition and properties.

If a gemstone is rare and in demand, then it is often imitated, and if possible, synthesized. That is because there is not enough of the natural gem to meet demand. While a rare natural gem is often not within the price range of most consumers, synthetics and imitations are much less expensive and some can be very affordable. Simulants such as mandmade glass, plastic, and cubic zirconia (CZ) are within reach of virtually all consumers. 

Heat Treatment

Gemstones have been heated to improve appearance since ancient times. Heat treatment is performed by a variety of methods, from very primitive to very sophisticated.

The list of heat treated stones is long. The most commonly heat-treated gems include amber, amethyst, aquamarine, citrine, ruby, sapphire, tanzanite, topaz, tourmaline, and zircon.

Most yellow citrine is not natural color, but created by heating purple amethyst. Pale sapphires are heated to a deeper brighter blue. 

Heat treatment is considered durable and permanent under normal wear and handling conditions. 

Lattice Diffusion

Some gems, especially corundum (ruby and sapphire) are subjected to a treatment known as lattice diffusion where they are exposed to very high temperatures in the presence of chemicals and color-causing agents that results only in a surface-related layer of color. Coloration can look patchy when partially removed by repolishing.

Lattice diffusion with beryllium can result in a deeper layer of color, sometimes throughout the entire stone, which increases the permanency of treatment.

Diffusion treated corundum is widespread in the trade. Without lattice diffusion treatment, most of these gems would never make it into the jewelry marketplace - they would not have been attractive enough or durable enough for use in jewelry.

Lattice diffused gems are extremely affordable in comparison to natural gems.

Lattice diffusion can sometimes be detected with a microscope based on altered inclusions within the stone, but confirmation often requires advanced lab procedures. 

High Pressure High Temperature - HPHT

High Pressure High Temperature (HPHT) Treatment is typically done with diamonds ro remove or change color.  HPHT can change the color of some brownish diamonds to colorless or near colorless. HPHT also can create some fancy diamond colors like green, blue, pink, yellow, and orangy yellow.

HPHT treatment is permanent and durable. While there may be signs of HPHT treatment that can be suggested by using standard gemological equipment, confirmed identification of HPHT requires the use of advanced spectroscopy equipment by experienced professionals in a gemological laboratory.

Fracture Filling

Diamond, emerald, and ruby often have surface-reaching fractures or cavities that inhibit their marketability for jewelry use. Filling these fractures and cavities with colorless glass, resin, wax, oil, or polymer improves the apparent clarity of these gems and can make them more stable. In extreme cases, especially as concerns lead glass filled rubies, the filler can add weight. Fillers also can include a dye that enhances gemstone color as well as clarity.

Filled diamonds, corundum, and emeralds are common. Detection can often be made with magnification.

Treatment is not permanent, and durability depends on the type of filler. Care should be exercised during repair, cleaning and wear. Avoid exposure to heat, chemicals, and temperature or pressure changes. 

Laser Drilling

Diamonds are sometimes laser drilled to improve apparent clarity by dissolving or reducing the appearance of dark internal inclusions.

Some diamond manufacturers use lasers to drill tiny tunnels in diamonds to access dark inclusions, which can then be vaporized by the laser, etched out with acid, bleached, or filled with the same material used to fill diamond fractures. 

Laser drill holes can be detected using magnification.


Gems are often exposed to artificial radiation to change color. The most commonly irradiated gems are diamond, pearl, quartz, sapphire, and topaz. Sometimes irradiation is followed by careful heating to further modify gemstone color, as is typically done to produce blue topaz.

Irradiated diamond, topaz and quartz are relatively stable, though care should be used during repairs and cleaning to protect against high temperatures, which could cause color changes.

However, the color of some other irradiated gems fades. Irradiated yellow and orange colors in sapphire fade to colorless after exposure to heat and light.

Heat and light can even cause the color of some naturally colored gems like amethyst, rubellite and kunzite to fade, so it is important not to wear these gems for too long in sunlight and do not store them in a glass case or near a heat source.

Bleaching and Colorless Impregnation

Jadeite is often bleached with acid to remove brown staining and then polymer impregnated to reduce porosity and improve durability. Bleaching is typically impossible to detect, and detection of impregnation typically requires sophisticated diagnostic equipment available only in a gemological laboratory.

Turquoise is often impregnated with wax or plastic, and sometimes dye is added to the impregnation material.

Opal is sometimes impregnated with plastic to improve luster and durability.

Tiger's-eye quartz, coral, and chalcedony are sometimes bleached to lighten color.

All types of light-colored cultured pearls are routinely bleached using chemicals such as hydrogen peroxide together with bright lights to further lighten and produce a more uniform color. 

Bleached gems tend to be more brittle and porous, which makes them more susceptible to asorbing oils and other possibly damaging liquids. Follow appropriate care instructions provided at time of purchase, or visit manufacturer's website. Jewelry care instructions for pearls and other gems are also provided at http://www.arpaiajewelry.com/pages/jewelry-care.


Dyeing has also been used to improve the color of gems since ancient times. Today, colored dyes are often introduced into porous or fractured gems to change their color. Sometimes non-porous gems are heated to more readily accept dyes.

The most commonly dyed gems are chaledony, coral, cultured and natural pearls, emerald, howlite, lapis, nephrite, quartz, ruby, and turquoise. It is interesting to note that the solid black stone often referred to as "black onyx" is not natural color but actually black dyed chalcedony. 

After bleaching, some freshwater and saltwater cultured light-colored pearls undergo a treatment called "pinking" to give them a subtle pink tint that makes them more marketable, especially in the asian markets where very pale pink is prefered to plain white. For a more detailed discussion of pearl treatments visit http://www.arpaiajewelry.com/pages/pearls.

Some dyed gems can be detected with the unaided eye, others by magnification or other standard gemological tests such as with the spectroscope or color filter, and sometimes the presence of dye requires advanced lab testing.

Dyed gems are susceptible to damage and should be kept away from all chemicals and solvents that could dissolve the dyes. Also, dyed gems should not be exposed to prolonged sunlight, which could advance fading.

Surface Modification

A gem's appearance can be improved or changed by backing, coating, and painting. The most commonly coated gems include coral, diamond, pearl, quartz, tanzanite, and topaz. Surface treatments can often be revealed by magnification.

Coated surfaces are subject to scratching, especially along facet edges and drill holes. Also, coatings can be partially worn or possibly even removed during harsh cleaning or repairs. Gentle wear, handling and cleaning, as well as safe protection during storage, is recommended.

Smoke and Sugar Treatments for Opal

Both processes work with porous opals to darken their color and bring out their play of color. These effects are limited to a shallow layer just below the surface. Opal treatments are detectible under magnification.

The Main Point

With gemstone jewelry, it is important to know what you are buying so that you can have an understanding of value and price. Treatments are required to be disclosed, and so should proper care recommendations. If necessary, be proactive and ask questions.

There is nothing wrong with buying green glass. In fact, it can be quite durable, pretty, and affordable. You just don't want to pay an emerald price for green glass.

Similarly, there is nothing wrong with buying a treated emerald, but you should know about the treatment, its proper care, and that you are paying a fair price and not the higher price one would pay for a natural emerald of same quality. 

If you are considering a significant rare gemstone purchase, a colored gemstone report from a reputable lab like GIA might be advisable.

This Newsletter is intended to be helpful, but may contain unintented errors, so please do not rely on it when considering jewelry purchases. Retailers are in the best position to provide and should provide all necessary information that you request and need to make an informed decision.

As always, when you make a purchase with Arpaia Jewelry, we are proud and pleased to provide full disclosure and all information necessary to care for your new jewelry purchase.

More detailed information on the care of fine jewelry is provided at: http://www.arpaiajewelry.com/pages/jewelry-care.