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Guide for Fraud and Misrepresentation in Colored Gemstones






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The Jewelry Hut
Jewelry and gems
The Buying Guide

Colored Gemstones

Fraud and misrepresentation in colored gems

We would like to begin by emphasizing here, as we did in the article on diamonds, that the percentage of misrepresentation and fraud among total jewelry transactions is quite low, and that most jewelers are reputable professionals in whom you can place your trust.  In the colored gem market, there is a greater occurrence of misrepresentation than in the diamond market, however, primarily because of the scientifically complex nature of colored gemstones. So it is even more important to be aware of deceptive practices you might encounter when buying a colored gem, both to protect yourself form the more obvious scams, and to better understand the importance of dealing with a reliable jeweler.  We also stress the importance, to an even greater degree, of seeking verification from a qualified gemologist; one with experience with color gems, when buying any expensive colored gem.  Take precaution that your gemstone is what it is represented to be.

Misrepresenting synthetic as natural gemstone

Today it is very important to verify the genuineness of any fine, valuable gemstone because the new generation of synthetic products is so similar to the natural that the two can be easily confused. Many very fine synthetics are available, and they can make attractive jewelry choices when properly represented. Still, you should protect yourself from intentional and sometimes unintentional misrepresentations.

Synthetics have been on the market for many yearsGood synthetic sapphires, rubies, and spinels have been manufactured commercially since the early 1900s, and very good synthetics emeralds since the 1940s. While these early synthetics were attractive and popular because of their very low price, they didn’t really look like natural gemstones.  Most looked “too good to be true,” so that they were readily distinguished from the real thing by a competent jeweler.
Today, this is often not the case. While older techniques for producing synthetics are still used and their products still easy to recognize, new, sophisticated methods result in products that no longer possess the signature characteristics with which gem dealers and jewelers have long been familiar.  To further complicate matters of identification, synthetics now often contain characteristics very similar to their natural counterparts.  As a result, some are being sold as natural, intentionally and unintentionally. A gemologist with extensive experience, or a gem testing laboratory such as GIA or AGL, however, can differentiate between between them and verify genuineness.
It is essential to have a highly qualified gemologist verify authenticity, particularly for fine gemstones like ruby, emerald, and sapphire.  Thousands of dollars may be at stake, for jewelers may innocently buy one of those gemstones believing it to be natural, and pass their error on to the customer.  Don’t delude yourself into believing that if a piece is purchased from a well respected firm it is always what it is represented to be;  even the best known firms have made mistakes in this area.  It may be inconvenient to obtain an expert analysis, and it may be inconvenient to obtain an expert analysis, and it may require an additional expense, but we believe it is better to be safe now than sorry later.
With sophisticated modern equipment and a greater knowledge of crystals, man can now “create” or “grow” almost any gemstoneAs a general rule, remember that any gem; amethyst, alexandrite, ruby, emerald, sapphire, opal, even turquoise, could be synthetic; that many synthetics are themselves expensive; and that most have become more difficult to distinguish from their natural counterparts, resulting inadvertent misrepresentation. So make sure you take time to verify a gemstone’s true identity.

Simulated gemstones

Simulated or imitation stones should not be confused with synthetics, which possess essentially the same physical, chemical, and optical properties of the natural gem. A simulated stone is usually a very inexpensive man-made imitation which resembles the natural stone color, but little else.  Many imitations are glass, but they can also be plastic.  Imitations, or “simulants” as they are also called, are very easily differentiated from the genuine by careful visual examination and simple gemological testing. There are glass simulated of all colored gemstones, and glass plastic simulated pearls, turquoise, and amber are also common.
Imitations are frequently found in estate jewelry, sometimes mixed with natural gems in the same piece.

Look-alike substitution

Another form of deception involves misrepresenting a more common, less expensive stone for a rarer, more expensive gem of similar color.  Today, as more and more natural gemstones in a wide variety of colors enter the market, both deliberate and accidental misrepresentation can occur.

Color alteration

Color enhancement of gemstones is ages old, and many of the techniques used today have been used for generations.  Many are routine, and do not in themselves constitute fraud.  Some treatments, however, should not be applied to certain gems, normally because the results are not permanent and color may revert to the original.  Such treatments are accepted by the trade.
Because color enhancement is so common, it’s important for the consumer to understand exactly which procedures re acceptable in the industry and which represent deceptive or fraudulent practices aimed at passing off inferior gemstones as much more expensive ones.
Here we will discuss various treatments, and explain which are routine, and which may constitute fraud or misrepresentation.

Heat treated stones

Subjecting gemstone to sophisticated heating procedures is the most commonly used method of changing or enhancing a gem’s color and is used routinely on a variety of gems to lighten, darken, or completely change color.  Heat treatment is not a fraudulent practice when used on certain gems, on which the results are permanent.  This procedure is an accepted practice routinely applied to the following:

  • Sapphire: To lighten or intensify color; to improve uniformity.
  • Amber: To deepen color and add “sun spangles.”
  • Aquamarine: To deepen color and remove any greenish undertone to produce a “bluer” blue.
  • Tanzanite: To produce a more desirable blue shade.
  • Tourmaline: To lighten the darker shades, usually of the green variety.
  • Amethyst: To lighten color; to change color of pale material to “yellow” stones sold as citrine and topaz.
  • Citrine: Often produced by heating other varieties of quartz.
  • Topaz: In combination with radiation, to produce shades of blue; to produce pink.
  • Zircon: To produce red, blue, or colorless gemstones.
  • Kunzite: To improve color.
  • Morganite: To change color from orange to pinkish.

The color obtained by these heating procedures is usually permanent.

Radiated gemstones

Radiation techniques are now in common use, produced by any of several methods, each of which has a specific application.  Sometimes radiation is used in combination with heat treatment.  As long as the technique produces stable results, color enhancement by radiation techniques is not considered fraudulent.
Radiation techniques are routinely used for the following stones:

  • Aquamarine: Used in conjunction with heat to improve blue.
  • Diamond: To change the color from an off-white color to a fancy color; green, yellow, etc.
  • Topaz: To change from colorless or nearly colorless to blue; to intensify yellow and orange shades.
  • Tourmaline: To intensify pink, red, purple, shades.
  • Pearl: To produce blue and shades of gray (“Black” pearls)
  • Yellow Beryl: Often produced by radiation.

Some very deep blue topazes have been found to be radioactive and may be harmful to the wearer.  Most topaz sold in the United States since 1992 has been tested for radiation level by the GIA or other centers established for that purpose.  Exercise caution when purchasing deep blue topaz outside the United States, in countries where radiation testing is not required.
As far as we know now, the color changes resulting from radiation treatment on the above gemstones are usually permanent.  Some gemstones subjected to radiation, however, obtain a beautiful color that is temporary. Some irradiated “blue” and “yellow” sapphire will fade quickly.  Irradiation of sapphires is not accepted in the trade.  We have seen nice “yellow” sapphires treated by radiation quickly lose their color when exposed to the flame of a cigarette lighter.  If you are considering a “yellow,” it may be worthwhile to try this simple flame  test if the jeweler will permit.  If not, be sure to have it “fade” tested by a qualified gemologist or gem lab.
The color of fancy colored diamonds can usually be verified as “natural” or “irradiated.”  However, for most other gems on which radiation is used, testing procedures for determining whether or not color is natural have not been developed as of this date.

Diffusion treated gemstones

Diffusion treatment involves introducing chemicals (titanium and iron, the same coloring agents present in natural blue sapphire) into the surface of colorless or nearly colorless sapphire, and heating the stone over a prolonged period.  This treatment produces a lovely blue color, but on the surface of he stone only; the center remains colorless.
Diffused sapphires are being substituted for non-diffused sapphires by unscrupulous merchants and purchased by dealers and jewelers unknowingly in parcels of stones that are subsequently mounted in jewelry.  They are also appearing in antique and estate jewelry.  When buying any fine sapphire today, it is important to purchase from a knowledgeable, reputable jeweler, and be especially wary of bargains!  Note: Diffusion treated ruby may soon be available and warrant the same caution.

Dyed gemstones

Gemstones have been dyed since earliest times.  Numerous examples of dyed chalcedony (an inexpensive variety of quartz) can be found in antique jewelry, imitating other gems. Gems that are frequently dyed include jade, opal, coral, lapis, and to a lesser degree poor quality star rubies, star sapphires and emeralds.
Dyed material may be very stable, but it can also be very temporary. We’ve seen dyed lapis in which the “blue” came off with a cotton ball moistened in fingernail polish remover.  Dyed gems may be genuine stones which have been dyed to enhance their color (as in dyeing pale green jadeite to a deeper green), or they may be different gem altogether.
Dyed gems should always cost less than gems with natural color.  Fine lapis and jadeite should always be checked for dyeing. Here are some other gemstones that often are dyed:

  • Chalcedony: Dyed to produce “black onyx,” which rarely occurs naturally, and “banded agate” with white bands alternating with strong colored bands; dyed reddish brown to sell as carnelian (which also occurs naturally); dyed green to imitate fine jadeite or chrysoprase (which also occurs naturally).
  • Jade (jadeite): Color frequently improved by dyeing to a beautiful emerald or young grass green color, to look like “imperial” jade. While jade occurs naturally in almost every color, it may also be dyed other colors.
  • Coral and lapis: Dyed to deepen the color, or create more uniform color.
  • Swiss lapis: Jasper dyed blue and sold as “lapis” or “Swiss lapis.”

Blackening techniques

Blackening techniques are used to alter color, not by dying but by introducing a chemical reaction (sugar acid chemical reaction) that introduces black carbon, which blackens the color.  The following stones commonly exposed to this treatment:

  • Opal: To blacken so as to resemble the more valuable, precious black opal.
  • Black onyx: Chalcedony is blackened by this technique to create the black onyx used today in most jewelry.


This is a process consisting of rubbing the stone with a tinted wax-like substance to hide surface cracks and blemish and to slightly improve color.  This is used often on cheaper Indian star rubies, and sometimes on stare sapphires.


This technique is commonly used on emeralds. The emerald is soaked in oil (which may or may not be tinted green). Its purpose is to fill fine cracks, which are fairly common in emerald.  These cracks look whitish and therefore weaken the green body color of the emerald.  The oil fills the cracks, making them disappear, and thereby improves the color by eliminating the white.
This is an accepted procedure and will normally last for many years. However, if the stone is put in a hot ultrasonic cleaner (which is dangerous to any emerald and never recommended), or soaked in an organic solvent such as gasoline, xylene, or substances containing these, such as paint remover, the oil may be slowly dissolved out of the cracks and the whitish blemish will then reappear, weakening the color. If this should happen, the gemstone can be re-oiled. Using green tinted oil, however, is not and accepted trade practice.


This technique is often used with cabochon (non-faceted) transparent (“jelly”) or semi-transparent opals to create a stone that looks like precious black opal.  This is done by putting the stone in a closed back setting that has a high rim (bezel). A black cement or paint is spread on the inside of the setting so that when the opal is placed inside, the light entering it gets trapped and reflected back, giving the opal the appearance of a fine black opal.

Foil backed gemstones

This technique is not frequently encountered in modern jewelry, but anyone interested in antique jewelry should be aware of it.  It is seen with both non-faceted and faceted gemstones, set usually in a closed back mounting.  This technique involves lining the inside of the setting with silver or gold foil to add brilliance and sparkle (as with foil backed glass imitating diamond), or with colored foil to change or enhance color by projecting color into the stone.  Always be apprehensive when considering a piece of jewelry that has a closed back.  While relatively common in antique jewelry, foil backing is also seen in modern jewelry.


This is a technique used on opals. It is used to give off white to tan colored opals from Mexico a more desirable, moderately dark coffee brown color that greatly enhances the opal fire.  It consists of taking a cut and polished opal, wrapping it tightly in brown paper, and putting it in a covered container over moderate heat until the paper is completely charred. When cooled and removed, the opal now has a much more intense brown body color and fire.  But if this smoke produced color coating were to be badly scratched, the underlying color would show through and the stone would have to be re-smoked.
This treatment can be easily detected by wetting the stone (preferably with saliva). While wet, some of the fire disappears, and then reappears after the surface has dried.

Fracture filling

As with diamonds, fractures which break the surface of a colored gem can be filled with a liquid glass or glass like substance.  The filler makes the cracks less visible and improves the stone’s overall appearance.  A coloring agent can also be added to the filler to simultaneously improve the gemstone’s overall color. Selling a filled gem without disclosure is not accepted trade practice.  To do so knowingly constitute fraud, but it’s being done, nonetheless, with increasing frequency.

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To Web Masters:

The article above can be used on your web site or newsletter.

When it is published, May I request that you include my name and resource box (the bio., contact and copyright information that follows the article.  I would also appreciate if you could send me an e-mail of notification along with a complimentary copy of publication.

Bijan Aziz is the owner and Web Master for The Jewelry Hut.

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