Gemstone Treatments and Enhancements
A Brief History of Gemstone Treatments
The treatment and enhancement of gemstones has existed for hundreds and hundreds of years. The first documentation of treatments was presented by Pliny the Elder. And, 2000 years later, many of these treatments are still being used today! Some enhancements improve on nature, cannot be detected and are permanent; this provides the gem market with a larger supply of beautiful gemstones. Other treatments produce dramatic changes in the gemstone itself or it's clarity; the irradiation and heating of colorless topaz that permanently transforms it into blue topaz is an excellent example. A few treatments are less stable and should be avoided by the knowledgeable buyer. Following is a description of some common treatments. This is just the tip of the iceberg. Please refer to the recommended reading list at the bottom of the page for further information.
In the past, treatments of gemstones were usually done by the cutter. The lapidary wanted the value of the finished product to be as high as possible. Today, there are centers, such as Bangkok in Thailand where there are facilities that specialize in treatment of both rough and fashioned gems. The heat treatment of corundum (rubies and sapphires) is an excellent example. The heat treatments of corundum (both simple heating and heating with a flux, such as beryllium) are often done before before cutting, and may not be disclosed to the lapidary before cutting is done.
Treatments and Pricing
There are some gemstones that would not even exist if it were not for treatments. The abundance of citrine, in shades of yellow, gold and orange is the result of heat treating amethyst. Naturally occurring citrine is quite rare in nature. If it was not for treatments the stone would be far more expensive than it is! Tanzanite in shades of violet and blue depends on heat treatment to produce enough supply to meet the demands of the public. Pink topaz is another example of a gem that would not be available without heat treatment. Not only are these treatments acceptable, they are necessary to keep these products affordable and available. Recent demand for unheated sapphires and rubies has caused a price increase of as much as 50%-100% for unheated material. Does this mean that the untreated gem is more beautiful? NO! In most cases the heating enhances the gemstone to make it more beautiful; the price premium is the result of the rarity of being unheated!.
Heating is the most common treatment available. It can cause the color of a stone to lighten, darken, or change completely. It can bring about an improvement in clarity and brightness. Heating is detectable only by trained observers in a laboratory setting and is usually irreversible under normal conditions. Unheated rubies and sapphires will contain microscopic rutile needles or tiny gas bubbles in pockets of liquid which are evidence that laboratories can use to guarantee that these stones have not been heated. If these gems are the finest color they will command premium prices due to their extreme rarity.
Within the last couple of decades, it was discovered, quite accidentally, that if sapphires were heated along with a flux containing beryllium, the color of the sapphire could be dramatically changed. See diffusion below.
The following gems are routinely heat treated:
zircon (both blue and colorless)
Oiling of emerald is universal, but not EVERY emerald is oiled, (fine untouched specimens will command astronomical prices). When the rough emerald is mined it is thrown into a barrel of oil; when it is cut, oil is used as a lubricant on the cutter's lap. The colorless oil seeps into the fissures on the surface of the emeralds. When the fractures contain the oil they are less eye visible. To complete this process oil is pressurized into the fissures of the polished stone. This is something that must be accepted; it's the way it is! The only way you will find an emerald that isn't oiled is if there are no fractures at the surface of the emerald, so no oil can get inside the stone. If color is equal, obviously you will pay more for an emerald if it has no fissures that reach the surface; they simply will have fewer inclusions. If an emerald that originally had fissures that reached the surface,is put into an ultrasonic or is steamed clean, then the oil may be leached out and fractures. This will make the surfacing inclusions appear whiter and more obvious. In this case, the stone can be re-oiled.
Recently, I have read articles that other colored stones such as rubies, alexandrite, other varieties of chrysoberyl, and demantoid garnets have been treated with oils and resins to make surfacing inclusions less visible. Occasionally colored oils are used on emeralds and rubies. The idea is to add color while concealing fractures. You want to avoid buying these because you can't judge the true color or know how bad the fractures are. This is done to deceive the buyer. Fortunately this is not common and it is unlikely you will encounter this if you buy from a reputable source in the United States. Synthetic resins can be used to fill in fractures in emeralds and other stones with fractures that reach the surface of the gem. Hardeners are often applied to make the process more permanent. The use of these resins, with hardeners (Like Opticon) are NOT acceptable treatments.
Irradiation means pounding material with subatomic particles or radiation. Sometimes irradiation is followed by heating to produce a better or new color for the gem. Blue topaz is the most common example. Although blue topaz occurs in nature, it is quite rare and pale in color. In the United States irradiated gems are regulated by the Nuclear Regulatory Agency to in an attempt to insure there is no harmful residual radiation. You do not have this protection if you buy it out of this country. Today irradiation of blue topaz has created shades not found in natural blue topaz; prices are very reasonable for irradiated blue topaz since there is a great deal of competition in the wholesale end of this market. If you could find an untreated blue topaz, it would sell for a price comparable to untreated Imperial Topaz. Tourmaline can be irradiated to darken pink stones into red ones; these are indistinguishable from natural red ones. Off colored diamonds can be irradiated and heated and turned into intense greens, yellows, blues, browns & pinks. These stones are fairly common. Irradiated diamonds will sell for much less per carat than the naturally colored ones of comparable color, clarity grade, and size Cultured pearls can be irradiated to produce gray or blue colors; but dyeing in these colors is more common. Irradiated pearls will sell for about the same price as the dyed pearls, this should be well below the prices asked for pearls with very fine colors. Varieties of quartz and spodumene are irradiated and subsequently annealed with heat to produce dramatic and desirable colors.
Without dyeing there would be no black onyx: this is not a natural color of chalcedony! Chalcedony or more commonly known as agate, is often dyed blue, green, or orange and carved into bowls, statues, or cut into beads. This is fine, as there are some lovely pieces around using this stuff, especially carved animals and the like and no one minds that it's not "natural". Japanese cultured pearls, which are grown in an Akoya oyster that produces pearls up to about l0 millimeters, grow into a limited selection of colors with various overtones of colors. If they are dark gray, bluish, violet, nearly black, or intense bronze, assume they are dyed. To meet current demand for pearls with rose overtones, some cultured pearls have been given a pink tint; this can be detected by looking for concentrations of dye around drill holes or around blemishes. On the other hand, South Sea cultured pearls which are generally larger than the Japanese cultured pearls, may grow into a variety of exotic colors naturally because they are grown in a different variety of oyster. Tahitian black pearls are a good example of naturally colored black pearls. Cultured pearls with a natural exotic color will command a much higher price than a dyed one. Dyeing of chalcedony and of pearls is prevalent, permanent, and acceptable. These colors do not occur in nature; no deception is involved. Dyeing of other materials, jade, lapis lazuli, turquoise, coral, rubies, emeralds and sapphire may be less acceptable. Generally, dyeing of these materials is done to disguise poor quality goods. Dyed lapis lazuli can be easily tested by rubbing it with a piece of cotton soaked with acetone (fingernail polish remover). If it is dyed, blue color will eventually rub off on the cotton. Dyed lapis should be much less expensive than fine natural lapis. In the case of lapis lazuli or turquoise, the natural material is not that expensive, so why bother with inferior material unless it is irresistibly cheap or you just love the color? Dyed lapis lazuli may bleed blue onto the wearer or his or her clothing (not a fun thing to remove, trust me). Dyed jade may be tricky to detect, so be careful if the price seems "too good". An inexpensive tool (around $30) called a Chelsea Filter and supplement emerald filters can somewhat useful detecting dyed jade but the sophistication of the bleaching and polymer impregnation of jadeite can be extremely hard to detect without the aid of spectrographic analysis. Coral beads may also be dyed. Suspect coral that has a very intense color, coupled with an inexpensive selling price. I recently encountered strands of sapphire beads which were quench cracked and died. The treatment was easily visible with microscopic observation, but it did not bleed at all when soaked in acetone. Click Here for Additional Information on Jade Treatments Impregnation and stabilization Impregnation and stabilization are common for turquoise. Impregnation is the infusion of wax or paraffin into a porous material. Stabilization is the introduction of a bonding agent, usually plastic, into a porous material. Of the two processes, stabilization is the most permanent. Impregnated pieces must be kept away from heat or the wax could melt & leak... not a pretty sight !!. Some gems are waxed on the surface to enhance luster but this is not very usual. The upside for stabilized turquoise, is that it will not absorb oils and discolor as untreated turquoise may. Opal can be stabilized with plastic to hide crazing, but this is not common at all and would only be done to deceive the buyer.
Bleaching is a process for organic gem materials such as ivory, coral, and for pearls and cultured pearls. It lightens the color and is permanent and undetectable. No price difference exists as a result. Coating Coating is a process (used and described for over 200 years! where a lacquer or film of some type is applied to improve a gem's appearance. Today, coatings are increasingly utilized to alter and improve the color of gems. Mystic topaz is an example of a coated gem that was conceived by Azotic Coating Technologies. The company is now coating topaz in all colors, including pinks and rich "imperial" tones. Recent reports have indicated that tanzanite is showing up in the labs with coatings on the pavilions to improve the appearance of saturation. Coatings are occasionally identified on diamonds to improve the apparent color of an off-colored stone and deceive a buyer. Opals may have a black coating on the back to intensify the play of color or to give the appearance of a black opal; this can take the form of a simple coat of black lacquer or what is called a "doublet." A doublet is a thin layer of opal cemented to a black onyx base.
Diffusion was originally used on sapphires. Chemicals, like beryllium, were infused at high temperatures, and actually penetrated the gems. Early diffusion only produced color on the surface of the gem's surface and was referred to as "Surface Diffusion". Surface diffusion was easily detectable with immersion, and often with simple magnification. Great advancements have been made in diffusion treatment in the last decade and it was discovered that if corundum is heated to very high temperatures for a long duration, the diffusion would penetrate the entire stone! It can improve color, change color, or create asterism (stars). Filling Filling is used on gems with surface fractures or cavities. Glass, plastic or other materials are used to fill these holes. This is sometimes done to rubies. With close examination with magnification you may be able to spot differences in surface luster, or see a spectral effect in fractures when viewed with dark-field illumination. The AIGS, The Asian Institute of Gemological Sciences, has done extensive research on filled rubies.
Diamonds with inclusions are sometimes filled with glass to make them appear clearer. Oved and Yehuda Diamonds have undergone this treatment. Filler can be damaged by heat, ultrasonic cleaning, and by re-tipping. The filling does not repair the inclusion, it just makes it less visible. If you look at a filled diamond closely, rotate it under light, you should be able to notice a bluish flash. Both Yehuda and Oved will usually refill your diamond for free if it is ever damaged. Check for guarantees before buying such a diamond.
Lasering is sometimes used on diamonds. The process drills very tiny holes into a diamond to provide access to an inclusion which detracts from the beauty of the stone. The inclusion can then be, vaporized or bleached to make it less obvious if it is not burned out by the lasering. Under magnification laser holes are visible when viewed at the correct angle. A lasered diamond would be classified in the slightly imperfect or imperfect category regardless of the improvement in apparent clarity and should be priced accordingly.
Gems that are Not Enhanced
There are some gemstones that are not known to be enhanced. These include: Garnets,(with the exception of demantoid), Peridot, Iolite, Spinel, varieties of Chrysoberyl, Tourmaline (with the exception of the Paraiba variety), Malachite, Hematite, and Feldspar with the probable exception of varieties of andesine and labradorite Keep in mind that new technology in gemstone treatment is always changing and improving and many are seriously difficult, if not impossible, to detect.
With some gemstones enhanced by specifically defined treatments according to the guidelines of the CIBJO, it is a requirement of the Trade in the US to make such disclosures and in any case a vendor should always disclose any known treatments or enhancements (remember, they may not always know themselves, with imported Gems) and record it on your bill of sale. Most vendors are honest and forthcoming, but it is YOUR RESPONSIBILITY TO ASK.
Caveat Emptor !!!