Gemstone Treatments and Enhancements
CLICK HERE FOR AN EXPLANATION OF SYMBOLS COMMONLY USED TO EXPLAIN TREATMENTS
Copyright © Barbra Voltaire, FGG, G.G. 1999
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.
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.
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 little, if any, black onyx: although natural black chalcedony has been claimed to be found in Namibia and Iran, I am at the time of this writing skeptical. 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
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.
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).
that are Not Enhanced