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Roger Weller, geology instructor regional geology planetary gems
Janice S. Hickey
Gems and the Treatments of Gems
The treating of gemstones to improve a stones look has been and continues to be a common practice in the jewelry industry. Gem Hut defines enhancement as “any treatment process other than cutting and polishing that improves the appearance (color/clarity/phenomena), durability, or availability of a gemstone. . . . A natural gemstone that is enhanced is still considered a natural gemstone.” (Gemstone). Common gems and the treatments routinely used to enhance them are provided below.
Agate (Quartz – chiefly Chalcedony):
According to “The Gemstone Information Encyclopedia,” many treatments are used
to alter quartz gems ranging from heat to radiation to dyes. A particular agate
is heated to around 500 degrees to create carnelian. At one time quartz was
heated then put into cold liquid to cause fractures. The fractures were then
dyed (What About). This practice of dyed agate continues to this day and the
effects created are nearly limitless.
Tumble Polished Agate Carnelian, rough
Photo by R Weller - Cochise College Photo by R
Weller – Cochise College
Amethyst (Quartz): Amethyst colors vary from pale lilac to deep purple. According to “The Gemstone Information Encyclopedia,” many treatments are used to alter quartz gems from heat to radiation to dyes. Irradiation of quartz containing iron creates the violet of amethyst. If a smoky color results, careful heating can often remove it without damaging the purple. Care is required as too much heat can result in a loss of color or the production of a yellow color - please see also Citrine (What About).
Faceted Ametrine with Amethyst and Citrine Gemmy Aquamarine Crystal
Photo by R. Weller – Cochise
College Photo by R. Weller –
Ametrine (Quartz): A bicolor amethyst citrine is called ametrine, which is caused by a partial conversion of an amethyst with heating of the stone to around 350 to 400 degrees as explained by “The Gemstone Information Encyclopedia.”
Aquamarine (Beryl): Aquamarine is generally a green blue color. To remove the yellow undertones to enhance the currently desired blue tone, a gentle heat is used. This process is explained in the article “What About Treated or Altered Gemstones?” Temperatures used are between 250 and 400 degrees for a few hours. To add yellow and emphasize the green hue irradiation is used, this is a treatment using electromagnetic or gamma rays.
Citrine (Quartz): Citrine is yellow quartz. According to “The Gemstone Information Encyclopedia,” many treatments are used to alter quartz gems ranging from heat to radiation to dyes. “Nearly all citrine used in the jewelry trade is made by heating amethyst to about 450 degrees for a period of time.” Higher temperatures of 500 to 575 degrees causes an orange brown red color referred to as Madeira Citrine. A bicolor amethyst citrine is called ametrine, which is caused by a partial conversion by heating to around 350 to 400 degrees (What About).
Diamond: “The Gemstone Information Encyclopedia” explains the numerous treatments common to diamonds. Irradiation is often used to change the color of diamonds. A number of colors can be produced by irradiation of diamonds originally found in less than favored colors. Generally, the treatment of these stones will produce a uniform color and the color is considered stable. Heating is then used to alter the color further, heating until it reaches the most pleasing shade. Most colored diamonds are treated in this manner and it should be disclosed to a buyer. It should be noted these colors are not naturally occurring. Another treatment called “Yehuda diamond treatment technique” involves a laser drilling into a flaw, then chemicals, such as an acid, are added to dissolve the inclusion and then the hole is filled with a glass-like product. The diamond appears to be a better quality at a more reasonable price. However, a diamond treated in this way is much more fragile and will not be able to tolerate the wear and tear, nor any repairs that may be needed, when used for wedding rings. This treatment is not difficult for a professional to detect (What About).
Emerald (Beryl): Emeralds are green of varying intensity. Most emeralds are treated with wax, oil, or plastic to fill the cracks and spaces common to emeralds. Occasionally these “fillers” are dyed green to enhance the color. Joel E. Arem in his book “Gems and Jewelry,” explains, “oil can be detected with ultraviolet light.” Weak stones are not made stronger by these techniques and care should be taken to protect jewelry made with treated stones. These treatments should be disclosed to a buyer. According to “The Gemstone Information Encyclopedia,” a new trend has been to grow synthetic coatings over a pale emerald to improve its appearance. This can be identified by testing and this too should be disclosed to a buyer (What About).
Garnet: Joel E. Arem in his book “Gems and Jewelry” explains garnet is not a single mineral but rather a collection of similar minerals known as the “garnet group” found in many silicate rocks. According to “The World Book Encyclopedia”, garnets occur in a wide range of colors including deep red, brown, black, yellow, and green (Gem). Generally, garnets are not treated to alter color.
Morganite (Beryl): To remove the
yellow, which causes the orange and salmon colors typical of morganite, a gentle
heat treatment is used. It is heated to temperatures between 250 and 400 degrees
for a few hours. Cally Hall confirms this heat process
leaves the morganite a purer pink.
Morganite Crystal Arizona Blue Opal, rough
Photo by R. Weller – Cochise
College Photo by R. Weller –
Opal (silicon oxide): Most opal is “common opal”, generally dull, gray, yellow and waxy looking. There are four types of gem opal: White opal, Black opal, Water opal, and Fire opal. These can contain all colors and as noted by Joel E. Arem has been described as “a mosaic of angular patches of fire.” The opal is often layered in doublets or triplets, where a layer of fine opal is cemented to a layer(s) of quartz for support and improved appearance. Opals can dry and become brittle with time and wear and make a poor choice for rings.
Ruby (corundum): Red
corundum is known as ruby. Numerous treatments are used including glass, oil,
and other fillings. Stones treated in this way remain fragile. They are less
valuable and treatment should be disclosed to a buyer. According to “The
Gemstone Information Encyclopedia”, heating to temperatures between 1600 and
1900 degrees for brief periods can eliminate some inclusions such as hairline
fractures. Continued heating, especially of a clear stone, can occasionally
result in a star sapphire Ruby. Heating to alter color is considered stable,
permanent, and not typically disclosed to a buyer
Star Ruby Cabochons Sapphire Mixed Colors
Photo by R. Weller – Cochise
College Photo by R. Weller –
Sapphire (corundum): All colors of corundum except red are known as sapphire. “The Gemstone Information Encyclopedia” provides vast information regarding the heating of sapphires. Heating to temperatures between 1500 and 1700 degrees tend to produce a deep yellow in pale stones and is also used to lighten dark blue sapphires sometimes this will cause a dark blue sapphire to turn green. These colors are considered stable and permanent. Similar temperatures will cause pale sapphires to turn a medium blue. This increases the value of the pale stones. Heating briefly to 1600 and 1900 degrees can reabsorb or re-dissolve inclusions. Infusion of additional elements can be accomplished by heating as well. However, these improvements are extremely thin and should be disclosed as they can be removed during repairs and they diminish the value of the stone. Sapphire can be treated with glass or oil to minimize flaws and cracks. These treatments do not improve the strength of an otherwise weak stone (What About).
Tanzanite (Zoisite): Tanzanite can be yellow, green (emerald green is very rare), and the blue to purple color most recognize. The majority of the tanzanite is a brown – root beer- color. “The Gemstone Information Encyclopedia” explains gentle heating for two hours at 370 degrees will result in the blue violet color people appreciate. Heating for too long creates a light blue color. Excess heat causes brittleness and ultimately destroys the stone. Heat treatment is rarely disclosed to buyers. It is considered stable and cannot be tested to determine if it has been heat-treated or not (What About).
Topaz: Topaz can be yellow, orange, brown, pink, violet, and blue depending on the imperfections it contains. Pointed out by “The Gemstone Information Encyclopedia” the yellow and browns are unstable and will eventually become colorless when exposed to sunlight. Virtually all blue topaz has been treated with irradiation. It is difficult to detect and determine if the stone was naturally blue or color treated. Topaz lacking color and value are often treated with nuclear radiation creating a brown topaz that is then heated to remove the brown and the resulting blue is permanent. Some topaz requires more and varied treatment to achieve the desired color. Treatments include gamma radiation, beta radiation and neutron (the most expensive) radiation. Radioactive stones must be stored until safe to be worn. These treatments are primarily performed outside the United States and consideration should be made as to the safety of these stones –especially those called “London Blue” as these generally come from neutron radiation (What About). According to Joel E. Arem, this topaz treatment “industry is now regulated by the Nuclear Regulatory Commission.”
Tourmaline: “The Gemstone Information Encyclopedia” explains that Tourmaline is found in “every shade of the rainbow.” Most tourmaline is not treated; however, the trend is changing particularly for pink and red stones. Irradiation will produce or strengthen the colors red or yellow. Heating on the other hand removes the pink or red component. The blue green and green can be lightened by heating to temperatures of 650 degrees. Beyond 725 degrees, tourmaline is destroyed. Some stones from Brazil are treated by heat (700 degrees) to remove color and then radiated to create a rose red color. This is the most common treatment of tourmaline and it cannot be detected and is rarely disclosed to a buyer (What About).
Turquoise: According to “The Gemstone Information Encyclopedia”, most turquoise is treated “with plastic bonding, chemical vapor penetration, paraffin or some other stabilizing agent to help the material retain its bright color…. [Less] than 10% of mined turquoise is used without some sort of treatment.” If turquoise is not treated is turns green with age. Plastic treatment will produce a stronger stone. Wax will not. Enhancing adds silica to the stone increasing its color and hardness. Four terms are common when referring to turquoise: Natural Turquoise, Stabilized Turquoise, Color-Treated Turquoise, and Reconstituted Turquoise. Natural turquoise means the stones are cut and polished and have not been altered. Stabilized turquoise means a natural mineral has been added to prevent the stone from changing color. Note that oil and wax are not permanent and are a poor choice as they deteriorate with time. Color-treated turquoise is similar to stabilization but a dye has also been added to the process. Reconstituted turquoise is made up of powder and chips of the stone mixed with plastic resin, dye and molded. Note, “high quality gem turquoise cannot be scratched with a knife” (What About).
Zircon: “The Gemstone Information Encyclopedia” explains zircon can be light blue, green blue, deep yellow, red, colorless, and most common brown. The popular blue zircons are created with heat treatment to about 1000 degrees in a reducing atmosphere created with coal or charcoal. They are considered stable. It is assumed colorless, red, and blue zircons have been treated although it is hard to distinguish treated gems from natural stones. Heat treatment is generally not disclosed to a buyer (What About).
A number of sources, including www.khulsey and www.gemhut, provide the following information for purposes of identifying enhancements made to gems.
Three broad categories are used:
“N” not enhanced, “E” normally enhanced, and “T” nontraditional enhancements.
Further identification is classified by the following letter symbols:
Semi-Permanent Gem Enhancements:
“B” Bleaching: Chemicals used to lighten and/or whiten gemstones or pearls.
“C” Coating: Surface enhanced by foiling, enameling, inking, lacquering, sputtering, or vapor deposition to improve appearance,
“D” Dyeing: Used to enhance or change the color and uniformity of gemstones or pearls.
“F” Filling: Surface cavities or fissures are filled with colorless glass, plastic, or resin.
“I” Impregnation: Treating with oil, wax, or resin to improve clarity and appearance.
“W” Waxing: Impregnation with colorless wax, paraffin, or oil to improve appearance.
Permanent Gem Enhancements:
“FH” Flux Healing: Heat enhancements to heal fissures and fractures.
“F” Fracture Filling: Injecting plastics or glass into fractures.
“H” Heat Treatment: Used to lighten, darken, or alter color.
“R” Irradiation: Exposure to radiation is used to add color intensity to
diamonds, gemstones, or pearls.
“U” Lattice Diffusion: High temperature heat treatment to produce color or asterism.
“L” Lasering: Laser and chemical treatment to remove inclusions.
Other Gem Enhancement Symbols:
“A” Not normally enhanced.
“G” Gamma/Electron Irradiation: Use of gamma or electron bombardment to change color – often followed by a heating process.
“I” Infilling: Filling of surface irregularities with glass, plastic, or other foreign substances to improve appearance.
“L” Lasering: Use of a laser combined with chemicals to reach and alter inclusions in diamonds.
“O” Oiling/Resin Infusion: Filling of surface cavities with colorless wax, natural resin, or other man made materials.
“S” Bonding: Use of a colorless bonding agent like plastic to improve appearance and durability.
“U” Diffusion: Chemicals and high temperature to produce color and asterism.
In the article “All About gemstones,” details are available to describe some of the treatments introduced above. Before making an investment in gems, it would be wise to investigate the treatments commonly used and to understand the impact the treatment has on the value and durability of the gemstone. Please refer to the resources found on the Work Cited page.
Arem, Joel E. Gems and Jewelry. Tucson: Geoscience Press, 1992.
“Gem.” The World Book Encyclopedia. 1963.
Awareness.” All About Gemstones. 27 Nov. 2008. Khulsey. 27 Nov. 2008.
Enhancements.” Gem Hut. 27 Nov. 2008. Gem Hut. 27 Nov. 2008.
Hall, Cally. Gem Stones. New York: DK, 1994.
“What About Treated
or Altered Gemstones? The Gemstone Information Encyclopedia. 27 Nov.
2008. Nevada Outback Gems. 27 Nov. 2008.