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GEMSTONES AND THEIR TREATMENT
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Most of Diamonds & Gemstones, with the notable exception of garnet and spinel,
have a particular treatment, or series of treatments that are used to increase
the marketability of the stone. |
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Follow this is a list represents common gemstones with the general treatments
they receive. |
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Alexandrite |
: None |
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Amethyst |
: Heat Treatment |
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Aquamarine |
: Heat Treatment
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Citrine |
: Heat Treatment
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Diamond |
: Irradiation, Lasering, HTHP
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Emerald |
: Filling, Impregnation, Waxing/Oiling
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Garnet |
: None
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Lapis Lazuli |
: Dyeing
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Opal |
: Waxing/Oiling
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Morganite |
: Irradiation
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Pearls |
: Bleaching, Dyeing, Irradiation
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Peridot |
: Impregnation, Waxing
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Rubelite |
: Heat Treatment, Irradiation
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Ruby |
: Heat Treatment, Flux healing, Fracture Filling
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Sapphire |
: Heat Treatment, Flux healing, Fracture Filling, Lattice Diffusion
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Spinel |
: None
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Tanzanite |
: Heat Treatment
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Topaz |
: Heat Treatment, Irradiation
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Tourmaline |
: Heat Treatment, Irradiation
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Zircon |
: Heat Treatment
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There is nothing intrinsically wrong with gemstone enhancements as long as you are made aware of their use. New treatments are being developed everyday, and gemological laboratory are constantly updating their testing technique to checking the unidentified gemstones enhancement that come the market |
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As consumers, we must rely on the gemological laboratory's ability to identify enhancements so that a gem's value can be properly accurate before a purchase has been made. Click here to request a gems certificate. |
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Detail of gemstone Treatment.
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Heating
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Heat altered gem material is changes or improves the
color. Some heat treatment is permanent and can lighten, darken, or completely
change the color of the gem. Some heat treatment is unstable and can revert to
the original pretreated color with time. Zircon can be unstable and after heat
treatment the stones can be exposed to sunlight for several days and then stored
in the dark up to a year to remove the unstable stones. |
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Heat treatment may change crystal inclusions within the gem, causing them to melt or explode. This may be detected with magnification by a skilled person, although it may be difficult to definitively state any color is natural when the gem material is flawless. |
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Temperatures used for heat treatments vary, depending on the material and desired color. Sometimes low temperature, such as that from an alcohol lamp, will change brown topaz to pink; very high temperatures, as high as 2050 degrees C, are needed for other alterations, such as titanium-rich milky sapphires to blue. |
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Most citrine is made by heating amethyst, and partial heating with a strong gradient results in ametrine - a stone partly amethyst and partly citrine. Much aquamarine is heat treated to remove yellow tones, change the green color into the more desirable blue or enhance its existing blue color to a purer blue. |
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Nearly all tanzanite is heated at low temperatures to remove brown undertones and give a more desirable blue/purple color. A considerable portion of all sapphire and ruby is treated with a variety of heat treatments to improve both color and clarity. |
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When jewelry containing diamonds is heated (for repairs) the diamond should be protected with boracic acid; otherwise the diamond (which is pure carbon) could be burned on the surface or even burned completely up. When jewelry containing sapphires or rubies is heated (for repairs) it should not be coated with boracic acid or any other substance, as this can etch the surface; it does not have to be "protected" like a diamond. |
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Irradiation
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Most blue topaz, both the lighter and the darker blue shades such as "London" blue, has been irradiated to change the color from white to blue. Some improperly handled gems which do not pass through normal legal channels may have a slight residual radiation, though strong requirements on imported stones are in place to ensure public safety. Most greened quartz (Oro Verde) is also irradiated to achieve the yellow-green color |
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Waxing/oilin |
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Emeralds containing natural fissures are sometimes filled with wax or oil to disguise them. This wax or oil is also colored to make the emerald appear of better color as well as clarity. Turquoise is also commonly treated in a similar manner. |
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Fracture filling |
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Fracture filling has been in use with different gemstones such as diamonds, emeralds and sapphires. In 2006 "glass filled rubies" received publicity. Rubies over 10 carat (2 g) with large fractures were filled with lead glass, thus dramatically improving the appearance (of larger rubies in particular). Such treatments are fairly easy to detect. |
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High-Temperature High-Pressure (HTHP) |
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High-Temperature (2,000º C) High-Pressure (70,000 atmospheres) treatment or HTHP was developed by General Electric in 1999, to lighten or totally remove a brownish hue in some Type IIa diamonds. Type I diamonds have nitrogen impurities that absorbing some of the blue light spectrum, thereby making the diamond appear yellow, while Type II diamonds have structural defects (aka plastic deformations) created during crystal growth, that can cause a brownish color. High-Temperature High-Pressure treatment can in some cases 'repair' these deformations, whitening the diamond's appearance. |
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Type I diamonds which have nitrogen impurities can also have their color altered using High-Temperature High-Pressure treatment. Using HTHP, a company called Nova Diamond creates fancy colors in vivid hues of yellow and green, bypassing the need for irradiation. |
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Diamonds treated by General Electric (Pegasus Overseas Ltd) to remove coloration have the logo "GE POL" laser-inscribed on the girdle, but laser-inscriptions can be removed by polishing. Detection of non-inscribed HTHP treated diamonds is accomplished by gemological testing laboratories using photoluminescence spectroscopy, 'Fourier Transform Spectroscopy' (FTIR) and 'Raman Spectroscopy' to analyze visible and infrared light absorption looking for telltale absorption lines that would indicate high temperature exposure. Additionally, telltale fingerprints that can be seen under a microscope may include dark cracks around inclusions, internal graining, haze, and partially healed feathers. |
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Dyeing |
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Dyeing is a treatment that alters the body color of a gem and has been done for thousands of years. For the dye to penetrate, fractures must exist. If the gem is not porous or fractured naturally, the opening for the dye to enter the stone is produced by "quench crackling," a heat-induced thermal shock, which creates a network of fractures the stability of dyed gems is dependent upon the type of dye, which varies from natural organic material to synthetic or precipitations of metallic salts. |
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