A gemstone treatment or enhancement refers to the method used to alter a gemstone, permanently or temporarily, to improve to improve its durability or appearance. Here is a list of treatment names and symbols used by the American Gem Trade Association (AGTA). A reputable seller will always disclose the method of enhancement, if known. Be aware that failure to identify known enhancement of gemstones is an unfair trade practice. The Federal Trade Commission also requires sellers (including jewelry stores) to disclose whether or not a stone is man-made or synthetic. Many stores engage in a sort of don't-ask-don't-tell scenario, where they buy gems without asking about enhancements. Sometimes gems are purposely misrepresented. Also, sometimes treatments of imported gems or older gems are unknown. Enhancements may affect the value of certain stones, so use this information as a guide when asking questions about gems.
Assembled items are made of multiple layers of materials or combinations of manufactured and/or natural materials. Examples include opal triplets and mosaics.
Bleaching is the use of chemical agents to lighten or to remove a gemstone’s color. Be aware that many pearls and mother-of-pearl are placed in sunlight for extended periods of time to lighten their color. This non-chemical form of bleaching still affects the durability of a pearl's nacre. Bleaching is a permanent treatment.
Coating is a surface enhancement applied to improve a gem's appearance, provide color, or contribute other special effects.
Dyeing is the application of coloring matter into a gemstone to give it a new color, intensify its present color, or improve its color uniformity. Dyes and natural gemstone colors may both be adversely affected by prolonged exposure to sunlight or fluoresent light.
The 'enhancement' code indicates that the type of gemstone is routinely enhanced. Many enhancements are difficult or impractical to prove, so a supplier may simply assume that such enhancement has been done to the particular gemstone material being described. If the specific type of enhancement is known, its enhancement symbol will be stated.
Filled gems are characterized by the presence of solidified borax or other colorless substance produced as a by-product of heat enhancement. The results are visible under properly illuminated 10x magnification.
Gamma or Electron Irradiated
Gamma and/or electron bombardment may be used to alter a gemstone’s color. Gamma or electron irradiation may be followed by a heating process.
Heat may be used to alter color, clarity, and/or other gem aspects. This is a gemstone treatment that has been used for centuries, possibly dating back to the Roman Empire. The results of heating are permanent under normal conditions. Usually, heating is not detectable. Unheated rubies and sapphires may contain microscopic rutile needles or tiny gas bubbles in pockets of liquid that can be used to determine that these stones have not been heated. If these gems are the finest color, they will command premium prices. Unless explicitly stated otherwise, assume the following gems are heated: rubies, sapphires, tanzanite, citrine, pink topaz, aquamarine, blue zircon, and colorless zircon.
Infilling is the intentional filling of cavities or fractures with glass, plastic, opticon with hardeners, and/or hardened foreign substances. Infilling is performed to improve durability and/or appearance of a gem and/or add weight.
Imitation gems are man-made products, fabricated using materials such as glass, ceramics, and/or plastics. Imitation gems resemble the appearance of a natural gemstone, but not duplicate its characteristic properties.
Lasering is the use of lasers and chemicals to reach and alter inclusions in gemstones, most notable diamonds. Lasering results in a visible trail that can be detected by a trained professional.
Natural stones are gems which are not known to be enhanced.
Oiled or Resin Infused
Oiling or resin infusion is the intentional filling of surface-breaking cavities of a colorless oil, wax, natural resin, or unhardened man-made material into fissured transparent/translucent gemstones. Oiling is performed to improve a gem's appearance (e.g., as for emeralds). Although unoiled emeralds can be found, they are unusual and neither more nor less valuable than oiled gems. When rough emerald is mined it is often placed into oil. When emeralds are cut, oil is used as a lubricant.
Irradiation refers to the use of neutrons with the combination of any other bombardment and/or heat treatment to alter a gem’s color.
Stabilized or Bonded
Bonding or stabilization is use of a colorless bonding agent, such as plastic, with a porous gemstone. The procedure is intended to enhance durability and/or appearance.
Synthetic gems are man-made materials which have essentially the same optical, physical, and chemical properties as the natural counterpart.
Diffusion is the use of chemicals in conjunction with high temperatures to produce color and/or asterism (star-like inclusions). Diffusion is not a generally accepted gemstone treatment, since only a slight layer is actually treated. Therefore, if the surface is chipped or abraded, it cannot be repolished without removing the effect.
Waxed or Oiled
Waxing or oiling is the impregnation of a colorless wax, paraffin, and/or oil in porous opaque gemstones to improve their appearance.