The AGTA Guide to Gemstone Enhancements

Educate yourself and your customers on the various gemstone enhancements and the symbols recognized by the AGTA.

Last edited: 5/28/2019
The AGTA Guide to Gemstone Enhancements

Rio Grande uses these symbols, set by the American Gem Trade Association (AGTA), to disclose any enhancements that may have been applied to our gemstones. For the benefit of your company and your customers, Rio Grande encourages you to use these symbols when you buy, display and sell stones and stone-set jewelry.

ASBL Assembled from multiple layers or combinations of manufactured and/or natural material fused, bonded or otherwise joined together to increase stability and/or imitate the appearance of a natural gemstone, create a unique design or generate unusual color combinations. Example: Opal triplets
B Bleached using heat, light and/or other agents to lighten or remove color.
C Coating on the surface with such enhancements as lacquering, enameling, inking, foiling or sputtering of films to improve appearance, provide color or add other special effects.
D Dyed by the introduction of coloring matter to give a new color, intensify present color or improve color uniformity.
E When used to describe turquoise, an electrochemical treatment to improve color. No resins or dyes are used.
F Filling of surface-breaking cavities or fissures with colorless glass, plastic, solidified borax or similar substances (visible under 10X magnification); improves durability, appearance and/or adds weight.
H Heated to effect desired alterations of color, clarity and/or phenomena. If residue of foreign substances in open fissures is visible under properly illuminated 10X magnification,“HF” should be used.
HP Heating and pressure combined to effect desired alterations of color, clarity and/or phenomena.
IMIT Imitation product fabricated in such materials as glass, ceramic or plastic designed to imitate or resemble the appearance, but not duplicate the characteristic properties of a natural gemstone. NOTE: A trade term equivalent to imitation is "simulated."
L A laser and chemicals used to reach and alter inclusions in gemstones, usually diamonds.
O Oiling/resin infusion; the filling of surface breaking fissures with colorless oil, wax, resin or other colorless substances, except glass or plastic, to improve the gemstone’s appearance.
R Irradiation using neutrons, gamma rays, beta particles or high energy electrons to alter color. May be followed by a heating process.
S Stabilized using a colorless bonding agent (such as plastic); used on porous gemstones to add durability and improve appearance (sometimes referred to as “I” impregnated).
SYN Synthetic materials that have essentially the same optical, physical and chemical properties as a naturally occurring gemstone. NOTE: Trade terms equivalent to synthetic are "lab-created" or "lab-grown."
U Diffusion; chemicals used in conjunction with high temperatures to produce color and/or asterism-producing inclusions.
W Waxing/oiling; impregnation of colorless wax, paraffin and oil in porous, opaque or translucent gemstones to improve appearance.

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