Gemstone Enhancements

American Gem Trade Association (AGTA) Gemstone Enhancement Codes

N - Natural: No modification (or currently has no known modification process).

B - Bleaching: The use of heat, light and/or other agents to lighten or remove a gemstone’s color.

C - Coating: The use of such surface enhancements as lacquering, enameling, inking, foiling, or sputtering of films to improve appearance, provide color, or add other special effects.

D - Dyeing: The introduction of coloring matter into a gemstone to give it new color, intensify present color or improve color uniformity

F - Filling: The filling of surface-breaking cavities or fissures with colorless glass, plastic, solidified borax or similar substances.  This process may improve durability and/or appearance, and/or to add weight.

H - Heating: The use of heat to effect desired alteration of color, clarity and/or phenomena. If residue of foreign substances in open fissures is visible under properly illuminated 10X magnification, H F should be used.

HP - Heating and Pressure: The use of heat and pressure combined to effect desired alterations of color, clarity and/or phenomena.

I - Impregnation: The impregnation of a porous gemstone with a colorless agent (usually plastic) to improve durability and appearance.

L - Lasering: The use of a laser and chemicals 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: The use of neutrons, gamma rays or beta particles (high energy electrons) to alter a gemstone’s color. The irradiation may be followed by a heating process.

U - Diffusion: The use of chemicals in conjunction with high temperatures to produce ARTIFICIAL color change and/or asterism-producing inclusions.

Note: It is a violation of the FTC Guides to fail to disclose diffusion on gemstones in advertising, promotional literature or commercial documents.

Suggested methods of disclosure are:

  • “(Gemstone): chemically colored (Color) by diffusion.”
    • Example: “Sapphire: chemically colored blue by diffusion.”

​If the color of the diffused gemstone does not permeate the entire stone, then the following statement must also appear:

“Although the color induced in diffusion treated gemstones is permanent, it does not permeate the entire gemstone; therefore, recutting or repolishing is not recommended.” 

W - Waxing/Oiling: The impregnation of a colorless wax, paraffin or oil in porous opaque or translucent gemstones to improve appearance.

ASBL - Assembled: “ASBL” is the tag code for products made of 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.​

  • ASBL Opals – (Various Combinations) Doublets and Triplets
  • ASBL Garnet & Glass Doublets
  • ASBL Sapphire – Synthetic Sapphire Doublets
  • ASBL Colorless Beryl – joined by green bonding adhesive (Triplets)
  • ASBL Mabe “Pearls” color coated, dyed, bleached, filled with hardened substances and a Mother of Pearl back.  Sometimes coating can be plastic or polymer to protect the thin nacre.
  • ASBL Bonded material such as Turquoise, Lapis, etc.

The “ASBL” coded stones require special care; avoid household chemicals, cosmetics, abrasives, and sudden shocks.

CMP - Composite: "CMP" is the tag code for products made of disparate parts or elements in their construction.

  • CMP Emeralds – Pieces of Emerald that are bonded together with polymer
  • CMP Turquoise – Crushed Turquoise that is reconstructed/reconstituted and bonded with polymer

The “CMP” coded stones require special care; avoid household chemicals, heat, abrasives, ultrasonic, and sudden shocks.