SYMBOLS FOR SPECIFIC FORMS OF ENHANCEMENT
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.