Symbols for Specific forms of Enhancement
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, which are visible under properly illuminated 10X magnification. The process will improve durability, appearance, and/or add weight.
H Heating ~ The use of heat to effect desired alteration of color, clarity, and/or phenomena (Residue of foreign substances in open fractures is not visible under properly illuminated 10X magnification).
HP Heat & Pressure ~ The use of heat and pressure combined to effect desired alterations of color and/or clarity.
I Impregnation ~ The impregnation of a porous gemstone with a colorless agent (usually plastic) to give it durability and improve appearance.
L Lasering ~ The use of a laser and chemicals to reach and alter inclusions in 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 Radiation ~ The use of neutrons requiring an environmental safety release from the Nuclear Regulatory Commission (NRC), Gamma and/or electron bombardment 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 color and/or asterism-producing inclusions.
W Waxing/Oiling ~ The impregnation of colorless wax, paraffin, and oil in porous opaque or translucent gemstones to improve appearance.