S.E. Needham
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Gemstone Enhancement Codes
Enhancement: Any treatment process other than cutting and polishing that improves the appearance (color/clarity/phenomena), durability, or availability of a gemstone.
N: The "N" symbol appears on the chart only for natural stones which are not currently known to be enhanced; however, the "N" symbol can also be used for other natural gemstones in the event that a gemstone has received no enhancement and the seller will provide a guarantee that there has been none.
E: The "E" symbol indicates that a gemstone has undergone its traditional enhancement 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, appearance, and/or 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 fractures is visible under properly illuminated 10X magnification HF should be used. |
HP Heat & Pressure: The use of heat and pressure combined to effect desired alterations of color clarity and/or phemonena. |
| I Impregantion: 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 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 gemstones appearance. |
| R Irradiation: The use of neutrons, gamma rays or beta particles (high energy electrons) to alter a gemstones 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 and/or asterism-producing inclusions. |
W Waxing/Oiling: The impregnation of a colorless wax, paraffin, and oil in porous opaque or translucent gemstones to improve appearance. |