American Gem Trade Association (AGTA) 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 stone 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.
SYMBOLS FOR SPECIFIC FORMS OF ENHANCEMENT
The use of heat, light and/or other agents to lighten or remove a gemstone's color.
The use of such surface enhancements as laquering, enameling, inking, foiling, or sputtering of films to improve appearance, provide color, or add other special effects.
The introduction of coloring matter into a gemstone to give it new color, intensify present color or improve color uniformity.
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. This process will improve durability, appearance, and/or add weight.
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.
The impregnation of a porous gemstone with a colorless agent (usually plastic) to give it durability and improve appearance.
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.
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.
The use of chemicals in conjunction with high temperatures to produce color and/or asterism-producing inclusions.
The impregnation of a colorless wax, paraffin, and oil in porous opaque or transluscent gemstones to improve appearance.
OTHER ENHANCEMENT CODES
The reproduction of natural gems with essentially the same composition and structure as their natural counterparts.
The process of producing a single stone from two or more separate pieces.