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

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 laquering, 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. This 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: IRRADIATION
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 a colorless wax, paraffin, and oil in porous opaque or transluscent gemstones to improve appearance.

OTHER ENHANCEMENT CODES

SYN: SYNTHETIC
The reproduction of natural gems with essentially the same composition and structure as their natural counterparts.

ASBL: ASSEMBLED
The process of producing a single stone from two or more separate pieces.

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