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Gemstone Enhancement Codes

Published by the American Gem Trade Association

Enhancement: Any treatment process other than cutting and polishing that improves the appearance (color/clarity/phenomena), durability, or availability of a gemstone.

N
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
E

The "E" symbol indicates that a gemstone has undergone its traditional enhancement process.

B
B
Bleaching

The use of heat, light and/or other agents to lighten or remove a gemstone's color.

C
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
D
Dyeing

The introduction of coloring matter into a gemstone to give it new color, intensify present color or improve color uniformity.

F
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
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
HP
Heat & Pressure

The use of heat and pressure combined to effect desired alterations of color clarity and/or phenomena.

I
I
Impregnation

The impregnation of a porous gemstone with a colorless agent (usually plastic) to improve durability and appearance.

L
L
Lasering

The use of a laser and chemicals to reach and alter inclusions in diamonds.

O
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
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
U
Diffusion

The use of chemicals in conjunction with high temperatures to produce artificial color and/or asterism-producing inclusions.

W
W
Waxing/Oiling

The impregnation of a colorless wax, paraffin, and oil in porous opaque or translucent gemstones to improve appearance.

All enhancement codes are standardized by the American Gem Trade Association