AGTA Codes

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

E: The “E” symbol indicates that a gemstone has undergone its traditional enhancement process.

AGTA examples - Code N

(N) Natural

No modification; natural stones which are not currently known to be enhanced (or currently has no known modification process).

AGTA examples - Code B

(B) Bleaching

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

AGTA examples - Code 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.

AGTA examples - Code D

(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 and/or appearance, and/or to add weight.

AGTA examples - Code H

(H) Heating

The use of heat to effect desired alteration of color, clarity and/or phenomena. If residue of foreign substances in open fissures is visible under properly illuminated 10X magnification, H F should be used.

AGTA examples - Code HP

(HP) Heating and Pressure

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

AGTA examples - Code I

(I) Impregnation

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

AGTA examples - Code IMIT

(IMIT) Imitation

A simulant, which is defined as a man-made single crystal product that is used to simulate the appearance, but not duplicate the characteristic properties of the natural gemstone it imitates.

(L) Lasering

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

AGTA examples - Code 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 gemstone's appearance.

AGTA examples - Code R

(R) Irradiation

The use of neutrons, gamma rays or beta particles (high energy electrons) to alter a gemstone's color. The irradiation may be followed by a heating process.

AGTA examples - Code SYN

(SYN) Synthetic

Synthetic materials that have essentially the same optical, physical and chemical properties as a naturally occurring counterpart. In all cases, stones must be referred to as "synthetic ruby," "laboratory grown sapphire," or "Chatham-Created emerald," etc.

AGTA examples - Code U

(U) Diffusion

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

(W) Waxing

Waxing/Oiling: The impregnation of a colorless wax, paraffin or oil in porous opaque or translucent gemstones to improve appearance.