American Gem Trade Association 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](http://assets.stullercloud.com/web/apps/images/contentBlock/AGTA/agta-n.jpg)
(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](http://assets.stullercloud.com/web/apps/images/contentBlock/AGTA/agta-b.jpg)
(B) Bleaching
The use of heat, light and/or other agents to lighten or remove a gemstone's color
![AGTA examples - Code C](http://assets.stullercloud.com/web/apps/images/contentBlock/AGTA/agta-c.jpg)
(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](http://assets.stullercloud.com/web/apps/images/contentBlock/AGTA/agta-d.jpg)
(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](http://assets.stullercloud.com/web/apps/images/contentBlock/AGTA/agta-h.jpg)
(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](http://assets.stullercloud.com/web/apps/images/contentBlock/AGTA/agta-hp.jpg)
(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](http://assets.stullercloud.com/web/apps/images/contentBlock/AGTA/agta-i.jpg)
(I) Impregnation
The impregnation of a porous gemstone with a colorless agent (usually plastic) to improve durability and appearance.
![AGTA examples - Code IMIT](http://assets.stullercloud.com/web/apps/images/contentBlock/AGTA/agta-imit.jpg)
(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](http://assets.stullercloud.com/web/apps/images/contentBlock/AGTA/agta-o.jpg)
(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](http://assets.stullercloud.com/web/apps/images/contentBlock/AGTA/agta-r.jpg)
(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](http://assets.stullercloud.com/web/apps/images/contentBlock/AGTA/agta-syn.jpg)
(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 "lab-created emerald," etc.
![AGTA examples - Code U](http://assets.stullercloud.com/web/apps/images/contentBlock/AGTA/agta-u.jpg)
(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.