Gemstone Treatment Guide

At NW Gems & Diamonds we believe in and give full disclosure of any and all known treatments of our gemstones and diamonds. Because many of our gems come direct from the cutting floor, as well as from our trade-trusted suppliers, you can have absolute confidence in the authenticity of our gemstones. We can also send any of our gemstones to GIA for certification for an additional fee. 

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

AGTA examples - Code N


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

AGTA examples - Code B


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

AGTA examples - Code C


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


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. This process may improve durability and/or appearance, and/or to add weight.

AGTA examples - Code H


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

Heating and Pressure (HPHT)

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

AGTA examples - Code I


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

AGTA examples - Code IMIT


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.


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

AGTA examples - Code 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


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


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


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


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