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 Home / Gem Library / Resources / Enhancement Codes November 21, 2017  

Definitions and Gemstone Enhancement Codes

The table below sets forth proper methods to comply with the FTC Guides. With the exception of the normal fashioning (cutting and polishing) of a diamond and other gemstone.


(N) None Indicates this particular gemstone has received no enhancement and the seller will guarantee this.

(D) Dyed

(E) Gemstone is routinely heated Indicates that this gemstone is routinely enhanced. The "E" symbol appears by gemstones that are routinely enhanced. Since many enhancements are difficult or impractical to prove definitively, the approach taken is, unless otherwise indicated, to assume that such enhancement has been applied to that particular gemstone. This assumption is made to protect both the buyer and seller. If a more specific method of enhancement is known, then the specific enhancement code will be used.

(G) Irradiation Gems may change color if exposed to radiation. This may come from radioactive elements within the Earth's crust, or from artificial sources. Natural radiation may take millions of years to have an effect, while artificial irradiation may take only few hours to change a gemsís color. In some cases a gem will revert to it's original color, or may fade with time. Irradiation is often used with blue topaz. The stone is irradiated brown and then heated to produce the blue color. Irradiated stones do not require special care.

Indicates the gemstone has undergone some form of Gamma or Electron Irradiation. This is the use of gamma and/or electron bombardment to alter a gemstone's color. May be followed by a heating process ("H"). Example: Blue Topaz is commonly enhanced in this manner.


(H) Heat Enhancement Indicates the stone has been heated to effect desired alteration of color, clarity, and/or phenomena. Example: Sapphire, Ruby, Tanzanite, Citrine, and Aquamarine are commonly enhanced in this manner.

(O) Oiling Indicates the introduction of a colorless oil into fissured or porous gemstones was made to improve appearance.

(O) Oiling/Resin Infusion Indicates the introduction of a colorless oil, wax, natural resin, or unhardened man-made materials into fissured or porous gemstones was made to improve appearance. Example: Commercial grade Emerald is commonly enhanced in this manner.

(T) Heat Treated (berylium) Any corundum that shows indications of having undergone heating accompanied by the introduction/diffusion of a chemical elements(s) (facilitating the modification or creation of color) from an external source shall be described as species, natural corundum, variety, sapphire/ruby; comments: indications of heating, lattice diffusion of a chemical element(s) from an external source or, the introduction of a chemical element(s) from an external source.

Treated Treated

Unknown Unknown



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