Here is a list of enhancement codes and their symbols used for Gemstones:

(B) = Bleaching

(C) = Coating

(D) = Dyeing

(F) = Filling

(H) = Heating

(HP) = Heat & Pressure

(I) = Impregnation

(L) = Lasering

(O) = Oiling

(R) = Irradiation

(U) = Diffusion

(W) = Waxing

The Enhancement Codes are from the American Gem Trade Association. Also, the “N” symbol is for natural stones, and the “E” symbol is used when the gemstone has been enhanced.

Enhancement is a process other then cutting and polishing that improves the appearance of the gemstone. 

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