Gemstone Enhancement Codes* N = Not Enhanced B = Bleaching C = Coating D = Dyeing F = Filling H = Heating HP = Heat & Pressure I = Impregnation L = Lasering O = Oiling/Resin R = Irradiation U = Diffusion SC = Special Care ASBL = Assembled CMP = Composite W = Waxing/Oiling in Opaque Stones *Codes and type of treatments must only be used as directed in the Gemstone Information Manual, available at www.agta.org These will help you understand more about how we grade the gemstones on our website. Please let us know if you have any questions.