American Gem Trade Association Enhancement Codes
N Natural
E Enhanced, which describes any of the following:
ASBL Assembled into single stones created with two or more separate pieces
B Bleached
C Coated with lacquer, enamel, foils, etc.
D Dyed to intensify color or uniformity
F Filling added to the surface with clear glass, plastic, or borax
H Heated to alter color, clarity, and/or phenomena
HP Heated and pressurized to affect color and clarity
I Impregnated with plastic to improve durability
L Lasers and chemicals used to alter inclusions (this one is for diamonds)
O Oil fills the surface fissures to improve appearance; wax and resin also used in this technique
R Irradiation (gamma and/or electron bombardment) is used to alter color.
SYN Synthetic-manmade, but created with the same composition and structure as the real thing
U Diffusion-a chemical/heat treatment to produce color and/or phenomena
W Wax or oil is introduced to opaque or translucent stone to improve appearance