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