Spectrum | Body Tone |
X1: Extra Wide Intense
X1-RO: Red-Orange shift X1-GG: Green-Gold shift
X1-GB: Green-Blue shift
X2: Wide Intense
X3: Evident
G1: Vivid Grain
G2: Dim Grain
PP: Poor |
Black (N1-N4) Dark (N5-N6) Light (N7-N9) Crystal (N7-N9) |
Gemval color grade system for natural opals is based on two independent scales: Spectrum and Body Tone.
Spectrum scale describes intensity of color play, spectral range of splashes, pattern coverage and overall quality of the pattern. Body Tone scale refers to the darkness/lightness of a basis mineral.
Gemval valuation system is not applicable to boulder, matrix, doublet, triplet opals or Mexican fire opals.