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Reference Values of Gems
Database updated: 01 November 2017
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Color grading system for Opals

The Gemval color grade system for natural opals is based on two independent scales:
- Spectrum &
- Body Tone

The Spectrum scale describes intensity of the color play as well as the spectral range of splashes, pattern coverage and overall quality of the pattern. The Body Tone scale refers to the darkness/lightness of a basic mineral.

The Gemval valuation system is not applicable to boulder, matrix, doublet and triplet opals or to Mexican fire opals.


Spectrum Body Tone

X1: Extra Wide Intense
Strong radiance and exceptional color play in a wide spectral range. Splashes fill over 90% of the body. Rich, contrasted pattern.

X1-RO: Red-Orange shift
Strong radiance, intense color play with a dominance of red, orange and yellow hues. Splashes fill over 90% of the body.
Rich, contrasted pattern.

X1-GG: Green-Gold shift
Strong radiance, intense color play with a dominance of green and warm yellow hues. Splashes fill over 90% of the body. Rich, contrasted pattern.

X1-GB: Green-Blue shift
Strong radiance, intense color play with a dominance of green, blue and violet hues. Splashes fill over 90% of the body. Rich, contrasted pattern.

X2: Wide Intense
Good radiance and wide color play with a single hue prevailing. Splashes fill over 70% of the body. Sharp, distinct pattern.

X3: Evident
Moderate radiance and reduced color play. Splashes fill over 50% of the body. Has a disproportional pattern.

G1: Vivid Grain
Strong radiance and color play. Splashes fill over 70% of the body. Sharp granular or pinpoint pattern.

G2: Dim Grain
Moderate radiance and reduced color play. Splashes fill over 50% of the body. Granular or dusty pattern.

PP: Poor
Poor radiance with scanty color play. Splashes fill less than 50% of the body. Poor, blurred pattern.

Black (N1-N4)

Dark (N5-N6)

Light (N7-N9)

Crystal (N7-N9)


 
 
 
 
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