Opal Brightness and Body Tone Guide

The Opal Body Tone Guide was designed and created by the Opal Association of Australia and acts as a guide for Black Opal and Boulder Opals. The Opal industry has recently also been using this guide for many Opal types including Ethiopian Opals.

Body Tone Guide

1. Body Tone N1 - N4 - Is for black tone body types.

2. Body Tone N5 - N6 - Is for Dark Opal, where the body tone is not dark enough to be classified as a Black Opal, and it is too dark to be classified as a light colored Opal. Most of this material will come from Lightning Ridge as well.

3. Body Tone N7 - N9 - Is for light coloured Opals mined also at Lightning Ridge but these lower body tone grades can and have been used on Coober Pedy Opals and Ethiopian Opals.

The body tone of an opal is different to the play of color displayed by precious opal. The body tone refers to the relative darkness or lightness of the opal. Thus you ignore the pattern, play of color and the base of the stone. This is assessed on a scale of body tone accepted in current opal nomenclature and adopted by the opal association.

Opal that has a distinct colored body with yellow, orange, red or brown tone can still be classed as black, dark or crystal Opal by reference to the scale of the base body chart. So any opal can be classed using the base body scale chart.

Opal Brightness Guide

The Opal Brightness Guide assists in assigning a value to how bright an Opal is to the naked eye. Opal brightness can be described as

• Vivid

• Very Bright

• Bright

• Moderate

• Subdued