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 N1 - N4 - Is for black tone body types.
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.
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.
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
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Over 5 years ago Opal buyers would constantly check and ask questions about Body tone for black opals.
Market trends have now changed, and most buyers ask about Brightness as well as Body tone.
Chinese buyers would only buy N1 body tone black opal and this placed a lot of demand for Body tone ahead of Brightness.
Today Brightness is the most important and has major consideration factor in valuing opals as well as the opal pattern.
Unfortunately we have two systems for Brightness ratings that have not been approved by Cibjo or leading gemmologist organizations.
On Opalauctions we recommend the Australian opal association Opal brightness Guide that places brightest opal at B1. compared to the original B5 rating.
Reply Tony translate
Or can we buy the rule Opal base body tone guide SVP
Yes here is link
I do get confused with body tone chart with brightness chart.
Its seems everyone states body tone of an opal but I think Brightness is just as important
Lot black opals now seem to be N2 to N3 as an average
I do not see many N1 black opals and they are all expensive now
That’s why I think Brightness is more important now and most are rated B3 to B4
May I make a suggestion that Brightness be added below Body tone on black opal listings