What are a detailed for opal grading when we mean below commercial, commercial, good,fine and extra fine
Opal is a stone where there is no specific grading scale as each is unique and relates to source. Different areas produce different types of opal, seam, crystal, black, fire, boulder and so on. From here is comes down to the colour, intensity, pattern, size, quality of cut and polish, stability of the opal structure etc.
Then is it a solid opal, doublet or triplet, colour enhanced, chemically treated and so on.
To truly understand opal and its value takes years of experience and there are no books to guide you, it’s all about being involved and learning from those who have been in the industry of many years.
Hi not sure where you are living but if you were in Australia you could do an advanced Opal course with the Gemmological Association of Australia
see the GAA website Advanced Opals – Gemmological Association of Australia
Depends on where the opal is from. Ethiopian is typically graded as aaa…aa…a…b…mine run/Australian is graded based on base color n1-n9, brightness 1-5, and a number of other factors…directionality, size, cut, weight…
Then add rarity of the colours, exhibited patterns, colour density, the list goes on and no two people will give the same value to an opal, it’s like the wild west.