The type IIA diamonds can be screened readily by testing for opacity or transparency to Short Wave UV and by testing for the presence of or lack of electrical conductivity.
These two simple tests will eliminate type IIB and all type I diamonds only leaving the very rare IaB and IIA types. In the vast majority of all diamonds we are told type IIA is only about a 1% occurence. Type IaB is only a tiny fraction of that. In large diamonds, we are given to understand type IIA is far more common than we have been led to believe. I have asked if they might be as high as 10% to 20% of diamonds 3 carat and larger. While I was not given a real answer, the smile on the faces of those asked indicated I was headed somewhere they did not wish to go with a direct answer. I feel that we may have to deal with a rather large number of potentially treated or treatable diamonds in the important and expensive large sizes eventhough we are told that overall these diamonds are very rare.However, once the diamonds have been screened by cheap and easy testing, if one needs to know more, then the fancy IR Spectroscope comes into play, but unless you are a scientist or work in a very world class lab, it is far from an essential tool for most gemologists at the present time. Maybe it will become a less costly tool and the need may grow to have them in normal gem labs. Time will tell.It is my understanding that IIA diamonds are not absolutely nitrogen free. This has been said to be a simplistic description but not exactly the case.
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David Atlas
Accredited Gem Appraisers