Topaz is most common in colorless and brown colors. Blue topaz is achieved by a combination of irradiation—which can turn the material brown—and heat treatment, if needed—which renders the stone blue.
According to Professor Jill Banfield of UC Berkeley, nuclear reactors “create an intense blue [in topaz] (that does not need secondary heat treatment).” Other irradiation methods require the heat treatment to achieve blue color.
(A description of the chemical process can be found on this Oak Ridge Associated Universities )
(A description of the chemical process can be found on this Oak Ridge Associated Universities )
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