About Blue Topaz
According to a well-known gem and jewelry industry magazine, " Colored Stone", since the early 2000s, blue topaz has become the second most popular gemstone in the world (sapphire is consistently number one). Topaz popularity is certainly not surprising. Topaz is a very hard material - 8 on the Mohs hardness scale - and blue topaz is a very pretty stone that is available in a wide range of vivid hues with a striking vitreous luster. It is also a very affordable gem when compared to the price per carat of similar colored gemstones such as aquamarine.
The second important thing is that topaz does not occur naturally in the deeply saturated blues you find on the market today. Blue topaz in nature is very rare indeed and tends to be a very pale blue. The vivid blues available on the market have all been produced by treatment and enhancement of colorless white topaz - with irradiation and often also with heat. The color change in blue topaz is considered permanent and stable. In the past, there was some controversy about the safety of this treatment for the consumer, but in July of 2007, the American Nuclear Regulatory Commission (NRC) tested 9 batches of irradiated blue topaz gems, averaging 500 carats each, and found that the results showed none of the enhanced topaz material posed health risks to consumers.
There are three different irradiation methods used to produce blue topaz. One method, used to produce a very pale blue hue is exposure to a gamma ray source in a cobalt irradiator. This method does not cause gemstones to be radioactive. The second method is electron bombardment in an accelerator. This is also known as 'linac' treatment and produces the color seen in 'sky blue' topaz. The third method of irradiation exposes topaz to fast neutrons in a nuclear reactor. This produces the darker hues known as 'London blue'. Due to residual radioactivity, irradiated topaz must be held in a secure facility for a specified period of time before it can be released for heating, cutting and polishing. The length of time varies from a few weeks for linear accelerator irradiated topaz, to a several years for topaz irradiated in a nuclear reactor.
- First Published: October-17-2007
- Last Updated: May-19-2017
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