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Cobalt Coated Tanzanites beginning to appear in volume

AnchorCert gemmologists assess many Tanzanites, grading them according to the AnchorCert Tanzanite system which offers simple consumer friendly classifications for clarity and intensity of colour.
Recently AnchorCert has received its first examples of tanzanites which had been enhanced by the latest process – cobalt coating. The treatment takes the form of a surface coating which can improve the apparent colour of the tanzanite by as much as two grades, ie from A or AA to AAA or AAAA. The colour enhancement makes the stone apparently better quality, and therefore more valuable, than it was originally. However, the cobalt can be polished off and the treatment should definitely be disclosed by the seller.

The treated stones received were between 30 points and one carat and the supplier knew that the stones would be submitted for certification. This suggests that some of the supply chain is buying and selling in good faith and not yet aware of the new treatment which only became available commercially within the last 12 months.

The cobalt treatment is sometimes quite hard to identify with a 10x loupe, but under higher magnification, using a gemmological microscope there are give away signs that AnchorCert gemmologists look for automatically and if the coating is at all imperfect they are easy to spot.

Senior Gemmologist Anu Manchanda explains “on a perfect example the only way we can tell with the naked eye is by the colour, which just doesn’t look right. When we check with a loupe we’ll see that the colour is patchy, particularly when viewed from the crown, and when we put the tanzanite under X –Ray Fluorescence it will show relatively high levels of cobalt. It is in circumstances like this that the wide range of expertise and equipment that we have at AnchorCert really comes into its own”

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