The Gemological Science International (GSI), recently said that it had “witnessed a case of extreme colour instability of a CVD diamond within its laboratory testing facility”.

GSI said that in the course of a standard testing procedure at its laboratory, a 2-carat CVD diamond was exposed to high powered UV rays and the result was that it went “from near colourless to blue colour”.

After this, the stone was put away in the vault for a week; and when it was brought out again, the stone still retained the blue colour.

“While it’s known that CVD diamonds can change colours under this type of ultraviolet light or extreme heat, typically a diamond of this variety returns to its normal colour after 30 minutes to an hour of direct sunlight,” GSI explained. “The GSI lab team discovered that under standard ambient lighting conditions, this particular stone took two and a half hours to return to normal colour.”

While the GSI team underlined the fact that most CVD diamonds do not change to this extreme, they stressed the importance of lighting conditions when colour grading diamonds.

“It is strongly suggested that all laboratory-grown CVD diamonds are placed in a full-spectrum light box for at least 30 minutes before colour grading,” said Nicolas Del Re, Chief Information Officer of GSI.

Further, he also cautioned, based on their findings, that “colour changes may happen through casual use as well”.

Del Re added: “When wearing out in the open, CVD diamonds may change in colouration upon even subtle exposures to electromagnetic radiation such as UV rays on a sunny beach or under a blacklight in a nightclub for example. We have the electrons in defects within a CVD diamond causing the energy state to change and in turn affect the way colour is absorbed on the visible spectrum.”