Lab Warns of Color Instability in CVD

RAPAPORT... Synthetic diamonds grown using chemical vapor deposition (CVD) could change color for an extended period following exposure to certain light forms, Gemological Science International (GSI) has warned. When testing a 2-carat CVD diamond,GSI exposed the stone to high-powered ultraviolet (UV) rays, during which it wentfrom near colorless to blue, the organization said Tuesday. This blue coloring remained despite a week in a vault, GSI explained.  Although CVD diamonds are known to change color understrong UV lighting or extreme heat, they generally return to normal after30 minutes to an hour of direct sunlight, GSI noted. However, the stone in question took two-and-a-half hours to return to its regular hue,it added, warning that color changes in CVD may occur through casual use. "When wearing [them] out in the open, CVD diamonds may change in coloration upon even subtle exposures to electromagnetic radiation, such as UV rays on a sunny beach, or under a blacklight in a nightclub, for example," said GSI chief information officer Nicolas Del Re. The stones change color due to photochronism, a process bywhich the electrons in defects within the CVD diamond cause the energy state tochange, thereby affecting the way color is absorbed on the visible spectrum,the organization explained. "It is strongly suggested that all laboratory-grown CVD diamonds are placed in a full-spectrum light box for at least 30 minutes before color grading," Del Re added.  Image: Examining a CVD diamond. (Gemological Science International)