Coated Diamonds Appear in New York

A not so easily detected coating for diamonds has made its appearance in New York, reports National Jeweler (December '83). A silicon and plastic composite is "sputtered" onto the diamond using plasma physics, leaving no brush marks and thereby making detection difficult without a microscope.
At present, very few stones have been examined, but alert has gone out to be aware of the process. Not only is the coating used for creating a "fancy" color for diamonds, but also to improve apparent color in the G to L range. Treatment for fancies is generally a heavier coating and is applied to the entire pavilion of a low color stone. For improvement of two or more grades, a coating with a slightly bluish cast is applied to the girdle.
Since color grading is generally not done with a microscope, this treatment may easily go unnoticed. The silicon component adds color while the plastic increases durability requiring an acid and acetone combination for the coating's removal.