Some natural diamonds contain dark inclusions of graphite or some other mineral, but these inclusions do not have a metallic luster. When examined between two polarizing filters oriented at an angle of 90 degrees to each other, a natural diamond often exhibits a dotted pattern or luminous mosaic of interference or “effort” colors. These interference colors result from the diamond being subjected to stresses while it was deep in the earth or during its explosive eruption on the earth’s surface. In contrast, synthetic diamonds grow in an almost uniform pressurized environment where they are not subjected to stress, so when examined in the same way, they show no deformation pattern or a weak band deformation pattern. The fluorescence of synthetic diamonds is also often very useful for identification, it is often stronger under a short wave than a long wave ultraviolet lamp and can show a distinctive pattern. Synthetic diamonds grown with HPHT tend to exhibit a cross-shaped fluorescence pattern on the crown or pavilion of the cut stone. Synthetic diamonds grown with CVD can exhibit a streaked pattern when viewed across the pavilion facets. Typical fluorescence colors are green, yellow-green, yellow, orange or red. When the ultraviolet lamp is turned off, the synthetic diamond may exhibit persistent phosphorescence for up to a minute or more.
The real identification challenge facing the jewelry trade is experimenting with very small diamonds that are sold in packages of several hundred to several thousand and which can include both natural and synthetic diamonds. To help the jewelry trade deal with this problem, there are now automated tools created and developed to test even very small diamonds called DiamondView
(Synthetic Diamond Detector).
In summary, synthetic diamonds are now being made available in increasing quantities for the use of jewelry; we know that they can be identified with a DiamondView that verifies samples of any size and color using the three basic checks which are photoluminescence, ultraviolet illumination and optical absorption. The detectable characteristics may vary under heat treatment (low or high pressure); these changes are identifiable and can provide unambiguous detection of synthetic diamonds grown with CVD or HTHP.