The fiery, rainbow colors emanating from a diamond as white light is broken-up into colors. EGL European Gemological Laboratory - EGL has franchises in a number of cities around the world which grade diamonds and offer a diamond grading certificate. The polished planes on the surface of a diamond. The rainbow colors seen in a diamond as a result of dispersion. The property in many diamonds that makes them glow in an environment rich in ultraviolet light.
Diamonds can fluoresce in a number of colors, but generally all but blue are to be avoided.
Faint to medium fluorescence is rarely detected under ordinary lighting conditions. Strong or very strong fluorescence may make a diamond appear milky or oily , especially in sunlight. Irregular in shape, they usually appear step-like or as a splinter. GIA-GTL Gemological Institute of America Gem Trade Lab. The well-respected independent laboratory which grades diamonds and includes a diamond grading report with each diamond.