The Fluorescence Factor

Fluorescence is another quality test for diamonds. It refers to the glow (mostly a blu or a yellow hue) that a diamond emits when placed under ultra-violet light. Faint fluorescence is not visible in the natural light, but anything more than that will make the diamond look milky, cloudy and it will not sparkle in all lights. Fluorescence is present in roughly 30 percent of diamonds at varying degrees. The presence of fluorescence affects price drastically, so always avoid purchasing diamonds with anything more than faint fluorescence. GIA has determined the Fluorescence Grade using the following intensity scale:

The higher the scale, the cheaper the diamond value. The presence of Fluorescence should not be a huge factor in your purchase decision from a visual standpoint.