Step 8: Checking for Fluorescence
A small percentage of diamonds have fluorescence. This means that they glow when stimulated by long-wave Ultra Violet light. The majority exhibit blue fluorescence but sometimes diamonds may fluoresce pink, orange, green or red. When measuring a diamond’s fluorescence, it is spilt into the following categories: None or Nil, Faint, Medium, Strong and Very Strong.
Generally, most fluorescence has little to no effect on the appearance of the diamond. Occasionally strong or very strong fluorescence may make the diamond appear cloudy and an experienced diamond grader could tell that the stone exhibits fluorescence. For example, when looking at a fluorescent diamond that is J color or lower, strong fluorescence may make the stone appear whiter when compared to a non-fluorescing diamond. It may also have the opposite effect on a high color diamond; D color may appear to have a blueness or cloudy appearance. Fluorescence currently has a negative effect on the value of the diamond; strong fluorescence can reduce the value of a diamond by up to 25%.