are exposed to invisible ultraviolet (UV) rays.
Having said this, fluorescence can cause a diamond to glow when exposed to ultraviolet light, due to trace minerals within the diamond. Though the intensity of the fluorescence can be graded with specialized ultra violet lamps, the ultraviolet rays from the natural sunlight will pick up some of the fluorescence.
Two important facts should be considered regarding fluorescence:
1. Color of fluorescence - Nearly 30% of natural diamonds in the market have some level of fluorescence in them and most commonly can be seen as blue and sometimes yellow. If the diamond fluorescence is blue, on occasion it may be considered to be a positive factor, since it can make the diamond look whiter, but not always. However, if the diamond fluorescence is yellow, this is a negative factor because the diamond will look lower in color under ultraviolet light.
2. Strength of fluorescence - The range of strengths can be found on a full grading report and will be listed as either; None, Faint, Medium, Strong or Very strong, as per above-noted diagram. A characteristic that sometimes follows a very strong fluorescence is a muddled or oily look to the diamond, even under normal lighting conditions. This negatively impacts a diamonds value, but may not be noticeable at first look.
Understanding fluorescence and their impact on a diamond's value may help you understand why sometimes you may see two separate diamonds with the same main 4 qualities (The Four C’s) but with varying prices.
For more information on your particular diamond(s), consult your Professional Jeweller.