It is widely considered that fluorescence in diamonds is a feature to avoid, despite the price advantages. The market reflects this view; you can often find considerable discounts on diamonds with high fluorescence ratings.
Fluorescence is an emission of light created when a stone or other material is exposed to ultraviolet (UV) light. This glow is only visible in the stone when subject to UV sources such as black lights. A diamond’s fluorescence rating is classified from Very Strong/Extreme, to Medium/Moderate, Faint/Slight or None/Negligible. In 90% of cases, the emanating light is blue, sometimes yellow and rarely other colors. This reaction is certified by gemologists and is described as one of the elements that characterize the quality of the stone.
Recent research by the GIA Gem Trade Laboratory found that only 20% of diamonds with “Very Strong” fluorescence resulted in a slight lack of transparency compared to non-fluorescent stones, while a lack of transparency was visible in only 5% of diamonds with “Medium” fluorescence, and less than 1% of diamonds with a “Slight” fluorescence.
Regarding its impact on a diamond’s whiteness, the study states that fluorescence was visible in only 20% of diamonds with a high color rating (D, E, F, G), while in diamonds with a color rating of I to Z, more than 70% appeared more white. It specified that: "This study intends to challenge the prejudices that the diamond industry has regarding the relatively negative effect given by fluorescence in stones with a higher color rating. The GIA results clearly show that you should evaluate each individual diamond based on its own peculiarities. "
Putting this into practical terms, a diamond with some fluorescence is not necessarily bad, as long as it does not have a “milky” effect and as long as it’s offered at a great price. Be careful not to buy a diamond that, even if it doesn’t have any fluorescence, could be less transparent (which is not very rare) due to microscopic inclusions already present in the stone. This would be the worst kind of purchase, no matter how good the price.
In the diamond industry, there are a lot of misunderstandings and prejudices that arise from incompetence and superficiality, which reflects negatively on the customer. Through this post, it’s my goal to share this information not only with those interested in gemology, but also for people who want to understand how to best evaluate and purchase a diamond.