Diamond Fluorescence: Is it Good or Bad?
When shopping for an engagement ring, you might come across a term that leaves many buyers confused: diamond fluorescence. This hidden natural characteristic can significantly impact a stone's price and appearance, but the advice surrounding it is often conflicting.
So, is diamond fluorescence a flaw to avoid, or a clever trick to help you save money? Let’s explore the reality behind the glow.
What is diamond fluorescence?
Fluorescence is the soft, coloured light a diamond can emit when exposed to ultraviolet (UV) light sources, like the sun. Diamonds with no fluorescence or very minimal fluorescence are considered the most desirable, and noticeable fluorescence is considered a diamond defect. Diamonds with strong fluorescence usually emit a blue light and appear hazy when exposed to ultraviolet light.
Do all diamonds fluoresce?
No, not all diamonds fluoresce under UV light. In fact, the majority do not. According to the Gemological Institute of America (GIA), only around 25% to 35% of diamonds exhibit some degree of fluorescence when exposed to UV light. Of that fluorescent percentage, only around 10% show strengths of fluorescence ("Strong" or "Very Strong") that might visibly impact the diamond's appearance. The remaining 65% to 75% of diamonds have no reaction to UV light and will receive a "None" grade on their certificate.
The diamond fluorescence scale
Diamond fluorescence is graded with descriptive terms that indicate the severity of the fluorescence when placed under UV light. The GIA rates diamond fluorescence as either None, Faint, Medium, Strong or Very Strong. During the grading process, the diamond will be compared to master diamonds of different fluorescence grades until a match is found.
- None - The diamond has no fluorescence
- Faint (Faint Blue) - The diamond has minimal fluorescence
- Medium (Medium Blue) - The diamond has slightly noticeable fluorescence, and may appear hazy in sunlight
- Strong (Medium Blue) - The diamond has noticeable fluorescence and will appear hazy in sunlight
- Very Strong (Very Strong Blue) - The diamond has severely noticeable fluorescence, and will appear very hazy in sunlight
Is diamond fluorescence good or bad?
Diamond fluorescence can be considered good or bad, depending on the diamond and its colour grade. In diamonds with a high quality colour grade, fluorescence is considered undesirable.
When diamonds are exposed under ultraviolet light, like sunlight, the diamond may emit a medium blue or strong blue light, and cause the diamond to look hazy. In poorer colour grades, however, the blue light emitted can counterbalance the yellowness of the diamond. In diamonds colour graded I–M, a degree of fluorescence can be favourable, but the stone may look hazy in sunlight.
At Queensmith, we recommend diamonds colour graded between D–F with None or Faint fluorescence for a bright, icy, crisp and clear looking diamond.
Our expert opinion on diamond fluorescence
Try to avoid diamonds with fluorescence and favour a high cut and colour grade for a diamond that will appear bright, icy and super sparkly.
Frequently asked questions
Do you have additional questions? No problem, let us help you through the process
Generally, yes. Because noticeable fluorescence is widely considered a defect in colourless diamonds, stones graded with Medium, Strong, or Very Strong fluorescence are usually priced lower than those graded as "None". While the discount might seem appealing, the trade-off is often a compromise in the stone's beauty. At Queensmith, we recommend investing in a diamond with "None" or "Faint" fluorescence to guarantee a bright, crisp, and clear appearance without any haziness.
Some do, but not all. Only around 30% of natural diamonds emit a soft, coloured glow—most commonly blue, when exposed to ultraviolet (UV) light sources, such as natural sunlight or a blacklight. The remaining 70% of diamonds do not react to UV light at all and are graded as having "None" on their certificate.
If your diamond glows blue under certain indoor lighting, it is likely exhibiting diamond fluorescence. Many modern daylight-mimicking LED lights emit trace amounts of UV rays. If your diamond has a Medium, Strong, or Very Strong fluorescence grade, these UV rays will trigger a reaction within the stone, causing it to emit a visible blue glow.
It can. In diamonds with poorer colour grades (typically graded I to M), a blue fluorescence can actually be favourable. Because blue counterbalances yellow, the blue light emitted can help cancel out the yellowness of the stone, making it appear slightly whiter. However, it is important to remember that even if the colour looks whiter, the fluorescence can still cause the stone to look hazy in natural sunlight.
Yes, it certainly can. When exposed to ultraviolet light, such as stepping outside into natural sunlight, diamonds with Strong or Very Strong fluorescence often take on a milky, cloudy, or hazy appearance. This severely masks the stone's natural fire and brilliance, preventing it from achieving that icy, super-sparkly look.
Our expert gemmologists recommend that you try to avoid diamonds with noticeable fluorescence. To ensure you get the most beautiful stone possible, we recommend opting for a diamond with a high colour grade (between D–F) and a fluorescence grade of either "None" or "Faint". Favouring an excellent cut and high colour grade over fluorescence ensures your diamond will always appear bright, icy, and incredibly sparkly.
Do you have additional questions? No problem, let us help you through the process
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