Diamond fluorescence is the visible glow, usually blue, that some diamonds give off under ultraviolet light. GIA says 25% to 35% of the diamonds it receives fluoresce, but only 10% of those strongly enough to affect appearance, and that fluorescence "isn’t bad for a diamond." It shows only while UV light is on the stone.
What is diamond fluorescence?
GIA's definition: "Fluorescence is the visible light some diamonds emit when exposed to ultraviolet (UV) rays. The strength and intensity of a diamond’s reaction to long-wave UV light is referred to as fluorescence." The glow stops when the UV does: "The light emitted from the diamond lasts as long as the diamond is exposed to the UV light." (GIA, How to Buy a Diamond: Diamond Fluorescence) Sunlight contains UV, which is why some diamonds can look slightly different outdoors than indoors.
Is fluorescence bad in a diamond?
Usually not. GIA's figures:
- "25% to 35% of the diamonds submitted to GIA exhibit some fluorescence, but only 10% of those show enough fluorescence to impact appearance."
- "In more than 95% of the diamonds that exhibit fluorescence, the color seen is blue."
- "A strongly fluorescing diamond that contains nano-inclusions may appear hazy or oily. Fewer than 0.2% of the fluorescent diamonds we see exhibit that appearance."
GIA's conclusion: "Fluorescence isn’t bad for a diamond, but it is important to know the fluorescence of your diamond before making your purchase."
Faint vs none vs strong blue fluorescence: what changes?
The report's fluorescence entry describes how strongly the stone glows under a UV lamp in the lab; GIA notes "Every GIA Diamond Grading Report includes a fluorescence evaluation." The rare hazy appearance GIA describes belongs to strongly fluorescing stones, so strong blue fluorescence is the range to look at in person, in daylight, before you decide. GIA also notes "A diamond with strong fluorescence may produce more contrast."
Do lab-grown diamonds have fluorescence?
Some do, and they often behave differently from mined diamonds. The American Gem Society describes the patterns (AGS, Detecting Laboratory-Grown Diamonds):
- HPHT-grown: "When they fluoresce, the reaction is typically stronger to a short-wave as compared to a long-wave ultraviolet lamp. In some cases, this material can exhibit persistent phosphorescence after the ultraviolet lamp has been turned off."
- CVD-grown: "Perhaps their most distinctive feature that a gemologist can check for is pink-to-orange or yellow-to-green fluorescence since most natural diamonds exhibit blue (or sometimes yellow) fluorescence colors."
In practice, the short-wave and colored reactions are clues gemologists use to identify lab-grown stones; they are not something you see in a restaurant or office. For how stones are identified, see how to tell if a diamond is lab-grown.
Should fluorescence change what you pay?
Treat it as one more fact to know, not a reason to panic. Since only a small share of fluorescent stones look different in normal light, judge the stone you are actually buying: look at it in daylight and indoors, beside a stone with little or no fluorescence, and decide whether you see a difference.
What should you check before you buy?
- Find the fluorescence entry on the grading report, and which lab issued it.
- If it reads Strong or Very Strong, look at the stone in daylight and in indoor light.
- Compare it beside a stone with none or faint fluorescence.
More on grading in our diamond clarity guide and 4Cs guide.
See lab-grown diamonds in Paramus
Browse our lab-grown diamond rings and bracelets, or book an appointment to see stones in different light before you choose.
Prestige Diamonds NJ
327 E State Route 4, Paramus, NJ 07652 (inside The Jewelry Center)
(201) 488-4280
