What You Should Know About Diamond Fluorescence

Round cut diamond header

Diamond fluorescence is a topic that many shoppers ask about. It’s a contested topic within the diamond industry itself, and experienced jewelers tend to have differing opinions about it. Here at Ritani, we’ve been crafting diamond jewelry for 20 years. Our diamond experts are here to provide objective answers to 12 of the most common diamond fluorescence questions.

Some jewelers say that fluorescence always has a negative effect on your diamond’s quality and appearance. But here at Ritani, we believe that diamond fluorescence is actually more a matter of personal taste. In fact, if you understand it correctly, it can be your friend when you’re ready to purchase.

1. What is diamond fluorescence?

“Fluorescence, in its most simple form, is the effect that ultraviolet (UV) light has on a diamond,” according to the GIA. UV lights (aka black lights), enhance the visibility of certain elements causing them to glow or radiate light. A diamond that glows under UV light is called ‘fluorescent’.

2. Do all GIA or AGSL certified diamonds receive a fluorescence grade?

Yes, every loose diamond with a GIA (Gemological Institute of America) certificate has a fluorescence grade. You can find the fluorescence grade in the “Additional Grading Criteria” section of the GIA grading report.
GIA-diamond-grading-report-sample

If your stone has been graded by the AGSL (American Gem Society Laboratories), you’ll find the fluorescence grade under the Comments section.

agsl-diamond-grading-report-fluorescence

3. What is the grading scale for diamond fluorescence?

Diamond fluorescence chart. Photo credit: Adiamor.

The GIA’s fluorescence scale runs from least to most fluorescent: None, Faint, Medium, Strong, and Very Strong. The AGSL used to use the grading term “Inert” in addition to None, but now they combined the two terms under a Negligible fluorescence grade.

GIA and AGS Fluorescence Grading Scales

GIA None Faint Medium Strong Very Strong
AGS Negligible Medium Strong Very Strong

4. What causes diamond fluorescence?

When you get to be over a billion years old, you tend to absorb a few things. Certain trace minerals within a diamond can cause it to glow – or “fluoresce”– under UV light. The trace minerals that cause this effect are aluminum, boron, and nitrogen.

diamond fluorescence scale from the GIA

5. How is a diamond’s fluorescence level determined?

Grading labs use UV spectrum lights and a master set of fluorescent diamonds for comparison in order to determine a diamond’s fluorescence grade. Over 95% of loose diamonds that have fluorescence have blue fluorescence, meaning they will glow a pale blue when put under a UV light. The next most common fluorescence color is yellow.

See ‘How does diamond fluorescence affect color?‘ for ways this fluorescence can work for you.

6. What is the average or most common fluorescence grade?

round cut diamond with a fluorescence grade of None

The most common diamond fluorescence grade is None. Only about a quarter to a third of loose diamonds have some level of visible fluorescence, and less than 10% of this subset have fluorescence that affects their appearance under regular (non-UV) light. The least common fluorescence grade is the highest: Very Strong.

7. Does diamond fluorescence affect any of the 4C grades? How about diamond polish or symmetry?

Diamond fluorescence can affect a diamond’s color under certain types of lighting, but not any of the other 4Cs, polish or symmetry.

8. How does diamond fluorescence affect color?

Fluorescence can affect a diamond’s color grade in one of two ways. On one hand, consider a diamond with a lower color grade such as K or L, but with a high blue fluorescence grade. The diamond’s fluorescence will actually negate the yellow hue and make it appear more white in natural daylight.

On the other hand, yellow fluorescence can have a negative effect on a diamond’s color. Say you have a diamond with yellow fluorescence and an H or I color grade. In full sunlight, the diamond will intensify the faint yellow color grade.

In addition, diamonds with yellow or white fluorescence can appear to have hazy or milky hues.

9. Does fluorescence affect certain diamond shapes more?

Sorry, no gaming the system with this one. All of the diamond shapes, from round to princess to asscher, are affected equally by diamond fluorescence.

10. Do fancy color diamonds receive fluorescence grades?

Yes, colored diamonds are graded for fluorescence just like colorless stones. Unlike white diamonds, though, the vast majority of fancy colored diamonds look better with None or Faint fluorescence grades. You can imagine how both blue and yellow fluorescence could dilute or degrade the color quality of a fancy colored diamond.

11. How does diamond fluorescence affect price?

A fluorescence grade of Faint to Very Strong can lower a diamond’s price. Diamonds with fluorescence grades of None tend to be priced at a premium, since the traditional wisdom says that fluorescence is undesirable. However, fluorescence isn’t necessarily a negative trait, which means you can save money by choosing a diamond with some level of fluorescence.

Remember, fluorescence affects the appearance of a very small minority of loose diamonds under natural light. Further, diamonds with lower color grades can actually look better with a bit of blue fluorescence. It follows that you can get excellent value by choosing a diamond with a lower color grade that is enhanced by its fluorescence.

12. When did diamond fluorescence become an important part of diamond grading?

The GIA conducted a comprehensive study in 1997 about diamond fluorescence and how it affects appearance and color. Ever since, fluorescence has been one of the most hotly debated topics in the diamond industry.

If you’re unsure whether to choose a diamond with fluorescence, the best thing to do is to see a few diamonds for yourself. Take advantage of Ritani’s Free In Store Preview, or simply go into a local jeweler and ask to compare a few fluorescent diamonds to diamonds without fluorescence.


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