By now, we're all familiar with the 4Cs: color, cut, clarity and carat.
But what about fluorescence?
What is it, and how does it affect your diamond?
For this discussion, I'm specifically talking about natural diamonds. Lab-grown diamonds can have fluorescence too, but because their color can be much more readily controlled during production—and high-color lab-grown diamonds are relatively accessible—the value strategy I'm about to describe doesn't have the same significance.
Fluorescence is a natural characteristic found in some diamonds that causes them to produce a visible glow when exposed to ultraviolet—or UV—light. Most commonly, that glow is blue.
It isn't a treatment that's added to the diamond, and it isn't something that can simply be removed. It's a characteristic of that particular stone.
GIA describes the strength of fluorescence as None, Faint, Medium, Strong or Very Strong.
In many diamonds, fluorescence will have little noticeable effect on their everyday appearance. But in the right natural diamond, it can actually work to your advantage.
As natural diamonds move lower on the color scale, they generally begin to show more yellow. This is where blue fluorescence becomes particularly interesting.
You've probably seen the same principle used elsewhere.
Some teeth-whitening products use blue or blue-violet tones to visually counteract yellow, making teeth appear whiter.
The same basic idea has been used in laundry for generations. Laundry bluing introduces a tiny amount of blue to counteract yellowing in white fabrics, making them appear brighter and whiter.
The blue doesn't actually remove the yellow. It visually counteracts it.
Now imagine two natural J-color diamonds.
Both have the same color grade and both have a noticeable warm or yellowish appearance.
The first has no fluorescence. Nothing is there to counteract that yellow, so what you see is simply the natural warmth of the diamond.
The second diamond has an appropriate amount of naturally occurring blue fluorescence. Under lighting that contains enough UV, that blue can visually counteract some of the yellow.
Suddenly, two natural diamonds with the same color grade on paper can appear noticeably different in person.
And that's where fluorescence can become your saving grace.
You're still buying a J-color natural diamond. It's still priced according to a J color grade. And depending on the stone and the market, the fluorescence itself may even contribute to a discount.
But under the right lighting, you may be looking at a diamond that appears whiter than the grade you're paying for.
That's where knowing what you're looking at can save you money.
And UV light isn't something you'll encounter only under a black light at a nightclub. Sunlight contains UV, which means this effect can occur in a very ordinary environment.
Of course, fluorescence isn't always better.
The whitening advantage of blue fluorescence is primarily useful when there's some yellow body color for it to visually counteract. If you already have a very high-color natural diamond, there's much less to gain from that effect.
And more fluorescence isn't automatically better.
Strong and Very Strong fluorescence should be evaluated carefully. In rare cases, diamonds with stronger fluorescence can have an undesirable hazy or oily appearance.
So I'm not suggesting that you shop for the strongest fluorescence you can find. I'm suggesting that you understand what it does.
In the right combination—a warmer natural diamond, an appropriate amount of blue fluorescence and a stone that looks beautiful when you actually examine it—a characteristic many customers have been taught to avoid can actually work in their favor.
With natural diamonds, where higher color grades can command substantial premiums, that can translate into real savings.
The 4Cs are important, but they're not the whole story.
Sometimes the best value in a natural diamond is hiding just outside the 4Cs.