By Alexia Sorokina, Gemmologist | Say Yes in Paris

Diamond fluorescence is one of the least understood factors in the market — and one of the most useful, if you know how to read it. When a diamond with strong blue fluorescence is placed under ultraviolet light, it glows. The market has decided this is a flaw. I have decided the market is wrong.

What fluorescence actually is

Fluorescence is a reaction to ultraviolet light. Certain diamonds — roughly 25 to 35 percent of all natural diamonds — contain structural elements that cause them to emit a soft glow when exposed to UV. The most common colour is blue. Less frequently, yellow or orange.

It is not a defect. It is not a treatment. It is a natural characteristic, present in the stone from the moment it formed, billions of years ago.

Why the market penalises it

At some point in the twentieth century, the diamond trade decided that fluorescence was undesirable. The reasoning was never entirely consistent — vague concerns about appearance, resistance to change, market convention. The result is that fluorescent diamonds are priced lower than non-fluorescent stones of identical colour, clarity and cut.

The discount varies. For any level of fluorescence, it can be 5 to 15 percent. Sometimes more. That discount is, in most cases, unjustified.

My recommendation: Faint Fluorescence

Here is the trick I share with every client. Faint Fluorescence is the sweet spot — and almost nobody talks about it.

A diamond graded Faint Blue Fluorescence has absolutely no visual impact. You will not see it in daylight. You will not see it at dinner. You will not see it anywhere. It is, to the naked eye and in every real-world condition, identical to a stone with No Fluorescence.

The price difference? Five to ten percent less than the equivalent No Fluorescence stone.

This is not a compromise. This is how you buy a better diamond for less money. I recommend Faint Fluorescence as a default to almost every client in any colour range.

When fluorescence works further in your favour

For diamonds in the H to J colour range, Faint Blue to Medium Blue fluorescence is an additional asset. The subtle glow counteracts the slight warmth of the stone and makes it appear more colourless in daylight, which contains ultraviolet rays. You pay less. The ring can look better.

When to be careful

Strong Blue fluorescence warrants a careful look in person before committing. In certain stones, particularly in higher colour grades, it can occasionally affect the appearance under direct sunlight.

Very Strong fluorescence I recommend avoiding altogether. The risk of visual impact is real, and the saving does not justify it.

How to read it on the certificate

On a GIA certificate, fluorescence appears in its own field: None, Faint, Medium, Strong, or Very Strong, followed by the colour — usually Blue.

None is standard. Faint is my recommendation. Medium is worth examining in person. Strong requires caution. Very Strong — pass.

What this means for your budget

Ask specifically to see Faint Fluorescence stones. The saving is immediate, the appearance is identical, and the money goes further toward carat, cut, or setting.

It is not a secret. It is simply the kind of thing a gemmologist tells you before you go shopping.

Alexia Sorokina is a gemmologist and jeweller with fifteen years of experience in natural diamonds. She is the founder of Say Yes in Paris, a bespoke engagement ring atelier and proposal concierge based in Paris.

To discuss your diamond, book an appointment — in our Paris atelier or by video.