Diamond Knowledge

Diamond Fluorescence: Good or Bad?

Fluorescence has a worse reputation than it deserves. For most diamonds it changes nothing you can see — and now and then it is a genuine saving.

← Part of the Brilliani Labs Diamond Guide

What is diamond fluorescence?

Diamond fluorescence is the visible glow some diamonds give off under ultraviolet light, an everyday part of daylight. On a report it describes the strength of that reaction; the glow lasts only while the stone is under UV. For the wider picture, see the Diamond Guide.

Is fluorescence good or bad?

For the great majority of diamonds it is neither — it has no effect you would notice in normal light. It is mostly a non-issue, and sometimes an opportunity.

Can fluorescence make a diamond look better?

Yes, sometimes. In diamonds with a little warmth (lower colour grades), blue fluorescence can make the stone appear a touch whiter in daylight, because the blue glow offsets faint yellow.

Can fluorescence ever be a negative?

Rarely. In a small minority of stones, very strong fluorescence can make a diamond look slightly hazy, milky or oily. This is uncommon, but it is why a strongly fluorescent diamond is worth viewing in person before buying.

How common is fluorescence?

Roughly a quarter to a third of diamonds show some fluorescence, and in the great majority of those the glow is blue.

Does fluorescence affect price?

Often, yes. Strong fluorescence is frequently discounted, especially in higher colour grades — which can make a fluorescent stone that looks perfectly good a smart saving.

Does fluorescence weaken a diamond?

No. A diamond that fluoresces is exactly as durable as one that does not. For more on this, see the Diamond Guide.

How is fluorescence graded?

By strength: typically None, Faint, Medium, Strong and Very Strong.

Should I avoid fluorescence?

There is no blanket rule. Judge the individual diamond: if it looks bright and clean to your eye, fluorescence is nothing to fear and can save you money.