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What is Diamond Fluorescence? – Diamonds Under Black Light

What is diamond fluorescence? Diamonds under black light or UV light glows blue or white are fake or real? These are the most common questions people ask me from Japan, United States, Singapore & Hong Kong.

So Today, in this blog post we will go to learn about diamond fluorescence.

What is Diamond Fluorescence?

what is diamond fluorescenceDiamond fluorescence, refer to the effect of UV light on a diamond. When a diamond is exposed to ultraviolet light (also known as black light) it glows blue. Sometimes you might see another colour too like yellow, green, red & white, but blue is the most common fluorescent colour in a diamond.

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Let’s make it more simple for understanding diamond fluorescence. When you stand under blue light or ultraviolet light in nightclub your teeth sometimes glow white looks more bright. Similarly, when a diamond is placed under black light, it glows. However, not all diamonds have fluorescence, some are fluorescent free called as “None” in GIA diamond report. Only 30% to 35% of diamonds have fluorescence.

Labs describe fluorescence by its intensity or strength of diamond’s reaction when sourced to UV light. Below are the 5 types of diamond fluorescence you will find on GIA diamond certificate.

  1. None Fluorescence – Diamonds with no fluorescence
  2. Faint Fluorescence – Diamonds with very slight fluorescence
  3. Medium Fluorescence – Diamonds with fluorescence
  4. Strong Fluorescence – Diamond with strong fluorescence
  5. Very Strong Fluorescence -Diamond with intense fluorescence

So, what is medium blue or strong blue fluorescence in the diamond report?

The term “blue” with fluorescence on report refers to the fluorescence colour of that diamond. You might have seen “Strong Blue” or “Medium Blue” stated on a diamond certificate, which means diamonds emit “blue” (fluorescence) light when sourced to UV light.

AGS lab uses the word “Negligible” on a certificate to describe a diamond with no fluorescence.

Diamond Fluorescence Value

Fluorescence has a great impact on diamond value. Diamond with strong fluorescence is 15 -20 % cheaper than of none fluorescent diamond. Below is just to give you a basic idea about diamond price difference with the change in fluorescence.

Example from Brian Gavin – Both diamonds with AGS lab certificate

Stone 1 – 1.05 G VS2 Ideal – Strong Blue fluorescence – 8148 US$

Stone 2 – 1.02 G VS2 Ideal – Negligible fluorescence – 10261 US$


Above example shows 18-22% price variation with two similar diamond with different fluorescence.

If you are looking for a diamond with fluorescence, I would recommend you to check Brian Gavin’s Blue collection. Brian Gavin is the best site for buying a fluorescent diamond.

How it works – Diamonds Under Black Light


(left) Holding pear shape diamond under black light & (right) diamond under daylight.

To understand, why diamond turns blue under black light. We first have to take look at the science of fluorescence.

What Causes Fluorescence In Diamonds

The Science – Chemical in diamond’s crystalline structure absorbs and re-emits energy as visible light known as fluorescence.

When elements such as nitrogen, boron or aluminium are presents in diamond’s automatic structure. Energy from UV light is been absorbed by electrons which react back to the higher state of energy, which we termed as “fluorescence” in diamond.

Diamond Fluorescence – Good or Bad

diamonds under black lightNow, the big question. Is fluorescence in diamond good? or bad?

Well, It completely depends on personal preferences. Below points might help to judge how good/bad is fluorescence in diamond.

  • If you buying the lower colour diamonds like “I-J-K-L colour”, consider buying it with faint/medium/strong fluorescence instead of none fluorescence. Why? Fluorescence in diamond create whiteness (brightness) and reduces yellowness, therefore, colour J sometimes look like a colour “I” in daylight.
  • “Very Strong” fluorescence sometimes results in haziness in diamond. Diamond with “very strong” fluorescence might look oily & hazy in daylight. Still, you can go with “faint” or “medium” fluorescence.
  • A diamond with fluorescence is cheaper.

Buying Fluorescent Diamonds Pros & Cons

Let us take a look at some pros and cons of buying fluorescent diamonds.

Pros of the fluorescent diamond.

  • Low In Price – On an average, you may get 15%-18% cheaper diamond if don’t mind buying a diamond with fluorescent.
  • Improves Color – Best part, Fluorescence in diamond sometimes improves its colour. It reduces yellowness, therefore, looks better in colour to observers.

Cons of the fluorescent diamond.

  • Hazy Diamond – “Very Strong” fluorescence might create a cloudy or hazy look in diamonds. Avoid buying such kind of diamond. It makes the stone look slightly foggy, or milky.

Quick Tip – How to tell if diamonds are real or fake?

My Personal views about diamond fluorescence

I personally like a fluorescent diamond. It is kind of extra cool “glowing in the black light” feature you get with diamond. I always advise consulting experts, gemologist or gem labs before making any purchase. Especially when you set your mind to buy “very strong/strong” fluorescent diamond.

Never buy blind, physically see the diamond before paying. Ask experts for help, your strong fluorescent diamond might look cloudy.

D-E-F colour with very strong fluorescence is less recommended.

In the end, fluorescence is moreover to individual tastes and not good or bad.

Make your decision wisely.

My recommendation for buying a fluorescent diamond online – Once you make up your mind for buying a fluorescent diamond, Now the question? Where to buy a fluorescent diamond online?

I recommend you to check Brian Gavin’s Blue collection. They have the largest choices for the fluorescent diamond than any other vendor online.

Sources & References for further information –

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