My Diamond is Fluorescent - Is this OK?

It's a tried and tested trick for those who want to get their hands on a big stone with a smaller budget, to pick stones with higher fluorescence. Especially through online sites, you can find dozens of big stones that appear to be thousands (tens or hundreds of) of pounds less than others with no discernible differences. There is a good video of the stone, where it looks pretty and a nice colour. And of course, there is no further information because you buy the stone as described. Check the stone report in more detail, and in at least half the instances you'd find the description "strong blue" next to fluorescence description. Which explains away quite a lot.

What is Diamond Fluorescence?

Diamond fluorescence, in its most simple form, is the effect that ultraviolet (UV) light has on a diamond. When you place white or light colours under a blue light or ultraviolet light, sometimes you can see whites get brighter or appear to glow. This is the same effect the diamond has under the UV rays. Fluorescence is the visible light that a diamond emits when it is exposed to the UV rays.

Fluorescence is naturally occurring, and at it's best it can make off white diamonds look whiter or more colourless. Around 30% of diamonds evaluated by the GIA have varying degrees of fluorescence detailed on the certificate.

What are the implications of buying a diamond with fluorescence detailed on it's report?

From a personal perspective, it only matters if it's visible. It's not true that fluorescence is only visible under UV or blue light, sunlight can bring it out as well (obviously, because that was the first source of UV light known to man!). In addition, for some stones, the light is irrelevant, the stone looks milky because of the levels.

For Faint to Medium fluorescence there is limited bearing on the overall appearance of the diamond and so less impact on stone value. The terrain shifts more when it's Strong and Very Strong - the impact it has on the sale/resale value of the stone is higher because optically there can be a visible difference. GIA* is fairly definite that the majority of consumers can't see this difference, I'm inclined to agree only when this is based on retailers showing like-for-like stones (which they nearly always do!).

There's a BUT coming isn't there..

Oh you know me so well.. From a diamond buyer's perspective, there is a difference which impacts the long term value of a stone. Strong Blues (or Very Strong) don't sell well. But the market opened up once sellers went straight to the consumer who can be relied on not to be expert.

In defiance of the GIA, I disagree that it's impossible to see a difference in all these stones, if they are placed next to a stone with no fluorescence and/or in direct sunlight. Some of them have a yellow tinge, or an 'oiliness' as described by the pros. Creating a three stone ring with the centre stone being strong blue and all of a sudden choosing the side stones becomes a headache if you are trying to match and ensure the centre stone looks the best.

Image of diamond under UV light showing strong blue fluorescence. Side stones have no fluorescence.e
A strong blue diamond under UV testing light. The side stones have no fluorescence which is why they remain colourless. Colour is all G.

But do I need to worry about my stone fluorescence?

No. Not if you are happy with the stone, and paid a price for it in the beginning that acknowledges the fact it has fluorescence. If you aren't interested in it as an investment. It is just part of the whole picture, there are other ways that diamond prices come down.

The word of caution is if you've bought a big stone thinking you've got something far cheaper that is just as good. There is no market for Strong Blues beyond offloading them directly to the unsuspecting public. Your stone has already dropped in value because you aren't going to find a diamond buyer willing to pay what you paid to buy it back. That is the reason why they are comparably lower in cost.

Happily in most cases, you won't see the quality difference provided you keep it clean, and don't compare it to a stone with less fluorescence!

To Sum Up

Fluorescence is no problem when;

  • It has been declared and costed accordingly
  • It's Faint to Moderate
  • You want to buy a bigger diamond with a smaller budget
  • You are buying an off white stone and it makes the stone appear whiter than it actually is
  • You don't mind a stone that glows faintly under UV light

Fluorescence is a problem when;

  • It's not declared
  • You want to buy a diamond that is going to hold its value
  • It makes the stone appear opaque oily, or milky
  • It's Strong to Strong blue and visible in sunlight
  • You like parties but not glowing diamonds (ask Elton John)

Buying a fluorescent diamond

If fluorescence is going to help with cost savings, try to avoid strong blues and consider the other stone traits carefully. You generally get what you pay for, and sometimes unfortunately you get less..

I did have a client bought in a strong blue to make into an engagement ring, it was a big rock.. He was amazed I nailed the value of it, (they are pretty easy to price for experts) and relieved that I felt what he'd paid was reflective of the stone value. (I couldn't tell him that we would have provided a bigger, better looking stone that was moderate fluorescence, for less. It's the general unfairness of the diamond market).

Looking to buy a diamond?

I'd not be doing my job properly if I didn't mention that we offer a diamond buying service, otherwise how would I know all this stuff? Or to see a few exceptional diamonds (some with faint fluorescence) click here to buy online.

*GIA are in my opinion, mostly reliable on their diamond appraisals, and have a good business. They also have some very large diamond businesses as important clients who sell cheap diamonds en-masse. So they are hardly going to say that Strong Blue is a bad thing and bite the big corporate hands that are pushing a lot of business their way..

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