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Yellow Diamonds and Fluorescence


nkc
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How much of an impact does Medium Blue or faint fluorescence have on the color of Fancy Intense yellow diamonds? 

What % price reduction should I expect to see if a FIY has medium fluorescence?

Would this still be a concern in Vivid Yellow diamonds?

This question assumes that the diamonds are graded by GIA.

Thank you,

Edited by nkc
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I seem to answer all of your question with 'it depends'...

Faint probably next to none in terms of appearance. Medium... it depends - not least because both FIY and 'medium blue' cover a hell of a lot of ground in terms of how intense the colour and the fluorescence are, and the intensity is not the only thing that matters - where the colour is generated and where the fluorescence comes from within the stone have a huge impact on what the overall effect is.

My wife has a FIY cushion (my avatar) with MB - it barely affects the way in which the diamond looks. We have another round FIY (small - 0.32 ct) with MB, and it looks like a U-V in bright sunlight. This despite the fact that you could put the two diamonds next to each other in interior light and the colours would look pretty much identical.

Which means that the answer to your second question is still 'it depends' - I would expect at least 15-20% from an 'identical' diamond with no fluorescence, but it could be more depending on the impact on appearance.

I wouldn't call it a concern - but it will definitely affect prices for a FVY; in fact more so. Whether you look at this as a 'plus' or a 'minus' depends on which side of the table you are (once again... it depends!)

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1 hour ago, davidelevi said:

 where the colour is generated and where the fluorescence comes from within the stone have a huge impact on what the overall effect is.

I'm not clear on the sentence above.

If FIY covers a wide range, how do I know where a diamond falls within this range and how do I determine the impact of the medium blue fluorescence on this diamond?

Edited by nkc
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"How do I..."

You have a pair of eyes. Use them. With a bit of luck, you have a seller that can help too. Observation and training, if you want a less flippant answer, but it amounts to the same thing.

These are all 'Fancy Intense Yellow' with no modifiers on the report. Same room, same photographer, same camera, mostly same (natural) lighting, no editing other than sizing/cropping trying to preserve scale (these stones go from 0.28 to 2.06 ct)

yellow diamonddiamondr7363-octagonal-canary-diamond-b.jpgdiamondyellow diamonddiamond

some have a much warmer/cooler yellow than others, and some are more saturated than others. Demonstrating this with photos (especially photos not made for that purpose) is hard. 

Especially with fancy colours, a lab report is definitely not enough to convey all that matters with regards to appearance, and the GIA colour system, articulated as it is, falls very short of that. If you can get hold of a copy of Stephen Hofer's Collecting and Classifying Coloured Diamonds, it's well worth looking at.

Re: the unclear sentence: the origin of colour (and fluorescence) in diamonds is largely due to atomic lattice-level effects: lattice deformations/defects and atomic-level substitution of carbon with nitrogen, boron or hydrogen. These deformations/defects/substitutions are not distributed homogeneously within the stone, even if to an unaided human eye the colour seems to be evenly distributed. Add on the internal natural reflections plus the effect of cutting... and you have a recipe for very different results even starting from the same apparent inputs.

Edited by davidelevi
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My favorite is the diamond in the top right picture. The second one on the left looks closer to a FY.

If all the diamonds in the pictures above were the same shape, carat weight, clarity, etc., would they be priced the same? In other words, does the color affect the price if they were all graded as FIY?

So, you are saying that I should be able to tell by looking at the diamonds.

I was under the impression that fluorescence makes the yellow color appear lighter under certain lighting conditions (I heard from others). Based on your explanation, I understand that color saturation is not necessarily affected by fluorescence. Do I understand this correctly?

Does the last paragraph apply when the GIA report says that the color is even?

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4 hours ago, nkc said:

The second one on the left looks closer to a FY.

Pretty much by definition there will be some FIY that are 'just on the other side' of FY (and there will be those that are just on the other side of FVY). I also think that the shape doesn't particularly help, unless one has a morbid fascination with coffins.

4 hours ago, nkc said:

If all the diamonds in the pictures above were the same shape, carat weight, clarity, etc., would they be priced the same? In other words, does the color affect the price if they were all graded as FIY?

Enormously. Saturation (which as you can see varies quite a bit) and hue both. Given the right (or wrong) combinations, you will even find a modest overlap between Fancy/Fancy Intense/Fancy Vivid prices - all else being equal.

4 hours ago, nkc said:

I should be able to tell by looking at the diamonds.

Yes - but training (even informally, as in 'looking at many different diamonds') is important, particularly if you haven't got all the diamonds there at the same time. Also, personal taste plays a role: I personally really like a slight orangey or even (sshh!) brown tinge, since it gives a warm hue that I love; I am lucky that this generally cheapens the stone, since top dollar is generally paid for a spectrally pure yellow.

4 hours ago, nkc said:

color saturation is not necessarily affected by fluorescence. Do I understand this correctly?

Nes. Or Yo. Visible effects are very different from stone to stone (and person to person: your 'glaringly, obviously different' is my 'meh. Same.'), and for some stones the effect is so small as to not be noticeable by a human eye. It will be there given sufficiently sensitive and precise equipment - which is why the presence of fluorescence "by itself" causes a discount.

4 hours ago, nkc said:

Does the last paragraph apply when the GIA report says that the color is even?

Yes. I cannot demonstrate this with DBL photos, but if you look at Hofer's book (which was written over 20 years ago, so before the current GIA colour grading system, which makes comparisons hard, since there is no statement by GIA on colour distribution on those stones), there are plenty of microscope photos showing colour zoning and patching - in stones that at 5-10x ("book photograph") show a very homogeneous colour distribution.

This is before we start looking at how reliably - or otherwise - the 'even distribution' description by GIA is applied... I've seen diamonds called 'even' that jumped 2 colour grades (from FL to FI) after a re-cut, indicating that the colour was not at all really evenly distributed, and a more saturated patch could be exploited to bring the colour out to the whole stone.

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Not quite. I think the one just below it would win. The one on top is slightly less saturated; on a good day at GIA I think the other one would have been called Vivid. Here are the two in more comparable light (also consider it's a 0.50 ct. SI1 vs. 2.01 ct IF, so the actual price difference is a factor of 13...)

canary diamonddiamond

Edited by davidelevi
Rearranged photos to be in same order as in previous post
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What are the deal proportions for this type of cut? Is there such a thing as ideal proportions for yellow diamonds or are they cut to show the best color?

I've looked at Tiffany yellow diamonds about a year ago and noticed that their depth was less than other non Tiffany including this diamond. This probably makes the diamond appear larger. Is this right?

Edited by nkc
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6 hours ago, nkc said:

Is there such a thing as ideal proportions for yellow diamonds or are they cut to show the best color?

Much the latter. Not least because colour is a much bigger driver of prices than 'cut quality' defined as liveliness and contrast (and possibly symmetry). In addition, fancy colours are much more often cut as non-rounds (for various reasons - colour transmission being one), which makes the whole concept of 'ideal proportions' rather cumbersome to apply.

FWIW, I would disagree that there are 'ideal proportions' for pretty much any diamond - a modern 'superideal' isn't necessarily more beautiful than an old cut.

6 hours ago, nkc said:

their depth was less than other non Tiffany including this diamond. This probably makes the diamond appear larger. Is this right?

Potentially yes - but I haven't seen enough Tiffany coloured diamonds to say whether this is generally the case. Also, while depth is a driver of weight vs. size, there are other ways of hiding weight in a diamond that don't necessarily involve depth, and lastly depth% is significantly influenced by the aspect ratio: if you take a square-girdle diamond it will have a lower depth % than a rectangular-girdle one of the same volume (weight), all else being "equal". This is purely mathematical and means nothing in terms of appearance.

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