Does a diamond's size affect it's color?

[Rockdiamond]

HI All,
The other day I posted a photo of a few diamonds, to show results from different labs for color.
This is the photo.


It was suggested that a diamond's mass impacts the way we grade it's color.
I have not used this methodology, however clearly others have, and I'd love to hear more about how others experience this phenomenon and how other pro's look at diamonds to grade color

I will photograph two stones with the same GIA grade of disparate size to see if we can find differences within the limitations of the lens.
I've already gotten the larger "E" color RBC ( about 3 and a half carats) and will procure a 1/2ct GIA graded "E" - hopefully photograph them tomorrow.
Neither stone will have fluorescence.

 

[JulieN]

I remember Oldminer posting about this: [URL='https://www.pricescope.com/community/threads/clarity-standards-vary-with-weight-size.43335/']https://www.pricescope.com/community/threads/clarity-standards-vary-with-weight-size.43335/[/URL]

 

[Rockdiamond]

Thanks for posting that link Julie.
In fact David Atlas was mentioning in the more recent thread of a few days back that GIA color grading standards have changes over the years- and I agree.
Therefore a discussion from 2006 may no longer be current- plus it's interesting.

 

[Rockdiamond]

I thought of another interesting aspect of this.
What about the other end of the spectrum?
Would GIA use different standards with a small Intense Yellow as a large intense yellow?

 

[Rosebloom]

RD - just wanted to say thank you for this thread and the previous one on the same topic. I really enjoy learning about this kind of thing - it's why I'm on Pricescope!

I do wonder why GIA grades colorless as "a chip of the stone" and fancies as they face up. I would love to see your comparison photos of the smaller and larger E colors. I have a five stone ring with .28 Ks and I love the color. But I'm not sure if that means I'd be comfortable with a 3 carat K or if I need to go to J or even I to achieve the same look.

 

[Rockdiamond]

You are so welcome Rosebloom!
About larger stones with a J-K color: It's so case by case.
You'd think two stones with the same GIA color grade are seemingly identical, and would "face up" the same. In reality they don't always face up in exact correlation to how they look from the pavilion- which is how colorless diamonds are graded. So not every K looks the same. But my feeling is that if the color of your 1/4ct stones suits you, a larger K color might as well.

With regards to GIA methodology- I do not believe it's entirely clear the exact method GIA uses when grading color. Having said that, I'm not sure- maybe someone knows if GIA publishes the methods used when they grade.
I would think they have multiple graders check the stone to get an average- especially when it comes to color.

 

[diamonds-are-friends]

are the grading standards the same for fancy cuts and round brilliants? In my understanding, it seems like fancy cuts are also graded beside masterstones in a faceup direction with different positions (at the sides, tips etc). The lowest color that is apparent to the grader will be used as the grade setter.

 

[Rosebloom]

Thanks RD! Very helpful!

 

[ChrisES]

My understanding from reading guides on places like Pricescope, Good Old Gold, etc., is that there is a range within each color, meaning that an E could be closer to D or closer to F, and of course that would make a difference. If I recall correctly the ranges get narrower as the scale approaches colorless, meaning that less variation is tolerated among Ds than among Es, etc.

For GIA specifically, I recall reading that they have their staff compare the stone to a master set, and that each stone is looked at by multiple eyes and some minimum number of people must agree on the grading. In other words, that the system is subjective. This makes sense to me insofar as GIA developed the system long before some of the current diamond evaluating technology was available, but I admit that I read all this second hand and do not know what GIA has or has not published about color grading.

And I know nothing about fancy colored stones.

To the question of whether or not size makes a difference, my intuition is that if the same methodology is used the system should be stricter for larger stones, since light passes through more material and can pick up more color. However, the photo in the OP seems to contradict this, with the larger GIA stone looking more yellow, and thus suggesting that they may in some way compensate for stone size.

I'm also curious about the position of the viewer when evaluating stones. The 3/4 view in the photo shows faceting and I wonder if that interferes - it seems to me that the way to evaluate color would be to look straight through the pavilion with the stone at eye level.

Lastly, thanks for posting this. Reminds me of reading your comparison posts on coloreddiamonds and watching Good Old Gold's comparions videos back when I was diamond shopping.

 

[Rockdiamond]

You're welcome guys!
CHris- I think part of what ca make this discussion more valuable is the mix of what we know about GIA methods ( which I don't believe is actually "documented") , and how the ramifications play out.
IOW- David Atlas may speak more about the technical aspects, while I can bring a perspective from a practical point of view.
Without a doubt there is a range of color within each grade.
Also true that fancy shapes present a different set of considerations.
For the purpose of starting the discussion, I'll use round diamonds for the first demo shot

 

[oldminer]

Just sticking to round diamonds and getting into the zone of common colors, such as G to L color. A 1 ct diamond looks lighter in color than a 3ct diamond of the same GIA color grade. This applies to all diamonds, but the effect is greater away from D/E where there is so little color present and increases in visibility as more tint creates greater absorption. Since no diamond is as large as a coffee table, we don't have the huge sample to compare to the tiny sample. Diamonds, nearly all being relatively tiny compared to a coffee table's width, have only very slight to slight increased absorption from the distance light travels through a small stone versus a larger stone.

The color grading convention for diamonds is unique. Since they are so highly valuable as they become larger the folks who put together the grading strategy worked out a color assessment system which favors the trade in diamond selling. It isn't a misrepresentation as much as it is a very inspiring take on how to color grade a large object using a rather tiny master object that absorbs less light due to size difference.

There is science now that can adjust for this delicate range of light absorption based on the thickness of the material being color graded so that a likeness of the GIA color grade can accurately be predicted or provided. It ends up that machine grading color is a feat which uses measures of light out to the 6th decimal place. We are speaking of extremely fine nuances of measurement which are required of devices to simulate what the expert grader's eyes usually do. Machines can be far more repeatable than human graders, but the trade has not yet come to that choice so far. I predict it will become a norm in years to come, but for now, not quite yet.

 

[Rockdiamond]

Great points Dave.
About the machine: My perspective , as a dealer, is that the machine is not going to ever become the norm.
Here's why I think it's the case:
1) The technology has been in place for years- so it's not like the trade is waiting for a breakthrough
2) My experience, after working with the machine and sending the stone to GIA was that GIA surely does not use the machine- or they calibrate it differently.
Our machine called the stone a "high H" and GIA gave it I color.

I can totally appreciate David's points because there's no doubt the role of technology will continue to increase in diamond cutting and grading.
When it comes to "guessing" what GIA will color grade a diamond, the best people in the trade will be no higher than maybe 85% correct in my experience.
I think that's part of what makes the different perspectives on this interesting.
We may never know exactly how GIA grades the diamonds, but learning how others do is interesting.


Dave- I had not thought about the ramifications of D-E versus a stone with more body color. That is a great point I didn't think of when I borrowed a few E color stones.
I should be able to get some shots this evening of both E color diamonds.
We'll try with J or K next- that should really show some differences.