Article Over Grading of Blue Fluorescent Diamonds Revisited

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Bryan, this is such a win win- I don't get your reluctance.
If you sample a bunch of SB stones in H-L colors you'll find one or more that lighten up a bit- whiten.

Once you do that, your own observation is all we need.
No corroboration.

Do you have good color vision?

If you do see what we're all are insisting actually exists, you'll simply realize that stones in this category are more attractive for your clients.
As it stands, your position would make it seem like you don't think your clients should buy MB/SB's because you believe they are misgraded- and then even if they're not, you're denying that some of these beauties actually benefit from having MB/SB.
Seems like the opposite of a win win- for you.

You are both acting like I have never observed blue fluorescent stones. It's absurd. Please re-read my posts.

If there is a particular stone or stones that you have looked at that you would like for me to see so that we can compare notes, I am happy to do that. Send it to me. Otherwise, I see no point in your exercise.

 

[Rockdiamond]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Umm......Bryan, it's you who's acting if you've never seen fl stones.
I'll be happy to send you a stone to look at Bryan. The L color we got today- it's a crazy stone. It's actually borderline hazy- but that aspect makes it really look white in any room where there's any sun at all.

I'd also be far happier if we could get past this discussion as two guys who share a love of Pricescope, diamonds and our businesses- with no hard feelings.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

I think you should concede the overgrading under current GIA-GTL practices may only be in the range of 0 - 2 grades and certainly for the SB diamonds its likely to fall in that range. VSB diamonds are so rare I am not sure they are really are going to drive a change by any laboratory and GIA-GTL has already said as much (see my post above).

Add 2 grades whitening(which grades? see below) to the expected grading accuracy between graders of 1 grade and you can quickly hit 3-4 grades off.
3 grades in higher colors where whitening is more likely to move a grade is a huge amount of money.

The same amount of whitening to move a g to an e would barely move a ijk in all but marginal cases.
The amount to move an e to f would not even register on the color scale at j.

That was not my statement Karl

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

While the historical context and old GIA-GTL practices are interesting I think they do not strengthen your argument for using a filter and diffuser.

We are now in an age of the GIA-GTL DiamondDock and you want GIA-GTL to improve on this, there will likely not be close to 4 grades of whitening expected anymore, you only published one stone out of 5 VST stones that even showed 4 grades of whitening comparing GIA-GTL(or AGSL) to your Source 7, this one stone could have been an anomaly it was only a small 0.63ct Marquise not the best representative example, I'd rather see a 1ct round, your masters weren't Marquise diamonds either.

I think you should concede the overgrading under current GIA-GTL practices may only be in the range of 0 - 2 grades and certainly for the SB diamonds its likely to fall in that range. VSB diamonds are so rare I am not sure they are really are going to drive a change by any laboratory and GIA-GTL has already said as much (see my post above).

There is so much to say about your posts that by the time a response gets posted, some other issue, question or disagreement has arisen and changed the conversation focus.

No concession is needed in that the 2010 study data confirms that with the prescribed grading practice of maintaining 7" distance (in the vicinity of 30uW of UV) the grade whitening has been reduced to 0-2 grades in all but some VSB's.

The study's 0.63ct VSB marquise, like Tom Tashey's 0.89ct VSB marquise was not an anomaly, as should be clear after hearing of GIA's founder Robert Shipley writing: “One of the most important causes of the anomalies that so often trouble a diamond grader is the change of color shown by many fluorescent stones when viewed under different light conditions. Often a fluorescent diamond which appears slightly yellowish under artificial light, appears distinctly bluish in daylight” (Shipley and Liddicoat, 1941). (Old GIA literature calls D-E-F colorless, G-J near colorless and K-M as slightly yellowish).

That "often encountered" change of color was at least 7 grades from its true unenhanced color of around K all the way to D and past to distinctly bluish in natural daylight.

The 2010 study documented the inconsistency in color grading blue fluorescent diamonds in the DiamondDock with its UV and VV allowed to vary over a 2.5 times range. The inconsistency problem was reinforced in recent conversations with Tom Tashey who related that from 2005 - 2008 he acted as Chief Gemological Officer to the World Gemological Institute and a professional consultant to the Israeli Diamond Industry (IDI). He ran studies of the recently arrived new lighting standard DiamondDocks. These studies are like the ones Sharon wishes were included in the 2010 study.

Using the DiamondDock with and without UV filter, he and the Israeli graders did not find much difference or improvement from the DiamondLite to the DiamondDock. They did not find as much improvement as the 2010 study's finding of four grades of fluorescence enhancement in the DiamondLite to two grades in the DiamondDock in 3 of the 5 VST Blues.

That reminded me of a what seemed a questionable statement from GIA Antwerp research gemologist Ron Geurtz. Ron is the developer of the DiamondDock. He told me that the year prior to switching from the DiamondLite to the DiamondDock at the Gem Trade Lab, both light boxes were used together to verify that they yielded the same results.

We appear to have a consensus that GIA was over grading excessively before 2000 using the DiamondLite. Should the consumer now be satisfied with a variable, inconsistent and unknown lesser amount of over grading since 2000 in the DiamondDock?

Although far from mainstream practice some gemologist-appraisers, as part of their appraisal services, offer to grade for the consumer both the true body color (graded in diffused LED lighting) as well as the fluorescence enhanced grade measured at 7 inches in GIA prescribed standard lighting.

If the two measurements were found to be within a grade that would go a long way in restoring trust and confidence in the purchase of a blue fluorescent diamond.

Michael can you present evidence of this VV variance?

Garry, as to your question that I bolded directly above, I think that is reference to the wide range of light intensity in the stated specs for the DiamondDock (bullet point #2):

DiamondDock lighting were given by King et al. (200, and include:
• Stable, fluorescent lamps 17 in. (43cm) or longer
• An intensity of light in the range of 2000–4500 lux at the surface of the
grading tray
• An 8–10 in. distance between the lamps and the grading tray
• A colour spectrum close to CIE D55-D65
• A colour temperature between 5500 K and 6500 K
• A colour rendering index of 90 or above
• No noticeable output in the short- or medium-wave UV range (or a filter available to eliminate UV in this range)
• An emission for long-wave UV (between 315 and 400 nm, close to the reference spectrum of D55-D65)

Right, Bryan,

The DiamondDock lighting specifications allow • An intensity of light in the range of 2000–4500 lux at the surface of the grading tray

For those who have not read the full article, in The Journal of Gemmology/ 2010 / Volume 32 / No. 1–4 at:
http://www.acagemlab.com/temp/CowingOvergrading.pdf

Here is the DiamondDock story:

2. GIA DiamondDock

In 2000 the GIA discontinued the manufacture and use of the DiamondLite and replaced it with the DiamondDock, which employs two 17 in. F15T8VLX Verilux full spectrum fluorescent tubes. Diamonds are graded on a white tray placed on the DiamondDock shelf, which means that there is a 7 in. grading distance from the light tubes (see discussion below).

The basic technical specifications of the DiamondDock lighting were given by King et al. (200, and include:
• Stable, fluorescent lamps 17 in. (43cm) or longer
• An intensity of light in the range of 2000–4500 lux at the surface of the grading tray
• An 8–10 in. distance between the lamps and the grading tray
• A colour spectrum close to CIE D55-D65
• A colour temperature between 5500 K and 6500 K
• A colour rendering index of 90 or above
• No noticeable output in the short- or medium-wave UV range (or a filter available to eliminate UV in this range)
• An emission for long-wave UV (between 315 and 400 nm, close to the reference spectrum of D55-D65)

The twin F15T8VLX fluorescent tubes or their equivalent is the standard lighting spelled out in the basic technical specifications for D-to-Z colour grading. (G&G, winter 200. Although a grading distance of 8-10 inches is specified, the shelf of the DiamondDock enforces a 7 inch grading distance from lamps to grading tray.

The exact distance is important to establish, because it in essence defines the chosen “standard” amount of UV and VV.
GIA researcher Ronald Geurtz (pers. com.) explained: “With the distance between shelf and the center of the bulb at 8-10 inches, the distance between the diamond and the surface of the bulb is around 7 inches.”

He notes an important point about this current lighting standard. The allowed range of light intensity of 2000-4500lux at the surface of the grading tray means the “standard” amount of UV and VV is also allowed to vary over the same 2.25 times range.

Such an large allowed variation of UV and VV defeats standardization of the amount of fluorescence stimulation in blue fluorescent diamonds. Even though lessened by the change from the DiamondLite, the post 2000 GIA requirement for long wave UV in the DiamondDock results in variable, inconsistent and unknown amounts of over grading.

Wouldn't the consumer be better served by grading for the diamond's true color, which was the goal advocated by founder Shipley and pre-2000 GIA teaching?

So in answer to my initial question Michael you have quoted information from GIA but you yourself have no evidence that VV varies by 2.25 or 2.5 times? Correct?
So this is hearsay.
In the refresher courses you mentioned, has anyone, including you, had access to DiamondDocks and measured the output / lux at 6 3/4 inches?
I know that Jonathon at GOG has one, plus AGSL - Jonathon's is pretty old and maybe he has not changed his tubes - perhaps David could shoot his Lux meter out? (An aside - DiamondDock was developed initially for cut grading - and IMHO it was lousy for that job, Michael is claiming it's lousy for color. hahaha)

At this time, I have no belief or evidence to say that GIA GTL has a wide variance in Lux with the DD's in any of its labs, and I expect they would have a checking and tube replacement ordinance in place. In addition, none of us knows what their digital tools can achieve. What David and I do know is we are comfortable with what we see in GIA color grading - and that was not the case 10 to 15 years ago. There are plenty of things I loath and detest about GIA grading and reporting, but face down D-Z color is not one. (face up and big size differences are)

 

[Karl_K]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

I think you should concede the overgrading under current GIA-GTL practices may only be in the range of 0 - 2 grades and certainly for the SB diamonds its likely to fall in that range. VSB diamonds are so rare I am not sure they are really are going to drive a change by any laboratory and GIA-GTL has already said as much (see my post above).

Add 2 grades whitening(which grades? see below) to the expected grading accuracy between graders of 1 grade and you can quickly hit 3-4 grades off.
3 grades in higher colors where whitening is more likely to move a grade is a huge amount of money.

The same amount of whitening to move a g to an e would barely move a ijk in all but marginal cases.
The amount to move an e to f would not even register on the color scale at j.

That was not my statement Karl

ok, sorry
Your post it was in is a mixed up mess, it is hard to tell who said what and when I sniped it that's how it came out.

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Umm......Bryan, it's you who's acting if you've never seen fl stones.
I'll be happy to send you a stone to look at Bryan. The L color we got today- it's a crazy stone. It's actually borderline hazy- but that aspect makes it really look white in any room where there's any sun at all.

I'd also be far happier if we could get past this discussion as two guys who share a love of Pricescope, diamonds and our businesses- with no hard feelings.

Let me see if I understand. You have spent the last several weeks littering this thread with shotgun scatter criticisms of the Cowing study, in particular sample size and flawed methodology, which you claim makes the study invalid. Now you are insisting that I should do some sort of study of a diamond or two, with no corroboration, and somehow that will be valid?

Your arguments are disingenuous at best.

At the very least Mr.Cowing should be given credit for gracefully enduring your rambling and insulting onslaught.

 

[Rockdiamond]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Hi Bryan,
Issue 1- Is GIA overgrading, as the title of the study suggests. This is the crucial issue for consumers.
IN that regard, a single opinion is simply insufficient to make that case.
We also have the fact that there has been no answer to my question about exactly how many people at GIA look at the diamond, or if they use alternative light sources besides the dock. So we don;t have the exact methodology- although the study implies we do.
Then the fact that if a problem existed, many people besides Garry and I would be screaming about it.
All the facts bear out Garry and my position- there's simply no issue to be handled regarding GIA color grading of fluoros.
This is crucial for consumers and it's why I've spent so much time and effort to demonstrate why the study is making an incorrect conclusion.

Issue 2- do certain fluoros benefit from whitening? The study indicates they don't, Garry and I say they can.
IN this area, which is less crucial, your observation would be sufficient. But instead of looking at actual diamonds, you insist on going back to light measurements, etc.
Consumers are not looking at their diamonds in a bubble. Whatever measurements are contained in the study miss vital elements present in "normal consumer lighting"
So, Garry and I are stating whitening can occur. As have many other people who are not participating in this discussion.
This aspect is almost comical. On the one hand, the study claims that GIA can't seem to figure how NOT to whiten the diamonds, yet consumers NEVER get to have whitening.
Illogical, no?

If you look back over the years, there's been times Garry and I were completely at odds- yet we have found a way to get past that, and find common ground. We're not a "likely" team. I mention this to point out how we are both on the same side this time.

SO- if you refuse to look at an SB L color that looks whiter than that in normal lighting, don't.
In that case, I'm sure you advise consumers not to consider fluoros- you'd kind of have to if you are so sure GIA can't grade them and that there's zero ancillary benefit.

Garry and I will continue to recommend them as a very attractive alternative for many people.

I'm still willing to ship you the stone.

 

[Rockdiamond]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Umm......Bryan, it's you who's acting if you've never seen fl stones.
I'll be happy to send you a stone to look at Bryan. The L color we got today- it's a crazy stone. It's actually borderline hazy- but that aspect makes it really look white in any room where there's any sun at all.

I'd also be far happier if we could get past this discussion as two guys who share a love of Pricescope, diamonds and our businesses- with no hard feelings.

Let me see if I understand. You have spent the last several weeks littering this thread with shotgun scatter criticisms of the Cowing study, in particular sample size and flawed methodology, which you claim makes the study invalid. Now you are insisting that I should do some sort of study of a diamond or two, with no corroboration, and somehow that will be valid?

Your arguments are disingenuous at best.

At the very least Mr.Cowing should be given credit for gracefully enduring your rambling and insulting onslaught.

This- Bryan, I do not believe the study was conceived for consumer consumption. Michael can correct me if I'm wrong.
But YOU are the one bringing up this study and putting others in the position of showing why there's errors in the conclusions.
Before you started doing that you should have looked at actual diamonds and taken more time to research if GIA is actually doing a poor job.
Michael- again I respect the effort you put in and I'm sorry to have had this discussion on a public forum.
I am very open to working with you anytime to further your studies.

 

[michaelgem]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

While the historical context and old GIA-GTL practices are interesting I think they do not strengthen your argument for using a filter and diffuser.

We are now in an age of the GIA-GTL DiamondDock and you want GIA-GTL to improve on this, there will likely not be close to 4 grades of whitening expected anymore, you only published one stone out of 5 VST stones that even showed 4 grades of whitening comparing GIA-GTL(or AGSL) to your Source 7, this one stone could have been an anomaly it was only a small 0.63ct Marquise not the best representative example, I'd rather see a 1ct round, your masters weren't Marquise diamonds either.

I think you should concede the overgrading under current GIA-GTL practices may only be in the range of 0 - 2 grades and certainly for the SB diamonds its likely to fall in that range. VSB diamonds are so rare I am not sure they are really are going to drive a change by any laboratory and GIA-GTL has already said as much (see my post above).

There is so much to say about your posts that by the time a response gets posted, some other issue, question or disagreement has arisen and changed the conversation focus.

No concession is needed in that the 2010 study data confirms that with the prescribed grading practice of maintaining 7" distance (in the vicinity of 30uW of UV) the grade whitening has been reduced to 0-2 grades in all but some VSB's.

The study's 0.63ct VSB marquise, like Tom Tashey's 0.89ct VSB marquise was not an anomaly, as should be clear after hearing of GIA's founder Robert Shipley writing: “One of the most important causes of the anomalies that so often trouble a diamond grader is the change of color shown by many fluorescent stones when viewed under different light conditions. Often a fluorescent diamond which appears slightly yellowish under artificial light, appears distinctly bluish in daylight” (Shipley and Liddicoat, 1941). (Old GIA literature calls D-E-F colorless, G-J near colorless and K-M as slightly yellowish).

That "often encountered" change of color was at least 7 grades from its true unenhanced color of around K all the way to D and past to distinctly bluish in natural daylight.

The 2010 study documented the inconsistency in color grading blue fluorescent diamonds in the DiamondDock with its UV and VV allowed to vary over a 2.5 times range. The inconsistency problem was reinforced in recent conversations with Tom Tashey who related that from 2005 - 2008 he acted as Chief Gemological Officer to the World Gemological Institute and a professional consultant to the Israeli Diamond Industry (IDI). He ran studies of the recently arrived new lighting standard DiamondDocks. These studies are like the ones Sharon wishes were included in the 2010 study.

Using the DiamondDock with and without UV filter, he and the Israeli graders did not find much difference or improvement from the DiamondLite to the DiamondDock. They did not find as much improvement as the 2010 study's finding of four grades of fluorescence enhancement in the DiamondLite to two grades in the DiamondDock in 3 of the 5 VST Blues.

That reminded me of a what seemed a questionable statement from GIA Antwerp research gemologist Ron Geurtz. Ron is the developer of the DiamondDock. He told me that the year prior to switching from the DiamondLite to the DiamondDock at the Gem Trade Lab, both light boxes were used together to verify that they yielded the same results.

We appear to have a consensus that GIA was over grading excessively before 2000 using the DiamondLite. Should the consumer now be satisfied with a variable, inconsistent and unknown lesser amount of over grading since 2000 in the DiamondDock?

Although far from mainstream practice some gemologist-appraisers, as part of their appraisal services, offer to grade for the consumer both the true body color (graded in diffused LED lighting) as well as the fluorescence enhanced grade measured at 7 inches in GIA prescribed standard lighting.

If the two measurements were found to be within a grade that would go a long way in restoring trust and confidence in the purchase of a blue fluorescent diamond.

Michael can you present evidence of this VV variance?

Garry, as to your question that I bolded directly above, I think that is reference to the wide range of light intensity in the stated specs for the DiamondDock (bullet point #2):

DiamondDock lighting were given by King et al. (200, and include:
• Stable, fluorescent lamps 17 in. (43cm) or longer
• An intensity of light in the range of 2000–4500 lux at the surface of the
grading tray
• An 8–10 in. distance between the lamps and the grading tray
• A colour spectrum close to CIE D55-D65
• A colour temperature between 5500 K and 6500 K
• A colour rendering index of 90 or above
• No noticeable output in the short- or medium-wave UV range (or a filter available to eliminate UV in this range)
• An emission for long-wave UV (between 315 and 400 nm, close to the reference spectrum of D55-D65)

Right, Bryan,

The DiamondDock lighting specifications allow • An intensity of light in the range of 2000–4500 lux at the surface of the grading tray

For those who have not read the full article, in The Journal of Gemmology/ 2010 / Volume 32 / No. 1–4 at:
http://www.acagemlab.com/temp/CowingOvergrading.pdf

Here is the DiamondDock story:

2. GIA DiamondDock

In 2000 the GIA discontinued the manufacture and use of the DiamondLite and replaced it with the DiamondDock, which employs two 17 in. F15T8VLX Verilux full spectrum fluorescent tubes. Diamonds are graded on a white tray placed on the DiamondDock shelf, which means that there is a 7 in. grading distance from the light tubes (see discussion below).

The basic technical specifications of the DiamondDock lighting were given by King et al. (200, and include:
• Stable, fluorescent lamps 17 in. (43cm) or longer
• An intensity of light in the range of 2000–4500 lux at the surface of the grading tray
• An 8–10 in. distance between the lamps and the grading tray
• A colour spectrum close to CIE D55-D65
• A colour temperature between 5500 K and 6500 K
• A colour rendering index of 90 or above
• No noticeable output in the short- or medium-wave UV range (or a filter available to eliminate UV in this range)
• An emission for long-wave UV (between 315 and 400 nm, close to the reference spectrum of D55-D65)

The twin F15T8VLX fluorescent tubes or their equivalent is the standard lighting spelled out in the basic technical specifications for D-to-Z colour grading. (G&G, winter 200. Although a grading distance of 8-10 inches is specified, the shelf of the DiamondDock enforces a 7 inch grading distance from lamps to grading tray.

The exact distance is important to establish, because it in essence defines the chosen “standard” amount of UV and VV.
GIA researcher Ronald Geurtz (pers. com.) explained: “With the distance between shelf and the center of the bulb at 8-10 inches, the distance between the diamond and the surface of the bulb is around 7 inches.”

He notes an important point about this current lighting standard. The allowed range of light intensity of 2000-4500lux at the surface of the grading tray means the “standard” amount of UV and VV is also allowed to vary over the same 2.25 times range.

Such an large allowed variation of UV and VV defeats standardization of the amount of fluorescence stimulation in blue fluorescent diamonds. Even though lessened by the change from the DiamondLite, the post 2000 GIA requirement for long wave UV in the DiamondDock results in variable, inconsistent and unknown amounts of over grading.

Wouldn't the consumer be better served by grading for the diamond's true color, which was the goal advocated by founder Shipley and pre-2000 GIA teaching?

So in answer to my initial question Michael you have quoted information from GIA but you yourself have no evidence that VV varies by 2.25 or 2.5 times? Correct?
So this is hearsay.
In the refresher courses you mentioned, has anyone, including you, had access to DiamondDocks and measured the output / lux at 6 3/4 inches?
I know that Jonathon at GOG has one, plus AGSL - Jonathon's is pretty old and maybe he has not changed his tubes - perhaps David could shoot his Lux meter out? (An aside - DiamondDock was developed initially for cut grading - and IMHO it was lousy for that job, Michael is claiming it's lousy for color. hahaha)

At this time, I have no belief or evidence to say that GIA GTL has a wide variance in Lux with the DD's in any of its labs, and I expect they would have a checking and tube replacement ordinance in place. In addition, none of us knows what their digital tools can achieve. What David and I do know is we are comfortable with what we see in GIA color grading - and that was not the case 10 to 15 years ago. There are plenty of things I loath and detest about GIA grading and reporting, but face down D-Z color is not one. (face up and big size differences are)

Heresay? Really? That was not my statement. Those were the words of DiamondDock inventor and GIA researcher Ron Geurtz pointing out to me that the allowed range of light intensity of 2000–4500 lux at the surface of the grading tray means that the amount of UV and visible violet also can vary over the same 2.25 times range. Such an allowed range of UV and visible violet could lead, in different instruments, to different colour grades for a blue fluorescent diamond.

In the 2010 study the variance in UV from GIA's DiamondDock to AGSL's DiamondDock likely resulted in the one grade difference between GIA grading and AGSL grading documented in the ST Blues.

A large allowed variation of UV and VV defeats standardization of the amount of fluorescence stimulation in blue fluorescent diamonds. Even though lessened by the change from the DiamondLite, the post 2000 GIA requirement for long wave UV in the DiamondDock results in variable, inconsistent and unknown amounts of over grading.

That begs the question asked:

Wouldn't the consumer be better served by grading for the diamond's true color, which was the goal advocated by founder Shipley and pre-2000 GIA teaching?

 

[Rockdiamond]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

GIA graded diamonds were exponentially less popular prior to 2000.
It's rare to find a cert that old on the market today to use for comparison- but it's really not relevant to GIA's current practice.
Again to point out- we don't know exactly how GIA is doing it- but we do know they produce very consistent color grades.
Given that I understand how difficult that is to do, I believe GIA is using procedures which make the whole distance from the bulb discussion irrelevant.

The gemologist-appraiser community is periodically given graduate course updates on GTL grading held at GIA that include observation of grading in the lab. With their 2008 article "Color grading “D-to-Z” diamonds at the GIA Laboratory" and these in house graduate seminars GIA has been transparent on "exactly how GIA is doing it"

There is only one way to "make the whole distance from the bulb discussion irrelevant." That is by grading for the true color in lighting that does not stimulate grade whitening fluorescence. That is accomplished either by grading in diffused LED lighting, or UV filtered and diffused fluorescent lighting.

I'm very honored that you finally responded to something I've written Michael- thank you.
Have you witnessed GIA color grading procedures?
If so, when?
How many graders look at the stone?
Are they given an opportunity to look a the stone under any other lighting than the dock?

Michael, I'm starting to feel just like Garry- you'll take a lot of time responding to one question- but can't take a moment to answer a simple series of questions that are integral to the discussion.
I take it you don't have answers to my questions.

 

[Rockdiamond]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

snip.. There are plenty of things I loath and detest about GIA grading and reporting, but face down D-Z color is not one. (face up and big size differences are)

To add more fuel to the fire-
My remarks are made with respect to D- N+- color.
Starting at around O-P, and moving down into FLY, FY , Intense and Vivid, the job of color grading MB/SB stones becomes exponentially more difficult- because they have more room to change color.
Plus grading at the bottom end of the alphabet is a bitch even for inert stones. The grades are much wider, so it's far more difficult to anticipate exactly what GIA will do.
With regards to GIA color grading of fluoros:
GIA is tougher on fluoros as compared to inert yellow diamonds.
When confronted with a tray of goods in U-V W-X and Y-Z stones, the deepest yellow colors face up in room lighting are always the fluoros.
Some will lighten considerably in sunlight, others less so.
Today I saw an S-T ( GIA graded) that looked as dark as an inert Fancy Light Yellow in normal daytime, non sunny room lighting, face up.
Sure enough- the stone was rated strong blue. It's a cloudy day, but the stone didn't even loose color at the window.
The cutter also showed me some incredibly vivid intense yellow stones- each one was MB/SB, facing up darker than an Intense should.
My takeaway from the way yellow grading is done is that GIA is erring on the conservative side with Yellow diamonds in MB/SB.
I would not call it a mistake as much as simply the way they do it.

Another point which backs up our lack of knowledge on GIA specific procedures is U-Z grading.
The published data says D-Z stones are graded from the pavilion, yet they really do seem to show a continuity with FLY and the darker grades when viewed though the table. That leads me to believe GIA uses techniques that allow them the freedom to look at the U-V, W-X and Y-Z stones face up and consider the diamond in that position as well as pavilion view.


Again, with subjective grades, compromises are a necessity.

 

[michaelgem]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

snip.. There are plenty of things I loath and detest about GIA grading and reporting, but face down D-Z color is not one. (face up and big size differences are)

To add more fuel to the fire-
My remarks are made with respect to D- N+- color.
Starting at around O-P, and moving down into FLY, FY , Intense and Vivid, the job of color grading MB/SB stones becomes exponentially more difficult- because they have more room to change color.
Plus grading at the bottom end of the alphabet is a bitch even for inert stones. The grades are much wider, so it's far more difficult to anticipate exactly what GIA will do.
With regards to GIA color grading of fluoros:
GIA is tougher on fluoros as compared to inert yellow diamonds.
When confronted with a tray of goods in U-V W-X and Y-Z stones, the deepest yellow colors face up in room lighting are always the fluoros.
Some will lighten considerably in sunlight, others less so.
Today I saw an S-T ( GIA graded) that looked as dark as an inert Fancy Light Yellow in normal daytime, non sunny room lighting, face up.
Sure enough- the stone was rated strong blue. It's a cloudy day, but the stone didn't even loose color at the window.
The cutter also showed me some incredibly vivid intense yellow stones- each one was MB/SB, facing up darker than an Intense should.
My takeaway from the way yellow grading is done is that GIA is erring on the conservative side with Yellow diamonds in MB/SB.
I would not call it a mistake as much as simply the way they do it.

Another point which backs up our lack of knowledge on GIA specific procedures is U-Z grading.
The published data says D-Z stones are graded from the pavilion, yet they really do seem to show a continuity with FLY and the darker grades when viewed though the table. That leads me to believe GIA uses techniques that allow them the freedom to look at the U-V, W-X and Y-Z stones face up and consider the diamond in that position as well as pavilion view.


Again, with subjective grades, compromises are a necessity.

David,

It could be fortuitous that you are bringing up issues of fancy diamond color grading. This is right at a time when the Accredited Gemologist Association with Antoinette Matlins, President Stuart Robertson and the AGA board is reconvening the AGA Task Force on Lighting and Color-Grading with the goal of addressing lighting standards for grading colored diamonds and other colored gemstones.

With your experience and knowledge and access to fancy color diamonds you could be a valuable and welcome contributor to this effort. As you might expect, most members of the task force are gemologists, appraisers, lighting equipment manufacturers such as Dazor and System Eickhorst, and lab participation such as Thomas Hainschwang of GGTL - GEMLAB Laboratory, so they are all busy making a living. Progress is slow, and this is a much more daunting undertaking than the relatively simpler D-Z color grading lighting standards.

Speaking for AGA we invite your participation in any capacity. Industry participation such as you could offer would be a valuable addition to this effort.

I will follow with what is our current understanding of GIA grading methodology for colored diamonds and other gemstones. A new thread might be an appropriate place for further discussion. Perhaps others seeing this post might also have an interest in being involved.

Michael D. Cowing, MSc, FGA
AGA Certified Gem Laboratory

 

[sharonp]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Sharon I have written several times in this discussion that in my view when there is enough illumination for consumers to see slight color differences face up that I consider grade whitening is very likely to be occurring hence fluoro is a benefit to consumers (aside from cash savings).

Then get a lux meter and UV meter and put some numbers and data to that opinion.

The way we grade diamond color in the industry is fundamentally flawed. Thomas Tashey is the longest most outspoken person on that case.
You can take a rough diamond, cut it in half and cut a round brilliant and a crushed ice cushion from the same rough and get similar table down grades and +2 grades face up lower for the cushion. So 'clearly defined table down' grading is nonsense (not to mention a 1ct G and a 10ct G look totally different in the same cut).

I was taught body color is a measure of the rarity of the rough and its value, D color being the most rare and sought after grade in the colorless range. The rough doesn't become more or less rare because of the shape its cut into.

If the rough is cut into a round the light path is short and the body color as seen faceup will be its whitest.
If the rough is cut into a crushed ice radiant the light path is long and the body color as viewed faceup will be significantly more tinted than a round polished from the same rough.

The true 'unmodified by cut' body color is more readily seen when both cuts are viewed table down as GIA currently grades D-Z color diamonds.

Why does the current practice have to be changed? If it was changed to grading faceup appearance(like a customer would view) you can forget about all shapes being cut except round in the colorless range. The incentive to the cutters to keep the highest color would trump most other considerations.

Garry I think you missed this post which seems particularly relevant given the last page of discussions.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Sharon I have written several times in this discussion that in my view when there is enough illumination for consumers to see slight color differences face up that I consider grade whitening is very likely to be occurring hence fluoro is a benefit to consumers (aside from cash savings).

Then get a lux meter and UV meter and put some numbers and data to that opinion.
Sharon I do not need to as I know from the Vegas experiance where the sun is very very bright that UV at my desks is not the factor that is making grade whitening happen. From Michaels paper plus the 2013 GIa one, I now am certain that the excitation from vivible light which easily passes through windows and what ever other light is available cause noticable face up grade whitening.
The way we grade diamond color in the industry is fundamentally flawed. Thomas Tashey is the longest most outspoken person on that case.
You can take a rough diamond, cut it in half and cut a round brilliant and a crushed ice cushion from the same rough and get similar table down grades and +2 grades face up lower for the cushion. So 'clearly defined table down' grading is nonsense (not to mention a 1ct G and a 10ct G look totally different in the same cut).

I was taught body color is a measure of the rarity of the rough and its value, D color being the most rare and sought after grade in the colorless range. The rough doesn't become more or less rare because of the shape its cut into.

If the rough is cut into a round the light path is short and the body color as seen faceup will be its whitest.
If the rough is cut into a crushed ice radiant the light path is long and the body color as viewed faceup will be significantly more tinted than a round polished from the same rough.

The true 'unmodified by cut' body color is more readily seen when both cuts are viewed table down as GIA currently grades D-Z color diamonds.

Why does the current practice have to be changed? If it was changed to grading faceup appearance(like a customer would view) you can forget about all shapes being cut except round in the colorless range. The incentive to the cutters to keep the highest color would trump most other considerations.

Garry I think you missed this post which seems particularly relevant given the last page of discussions.

Sharon D Flawless is most rare and I do not care for that category. I like and sell beautiful diamonds that my customers want. I do not mind what GIA and others choose to teach - rarity is a bad way to price and value diamonds. I prefer to value diamonds based on their beauty. e.g. if you look at the cut of 100 D Flawless stones you may find a few that are well cut. If you take a same random 100 medium/strong blue G VS2's there is going to be many more very nice and even beautiful looking diamonds than in the D Fl parcel.
Give me beauty over rarity any day!

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

snip.. There are plenty of things I loath and detest about GIA grading and reporting, but face down D-Z color is not one. (face up and big size differences are)

To add more fuel to the fire-
My remarks are made with respect to D- N+- color.
Starting at around O-P, and moving down into FLY, FY , Intense and Vivid, the job of color grading MB/SB stones becomes exponentially more difficult- because they have more room to change color.
Plus grading at the bottom end of the alphabet is a bitch even for inert stones. The grades are much wider, so it's far more difficult to anticipate exactly what GIA will do.
With regards to GIA color grading of fluoros:
GIA is tougher on fluoros as compared to inert yellow diamonds.
When confronted with a tray of goods in U-V W-X and Y-Z stones, the deepest yellow colors face up in room lighting are always the fluoros.
Some will lighten considerably in sunlight, others less so.
Today I saw an S-T ( GIA graded) that looked as dark as an inert Fancy Light Yellow in normal daytime, non sunny room lighting, face up.
Sure enough- the stone was rated strong blue. It's a cloudy day, but the stone didn't even loose color at the window.
The cutter also showed me some incredibly vivid intense yellow stones- each one was MB/SB, facing up darker than an Intense should.
My takeaway from the way yellow grading is done is that GIA is erring on the conservative side with Yellow diamonds in MB/SB.
I would not call it a mistake as much as simply the way they do it.

Another point which backs up our lack of knowledge on GIA specific procedures is U-Z grading.
The published data says D-Z stones are graded from the pavilion, yet they really do seem to show a continuity with FLY and the darker grades when viewed though the table. That leads me to believe GIA uses techniques that allow them the freedom to look at the U-V, W-X and Y-Z stones face up and consider the diamond in that position as well as pavilion view.


Again, with subjective grades, compromises are a necessity.

I concur David.
One of my secret practices when selecting fancy yellows is to move the stone right up to the lamp tube and watch for bleaching - and it does not only occur with diamonds graded blue fluoro by GIA - there is a small subset of stones that have not been graded as such that loose some color. I think the 2013 GIA article makes that point well - there can be multiple atomic defects that not only have their own effects, but they also react with the effects of neighboring defects.

So folks, I think we all agree with David that grade bleaching in fancy colored diamonds is a real issue.
So all you people on the opposite side of the fence:
SHOULD GIA GTL REMOVE THE UV IN THEIR FANCY COLORED GRADING LIGHTING?

 

[Rockdiamond]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

snip.. There are plenty of things I loath and detest about GIA grading and reporting, but face down D-Z color is not one. (face up and big size differences are)

To add more fuel to the fire-
My remarks are made with respect to D- N+- color.
Starting at around O-P, and moving down into FLY, FY , Intense and Vivid, the job of color grading MB/SB stones becomes exponentially more difficult- because they have more room to change color.
Plus grading at the bottom end of the alphabet is a bitch even for inert stones. The grades are much wider, so it's far more difficult to anticipate exactly what GIA will do.
With regards to GIA color grading of fluoros:
GIA is tougher on fluoros as compared to inert yellow diamonds.
When confronted with a tray of goods in U-V W-X and Y-Z stones, the deepest yellow colors face up in room lighting are always the fluoros.
Some will lighten considerably in sunlight, others less so.
Today I saw an S-T ( GIA graded) that looked as dark as an inert Fancy Light Yellow in normal daytime, non sunny room lighting, face up.
Sure enough- the stone was rated strong blue. It's a cloudy day, but the stone didn't even loose color at the window.
The cutter also showed me some incredibly vivid intense yellow stones- each one was MB/SB, facing up darker than an Intense should.
My takeaway from the way yellow grading is done is that GIA is erring on the conservative side with Yellow diamonds in MB/SB.
I would not call it a mistake as much as simply the way they do it.

Another point which backs up our lack of knowledge on GIA specific procedures is U-Z grading.
The published data says D-Z stones are graded from the pavilion, yet they really do seem to show a continuity with FLY and the darker grades when viewed though the table. That leads me to believe GIA uses techniques that allow them the freedom to look at the U-V, W-X and Y-Z stones face up and consider the diamond in that position as well as pavilion view.


Again, with subjective grades, compromises are a necessity.

David,

It could be fortuitous that you are bringing up issues of fancy diamond color grading. This is right at a time when the Accredited Gemologist Association with Antoinette Matlins, President Stuart Robertson and the AGA board is reconvening the AGA Task Force on Lighting and Color-Grading with the goal of addressing lighting standards for grading colored diamonds and other colored gemstones.

With your experience and knowledge and access to fancy color diamonds you could be a valuable and welcome contributor to this effort. As you might expect, most members of the task force are gemologists, appraisers, lighting equipment manufacturers such as Dazor and System Eickhorst, and lab participation such as Thomas Hainschwang of GGTL - GEMLAB Laboratory, so they are all busy making a living. Progress is slow, and this is a much more daunting undertaking than the relatively simpler D-Z color grading lighting standards.

Speaking for AGA we invite your participation in any capacity. Industry participation such as you could offer would be a valuable addition to this effort.

I will follow with what is our current understanding of GIA grading methodology for colored diamonds and other gemstones. A new thread might be an appropriate place for further discussion. Perhaps others seeing this post might also have an interest in being involved.

Michael D. Cowing, MSc, FGA
AGA Certified Gem Laboratory

Michael- Yes, I'd be extremely grateful to be included.
Do you ever get to NYC?

 

[Karl_K]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Sharon D Flawless is most rare and I do not care for that category. I like and sell beautiful diamonds that my customers want. I do not mind what GIA and others choose to teach - rarity is a bad way to price and value diamonds. I prefer to value diamonds based on their beauty. e.g. if you look at the cut of 100 D Flawless stones you may find a few that are well cut. If you take a same random 100 medium/strong blue G VS2's there is going to be many more very nice and even beautiful looking diamonds than in the D Fl parcel.
Give me beauty over rarity any day!

I agree 100% but the industry has preached and the entire price scheme is build on rarity or the illusion there of.
There for when it comes to pricing the rarity grade is what sets the price(based on market forces for that combo). Cut grading does have an effect on price, but cut ratings are not beauty ratings either.

 

[michaelgem]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

snip.. There are plenty of things I loath and detest about GIA grading and reporting, but face down D-Z color is not one. (face up and big size differences are)

To add more fuel to the fire-
My remarks are made with respect to D- N+- color.
Starting at around O-P, and moving down into FLY, FY , Intense and Vivid, the job of color grading MB/SB stones becomes exponentially more difficult- because they have more room to change color.
Plus grading at the bottom end of the alphabet is a bitch even for inert stones. The grades are much wider, so it's far more difficult to anticipate exactly what GIA will do.
With regards to GIA color grading of fluoros:
GIA is tougher on fluoros as compared to inert yellow diamonds.
When confronted with a tray of goods in U-V W-X and Y-Z stones, the deepest yellow colors face up in room lighting are always the fluoros.
Some will lighten considerably in sunlight, others less so.
Today I saw an S-T ( GIA graded) that looked as dark as an inert Fancy Light Yellow in normal daytime, non sunny room lighting, face up.
Sure enough- the stone was rated strong blue. It's a cloudy day, but the stone didn't even loose color at the window.
The cutter also showed me some incredibly vivid intense yellow stones- each one was MB/SB, facing up darker than an Intense should.
My takeaway from the way yellow grading is done is that GIA is erring on the conservative side with Yellow diamonds in MB/SB.
I would not call it a mistake as much as simply the way they do it.

Another point which backs up our lack of knowledge on GIA specific procedures is U-Z grading.
The published data says D-Z stones are graded from the pavilion, yet they really do seem to show a continuity with FLY and the darker grades when viewed though the table. That leads me to believe GIA uses techniques that allow them the freedom to look at the U-V, W-X and Y-Z stones face up and consider the diamond in that position as well as pavilion view.


Again, with subjective grades, compromises are a necessity.

I concur David.
One of my secret practices when selecting fancy yellows is to move the stone right up to the lamp tube and watch for bleaching - and it does not only occur with diamonds graded blue fluoro by GIA - there is a small subset of stones that have not been graded as such that loose some color. I think the 2013 GIA article makes that point well - there can be multiple atomic defects that not only have their own effects, but they also react with the effects of neighboring defects.

So folks, I think we all agree with David that grade bleaching in fancy colored diamonds is a real issue.
So all you people on the opposite side of the fence:
SHOULD GIA GTL REMOVE THE UV IN THEIR FANCY COLORED GRADING LIGHTING?

So folks, I think we all agree with David that grade bleaching in fancy colored diamonds is a real issue.
So all you people on the opposite side of the fence:
SHOULD GIA GTL REMOVE THE UV IN THEIR FANCY COLORED GRADING LIGHTING?

Great question Garry,

It could be generalized by asking of the GIA or the Lighting Standards Committee the question:

Since many fancy colored diamonds and some highly fluorescent yellow tinted white diamonds look so much different in different lighting, what should be the properties of the light chosen in which to grade them?

Since no single lighting environment can reveal the diamond's changing appearance, a necessary part of the answer may be to do what Garry and David have been doing, grade the color in more than one lighting.

Two standard light sources that reveal and document the appearance changes could be chosen. One might be chosen that represents the properties of the light present in typical indoor, artificial lighting circumstances, and the other that represents, as the GIA's lighting attempts to do, the properties of "a color spectrum close to CIE D55-D65 with No noticeable output in the short- or medium-wave UV range (or a filter available to eliminate UV in this range). The latter lighting was chosen by GIA to represent daylight through a plane glass window, which filters out short- or medium-wave UV.

In that way the consumer would have a much fuller understanding of the properties leading to judgment of the value of the diamond he or she is considering.

The best example of the need for grading in two lighting environments was the experience of Antoinette Matlins and her sister Catherine Bonanno. They were at a pre-auction viewing at a NY auction house looking for a diamond listed as a natural fancy green graded by GIA. They could not find any green fancy color diamond. When they matched the lot number to the stone what they saw in the auction house lighting was a canary yellow diamond.

The face-up appearance in the Macbeth Judge II lighting used by GIA GTL to grade fancy color diamonds apparently had a strong enough UV component to cause the diamond's blue fluorescence in combination with its yellow body color to appear and be graded fancy green.

Image if you were a foreign bidder for this natural green diamond based upon the GIA grading report. After winning the bid you received the package to find you had bought a highly fluorescent canary yellow.

You may say they should have known better and paid attention to the indication of fluorescence, but it was a revelation to the two expert gemologist daughters of the renowned gemologist, Antonio Bonanno, founder of the Columbia School of Gemology.

How much better would it have been, and how much more complete the picture of this diamond, if the grading report had included grades from two standard light sources like the two mentioned?

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Sharon D Flawless is most rare and I do not care for that category. I like and sell beautiful diamonds that my customers want. I do not mind what GIA and others choose to teach - rarity is a bad way to price and value diamonds. I prefer to value diamonds based on their beauty. e.g. if you look at the cut of 100 D Flawless stones you may find a few that are well cut. If you take a same random 100 medium/strong blue G VS2's there is going to be many more very nice and even beautiful looking diamonds than in the D Fl parcel.
Give me beauty over rarity any day!

I agree 100% but the industry has preached and the entire price scheme is build on rarity or the illusion there of.
There for when it comes to pricing the rarity grade is what sets the price(based on market forces for that combo). Cut grading does have an effect on price, but cut ratings are not beauty ratings either.

If you took a poll of three flawless diamonds, price not a factor, all three ideal cut, one colorless, one-near colorless, and one faint yellow- how do you think the voting would go? (and no complicating fluoro )

While some may in fact choose a stone with color, I predict the majority would choose colorless. When it comes to color (in the normal range) I don't think valuation is solely based on rarity. It is, I agree, more true with regard to the top clarity grades.

I agree with Garry's point that if you look at the D IF category as a whole, you would probably find many more beautiful stones in lower colors and clarities. And as he mentioned, that is an indication of how just how important cut quality is to beauty. But Cut is considered by most everybody to be the most important of the 4 CS and so is given priority (at least by most in the pricescope community) in the overall quality/beauty assessment when shopping for a diamond.

My view is captured in the immortal words of one of my favorite songs by the band Little Feat- "I've been rich and I've been poor. Been in love a couple of times before. If I had to choose you know, between the two, I'd take both rich and in love- I ain't no fool!"

Give me D FL Super Ideal!!!

 

[Rockdiamond]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

snip.. There are plenty of things I loath and detest about GIA grading and reporting, but face down D-Z color is not one. (face up and big size differences are)

To add more fuel to the fire-
My remarks are made with respect to D- N+- color.
Starting at around O-P, and moving down into FLY, FY , Intense and Vivid, the job of color grading MB/SB stones becomes exponentially more difficult- because they have more room to change color.
Plus grading at the bottom end of the alphabet is a bitch even for inert stones. The grades are much wider, so it's far more difficult to anticipate exactly what GIA will do.
With regards to GIA color grading of fluoros:
GIA is tougher on fluoros as compared to inert yellow diamonds.
When confronted with a tray of goods in U-V W-X and Y-Z stones, the deepest yellow colors face up in room lighting are always the fluoros.
Some will lighten considerably in sunlight, others less so.
Today I saw an S-T ( GIA graded) that looked as dark as an inert Fancy Light Yellow in normal daytime, non sunny room lighting, face up.
Sure enough- the stone was rated strong blue. It's a cloudy day, but the stone didn't even loose color at the window.
The cutter also showed me some incredibly vivid intense yellow stones- each one was MB/SB, facing up darker than an Intense should.
My takeaway from the way yellow grading is done is that GIA is erring on the conservative side with Yellow diamonds in MB/SB.
I would not call it a mistake as much as simply the way they do it.

Another point which backs up our lack of knowledge on GIA specific procedures is U-Z grading.
The published data says D-Z stones are graded from the pavilion, yet they really do seem to show a continuity with FLY and the darker grades when viewed though the table. That leads me to believe GIA uses techniques that allow them the freedom to look at the U-V, W-X and Y-Z stones face up and consider the diamond in that position as well as pavilion view.


Again, with subjective grades, compromises are a necessity.

I concur David.
One of my secret practices when selecting fancy yellows is to move the stone right up to the lamp tube and watch for bleaching - and it does not only occur with diamonds graded blue fluoro by GIA - there is a small subset of stones that have not been graded as such that loose some color. I think the 2013 GIA article makes that point well - there can be multiple atomic defects that not only have their own effects, but they also react with the effects of neighboring defects.

So folks, I think we all agree with David that grade bleaching in fancy colored diamonds is a real issue.
So all you people on the opposite side of the fence:
SHOULD GIA GTL REMOVE THE UV IN THEIR FANCY COLORED GRADING LIGHTING?

So folks, I think we all agree with David that grade bleaching in fancy colored diamonds is a real issue.
So all you people on the opposite side of the fence:
SHOULD GIA GTL REMOVE THE UV IN THEIR FANCY COLORED GRADING LIGHTING?

Great question Garry,

It could be generalized by asking of the GIA or the Lighting Standards Committee the question:

Since many fancy colored diamonds and some highly fluorescent yellow tinted white diamonds look so much different in different lighting, what should be the properties of the light chosen in which to grade them?

Since no single lighting environment can reveal the diamond's changing appearance, a necessary part of the answer may be to do what Garry and David have been doing, grade the color in more than one lighting.

Two standard light sources that reveal and document the appearance changes could be chosen. One might be chosen that represents the properties of the light present in typical indoor, artificial lighting circumstances, and the other that represents, as the GIA's lighting attempts to do, the properties of "a color spectrum close to CIE D55-D65 with No noticeable output in the short- or medium-wave UV range (or a filter available to eliminate UV in this range). The latter lighting was chosen by GIA to represent daylight through a plane glass window, which filters out short- or medium-wave UV.

In that way the consumer would have a much fuller understanding of the properties leading to judgment of the value of the diamond he or she is considering.

The best example of the need for grading in two lighting environments was the experience of Antoinette Matlins and her sister Catherine Bonanno. They were at a pre-auction viewing at a NY auction house looking for a diamond listed as a natural fancy green graded by GIA. They could not find any green fancy color diamond. When they matched the lot number to the stone what they saw in the auction house lighting was a canary yellow diamond.

The face-up appearance in the Macbeth Judge II lighting used by GIA GTL to grade fancy color diamonds apparently had a strong enough UV component to cause the diamond's blue fluorescence in combination with its yellow body color to appear and be graded fancy green.

Image if you were a foreign bidder for this natural green diamond based upon the GIA grading report. After winning the bid you received the package to find you had bought a highly fluorescent canary yellow.

You may say they should have known better and paid attention to the indication of fluorescence, but it was a revelation to the two expert gemologist daughters of the renowned gemologist, Antonio Bonanno, founder of the Columbia School of Gemology.

How much better would it have been, and how much more complete the picture of this diamond, if the grading report had included grades from two standard light sources like the two mentioned?

MIchael- part of the essence of this discussion is GIA methodology.
We simply don't have the specific answers on exactly how GIA gets its results. I do not see specific answers to how many lights they use. Or how many times a stone is looked at. I can't imagine a grader shielding their eyes so that they can't see the diamond away from a dock.

As long as we're scratching the surface of a subject: They might use even different lighting for different colors.

For example, green, in particular, is probably the toughest color to grade.
Of course we know it's caused by natural radiation- but for my money the reason it's such a tough shade to grade consistently has more to do with the color itself.
A Vivid Canary yellow diamond is a lot brighter than the greenest green diamond ( without fluorescence). SO the color itself is harder to detect- this means Fancy Green is waaaay less saturated green, than a Fancy Yellow's yellow saturation.
I don't know what happened at the auction you mentioned, but I would advise overseas buyers to have a very good set of eyes, experienced in the specific color they are interested in to inspect any costly FCD they would be bidding on. Pure green ( no modifier) is so very rare, many well experienced gemologists may have not seen a lot of it.

A part of the discussion which may be tough for some to accept:
GIA is not in the business of telling us which is a good diamond.
They identify characteristics in a lab. Some of those characteristics, such as fluoro, can cause different effects to the appearance and price of the stone in the real world, outside the laboratory environment.
Not all SB stones are equal, in some very crucial aspects.

 

[michaelgem]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Sharon I have written several times in this discussion that in my view when there is enough illumination for consumers to see slight color differences face up that I consider grade whitening is very likely to be occurring hence fluoro is a benefit to consumers (aside from cash savings).

Then get a lux meter and UV meter and put some numbers and data to that opinion.

The way we grade diamond color in the industry is fundamentally flawed. Thomas Tashey is the longest most outspoken person on that case.
You can take a rough diamond, cut it in half and cut a round brilliant and a crushed ice cushion from the same rough and get similar table down grades and +2 grades face up lower for the cushion. So 'clearly defined table down' grading is nonsense (not to mention a 1ct G and a 10ct G look totally different in the same cut).

I was taught body color is a measure of the rarity of the rough and its value, D color being the most rare and sought after grade in the colorless range. The rough doesn't become more or less rare because of the shape its cut into.

If the rough is cut into a round the light path is short and the body color as seen faceup will be its whitest.
If the rough is cut into a crushed ice radiant the light path is long and the body color as viewed faceup will be significantly more tinted than a round polished from the same rough.

The true 'unmodified by cut' body color is more readily seen when both cuts are viewed table down as GIA currently grades D-Z color diamonds.

Why does the current practice have to be changed? If it was changed to grading faceup appearance(like a customer would view) you can forget about all shapes being cut except round in the colorless range. The incentive to the cutters to keep the highest color would trump most other considerations.

Garry I think you missed this post which seems particularly relevant given the last page of discussions.

Sharon you are right on.

The reason diamonds are graded face-down against a white background in diffuse lighting is to minimize the sparkle and reflections removing the impact on color perception of the diamond's cut. The color fineness/whiteness like the clarity/purity is graded this way as a basic property of beauty and rarity, kept separate from the impact on perceived color due to the cut.

If an R-S-T through X-Y-Z low color diamond cut as a princess is submitted to GIA for grading in the D-Z system, it will be graded table down in the DiamondDock. If the same diamond is resubmitted for a fancy color grade it will be evaluated face-up in the Macbeth Judge II


Here the longer path length of light reflecting around in a princess cut viewed face-up intensifies the color saturation. The R-S-T-X-Y-Z low color stone likely will grade a light fancy or even fancy yellow. Recutting off color old mine cuts to princess cuts has long been successfully accomplished dramatically increasing their value. The same old miner recut to a round would have lower yield and have a much lower value due to shorter path lengths resulting in the washing out of color.

 

[Rockdiamond]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Sharon you are right on.

The reason diamonds are graded face-down against a white background in diffuse lighting is to minimize the sparkle and reflections removing the impact on color perception of the diamond's cut. The color fineness/whiteness like the clarity/purity is graded this way as a basic property of beauty and rarity, kept separate from the impact on perceived color due to the cut.

If an R-S-T through X-Y-Z low color diamond cut as a princess is submitted to GIA for grading in the D-Z system, it will be graded table down in the DiamondDock. If the same diamond is resubmitted for a fancy color grade it will be evaluated face-up [\b]in the Macbeth Judge II


Here the longer path length of light reflecting around in a princess cut viewed face-up intensifies the color saturation. The R-S-T-X-Y-Z low color stone likely will grade a light fancy or even fancy yellow. Recutting off color old mine cuts to princess cuts has long been successfully accomplished dramatically increasing their value. The same old miner recut to a round would have lower yield and have a much lower value due to shorter path lengths resulting in the washing out of color.

Regarding the statement: I believe you meant to say modified brilliant ( such as a cushion or radiant) as opposed to princess. Which is an interesting point. Do you believe they grade RBC differently than fancy shapes at the bottom of the alphabet?
Regardless the part about submitting a diamond for a fancy color report is incorrect.
I know this because we have a little secret way to save a bit of money.
We like to order the Diamond Dossier from GIA on stones under 2.00ct as it saves some money and we like the report.
If I suspect a stone is Fancy Light Yellow I ask for the Dossier. GIA does not offer dossier for fancy colors so they will let me know if the stone passes the FLY barrier- at which point I have to get the full report - or they will return the stone.
You're not going to pull a lot of wool over GIA's eyes. They run an impressive operation here in NYC. They look at the stones both ways ( table and pavilion) and determine - they'd have to if you think about it.
Oops - I gave away our money saving secret

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Sharon D Flawless is most rare and I do not care for that category. I like and sell beautiful diamonds that my customers want. I do not mind what GIA and others choose to teach - rarity is a bad way to price and value diamonds. I prefer to value diamonds based on their beauty. e.g. if you look at the cut of 100 D Flawless stones you may find a few that are well cut. If you take a same random 100 medium/strong blue G VS2's there is going to be many more very nice and even beautiful looking diamonds than in the D Fl parcel.
Give me beauty over rarity any day!

I agree 100% but the industry has preached and the entire price scheme is build on rarity or the illusion there of.
There for when it comes to pricing the rarity grade is what sets the price(based on market forces for that combo). Cut grading does have an effect on price, but cut ratings are not beauty ratings either.

If you took a poll of three flawless diamonds, price not a factor, all three ideal cut, one colorless, one-near colorless, and one faint yellow- how do you think the voting would go? (and no complicating fluoro )

While some may in fact choose a stone with color, I predict the majority would choose colorless. When it comes to color (in the normal range) I don't think valuation is solely based on rarity. It is, I agree, more true with regard to the top clarity grades.

I agree with Garry's point that if you look at the D IF category as a whole, you would probably find many more beautiful stones in lower colors and clarities. And as he mentioned, that is an indication of how just how important cut quality is to beauty. But Cut is considered by most everybody to be the most important of the 4 CS and so is given priority (at least by most in the pricescope community) in the overall quality/beauty assessment when shopping for a diamond.

My view is captured in the immortal words of one of my favorite songs by the band Little Feat- "I've been rich and I've been poor. Been in love a couple of times before. If I had to choose you know, between the two, I'd take both rich and in love- I ain't no fool!"

Give me D FL Super Ideal!!!

Bryan I would take the 2 or 3 G SI1 medium or strong blue's every day for the same price as just one crappy cut non D FL's. Or better still - one nearly twice the weight. And by the very nature of the rareness function - I am not alone, because there are many more G or there abouts than D and many more SI or there abouts than FL - and they all find nice homes, and they all have more chance of being more sparkly than the D FL. But I would say that because of the available technology, there are many more flawless and VVS stones being polished today than the market can accept - especially now that ol rich countries are poorer and China and India are cracking down on bribery and corruption. So enjoy your D Fl's - they will be worth-less.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

snip.. There are plenty of things I loath and detest about GIA grading and reporting, but face down D-Z color is not one. (face up and big size differences are)

To add more fuel to the fire-
My remarks are made with respect to D- N+- color.
Starting at around O-P, and moving down into FLY, FY , Intense and Vivid, the job of color grading MB/SB stones becomes exponentially more difficult- because they have more room to change color.
Plus grading at the bottom end of the alphabet is a bitch even for inert stones. The grades are much wider, so it's far more difficult to anticipate exactly what GIA will do.
With regards to GIA color grading of fluoros:
GIA is tougher on fluoros as compared to inert yellow diamonds.
When confronted with a tray of goods in U-V W-X and Y-Z stones, the deepest yellow colors face up in room lighting are always the fluoros.
Some will lighten considerably in sunlight, others less so.
Today I saw an S-T ( GIA graded) that looked as dark as an inert Fancy Light Yellow in normal daytime, non sunny room lighting, face up.
Sure enough- the stone was rated strong blue. It's a cloudy day, but the stone didn't even loose color at the window.
The cutter also showed me some incredibly vivid intense yellow stones- each one was MB/SB, facing up darker than an Intense should.
My takeaway from the way yellow grading is done is that GIA is erring on the conservative side with Yellow diamonds in MB/SB.
I would not call it a mistake as much as simply the way they do it.

Another point which backs up our lack of knowledge on GIA specific procedures is U-Z grading.
The published data says D-Z stones are graded from the pavilion, yet they really do seem to show a continuity with FLY and the darker grades when viewed though the table. That leads me to believe GIA uses techniques that allow them the freedom to look at the U-V, W-X and Y-Z stones face up and consider the diamond in that position as well as pavilion view.


Again, with subjective grades, compromises are a necessity.

I concur David.
One of my secret practices when selecting fancy yellows is to move the stone right up to the lamp tube and watch for bleaching - and it does not only occur with diamonds graded blue fluoro by GIA - there is a small subset of stones that have not been graded as such that loose some color. I think the 2013 GIA article makes that point well - there can be multiple atomic defects that not only have their own effects, but they also react with the effects of neighboring defects.

So folks, I think we all agree with David that grade bleaching in fancy colored diamonds is a real issue.
So all you people on the opposite side of the fence:
SHOULD GIA GTL REMOVE THE UV IN THEIR FANCY COLORED GRADING LIGHTING?

So folks, I think we all agree with David that grade bleaching in fancy colored diamonds is a real issue.
So all you people on the opposite side of the fence:
SHOULD GIA GTL REMOVE THE UV IN THEIR FANCY COLORED GRADING LIGHTING?

Great question Garry,

It could be generalized by asking of the GIA or the Lighting Standards Committee the question:

Since many fancy colored diamonds and some highly fluorescent yellow tinted white diamonds look so much different in different lighting, what should be the properties of the light chosen in which to grade them?

Since no single lighting environment can reveal the diamond's changing appearance, a necessary part of the answer may be to do what Garry and David have been doing, grade the color in more than one lighting.

Two standard light sources that reveal and document the appearance changes could be chosen. One might be chosen that represents the properties of the light present in typical indoor, artificial lighting circumstances, and the other that represents, as the GIA's lighting attempts to do, the properties of "a color spectrum close to CIE D55-D65 with No noticeable output in the short- or medium-wave UV range (or a filter available to eliminate UV in this range). The latter lighting was chosen by GIA to represent daylight through a plane glass window, which filters out short- or medium-wave UV.

In that way the consumer would have a much fuller understanding of the properties leading to judgment of the value of the diamond he or she is considering.

The best example of the need for grading in two lighting environments was the experience of Antoinette Matlins and her sister Catherine Bonanno. They were at a pre-auction viewing at a NY auction house looking for a diamond listed as a natural fancy green graded by GIA. They could not find any green fancy color diamond. When they matched the lot number to the stone what they saw in the auction house lighting was a canary yellow diamond.

The face-up appearance in the Macbeth Judge II lighting used by GIA GTL to grade fancy color diamonds apparently had a strong enough UV component to cause the diamond's blue fluorescence in combination with its yellow body color to appear and be graded fancy green.

Image if you were a foreign bidder for this natural green diamond based upon the GIA grading report. After winning the bid you received the package to find you had bought a highly fluorescent canary yellow.

You may say they should have known better and paid attention to the indication of fluorescence, but it was a revelation to the two expert gemologist daughters of the renowned gemologist, Antonio Bonanno, founder of the Columbia School of Gemology.

How much better would it have been, and how much more complete the picture of this diamond, if the grading report had included grades from two standard light sources like the two mentioned?

Michael I doubt many consumers, and I am certain very few retail salespeople want to have 2 color grades on a certificate.
As David will confirm, if you look in a typical diamond dealers lighting at a selection of say GIA fancy yellow diamonds, of any grade, but for e.g. say Fancy Yellow, and say half are strong blue, and half are none - the strong blues will be far stronger looking yellows.

The point to this example is, that by your rules, that same lighting would result in over grading of a strong blue H diamond and it would "really be an I or a J".
Do you see where and why you are wrong?

 

[michaelgem]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Sharon you are right on.

The reason diamonds are graded face-down against a white background in diffuse lighting is to minimize the sparkle and reflections removing the impact on color perception of the diamond's cut. The color fineness/whiteness like the clarity/purity is graded this way as a basic property of beauty and rarity, kept separate from the impact on perceived color due to the cut.

If an R-S-T through X-Y-Z low color diamond cut as a princess is submitted to GIA for grading in the D-Z system, it will be graded table down in the DiamondDock. If the same diamond is resubmitted for a fancy color grade it will be evaluated face-up [\b]in the Macbeth Judge II


Here the longer path length of light reflecting around in a princess cut viewed face-up intensifies the color saturation. The R-S-T-X-Y-Z low color stone likely will grade a light fancy or even fancy yellow. Recutting off color old mine cuts to princess cuts has long been successfully accomplished dramatically increasing their value. The same old miner recut to a round would have lower yield and have a much lower value due to shorter path lengths resulting in the washing out of color.

Regarding the statement: I believe you meant to say modified brilliant ( such as a cushion or radiant) as opposed to princess. Which is an interesting point.

The path lengths of light in the princess are generally longer, absorbing more color than the typical radiant whose pavilion was designed for brilliance similar to the round, so recutting to a princess is the better way to increase color in order to obtain a fancy color grade from off color old miners.

Do you believe they grade RBC differently than fancy shapes at the bottom of the alphabet? Regardless the part about submitting a diamond for a fancy color report is incorrect.

The understanding was you could submit a diamond to GIA requesting a fancy color grade evaluation.

My belief and understanding derive from my Diamond Course studies, and graduate course seminars at GIA and AGS, and many interactions and discussions with fellow gemologist/appraisers, GIA researchers and grading instructors including brothers Phil Yantzer, VP at GIA, and Peter Yantzer, AGS Lab director, as well as former GIA supervisors and instructors Gary Roskin and Tom Tashey and others over the course of many years. The name dropping is to emphasize the importance in the profession of gemology/appraising of keeping abreast of diamond grading practice especially at GIA GTL.

A diamond, whether a RBC or a fancy shape, submitted to GIA for a D-Z color rating is graded in the same manner table down in the DiamondDock whatever its color. In grading fancy shapes like the marquise, the color often appears a lower grade looking lengthwise verses widthwise. GIA recommends either averaging the two grades or looking at the color of the marquise in profile rotated halfway between at 45 degrees.

If the D-Z color is in the RST-XYZ range one would hope the grader also evaluates the diamond face-up to determine the potential for a light fancy or fancy color grade and then advises the client of that fancy color call. We should check with GIA for a definitive answer on this.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Sharon you are right on.

The reason diamonds are graded face-down against a white background in diffuse lighting is to minimize the sparkle and reflections removing the impact on color perception of the diamond's cut. The color fineness/whiteness like the clarity/purity is graded this way as a basic property of beauty and rarity, kept separate from the impact on perceived color due to the cut.

If an R-S-T through X-Y-Z low color diamond cut as a princess is submitted to GIA for grading in the D-Z system, it will be graded table down in the DiamondDock. If the same diamond is resubmitted for a fancy color grade it will be evaluated face-up [\b]in the Macbeth Judge II


Here the longer path length of light reflecting around in a princess cut viewed face-up intensifies the color saturation. The R-S-T-X-Y-Z low color stone likely will grade a light fancy or even fancy yellow. Recutting off color old mine cuts to princess cuts has long been successfully accomplished dramatically increasing their value. The same old miner recut to a round would have lower yield and have a much lower value due to shorter path lengths resulting in the washing out of color.

Regarding the statement: I believe you meant to say modified brilliant ( such as a cushion or radiant) as opposed to princess. Which is an interesting point.

The path lengths of light in the princess are generally longer, absorbing more color than the typical radiant whose pavilion was designed for brilliance similar to the round, so recutting to a princess is the better way to increase color in order to obtain a fancy color grade from off color old miners.

Do you believe they grade RBC differently than fancy shapes at the bottom of the alphabet? Regardless the part about submitting a diamond for a fancy color report is incorrect.

The understanding was you could submit a diamond to GIA requesting a fancy color grade evaluation.

My belief and understanding derive from my Diamond Course studies, and graduate course seminars at GIA and AGS, and many interactions and discussions with fellow gemologist/appraisers, GIA researchers and grading instructors including brothers Phil Yantzer, VP at GIA, and Peter Yantzer, AGS Lab director, as well as former GIA supervisors and instructors Gary Roskin and Tom Tashey and others over the course of many years. The name dropping is to emphasize the importance in the profession of gemology/appraising of keeping abreast of diamond grading practice especially at GIA GTL.

A diamond, whether a RBC or a fancy shape, submitted to GIA for a D-Z color rating is graded in the same manner table down in the DiamondDock whatever its color. In grading fancy shapes like the marquise, the color often appears a lower grade looking lengthwise verses widthwise. GIA recommends either averaging the two grades or looking at the color of the marquise in profile rotated halfway between at 45 degrees.

If the D-Z color is in the RST-XYZ range one would hope the grader also evaluates the diamond face-up to determine the potential for a light fancy or fancy color grade and then advises the client of that fancy color call. We should check with GIA for a definitive answer on this.

Michael it is not important but radiant, cushion and ovals obtain the greater ray path length than princess cuts. Try modelling this in DianCalc.

 

[michaelgem]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Michael, as I read your paper I have a couple more questions for you. I am personally more experienced with reading medical journals (more specifically pharmaceutical research) and am accustomed to finding the "limitations" section at the end. I am curious as to whether you formulated a list of limitations and what that list may look like?

As a reader, the first question I am asking myself is what are your credentials and training as a diamond grader?
What sort of master set of stones did you use for your grading of these 25 stones?
Was the selection of diamonds to be used done at random and why only 25 stones?
Were the specified light sources the ONLY source of light in the room at the time of grading?

I hope you don't take these questions as an indication of me trying to poke holes in your study. They are very real questions I would like to know in order to evaluate the study. I happen to come into this discussion feeling like a UV filter should be used for diamond grading and don't see why the use of a filter would be detrimental to the consumer. If UV light is causing a chameleon effect on stones that is dependent upon the lighting it should be eliminated as a variable, especially considering that we don't know why certain fluorescing stones behave one way and others seem to behave another way.

This post by pfunk encompasses most all questions asked about my color grading methodology, limitations and skill asked over many pages by everyone including Sharon, Garry, David and Karl. So this response is to and for everyone who asked.

As a reader, the first question I am asking myself is what are your credentials and training as a diamond grader?

Credentials and training in diamond grading are a subset of gemology credentials. In the US there are two main avenues to a credential in gemology. One is the Diploma Course and examination to obtain the designation FGA (Fellow of the Gemmological Association of Great Britain). The other is the more widely held (in the US) Diploma course and examination to obtain the credential GG ( Graduate Gemologist) at GIA. It is generally acknowledged in the appraisal community that the FGA program is more academically rigorous and challenging, but in the field of diamond grading GIA is the acknowledged leader and their diamond course superior.

My gemology diploma is FGA, and I own and have researched all four generations of GIA Graduate Gemologist courses from the 60's to the present. I hold the certification by the Accredited Gemologist Association, Certified Gemological Laboratory(CGL) and am a Senior Member of that Association. Senior Member status with the National Association of Jewelry Appraisers was attained after years of continuing education in the fields of gemology and appraising.

What sort of master set of stones did you use for your grading of these 25 stones?

I employed my 10 stone set of quarter carat to three-eighth carat masters built during the 80's by sending stones to GIA where their top color grader (now retired) Karen Hurwit graded them as Masters. I also had access to and employed what I believe for several reasons to be the best 10 stone master set Karen ever put together. That set of Lazar Kaplin Ideal cut diamond masters was made for diamond dealer and CZ master manufacturer Barry Ellin. Here is a photo of that master stone set of nine, whole-grade master diamonds from E to L and N from my article "A place for CZ masters in diamond colour grading" in the Journal of Gemmology / 2008 / Volume 31 / No. 3/4.


For those interested in greater depth of understanding of color grading this article:
( http://acagemlab.com/temp/CowingCZ.pdf ) goes way beyond a "Consumer's Report" style evaluation of the two major CZ master sets available and widely in use in the US.

Findings are reported of studies in five areas related to diamond color grading:

1. The historical development by the Gemological Institute of America (GIA) of a color grading standard beginning with the GIA color grading ‘yardstick’.

2. Industry and GIA teaching of methods and recommendations for color grading using GIA Diamond Masters, which reduce the subjectivity of color grading.

3. The pros and cons in the use of CZ master stones in diamond color grading.

4. A study of grading light environments using five lighting types that resulted in additional recommendations for color grading using diamond or CZ master stones.

Was the selection of diamonds to be used done at random and why only 25 stones?

For the Medium, Strong and Very Strong Blues, the 25 diamond database was made up of the first five stones of each strength having post-2000 GIA grading reports that I was able to obtain. The faint and none used as a control were likewise randomly obtained, most with GIA grading reports. Antoinette Matlins happened fortuitously to have the VST Blue cushion #5 that turned out to be the true blue-white top color diamond historically called Jager.

Were the specified light sources the ONLY source of light in the room at the time of grading?

Grading was done in each light in an otherwise relatively dark room.

Finally, remember the grading in GIA DiamondDock standard lighting is by GIA GTL, and AGSL as well as me. As Bryan has pointed out, all three agree within tolerance on the grades of the study's 10 non-fluoresent control diamonds. This close correlation in grading supports the grading skill and consistency of all three. It is only as the strength of the diamond's fluorescence goes from medium to strong to very strong blue that differences and inconsistencies arise and worsen.

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Sharon D Flawless is most rare and I do not care for that category. I like and sell beautiful diamonds that my customers want. I do not mind what GIA and others choose to teach - rarity is a bad way to price and value diamonds. I prefer to value diamonds based on their beauty. e.g. if you look at the cut of 100 D Flawless stones you may find a few that are well cut. If you take a same random 100 medium/strong blue G VS2's there is going to be many more very nice and even beautiful looking diamonds than in the D Fl parcel.
Give me beauty over rarity any day!

I agree 100% but the industry has preached and the entire price scheme is build on rarity or the illusion there of.
There for when it comes to pricing the rarity grade is what sets the price(based on market forces for that combo). Cut grading does have an effect on price, but cut ratings are not beauty ratings either.

If you took a poll of three flawless diamonds, price not a factor, all three ideal cut, one colorless, one-near colorless, and one faint yellow- how do you think the voting would go? (and no complicating fluoro )

While some may in fact choose a stone with color, I predict the majority would choose colorless. When it comes to color (in the normal range) I don't think valuation is solely based on rarity. It is, I agree, more true with regard to the top clarity grades.

I agree with Garry's point that if you look at the D IF category as a whole, you would probably find many more beautiful stones in lower colors and clarities. And as he mentioned, that is an indication of how just how important cut quality is to beauty. But Cut is considered by most everybody to be the most important of the 4 CS and so is given priority (at least by most in the pricescope community) in the overall quality/beauty assessment when shopping for a diamond.

My view is captured in the immortal words of one of my favorite songs by the band Little Feat- "I've been rich and I've been poor. Been in love a couple of times before. If I had to choose you know, between the two, I'd take both rich and in love- I ain't no fool!"

Give me D FL Super Ideal!!!

Bryan I would take the 2 or 3 G SI1 medium or strong blue's every day for the same price as just one crappy cut non D FL's. Or better still - one nearly twice the weight. And by the very nature of the rareness function - I am not alone, because there are many more G or there abouts than D and many more SI or there abouts than FL - and they all find nice homes, and they all have more chance of being more sparkly than the D FL. But I would say that because of the available technology, there are many more flawless and VVS stones being polished today than the market can accept - especially now that ol rich countries are poorer and China and India are cracking down on bribery and corruption. So enjoy your D Fl's - they will be worth-less.

Garry,
You violated the rules of the poll! My point was that color (as in 'lack thereof') is a beauty factor, not only a rarity factor.

Your argument is that if you take the 4 cs together there is more VALUE to be derived in lower colors and clarities when you consider the impacts of cut and size. I believe we all agree with that. And of course you positively value fluorescence in that matrix, which many others do as well.

As for D FL becoming worthless, I guess we should all be looking for another line of work. Meanwhile, just send any worthless diamonds my way. I will dispose of them for you

This amounted to a threadjack, for which I apologize. I find the conversation about grading methods between lower D-Z and fancy color to be quite interesting and informative. (Maybe that deserves a thread of its own as it has departed from the specific topic of the thread.)

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Hi Bryan - I wrote worth-less not worthless.
Surely you have noticed the big discounts on high color clarity fungible RBC diamonds?

 

[Rockdiamond]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Michael, as I read your paper I have a couple more questions for you. I am personally more experienced with reading medical journals (more specifically pharmaceutical research) and am accustomed to finding the "limitations" section at the end. I am curious as to whether you formulated a list of limitations and what that list may look like?

As a reader, the first question I am asking myself is what are your credentials and training as a diamond grader?
What sort of master set of stones did you use for your grading of these 25 stones?
Was the selection of diamonds to be used done at random and why only 25 stones?
Were the specified light sources the ONLY source of light in the room at the time of grading?

I hope you don't take these questions as an indication of me trying to poke holes in your study. They are very real questions I would like to know in order to evaluate the study. I happen to come into this discussion feeling like a UV filter should be used for diamond grading and don't see why the use of a filter would be detrimental to the consumer. If UV light is causing a chameleon effect on stones that is dependent upon the lighting it should be eliminated as a variable, especially considering that we don't know why certain fluorescing stones behave one way and others seem to behave another way.

This post by pfunk encompasses most all questions asked about my color grading methodology, limitations and skill asked over many pages by everyone including Sharon, Garry, David and Karl. So this response is to and for everyone who asked.

As a reader, the first question I am asking myself is what are your credentials and training as a diamond grader?

Credentials and training in diamond grading are a subset of gemology credentials. In the US there are two main avenues to a credential in gemology. One is the Diploma Course and examination to obtain the designation FGA (Fellow of the Gemmological Association of Great Britain). The other is the more widely held (in the US) Diploma course and examination to obtain the credential GG ( Graduate Gemologist) at GIA. It is generally acknowledged in the appraisal community that the FGA program is more academically rigorous and challenging, but in the field of diamond grading GIA is the acknowledged leader and their diamond course superior.

My gemology diploma is FGA, and I own and have researched all four generations of GIA Graduate Gemologist courses from the 60's to the present. I hold the certification by the Accredited Gemologist Association, Certified Gemological Laboratory(CGL) and am a Senior Member of that Association. Senior Member status with the National Association of Jewelry Appraisers was attained after years of continuing education in the fields of gemology and appraising.

What sort of master set of stones did you use for your grading of these 25 stones?

I employed my 10 stone set of quarter carat to three-eighth carat masters built during the 80's by sending stones to GIA where their top color grader (now retired) Karen Hurwit graded them as Masters. I also had access to and employed what I believe for several reasons to be the best 10 stone master set Karen ever put together. That set of Lazar Kaplin Ideal cut diamond masters was made for diamond dealer and CZ master manufacturer Barry Ellin. Here is a photo of that master stone set of nine, whole-grade master diamonds from E to L and N from my article "A place for CZ masters in diamond colour grading" in the Journal of Gemmology / 2008 / Volume 31 / No. 3/4.


For those interested in greater depth of understanding of color grading this article:
( http://acagemlab.com/temp/CowingCZ.pdf ) goes way beyond a "Consumer's Report" style evaluation of the two major CZ master sets available and widely in use in the US.

Findings are reported of studies in five areas related to diamond color grading:

1. The historical development by the Gemological Institute of America (GIA) of a color grading standard beginning with the GIA color grading ‘yardstick’.

2. Industry and GIA teaching of methods and recommendations for color grading using GIA Diamond Masters, which reduce the subjectivity of color grading.

3. The pros and cons in the use of CZ master stones in diamond color grading.

4. A study of grading light environments using five lighting types that resulted in additional recommendations for color grading using diamond or CZ master stones.

Was the selection of diamonds to be used done at random and why only 25 stones?

For the Medium, Strong and Very Strong Blues, the 25 diamond database was made up of the first five stones of each strength having post-2000 GIA grading reports that I was able to obtain. The faint and none used as a control were likewise randomly obtained, most with GIA grading reports. Antoinette Matlins happened fortuitously to have the VST Blue cushion #5 that turned out to be the true blue-white top color diamond historically called Jager.

Were the specified light sources the ONLY source of light in the room at the time of grading?

Grading was done in each light in an otherwise relatively dark room.

Finally, remember the grading in GIA DiamondDock standard lighting is by GIA GTL, and AGSL as well as me. As Bryan has pointed out, all three agree within tolerance on the grades of the study's 10 non-fluoresent control diamonds. This close correlation in grading supports the grading skill and consistency of all three. It is only as the strength of the diamond's fluorescence goes from medium to strong to very strong blue that differences and inconsistencies arise and worsen.

Michael, thanks for posting this- but haven't we moved past the point in the discussion regarding GIA and systematic overgrading of MB/SB stones?
It's not happening and there's been no credible evidence shown to substantiate the claim.

Let's agree you saw a stone as a J color that GIA saw as a G and AGSL saw as an H.
Maybe it was an anomaly. Maybe the methods you used produced an errant result- but it's important to make sure this part is clear.
It's possible to find errors in GIA grades- but they are quite rare and indicate no systematic problem