Article Over Grading of Blue Fluorescent Diamonds Revisited

[sharonp]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

The obvious solution in my mind is to simply increase the grading distance from the light source to the point where UV is eliminated. VV may still be present, but not in sufficient intensity to cause color masking and to therefore introduce grading inaccuracy.

michaelgem » 08 Mar 2016 21:35

At this distance the main difficulty grading is not light intensity, which was more than adequate. It was the quality of the light. Even when you are only 7 inches from the tubes in the DiamondDock reflections and sparkle make it difficult to gauge the body color against the masters. That is why there is a tendency to raise the tray closer to the tubes where the illumination is more diffuse and the body color more discernible, but also where the UV and visible light intensity enhances the color

Bryan that isn't so obvious to me for practical reasons, for starters GIA isn't likely to make to make a 3 foot+ diamond dock with big lighting tubes. Then there are also light quality problems.

 

[Karl_K]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

It seems abundantly clear from this data that there is an undeniable trend suggesting that color grading accuracy would be significantly improved for blue fluorescent stones if they were graded in an environment free of grade whitening levels of UV and VV.

This is not alarmism. This is common sense.

Bryan the red part is wrong. Surly you understand it?
In this photo, a south facing afternoon window is = to a north facing Northern hemisphere window taken with a 415 nm lens filter shows that there is in a room (northern equivalent light) an abundant source of light that Michael's and the GIA's 2013 article prove has a strong whitening effect on N3 centers in the most common fluorescent cape series colorless diamonds.
Why would you state that VV should be excluded?

Garry that may not be a lot of light at all. The camera will adjust shutter and f-stop and iso to get an image down to very tiny amounts of light. Please email me the full image right from the camera.
What would be interesting is building a dark box with the filter set up as a projection light source into the box and with the camera manually set, take some pictures of the effects on a very strong blue fluorescent diamond with different light sources going into the filter.
While the response of the light meter may be suspect under VV it would also be interesting to get meter readings with and without the filter.

 

[Karl_K]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

David,
You are right the studies are way to limited to conclusively prove there is a wide ranging grading issue.
On the other hand it does point to that there might be a wider problem.
You are also wrong in saying there is no issue as if it where a fact.
If in your opinion there is no issue then that's kewl, I will take that into consideration.

Personally I would like to see filters used when grading to be on the safe side.

 

[sharonp]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

It seems abundantly clear from this data that there is an undeniable trend suggesting that color grading accuracy would be significantly improved for blue fluorescent stones if they were graded in an environment free of grade whitening levels of UV

Actually the data is inconclusive in that part.

Under the strongest UV Source 1 ( Diamondlite 2 - 3 inches away) look at filtered(1 uw/cm2) and unfiltered(150 uw/cm2).

The VSB samples Stones 1, 2 and 4 have two or more grade differences between filtered and unfiltered.

For all of the Strong and Medium Fluoro samples (5 - 15) there is no difference between UV filtered and unfiltered except 9 and 14 which only had a 1 grade difference. Removing UV alone had negligible effect for Strong and Medium Fluoro diamonds in the presence of strong white light.

I did a quick estimate on Bluenile and less than 0.2% of diamonds in their inventory have VSB fluoro. If one adds all SB and MB it is above 9%.

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

The obvious solution in my mind is to simply increase the grading distance from the light source to the point where UV is eliminated. VV may still be present, but not in sufficient intensity to cause color masking and to therefore introduce grading inaccuracy.

michaelgem » 08 Mar 2016 21:35

At this distance the main difficulty grading is not light intensity, which was more than adequate. It was the quality of the light. Even when you are only 7 inches from the tubes in the DiamondDock reflections and sparkle make it difficult to gauge the body color against the masters. That is why there is a tendency to raise the tray closer to the tubes where the illumination is more diffuse and the body color more discernible, but also where the UV and visible light intensity enhances the color

Bryan that isn't so obvious to me for practical reasons, for starters GIA isn't likely to make to make a 3 foot+ diamond dock with big lighting tubes. Then there are also light quality problems.

Sharon,
From what I see in the data related to the the intensity dropoff, it would not have to be 3 ft. It could very well be that 1 ft would do it. Having said that, I have no illusions that GIA will change their current approach. They took a good step in the direction of reducing the problem with the release of the diamond dock. Unfortunately, it did not fully resolve the issue.

I think the practical takeaway for consumers is to, during their return period, have their blue fluorescent diamonds independently verified by a knowledgeable gemologist who is equipped to color grade the diamond in a UV free environment (against a set of GIA masters), and can also assess any potential undesirable transparency issues. And not to be persuaded by the merchant that their diamond will normally look any whiter than the verified lab color grade. Any whitening that might accrue to them in certain circumstances will be the cherry on top of the cake.

 

[Karl_K]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

While the response of the light meter may be suspect under VV it would also be interesting to get meter readings with and without the filter.

That will not work as the Minimum Transmission (%) of the filter may be as low as 40% or as high as 95%
What is the spec of the filter?

 

[sharonp]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Garry that may not be a lot of light at all.

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Garry that may not be a lot of light at all.

What is known about the reflective film that is typically put on modern buildings in terms of it's effect on color rendition and in particular, on UV filtering?

 

[sharonp]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

 

[Rockdiamond]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

David,
You are right the studies are way to limited to conclusively prove there is a wide ranging grading issue.
On the other hand it does point to that there might be a wider problem.
You are also wrong in saying there is no issue as if it where a fact.
If in your opinion there is no issue then that's kewl, I will take that into consideration.

Personally I would like to see filters used when grading to be on the safe side.

Thanks Karl- to clarify my point on overgrading: The study can not be considered proof of an overgrading problem. Putting all other issues aside, there's no corroboration of Michael's grading. This invalidates any conclusions - other than conclusions drawn by comparing GIA and AGSL grades. Michael could be the best color grader in the world- we'd still need peer review of his grades to take the results seriously.
Sharon and Bryan, you never responded to that point.
Furthermore, no one in this discussion knows exactly how GIA performs color grading. What the intensity, under which conditions the stones are looked at in specifics. Nor will GIA discuss them.This means we can discuss this till the cows come home, it will not affect GIA procedures.

True, in my experience this is not a problem- but also true that is only my experience. But we also have empirical price data showing how D-E-F MB/SB stones are pretty heavily discounted.
So if there really is an overgrading problem, where can we see evidence of it?
For my money, Pricescope has offered the most transparent look into real consumers discussing their issues available on the internet. Excellent crowd sourcing as it were
If there was some sort of problem, it certainly might have come up in over 10 years here.

 

[Karl_K]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Garry that may not be a lot of light at all.

What is known about the reflective film that is typically put on modern buildings in terms of it's effect on color rendition and in particular, on UV filtering?

UV,
95% for internal films up to 99.9% for external files when new and properly installed, coatings range from 65% to 85%
But they do not typically block VV. Typical is 300 to 400 nm.
The bottom of the pdf where they test it with better equipment is the most interesting,
http://cool.conservation-us.org/waac/wn/wn30/wn30-2/wn30-204.pdf

 

[sharonp]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Garry that may not be a lot of light at all.

What is known about the reflective film that is typically put on modern buildings in terms of it's effect on color rendition and in particular, on UV filtering?

Put on modern buildings??? (none)
Put on the windows, it filters out UVB 100% not UVA (320 - 400nm) not VV.

 

[sharonp]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Furthermore, no one in this discussion knows exactly how GIA performs color grading

http://www.gia.edu/gems-gemology/winter-2008-color-grading-d-to-z-diamonds-king
Particularly Pages 303 - 305.

What part of the very detailed article about GIA's grading conditions is unknown to you AFTER READING?
It is also insulting to the author you keep repeating that in this thread when:

1) Michael measured the UV intensity and light intensity in the AGSL grading diamond dock with Peter Yantzer which is practically identical to the GIA-GTL box and within the range of GIA-GTL's published specs.

There lab director Peter Yantzer kindly allowed me access to their DiamondDock. His top two graders individually graded and provided me reports on all 25 diamonds.

2) The author has touched on lab color grading multiple times in his numerous publications(incomplete list below):

Journal of Gemmology, “Diamond brilliance: theories, measurement and judgment”, 2000
Journal of Gemmology, “Describing diamond beauty – The optical performance of a diamond”, 2005
Journal of Gemmology, “Accordance in Round Brilliant Diamond Cutting”, 2007
Journal of Gemmology, “A Place for CZ Masters in Diamond Color Grading”, 2008
Journal of Gemmology, “The Over-Grading of Blue Fluorescent Diamonds”, 2010
Journal of Gemmology, “Objective Diamond Clarity Grading”, 2014
Gems and Jewellery, “The Central Ideal”, 2009
Gems and Jewellery, “A Cure for the Fluorescence Blues”, 2010

 

[sharonp]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

But we also have empirical price data showing how D-E-F MB/SB stones are pretty heavily discounted.

This is from 1998 rappoport, which trademember would like to do a little work and update it?

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

The issue of indoor sunlight (through windows) was touched on in the 2010 study:

Away from open daylight and indoors, the UV intensities dropped by factors of 100 to 1000, and in typical artificial light to less than 1µW/cm2. The greatest indoor sources of UV at noon were large glass windows and doors which faced daylight. These large glass areas filter out short wave UV, but pass a proportion of long wave UV. At the window surface the reading at the December 2008 date and time was 150 µW/cm2 dropping to 65 µW/cm2 at 3 ft and 35 µW/cm2 at 6 ft.

It goes on to say:

In all other areas illuminated by artificial fuorescent and incandescent ceiling illumination the readings at typical 3–4 ft viewing distances from ceiling lights were an essentially UV-free, 0–1 µW/cm2.These readings are consistent with results from extensive surveys conducted by the author and others and provide support for the observation that at distances of more than 3 ft from artificial illumination,including ceiling mounted fluorescent lighting, indoor light is essentially UV free.

And mentions the VV component by saying:

In addition, because the light intensity is below 400 fc, usually under 100 fc and often less than 50 fc, there is no noticeable stimulation of fluorescence from the visible violet.

 

[Rockdiamond]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

HI Sharon,
The article does spell out a lot of details, it's true. I had not read it. I based my statements on GIA not discussing specific methods because I have spoken to GIA personnel about this in the past.

I did notice this from page 307. This backs up what I've been saying about a single color grader.

To control for potential perception differences
from individual to individual, GIA’s grading process
requires a minimum of two or three random, independent
opinions (depending on the size of the
stone). A consensus is required before a color grade is
finalized. For larger or potentially D-color stones, the
laboratory’s computer operating system identifies
the need for the most experienced graders. Last, to
avoid the potential of reduced accuracy due to eye
fatigue, color grading sessions are limited to approximately
one hour, at which point a minimum break
of one hour must be taken.

With regards to Rappaport pricing studies.
I believe what I did a few pages back with 1.00-1.05 D-E-F VS1 XXX RBC gives us a general idea that discounts have increased since 1998. I personally have found that to be true.

 

[sharonp]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

From what I see in the data related to the the intensity dropoff, it would not have to be 3 ft. It could very well be that 1 ft would do it.

To maintain the quality of light and uniform conditions the lexan filter and diffusers in the existing GIA-GTL diamond dock makes more sense. I haven't seen the setup up close or graded diamonds, but if light quality depends on distance than increasing distance is not a solution.

think the practical takeaway for consumers is to, during their return period, have their blue fluorescent diamonds independently verified by a knowledgeable gemologist who is equipped to color grade the diamond in a UV free environment (against a set of GIA masters)

I think that approach is the opposite of practical. Finding an appraiser with a complete set of masters, a GIA diamond dock and the ability to grade within +/- 1 grade of GIA-GTL is already daunting. Adding the requirement that the appraiser follow an unproven and less than clear method to reduce/eliminate UV/VV adds even more uncertainty. For all but VSB diamonds 1 - 2 grades is the maximum difference expected so accuracy becomes a problem.

A good independent appraiser should inform the customer of the discount/premium range for their customer's diamond and price comparison Fluoro versus Non Fluoro. If they are good they could advise the client if the diamond is fairly priced for their market based on the grading report. The market doesn't push a Strong Blue down 2 grades in price, (say from D to F) as Michael's paper has suggested in his SB samples, so I don't see how an appraiser claiming a D is true F(in non UV/VV) really helps the consumer.

And not to be persuaded by the merchant that their diamond will normally look any whiter than the verified lab color grade. Any whitening that might accrue to them in certain circumstances will be the cherry on top of the cake.

Your statement is too general, there is enough sunlight outside and even inside to cause whitening. It is more apparent in the near colorless and faint yellow ranges than in the colorless range but people see it and the market prices it in(imperfectly). I don't think most mere mortals can discern between one or two color grades especially face up in a setting and especially in the colorless range.I highly doubt in most cases the consumer can see the whitening(whether present or not) for SB and MB or be able to notice that their diamond has more tint than its grade in weaker UV/VV lighting.

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

From what I see in the data related to the the intensity dropoff, it would not have to be 3 ft. It could very well be that 1 ft would do it.

To maintain the quality of light and uniform conditions the lexan filter and diffusers in the existing GIA-GTL diamond dock makes more sense. I haven't seen the setup up close or graded diamonds, but if light quality depends on distance than increasing distance is not a solution.
Agreed, it makes more sense to filter/diffuse to eliminate grade whitening from fluoro. No need to manufacture new docks or change typical grading practices.

think the practical takeaway for consumers is to, during their return period, have their blue fluorescent diamonds independently verified by a knowledgeable gemologist who is equipped to color grade the diamond in a UV free environment (against a set of GIA masters)

I think that approach is the opposite of practical. Finding an appraiser with a complete set of masters, a GIA diamond dock and the ability to grade within +/- 1 grade of GIA-GTL is already daunting. Adding the requirement that the appraiser follow an unproven and less than clear method to reduce/eliminate UV/VV adds even more uncertainty. For all but VSB diamonds 1 - 2 grades is the maximum difference expected so accuracy becomes a problem.
You are correct that very few appraisers are so equipped, however I believe developing this capability would be a worthwhile service and a differentiator for an appraiser. There are some who do offer this level of consultation.

A good independent appraiser should inform the customer of the discount/premium range for their customer's diamond and price comparison Fluoro versus Non Fluoro. If they are good they could advise the client if the diamond is fairly priced for their market based on the grading report. The market doesn't push a Strong Blue down 2 grades in price, (say from D to F) as Michael's paper has suggested in his SB samples, so I don't see how an appraiser claiming a D is true F(in non UV/VV) really helps the consumer.
A good appraiser will clearly offer advice about pricing and valuation supported with comparables. An important discussion for a consumer to have with an appraiser is future liquidity, if they have any intention of ever selling or trading the diamond. In this regard, fluorescence can have a significant impact that is important for the consumer to understand.

And not to be persuaded by the merchant that their diamond will normally look any whiter than the verified lab color grade. Any whitening that might accrue to them in certain circumstances will be the cherry on top of the cake.

Your statement is too general, there is enough sunlight outside and even inside to cause whitening. It is more apparent in the near colorless and faint yellow ranges than in the colorless range but people see it and the market prices it in(imperfectly). I don't think most mere mortals can discern between one or two color grades especially face up in a setting and especially in the colorless range.I highly doubt in most cases the consumer can see the whitening(whether present or not) for SB and MB or be able to notice that their diamond has more tint than its grade in weaker UV/VV lighting.
You are right, it is a general statement. A consumer who spends alot of time outdoors or close to windows may get more benefit than someone who spends most of the daylight hours in an office. My point is that for most people it is better not to depend on extra whitening when making the purchase decision. Let it be a bonus when it happens.

 

[michaelgem]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

It seems abundantly clear from this data that there is an undeniable trend suggesting that color grading accuracy would be significantly improved for blue fluorescent stones if they were graded in an environment free of grade whitening levels of UV

Actually the data is inconclusive in that part.

Under the strongest UV Source 1 ( Diamondlite 2 - 3 inches away) look at filtered(1 uw/cm2) and unfiltered(150 uw/cm2).

The VSB samples Stones 1, 2 and 4 have two or more grade differences between filtered and unfiltered.

For all of the Strong and Medium Fluoro samples (5 - 15) there is no difference between UV filtered and unfiltered except 9 and 14 which only had a 1 grade difference. Removing UV alone had negligible effect for Strong and Medium Fluoro diamonds in the presence of strong white light.

I did a quick estimate on Bluenile and less than 0.2% of diamonds in their inventory have VSB fluoro. If one adds all SB and MB it is above 9%.

Sharon,

I will prepare a more detailed response when time permits, but I want to say that you are analyzing and making admirable use of the data and grading by GIA, AGSL and me. The hope is that others will better understand the article's conclusions and recommendations by doing the same.

Your observation that "Removing UV alone had negligible effect for Strong and Medium Fluoro diamonds in the presence of strong white light" indicates the importance of the contribution to fluorescence of excitation from the 405nm deep visible violet mercury vapor peak present in all fluorescent lighting. By requiring grading at 7 (8.5) inches from the Verilux tubes in the DiamondDock, GIA not only ameliorated the color enhancement caused by blue fluorescence due to UV, but also that caused by the Visible Violet through reduction in light level to around 350fc from the grade enhancing 600fc typical in the DiamondLite and close to the GIA Microscope Lamp.

 

[sharonp]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Your observation that "Removing UV alone had negligible effect for Strong and Medium Fluoro diamonds in the presence of strong white light" indicates the importance of the contribution to fluorescence of excitation from the 405nm deep visible violet mercury vapor peak present in all fluorescent lighting.

I don't know how good your lexan filter is but assuming it worked to reduce UV to negligible through the entire longwave spectrum, the whitening difference between Source 1 filtered for UV and Source 7 should be from the VV. One cannot just eliminate only VV wavelengths(unless you wanted to use red light), you have to attenuate the light of all visible wavelengths to reduce the VV. Does the diffuser reduce the quality of light as well?

By requiring grading at 7 (8.5) inches from the Verilux tubes in the DiamondDock, GIA not only ameliorated the color enhancement caused by blue fluorescence due to UV, but also that caused by the Visible Violet through reduction in light level to around 350fc from the grade enhancing 600fc typical in the DiamondLite and close to the GIA Microscope Lamp.

Well they did, but not by a significant amount. Comparing Source 1(GIA Diamondlite unfiltered) to Source 2(GIA Diamond Dock)

Sample 3 and 4 reduced by two grades
Samples 2 and 9 reduced by 1 grade.
Sample 23 reduced by 1 grade but this wasn't attributed to Fluoro as the sample had none.

The rest of the 20 samples showed no change from Diamondlite conditions to Diamond Dock. Only the VSB diamonds(not all) showed a significant difference.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

double post

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

While the response of the light meter may be suspect under VV it would also be interesting to get meter readings with and without the filter.

That will not work as the Minimum Transmission (%) of the filter may be as low as 40% or as high as 95%
What is the spec of the filter?

This filter blocks all the 405 nm that Michael is banging on about. It has a very tight range.

From what Sharon has posted there is a lot of VV inside.
Without it it is almost impossible to detect a 2 grade color difference.
This is why educated consumers, like the ones here on Pricescope mostly prefer Fluoro blue diamonds.

 

[sharonp]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

While the response of the light meter may be suspect under VV it would also be interesting to get meter readings with and without the filter.

That will not work as the Minimum Transmission (%) of the filter may be as low as 40% or as high as 95%
What is the spec of the filter?

This filter blocks all the 405 nm that Michael is banging on about. It has a very tight range.

From what Sharon has posted there is a lot of VV inside.
Without it it is almost impossible to detect a 2 grade color difference.
This is why educated consumers, like the ones here on Pricescope mostly prefer Fluoro blue diamonds.

Garry I suspect that coating is Yellow and you put that on a filter you will get yellow light shining on the diamonds. You can't selectively filter VV for this purpose only attenuate the entire visible range.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Could someone find a link to the survey on preferences for or against fluoro diamonds some consumers ran here about 5 to 10 years ago please?

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

While the response of the light meter may be suspect under VV it would also be interesting to get meter readings with and without the filter.

That will not work as the Minimum Transmission (%) of the filter may be as low as 40% or as high as 95%
What is the spec of the filter?

This filter blocks all the 405 nm that Michael is banging on about. It has a very tight range.

From what Sharon has posted there is a lot of VV inside.
Without it it is almost impossible to detect a 2 grade color difference.
This is why educated consumers, like the ones here on Pricescope mostly prefer Fluoro blue diamonds.

Garry I suspect that coating is Yellow and you put that on a filter you will get yellow light shining on the diamonds. You can't selectively filter VV for this purpose only attenuate the entire visible range.

Sharon this filter only allows VV to pass through - and only half of it at that. It is not a yellow filter.

 

[michaelgem]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Your observation that "Removing UV alone had negligible effect for Strong and Medium Fluoro diamonds in the presence of strong white light" indicates the importance of the contribution to fluorescence of excitation from the 405nm deep visible violet mercury vapor peak present in all fluorescent lighting.

I don't know how good your lexan filter is but assuming it worked to reduce UV to negligible through the entire longwave spectrum, the whitening difference between Source 1 filtered for UV and Source 7 should be from the VV. One cannot just eliminate only VV wavelengths(unless you wanted to use red light), you have to attenuate the light of all visible wavelengths to reduce the VV. Does the diffuser reduce the quality of light as well?

By requiring grading at 7 (8.5) inches from the Verilux tubes in the DiamondDock, GIA not only ameliorated the color enhancement caused by blue fluorescence due to UV, but also that caused by the Visible Violet through reduction in light level to around 350fc from the grade enhancing 600fc typical in the DiamondLite and close to the GIA Microscope Lamp.

Well they did, but not by a significant amount. Comparing Source 1(GIA Diamondlite unfiltered) to Source 2(GIA Diamond Dock)

Sample 3 and 4 reduced by two grades
Samples 2 and 9 reduced by 1 grade.
Sample 23 reduced by 1 grade but this wasn't attributed to Fluoro as the sample had none.

The rest of the 20 samples showed no change from Diamondlite conditions to Diamond Dock. Only the VSB diamonds(not all) showed a significant difference.

Michael: Your observation that "Removing UV alone had negligible effect for Strong and Medium Fluoro diamonds in the presence of strong white light" indicates the importance of the contribution to fluorescence of excitation from the 405nm deep visible violet mercury vapor peak present in all fluorescent lighting.

Sharon: I don't know how good your lexan filter is but assuming it worked to reduce UV to negligible through the entire longwave spectrum, the whitening difference between Source 1 filtered for UV and Source 7 should be from the VV.



Michael: You are right. Both methods, the lexan filter and the 3ft distance, reduce the UV to less than 1 uWatt, but only the distance method reduces the visible light intensity below the necessary 400fc to avoid grade whitening. That is the reason for the necessity, when grading close to the fluorescent lighting, for the white diffuser which attenuates the visible light including the VV wavelengths to under 400fc.

Sharon: One cannot just eliminate only VV wavelengths(unless you wanted to use red light), you have to attenuate the light of all visible wavelengths to reduce the VV. Does the diffuser reduce the quality of light as well?

Michael: White diffusers like the one on the GIA microscope light reduce the visible light intensity by absorbing energy equally across all visible wavelengths including the visible violet. If it did not the quality/color of the light would change. (For example, if the VV and blue energy were attenuated more, the light quality would become yellowish, as happens in Cape Series type 1A diamonds.) The white plastic diffuser acts to lower light intensity similarly to a neutral density filter in photography, it absorbs/reduces all visible energy equally maintaining the color/quality/color temperature of the light.

Michael: By requiring grading at 7 (8.5) inches from the Verilux tubes in the DiamondDock, GIA not only ameliorated the color enhancement caused by blue fluorescence due to UV, but also that caused by the Visible Violet through reduction in light level to around 350fc from the grade enhancing 600fc typical in the DiamondLite and close to the GIA Microscope Lamp

Sharon: Well they did, but not by a significant amount. Comparing Source 1(GIA Diamondlite unfiltered) to Source 2(GIA Diamond Dock)
Sample 3 and 4 reduced by two grades
Samples 2 and 9 reduced by 1 grade.
Sample 23 reduced by 1 grade but this wasn't attributed to Fluoro as the sample had none.

The rest of the 20 samples showed no change from Diamondlite conditions to Diamond Dock. Only the VSB diamonds(not all) showed a significant difference.

Michael: Your right except for the difference between Diamondlite conditions to AGSL's Diamond Dock.
Recall from the article: Looking at the scatter plot of the ‘Strong Blue’ diamonds #6 to #10 a quite consistent two grade whitening is evident in the unfiltered DiamondLite as well as in the DiamondDock standard Verilux lighting used in the GIA and the author’s grading, compared with the grades obtained in UV-free light. AGSL’s grading of these ‘Strong Blue’ diamonds differed, obtaining on average only one grade of whitening in their DiamondDock lighting.

The conclusion was: Judging from this limited sample size, the change in lighting from the DiamondLite to the DiamondDock, while clearly reducing the likely amount of over grading in ‘Very Strong Blue’ diamonds, appears to result in a less consistent reduction in the ‘Strong Blue’ fluorescent diamonds. The same can be said for the less consistent reduction seen in the half to one grade whitening typically seen in the ‘Medium Blue’ diamonds in the unfiltered DiamondLite.

Besides human grading variability, this lack of consistency is likely related to the stated wide allowed range in strength of UV and visible light in the unfiltered Diamond Dock lighting. The light intensity measured at the tray in the AGSL DiamondDock was weaker at 230fc compared to 350fc measured at the same 7inches in the same Verilux tubes (obtained with the DiamondDocks that AGSL bought from GIA). This is a good illustration of the inevitable inconsistency that results when grading in lighting with fluorescence enhancing amounts of UV and VV.

This all led to the conclusion: A more practical way to eliminate UV in grading illumination, and at the same time not noticeably affect the visible spectrum is filtration by polycarbonate plastic, such as Lexan or Makrolon. As shown in Figure 6, polycarbonate is an effective and inexpensive filter to remove UV below 385 nm. At the same time there is negligible change to the visible spectrum that could affect grading the D-Z tints of yellow in diamond.

To reduce fluorescence stimulated by visible violet, an equally practical and inexpensive solution is the use of flat-white plastic diffusers which attenuate violet and all visible wavelengths equally. Below 400 fc or about 4000 lux, the reduced amount of visible violet was found to not excite noticeable fluorescence, and the diamond’s color is unaffected. Such white diffusers have the additional feature of reducing spectral reflections and glare. They were employed on GIA microscope lights (Figure 10) for this purpose and to filter UV. (Note that although they did a good job of reducing reflections and glare, they did not reduce the UV or the light intensity enough to avoid all grade whitening fluorescence.)

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Your observation that "Removing UV alone had negligible effect for Strong and Medium Fluoro diamonds in the presence of strong white light" indicates the importance of the contribution to fluorescence of excitation from the 405nm deep visible violet mercury vapor peak present in all fluorescent lighting.

I don't know how good your lexan filter is but assuming it worked to reduce UV to negligible through the entire longwave spectrum, the whitening difference between Source 1 filtered for UV and Source 7 should be from the VV. One cannot just eliminate only VV wavelengths(unless you wanted to use red light), you have to attenuate the light of all visible wavelengths to reduce the VV. Does the diffuser reduce the quality of light as well?

By requiring grading at 7 (8.5) inches from the Verilux tubes in the DiamondDock, GIA not only ameliorated the color enhancement caused by blue fluorescence due to UV, but also that caused by the Visible Violet through reduction in light level to around 350fc from the grade enhancing 600fc typical in the DiamondLite and close to the GIA Microscope Lamp.

Well they did, but not by a significant amount. Comparing Source 1(GIA Diamondlite unfiltered) to Source 2(GIA Diamond Dock)

Sample 3 and 4 reduced by two grades
Samples 2 and 9 reduced by 1 grade.
Sample 23 reduced by 1 grade but this wasn't attributed to Fluoro as the sample had none.

The rest of the 20 samples showed no change from Diamondlite conditions to Diamond Dock. Only the VSB diamonds(not all) showed a significant difference.

Michael: Your observation that "Removing UV alone had negligible effect for Strong and Medium Fluoro diamonds in the presence of strong white light" indicates the importance of the contribution to fluorescence of excitation from the 405nm deep visible violet mercury vapor peak present in all fluorescent lighting.

Sharon: I don't know how good your lexan filter is but assuming it worked to reduce UV to negligible through the entire longwave spectrum, the whitening difference between Source 1 filtered for UV and Source 7 should be from the VV.



Michael: You are right. Both methods, the lexan filter and the 3ft distance, reduce the UV to less than 1 uWatt, but only the distance method reduces the visible light intensity below the necessary 400fc to avoid grade whitening. That is the reason for the necessity, when grading close to the fluorescent lighting, for the white diffuser which attenuates the visible light including the VV wavelengths to under 400fc.

Sharon: One cannot just eliminate only VV wavelengths(unless you wanted to use red light), you have to attenuate the light of all visible wavelengths to reduce the VV. Does the diffuser reduce the quality of light as well?

Michael: White diffusers like the one on the GIA microscope light reduce the visible light intensity by absorbing energy equally across all visible wavelengths including the visible violet. If it did not the quality/color of the light would change. (For example, if the VV and blue energy were attenuated more, the light quality would become yellowish, as happens in Cape Series type 1A diamonds.) The white plastic diffuser acts to lower light intensity similarly to a neutral density filter in photography, it absorbs/reduces all visible energy equally maintaining the color/quality/color temperature of the light.

Michael: By requiring grading at 7 (8.5) inches from the Verilux tubes in the DiamondDock, GIA not only ameliorated the color enhancement caused by blue fluorescence due to UV, but also that caused by the Visible Violet through reduction in light level to around 350fc from the grade enhancing 600fc typical in the DiamondLite and close to the GIA Microscope Lamp

Sharon: Well they did, but not by a significant amount. Comparing Source 1(GIA Diamondlite unfiltered) to Source 2(GIA Diamond Dock)
Sample 3 and 4 reduced by two grades
Samples 2 and 9 reduced by 1 grade.
Sample 23 reduced by 1 grade but this wasn't attributed to Fluoro as the sample had none.

The rest of the 20 samples showed no change from Diamondlite conditions to Diamond Dock. Only the VSB diamonds(not all) showed a significant difference.

Michael: Your right except for the difference between Diamondlite conditions to AGSL's Diamond Dock.
Recall from the article: Looking at the scatter plot of the ‘Strong Blue’ diamonds #6 to #10 a quite consistent two grade whitening is evident in the unfiltered DiamondLite as well as in the DiamondDock standard Verilux lighting used in the GIA and the author’s grading, compared with the grades obtained in UV-free light. AGSL’s grading of these ‘Strong Blue’ diamonds differed, obtaining on average only one grade of whitening in their DiamondDock lighting.

The conclusion was: Judging from this limited sample size, the change in lighting from the DiamondLite to the DiamondDock, while clearly reducing the likely amount of over grading in ‘Very Strong Blue’ diamonds, appears to result in a less consistent reduction in the ‘Strong Blue’ fluorescent diamonds. The same can be said for the less consistent reduction seen in the half to one grade whitening typically seen in the ‘Medium Blue’ diamonds in the unfiltered DiamondLite.

Besides human grading variability, this lack of consistency is likely related to the stated wide allowed range in strength of UV and visible light in the unfiltered Diamond Dock lighting. The light intensity measured at the tray in the AGSL DiamondDock was weaker at 230fc compared to 350fc measured at the same 7inches in the same Verilux tubes (obtained with the DiamondDocks that AGSL bought from GIA). This is a good illustration of the inevitable inconsistency that results when grading in lighting with fluorescence enhancing amounts of UV and VV.

This all led to the conclusion: A more practical way to eliminate UV in grading illumination, and at the same time not noticeably affect the visible spectrum is filtration by polycarbonate plastic, such as Lexan or Makrolon. As shown in Figure 6, polycarbonate is an effective and inexpensive filter to remove UV below 385 nm. At the same time there is negligible change to the visible spectrum that could affect grading the D-Z tints of yellow in diamond.

To reduce fluorescence stimulated by visible violet, an equally practical and inexpensive solution is the use of flat-white plastic diffusers which attenuate violet and all visible wavelengths equally. Below 400 fc or about 4000 lux, the reduced amount of visible violet was found to not excite noticeable fluorescence, and the diamond’s color is unaffected. Such white diffusers have the additional feature of reducing spectral reflections and glare. They were employed on GIA microscope lights (Figure 10) for this purpose and to filter UV. (Note that although they did a good job of reducing reflections and glare, they did not reduce the UV or the light intensity enough to avoid all grade whitening fluorescence.)

Michael is this your opinion or a fact based on evidence and testing?

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Furthermore, no one in this discussion knows exactly how GIA performs color grading

http://www.gia.edu/gems-gemology/winter-2008-color-grading-d-to-z-diamonds-king
Particularly Pages 303 - 305.

What part of the very detailed article about GIA's grading conditions is unknown to you AFTER READING?
It is also insulting to the author you keep repeating that in this thread when:

1) Michael measured the UV intensity and light intensity in the AGSL grading diamond dock with Peter Yantzer which is practically identical to the GIA-GTL box and within the range of GIA-GTL's published specs.

There lab director Peter Yantzer kindly allowed me access to their DiamondDock. His top two graders individually graded and provided me reports on all 25 diamonds.

2) The author has touched on lab color grading multiple times in his numerous publications(incomplete list below):

Journal of Gemmology, “Diamond brilliance: theories, measurement and judgment”, 2000
Journal of Gemmology, “Describing diamond beauty – The optical performance of a diamond”, 2005
Journal of Gemmology, “Accordance in Round Brilliant Diamond Cutting”, 2007
Journal of Gemmology, “A Place for CZ Masters in Diamond Color Grading”, 2008
Journal of Gemmology, “The Over-Grading of Blue Fluorescent Diamonds”, 2010
Journal of Gemmology, “Objective Diamond Clarity Grading”, 2014
Gems and Jewellery, “The Central Ideal”, 2009
Gems and Jewellery, “A Cure for the Fluorescence Blues”, 2010

Sharon the unkown and unknowable part of GIA's color grading is the instrumental method.
Given GIA GTL grade way more diamonds in India than anywhere else in the world, do you think they do not use their patented instrument they subtly mention in the 2008 article - perhaps even more than suggested?
How does that instrument measure effects that the human eye can see?

Michael has spent a lot of time discussing Diamondlite etc - its history baby!

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

This topic is way more complex than we can 'compute' which is why I keep asking, begging, pleading for us to do a real study.

Here is another left field example:
The amount of VV and UV have an effect of removing yellow because the 415 line is a complementary color that reduces human perception of yellowness.
But we see way more yellow than we do blue. (and much more green), because that is how we are built.
So debating what is and is not present is a waste of time compared to real world testing with a decent number of randomly chosen samples recently graded by GIA.

https://en.wikipedia.org/wiki/Color_vision#/media/File:Eyesensitivity.svg please check the link - its a self explanatory pic

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Rather that continue to copy the long thread above to make a point about a single aspect, let me copy a snippet to make a specific point which I think is good to keep in mind when evaluating this study:

The conclusion was: Judging from this limited sample size, the change in lighting from the DiamondLite to the DiamondDock, while clearly reducing the likely amount of over grading in ‘Very Strong Blue’ diamonds, appears to result in a less consistent reduction in the ‘Strong Blue’ fluorescent diamonds. The same can be said for the less consistent reduction seen in the half to one grade whitening typically seen in the ‘Medium Blue’ diamonds in the unfiltered DiamondLite.

Besides human grading variability, this lack of consistency is likely related to the stated wide allowed range in strength of UV and visible light in the unfiltered Diamond Dock lighting. The light intensity measured at the tray in the AGSL DiamondDock was weaker at 230fc compared to 350fc measured at the same 7inches in the same Verilux tubes (obtained with the DiamondDocks that AGSL bought from GIA). This is a good illustration of the inevitable inconsistency that results when grading in lighting with fluorescence enhancing amounts of UV and VV.

In addition to the variables being identified here, we should keep in mind the variability in the flurorescence strength as reported by the lab in the first place. As the author makes mention of in the article, there appears to be fairly significant differences in some of the samples judging for the images.

Although GIA uses fluorescent masters, and I understand now has proprietary technology that is being used to do some of the fluoro grading or pre-grading, fluoro reporting is not nearly as granular as color grading. This is another reason that I believe you need to look for trends in the observations rather than try to parse individual data points.

Therefore, if the trend we see in the observations is consistent with the measurements of the light at the point of observation, and and are consistent with what we know about excitation of N3 centers, then I think you can reasonably conclude that, despite the relatively small sample size and despite some variables impacting the data, that the author's conclusions that current color grading practices can and should be improved have serious merit.

The fact that the conclusions of this study and the observations by the Tashey study are also consistent, lends additional weight.

One might say: ' if it looks like a duck, walks like a duck, and quacks like a duck, then it is probably a duck'.