Why did GIA included Steep Deep diamonds in ''Excellent''

[Garry H (Cut Nut)]

That is a question that many are asking.
Why did GIA included Steep Deep diamonds in ''Excellent''

I think I know why - it is all in the shade of the trays they used to sit the diamonds in for the observation surveying they did. Black, gray and white. They choose light gray.

Plus the binary sight phenonemon we mostly all enjoy.

I do not want to say they were right or wrong, but I invite everyone to discuss and debate the issue.

Those who have the Foundation article - refer to page 222.
Someone might like to find on their website a direct quote wwhere they discuss the choices of tray shade. (it is OK to copy and paste small sections of info for educational purposes)

PS this is part of the reason Sergey removed light leakage from DiamCalc when he realised he was going up a dead end alley. AGS are at the same dead end now they are trying to crack the Scintillation puzzle (which Sergey has the solution for)

 

[Garry H (Cut Nut)]

I have taken as an example, the stone from the right side that Leonid made in a screen shot from GIA''s new facetware site. (post a link please someone.)

Here I introduce an ideal-scope shot as seen from 2 eyes at 5 degrees of angle away from the centre.
The central image is a crude overlay of the two in photoshop. You see the stone improves slightly.
Also the diamcalc light return is better for the 2 eyed stereoscopic view than it is for the mono viewe.

 

[Garry H (Cut Nut)]

The top 3 images are the same stone in DiamCalc with black backlight (none), gray and full backlight 9all e it at a dimmer brightness than that from the front)

The rest arewhat you would likely see with each eye and my rough composites of what you see with both eyes.
If anyone can do a better job of the composites I will email them.
But as Sergey says - we see much more good stuff with both eyes than each eye does - (one of the BScope problems).

I think we can see that leakage is not as much a problem with stereoscopic vison as we all thought from using mono idealscope views.

(BTW I have a rough binocular ideal-scope on my microscope)

 

[belle]

link to facetware

quote from gia regarding viewing conditions:

"Our common viewing environment consists of a neutral gray box with a combination of daylight-equivalent fluorescent bulbs and overhead white LEDs (light-emitting diodes). Intensities of the two light sources were established by determining when a set of reference diamonds showed the same relative amounts of brightness and fire respectively as they showed in the dealer- and retail-equivalent lighting conditions we described in the article. In this way we were able to combine the observable appearance aspects of brightness and fire in a single viewing environment, while also preserving the general qualities of both dealer and retail lighting."

 

[strmrdr]

oh boy here we go again.
The additive views as you posted is not the same way the human eyes work.
GIA actually found this out and used it for justification for one eye looking into their viewing box being ok.


edit> Garry the way I worded that above was kinda rude.
I'm Sorry

 

[JohnQuixote]

For those interested in keeping score at home, here’s the pertinent into from page 222 of the foundation article.

"During our overall testing with trade members and our Overall observation team, we also found that in many cases background color could affect the ease with which observers distinguished the face-up appearance of one diamond from another. We determined that white trays (which mimic the white folded cards and white display pads often used in the trade) can sometimes cause a diamond to look brighter by hiding or masking areas of light leakage (areas where light is not returned from the diamond because it exits out the pavilion rather than back to the observer). Alternately, black trays were shown to demonstrate possible areas of light leakage, but in many cases they overemphasized them so the diamond looked too dark. We found that a neutral gray tray (similar in color to the walls of our CVE*) was the most appropriate choice for assessing a round brilliant's overall face-up appearance.”

* The CVE was GIA’s “Common Viewing Environment.” This was a neutral gray box with a combination of daylight-equivalent fluorescent lamps and overhead white LEDs, used to view the overall cut appearance and quality of diamonds.

 

[Garry H (Cut Nut)]

Folks Storm is referring to an old war, we have had running, about dominant eye sight.

In the case of seeing a sparkle or a dark zone, both eyes gather information, and our minds use the information in different ways.
I hope Sergey has some time to explain this as he has read numerous texts etc.

But this is easy for all to try:

Find out which is your dominant eye by looking at a distant point, with both eyes open, through an ''OK'' sign made with one hand stretched out at arms length. Close alternate eyes while focused on the distant point. One of your eyes can still see the point thru the hole your finger and thumb make.

Now look at a big diamond in a steady seated position. Find a flash that is visible with your non dominant eye. Ideally the flash is not visible thru the dominant eye. Wowsa - with both eyes open the flash is still there.
Conclusion #1 - non dominant eyes register nice things.

Next experiment
Find an obvious dark zone with your non dominant eye. But make sure that with your dominant eye the dark zone does not have a bright sparkle over it. Ideally it should have a slightly paler appearance through the dominant eye and be really dark with the non dominant eye.
Wowza - with both eyes open the dark zone is dark!
Conclusion #2 Dark zones also stand out more in our mind than in-between zones.

So Storm (who is still my friend

) do you agree with this?
Please folks do the experiment - it is really important and I would like many opinions, including dissenting ones.

BTW this is the color of the CDAXVE or whatever they call it in the photo from the GIA website. A fairly dark gray. But it would be great if someone could give us the panetone or some other code # please?

 

[mkb]

Loved doing that test gary, but having only one eye I found it rather difficult

luc

 

[Lorelei]

Neato Gary - worked for me! Thanks

 

[strmrdr]

Garry in the above experiment the eyes see the same object in 2 different locations.
If the eyes were merely additive we would see 2 objects.
The brain compensates for the 2 images by doing other processing not simply overlapping the 2 images.
There is a actually a medical condition where the persons brain does not properly compensate and the person does see the 2 images depth perception is none existent for people with it and it often leads to confusion.
Can you imaging trying to pick up an object that appears in 2 places at the same time?
Simple overlapping can not work.

 

[Garry H (Cut Nut)]

Exactly what I am saying Storm.
The brain takes the dominant sparkles or dark zones of strong contrast in the diamond from each eye (not only the info from the dominant eye) and merges the information in our perception.

So therefore if a diamond has a dead dark zone, I believe it will be visible to each eye, unless it is masked by a bright spot.
The stars that you H&A''s freaks love so much are dark zones, but fortunately the eye that sees the dark zone sometimes is over ridden by the sparkle coming from the view point of the other eye.

Can you find a way to merge the two images to make what we really see - the opacity overlays was hout the dispersed colors

 

[strmrdr]

hmmm
So your saying feed one eye a black circle and feed the other eye the same back circle with a white dot on it and the brain will put them together as a black circle with a white dot.
For such a simple model that is likely the case.
But for a complex model like a full diamond I know of no way of predicting what the brain will actually "see" as the final outcome.

Wasn''t the gia light box one eye only?
So if they based it on that this conversation isn''t relevant.
Im confused

 

[belle]

from gia:

"When you used domes for establishing the brightness metric, did the observers close one eye to look through the holes in the domes? Wouldn’t this be a problem since humans use two eyes?

First, the domes were not used to “establish” the brightness metric; they were used to check that our computer models gave the same results as human observers for the same environmental conditions. The final brightness model we adapted was the one that best fit the brightness observation data from human observers using both eyes, and using a standardized lighting environment based on actual environments used in the trade. By ranking with observations in real environments, we use the actual human visual system to evaluate brightness, rather than a computerized attempt to model the complex visual system.

Second, observers were not asked to close one eye. In fact, as part of the set of dome observations, some large domes were built with holes up to three inches in diameter, in which observers could look with both eyes; these gave the same observation results as smaller domes with the same configuration. These tests confirmed what a vision specialist told us—that when looking at most small objects, a dominant eye takes control."

 

[mmorrison]

I''m half and half understanding you guys, but storm''s post gave me an idea

I easily found my dominant eye (right) with Gary''s advice

Now I opened up mspaint and made huge black circles with a gray background, and one with a white dot in the middle

I held up my hands so that I could only see one circle with each eye

no matter which side the dot was on (dominant eye or not) I only saw the white dot in that eye

maybe I am not doing this experiment right but still found it interesting
here is a link to the picture: http://img18.imageshack.us/img18/269/circles2te.png

 

[belle]

garry,
i tried the experiment using my hand and discovered that the result of ''dominance'' depended on which hand i was using. i.e., the ''dominant'' eye was different depending on using the left or right hand.
in an attempt to standardize the experiment a bit, i used a compact disc to view through. holding the cd directly in front of me at an arms length away, i was able to determine my ''dominant'' eye. HOWEVER, this ''dominance'' also changed with the distance of the focal object. with objects less than about 5ft. away, my right eye was dominant. with objects greater than about 10ft. away, my left eye was dominant.

 

[Regular Guy]

Date: 8/9/2005 12:12:33 PM
Author: belle
garry,
i tried the experiment using my hand and discovered that the result of ''dominance'' depended on which hand i was using. i.e., the ''dominant'' eye was different depending on using the left or right hand.
in an attempt to standardize the experiment a bit, i used a compact disc to view through. holding the cd directly in front of me at an arms length away, i was able to determine my ''dominant'' eye. HOWEVER, this ''dominance'' also changed with the distance of the focal object. with objects less than about 5ft. away, my right eye was dominant. with objects greater than about 10ft. away, my left eye was dominant.

You''ll find, Belle, that this phenomena alternates every 5 feet. Try it!

No actually, I''m breaking your back. But this is very interesting. Earlier this am, I thought I was satisfied to have learned my left eye was dominant. But now trying Belle''s suggestion of using the other hand, I see that, while my left eye dominance is clear with my right hand extended, when I instead extend my left hand, the "real" view visible between my circled fingers becomes blurry, when using both eyes, and it is ambivalent. Surely there is some hemispheric wiring phenomena going on.

 

[belle]

Date: 8/9/2005 2:37:55 AM
Author: Garry H (Cut Nut)
Now look at a big diamond in a steady seated position. Find a flash that is visible with your non dominant eye. Ideally the flash is not visible thru the dominant eye. Wowsa - with both eyes open the flash is still there.
Conclusion #1 - non dominant eyes register nice things.

if this were the case i should not be able to find of flash of sparkle with my 'dominant' eye, yet i can consistently but not predictably, find a flash of sparkle from both eyes, with which, when one eye is closed the other eye does not have the sparkle in focus.

 

[JohnQuixote]

Interesting stuff.

For another experiment, a little closer in, open the page mmorrison linked, here.

You can see how distance vision is different than close vision. The dominant eye takes over completely at a distance, but they work together much more in close-up views.

Using only the circle on the right, do Garry's 'ok' sign experiment. I have a large monitor. With the circle/dot a little over a foot beyond my outstretched ok sign both of my eyes sought the target and closing one, then the other eye resulted in the 'at a distance' appearances below for each eye. As I brought myself closer to the circle/dot the images appeared to get closer together.

They will continue to do so until you reach your near point of accomodation (the distance at which focus is attained without strain, also considered the distance of most distinct vision). For a majority of humans this will be around 25cm. In very young people and in those with nearsightedness the distance is less. This near point recedes with age, possibly causing farsighted condition.

 

[strmrdr]

Date: 8/9/2005 11:47:35 AM
Author: mmorrison
I''m half and half understanding you guys, but storm''s post gave me an idea


I easily found my dominant eye (right) with Gary''s advice


Now I opened up mspaint and made huge black circles with a gray background, and one with a white dot in the middle


I held up my hands so that I could only see one circle with each eye


no matter which side the dot was on (dominant eye or not) I only saw the white dot in that eye


maybe I am not doing this experiment right but still found it interesting

here is a link to the picture: http://img18.imageshack.us/img18/269/circles2te.png

They have to appear to be coming from the same place for it to work.
its a lot trickier than it sounds.
only way I can think of going it would be lcd lens for each eye with everything else blocked.
Then carefully position the black dots on each screen so they appear to be one then add a white dot to one of them and record the results the person gets.

 

[Garry H (Cut Nut)]

Sergey has that LCD system with 50 hertz glasses activated by the computer screen image which generates full color 3D images and allows one to conduct these experiments.

This image is one that he uses to demonstrate the idea.

So Storm, can I have your agreement to move forward now and get to the basic question.

Does stereo scopic viewing and leakage helped with a lighter gray background establish a reasonable basis for GIA to call Steep Deep diamonds (C36 P41.4) Excellent performers?

Is AGS and HCA wrong and GIA right?
Does the truth lie somewhere between (ie we are all wrong?)

 

[strmrdr]

Garry this isn''t the answer your looking for but:
GIA giving an opinion that any diamond is an excellent performer pulls 0 and I mean 0 weight with me.
They have not given me enough data to evaluate their criteria nor their methods.

Same goes to some extent with AGS new system there are two many unanswered questions but there are far more questions about the GIA system.

I will go one step farther and give my opinion that to me the GIA cut grade system is at this point absolutely useless.
Until I get enough information to properly evaluate it that will remain my opinion.

 

[Garry H (Cut Nut)]

Storm it is possible to examine the boundary of their Ex Vg using their software.
(Although they note that this is not allowed on their website).

Leonid has, for educational purposes, shown us some examples at the top of this thread that are contentious.

Dont go all limp wimpy on us. We have some info to play with now - just what is on this thread is enough to start to play with.

 

[adamasgem]

RE: Gary Holloway: "BTW this is the color of the CDAXVE or whatever they call it in the photo from the GIA website. A fairly dark gray. But it would be great if someone could give us the panetone or some other code # please?"

Hi Gary.. Thanks for inviting me to this thread..

1) As to what "paint" they are using and the spectral reflectivity, if someone would send me one of the GIA anything for a buck "boxes", I''d be happy to measure the spectral reflectivity of the "neutral gray" they use.. typically one would use a 50% neutral matte gray to establish references.

2) I do have all the Munsell spectral reflectivity data for the Munselle matte chips in my SAS2000 software and when I get back Friday from the west coast I can post an example, but usually there is some non neutral absortion dependent on the substrate and the binders used vis-a-vie what is put on paper..

Let me say additionally:

1) that what you are going to "see" in the GIA "common" viewing environment box is going to be anything but "common", due to the variability of the observation viewpoint and positioning of the stone.. and I strongly think (believe) that may be the overriding factor, with binocular vision effects winding up being secondary. I think you proved my point (and data) on another thread regardng the "azimuth and tilt viewpoints" using diamondcalc renderings

2) Color wise, "white" LEDS have a "Big" broadband spike in the "blue" region on the spectrum, and fluorescents have multiple "color" spikes dependent on the phosphors used, so judgement of "fire'' might be seriously altered..

I haven''t gotton a chance to play with the GIA anything for a buck software, but let me say that symmetry of a stone is paramount and that using AVERAGES of cutting parameters (table size, crown angle, etc) with the assumption of symmetry brings us back to the dark ages of cut grading, and may give misleading good/bad inferences.

Lastly, I think the "neutral gray" thing is an WELL intentioned attempt by GIA to to reflect reality and the real world, light typically comes comes from above, and all the modeling publically presented to the trade by GIA in the brilliance and fire articles is inconsistent with the real world, as I have pointed out before.

Lastly, because all diamonds leak light, dependent of the input angular distribution and the cut parameters, a "gray" grading tray is probably better than a white background, attenuating the returned "leaked" light from the pavilion, much the same as light reentering the stone which is reflected back from the skin

The "black hole" used at the girdle plane and the "black hole" used to model the head is incorrect. Diamond cutting has its highest efficiency of light return for overhead, high angle lighting, not from the side..

More later but I''ve got to catch a plane today..

Marty

 

[adamasgem]

I might add, that the general GIA expansion of the range of "ideal cuts" is probably more driven by politics and selling paper, than science, unfortunately.., but we can''t tell where their "real boundaries" are yet, because we don''t know the theoretical definition of their lighting environment, garbage in, garbage out as we say in the computer world.

 

[strmrdr]

This is fairly typical of "white" leds and what Marty is talkin about with them.

 

[strmrdr]

here is why:

LEDs are monochromatic (one color) devices. The color is determined by the bandgap of the semiconductor used to make them. Red, green, yellow and blue LEDs are fairly common. White light contains all colors and cannot be directly created by a single LED. The most common form of "white" LED really isn't white. Its a Gallium Nitride blue LED coated with a phosphor that, when excited by the blue LED light, emits a broad range spectrum that in addition to the blue emission, makes a fairly white light.

From:
http://www.trainweb.org/girr/tips/tips7/white_led_tips.html

The same data is available from several other sources but that was the first one to come up on a search.

More info here:
http://ledmuseum.home.att.net/ledwht.htm

 

[Garry H (Cut Nut)]

Date: 8/10/2005 11:50:46 AM
Author: adamasgem
RE: Gary Holloway: But it would be great if someone could give us the panetone or some other code # please?''

Hi Gary.. Thanks for inviting me to this thread.. Thanks for th considered response Marty. Now that it is nearly Vampire time you are probably emerging for discussions

1) typically one would use a 50% neutral matte gray to establish references. hopefully some one from GIA might answer the question?

Let me say additionally:

1) that what you are going to ''see'' in the GIA ''common'' viewing environment box is going to be anything but ''common'', due to the variability of the observation viewpoint and positioning of the stone.. and I strongly think (believe) that may be the overriding factor, with binocular vision effects winding up being secondary. I think you proved my point (and data) on another thread regardng the ''azimuth and tilt viewpoints'' using diamondcalc renderings They allowed people to move the stones around and bring them closer and further away, so I think that bit was OK Marty

2) Color wise, ''white'' LEDS have a ''Big'' broadband spike in the ''blue'' region on the spectrum, and fluorescents have multiple ''color'' spikes dependent on the phosphors used, so judgement of ''fire'' might be seriously altered..I tend to agree with you and storm if they have used the very cold blueish LED''s
I experimented a year or 2 ago with strips of LED''s in my store and found the color was not ''real''. Marty if there is too much blue would that lead to different spectral colors in fire that you would observe?

I haven''t gotton a chance to play with the GIA anything for a buck software, but let me say that symmetry of a stone is paramount and that using AVERAGES of cutting parameters (table size, crown angle, etc) with the assumption of symmetry brings us back to the dark ages of cut grading, and may give misleading good/bad inferences.You have played with this from 8*''s perspective and maybe you are right - but maybe you began with a biased view and discovered what you set out to discover? i do not think we can assume that GIA are wrong about VG sym being all that is required to meet the level of human perceptive ability.

Lastly, I think the ''neutral gray'' thing is an WELL intentioned attempt by GIA to to reflect reality and the real world, light typically comes comes from above, and all the modeling publically presented to the trade by GIA in the brilliance and fire articles is inconsistent with the real world, as I have pointed out before. Have you seen Sergey''s spoon test? do this - carry a spoon with you from room to room (you will have to be awake during the day Marty and i am not sure if that is feasible - so you could ask someone else to do this test ). put the spon upside down at desk top / table top and see the difference between light intensity from windows and ceiling lights - amazingly fluoro lights are not as intense as light from windows - only very bright halogens are more intense - but have much less light - but they contribute to fire because they are smallish point sources.

Lastly, because all diamonds leak light, dependent of the input angular distribution and the cut parameters, a ''gray'' grading tray is probably better than a white background, attenuating the returned ''leaked'' light from the pavilion, much the same as light reentering the stone which is reflected back from the skin

The ''black hole'' used at the girdle plane and the ''black hole'' used to model the head is incorrect. Diamond cutting has its highest efficiency of light return for overhead, high angle lighting, not from the side..see my comments above - I think this is not awalys so, although I agree that girdle leakage can be a bebefit - i found this to be true for Regent cuts which are usually set with their 4 large side girdle facets open and the light entering from around 45 degrees above the horizon often leaves in a viewable direction - but Sergey''s ETAS can be used to show this phenonemon beuatifully.

More later but I''ve got to catch a plane today..

Marty

So I think we agree the lighting using LED''s is a big question that needs some answers, but I still am not sure that a lab like GIA should fundementally base its grading of diamond appearance on how diamonds appear in diamontaires fluoro lit offices and jewellery stores? Surley consumers want the reasurance that their diamonds will look best when they wear them out to parties and in the super market so the check-out chick says "oh ah what lovely diamonds you have Granmama".

I have not made my mind up yet that GIA''s gray tray is good or bad. But i can see that there is no need to now think (as Paul from antwerp has feared) that there is some conspiracy theory at work - because if you tested diamonds on a light enough gray tray then clean leaky stones in bright lighting will look great. And that means the old AGS Steep Deeps that we all contributed to down grading of, could have been better performing stones than we all came to believe.

So again folks - thi is I believe time for us to make some serious re-analysis of all our assumptions.

Is it valid that some light, or enough light enters the pavilion on pieces of worn jewellry in various settings to make GIA''s results valid?

The main question here is - how many diamonds are set so light can get in the back?

I think 99% of earrings and pendants should be modelled on black trays. And my own experiment with Drena''s earrings with one shallow vs one "ideal" cut stone in each ear clearly showed that shallower stones make much better earrings when worn and when they have a bit of normal dirt on them. (A number of people observed this test in Vegas this year and all agreed. I conducted the test over about 6 months, and as a reward Drena went from 1ct to 1 1/4ct each ear

).

Now as for rings - say 66%??? are set in 4 or 6 prong settings and can get some light in the pavilion. Reasonable?
Is a say 50% gray tray a reasonable test?
Does dirt make this better or worse?
More applicable or less?

 

[strmrdr]

I dont know Garry I have a hard time calling a RB diamond with that much leakage exellent.
I dont think there is a question that a better performing diamond would look better.
How much so is I think the question of the day.

 

[adamasgem]

Date: 8/11/2005 3:51:22 AM
Author: Garry H (Cut Nut)

Date: 8/10/2005 11:50:46 AM
Author: adamasgem
RE: Gary Holloway: But it would be great if someone could give us the panetone or some other code # please?''

Hi Gary.. Thanks for inviting me to this thread.. Thanks for th considered response Marty. Now that it is nearly Vampire time you are probably emerging for discussions

I sometimes bite !!!!!

1) typically one would use a 50% neutral matte gray to establish references. hopefully some one from GIA might answer the question?

Let me say additionally:

1) that what you are going to ''see'' in the GIA ''common'' viewing environment box is going to be anything but ''common'', due to the variability of the observation viewpoint and positioning of the stone.. and I strongly think (believe) that may be the overriding factor, with binocular vision effects winding up being secondary. I think you proved my point (and data) on another thread regardng the ''azimuth and tilt viewpoints'' using diamondcalc renderings They allowed people to move the stones around and bring them closer and further away, so I think that bit was OK Marty All of which changes the viewer''s perspective and is hardly standardized

2) Color wise, ''white'' LEDS have a ''Big'' broadband spike in the ''blue'' region on the spectrum, and fluorescents have multiple ''color'' spikes dependent on the phosphors used, so judgement of ''fire'' might be seriously altered..I tend to agree with you and storm if they have used the very cold blueish LED''s
I experimented a year or 2 ago with strips of LED''s in my store and found the color was not ''real''. Marty if there is too much blue would that lead to different spectral colors in fire that you would observe? The apparent "strength" of the fire changes

I haven''t gotton a chance to play with the GIA anything for a buck software, but let me say that symmetry of a stone is paramount and that using AVERAGES of cutting parameters (table size, crown angle, etc) with the assumption of symmetry brings us back to the dark ages of cut grading, and may give misleading good/bad inferences.You have played with this from 8*''s perspective and maybe you are right - but maybe you began with a biased view and discovered what you set out to discover? i do not think we can assume that GIA are wrong about VG sym being all that is required to meet the level of human perceptive ability. Gary, time to BITE. What I have done is from MY PERSPECTIVE, and no one elses. I set out to create a repeatable and unbiasing enviornment for assessing fire, and let the chips fall where they may.. and they fell showing that symmetry was paramount

Lastly, I think the ''neutral gray'' thing is an WELL intentioned attempt by GIA to to reflect reality and the real world, light typically comes comes from above, and all the modeling publically presented to the trade by GIA in the brilliance and fire articles is inconsistent with the real world, as I have pointed out before. Have you seen Sergey''s spoon test? do this - carry a spoon with you from room to room (you will have to be awake during the day Marty and i am not sure if that is feasible - so you could ask someone else to do this test ). put the spon upside down at desk top / table top and see the difference between light intensity from windows and ceiling lights - amazingly fluoro lights are not as intense as light from windows - only very bright halogens are more intense - but have much less light - but they contribute to fire because they are smallish point sources.

In one case you diffuse and in the other you concentrate light

Lastly, because all diamonds leak light, dependent of the input angular distribution and the cut parameters, a ''gray'' grading tray is probably better than a white background, attenuating the returned ''leaked'' light from the pavilion, much the same as light reentering the stone which is reflected back from the skin

The ''black hole'' used at the girdle plane and the ''black hole'' used to model the head is incorrect. Diamond cutting has its highest efficiency of light return for overhead, high angle lighting, not from the side..see my comments above - I think this is not awalys so, although I agree that girdle leakage can be a bebefit - i found this to be true for Regent cuts which are usually set with their 4 large side girdle facets open and the light entering from around 45 degrees above the horizon often leaves in a viewable direction - but Sergey''s ETAS can be used to show this phenonemon beuatifully. My comments had to do with the artificial "allowable" angular distribution for facets other than the table in the original GIA brilliance study. The table could collect light from +/- 90 degrees whereas the rest of the crown facets had differing input angle distributions, artificially cut off

More later but I''ve got to catch a plane today..

Marty

So I think we agree the lighting using LED''s is a big question that needs some answers, but I still am not sure that a lab like GIA should fundementally base its grading of diamond appearance on how diamonds appear in diamontaires fluoro lit offices and jewellery stores? Surley consumers want the reasurance that their diamonds will look best when they wear them out to parties and in the super market so the check-out chick says ''oh ah what lovely diamonds you have Granmama''.

I don''t think that consumers give a rats rearend how their diamonds look to strangers in a supermarket, but that is only my opinion..

I have not made my mind up yet that GIA''s gray tray is good or bad. But i can see that there is no need to now think (as Paul from antwerp has feared) that there is some conspiracy theory at work - because if you tested diamonds on a light enough gray tray then clean leaky stones in bright lighting will look great. And that means the old AGS Steep Deeps that we all contributed to down grading of, could have been better performing stones than we all came to believe.

Is the object of the exercise to objectively evaluate the quantity and quality a diamond''s light return when light enters the crown or when attenuated light (both in intensity and spectrum) enters from below the girdle plane.

So again folks - thi is I believe time for us to make some serious re-analysis of all our assumptions.

Is it valid that some light, or enough light enters the pavilion on pieces of worn jewellry in various settings to make GIA''s results valid?

It appears to me that the common viewing environment and the theoretical studies presented are inconsistent

The main question here is - how many diamonds are set so light can get in the back?

I think 99% of earrings and pendants should be modelled on black trays. And my own experiment with Drena''s earrings with one shallow vs one ''ideal'' cut stone in each ear clearly showed that shallower stones make much better earrings when worn and when they have a bit of normal dirt on them. (A number of people observed this test in Vegas this year and all agreed. I conducted the test over about 6 months, and as a reward Drena went from 1ct to 1 1/4ct each ear

). But then again, aren''t you a bit biased towrd shallower stones

Now as for rings - say 66%??? are set in 4 or 6 prong settings and can get some light in the pavilion. Reasonable?
Is a say 50% gray tray a reasonable test? It is more reasonable than 100% intensity from the side
Does dirt make this better or worse? Grease, as in body oils, not "dirt" per se
More applicable or less?

 

[adamasgem]

Date: 8/10/2005 1:18:51 PM
Author: strmrdr
This is fairly typical of ''white'' leds and what Marty is talkin about with them.

Thanks for posting it. The LED color temperature distribution is VERY different than the D65 spectrum used in the GIA fire article