IGI, GiA, AGL-gem labs

[Garry H (Cut Nut)]

I engage in R&D only if I understand how to use the result in case of success. Here, I don’t know how to use the result, whether in case of success or failure. Moreover, I don't understand what would even be considered a success here.

Success relates to how a diamond performs in real world conditions - not just at point of sale.
Modelling Fluorite, RI 1.43 and close to that of many oils I created this example.
Note that I can not adjust the crown refraction for diamond, which bends the light more than in this example, but the principle holds as our two eyes are not lined up with the ray anyway.

 

[Karl_K]

Show us the IS image for the reduced RI @Garry H (Cut Nut) that would be more informative than a single ray and more valid.
Thanks

 

[Garry H (Cut Nut)]

Show us the IS image for the reduced RI @Garry H (Cut Nut) that would be more informative than a single ray and more valid.
Thanks

Karl this is not accurate because the crown is refracting at 1.43RI, not at 2.412.
40.25 - you can just make out a bit of star - and I think the red outer girdle is reflection not returned light.

At 41.25 pavilion angle


If anyone wants to play you can ghange RI here - choose View/Modify props

 

[Karl_K]

@Garry H (Cut Nut) that's what I thought, just changing the overall RI doesn't seem to be a reasonable approximation.

Edit: you could do the IS test live, take image, add oil, take another.

 

[Serg]

Karl this is not accurate because the crown is refracting at 1.43RI, not at 2.412.
40.25 - you can just make out a bit of star - and I think the red outer girdle is reflection not returned light.

At 41.25 pavilion angle


If anyone wants to play you can ghange RI here - choose View/Modify props

These ASET images clearly demonstrate the futility of the test where the crown has an RI of 2.42 and the pavilion has an RI of 1.5. This is because changing the RI of the crown does not affect the angle at which light entering through the table will hit the pavilion facets, resulting in a region of almost complete leakage under the table, as shown in these images. A cut without a table and optimized for an RI 1.5 pavilion has virtually no commercial prospects on the market. The photograph also shows that dirty diamonds lack Fire, and this cannot be changed by optimizing the cut for a different RI of the pavilion.

 

[Garry H (Cut Nut)]

These ASET images clearly demonstrate the futility of the test where the crown has an RI of 2.42 and the pavilion has an RI of 1.5. This is because changing the RI of the crown does not affect the angle at which light entering through the table will hit the pavilion facets, resulting in a region of almost complete leakage under the table, as shown in these images. A cut without a table and optimized for an RI 1.5 pavilion has virtually no commercial prospects on the market. The photograph also shows that dirty diamonds lack Fire, and this cannot be changed by optimizing the cut for a different RI of the pavilion.

Definitely inconclusive regarding this very shallow diamond on the right, but I think it does show a little more colours than the Tolkowsky on the right.
The photo was taken late at night about 15-18 years ago after quite a bit to drink with John Pollard, Pete Yantzer and a few other including some AGS lab folk, Paul and Lieve.

 

[Garry H (Cut Nut)]

These ASET images clearly demonstrate the futility of the test where the crown has an RI of 2.42 and the pavilion has an RI of 1.5. This is because changing the RI of the crown does not affect the angle at which light entering through the table will hit the pavilion facets, resulting in a region of almost complete leakage under the table, as shown in these images. A cut without a table and optimized for an RI 1.5 pavilion has virtually no commercial prospects on the market. The photograph also shows that dirty diamonds lack Fire, and this cannot be changed by optimizing the cut for a different RI of the pavilion.

PS Sergey they are Ideal-scope not ASET images.
Here is ASET white

 

[Serg]

PS Sergey they are Ideal-scope not ASET images.
Here is ASET white

ASET and IS show same result

 

[Serg]

Karl this is not accurate because the crown is refracting at 1.43RI, not at 2.412.
40.25 - you can just make out a bit of star - and I think the red outer girdle is reflection not returned light.

At 41.25 pavilion angle


If anyone wants to play you can ghange RI here - choose View/Modify props

These IS images show that there is no difference between P41.25 and P40.25 in terms of light leakage under the table through dirty pavilion facets. So, what is the point of a shallow pavilion? A shallow pavilion reduces Fire, decreases DETAS, decreases Life, increase the negative effects of Head Obscuration,
but does not provide any real protection against contamination.

 

[V_sh]

This again is a question of balancing between False Positive and False Negative errors. Demanding that both be zero is unreasonable for most real tasks. There is a reasonable level of errors, and those who demand that there be no errors, such as no errors in evaluating clarity or color, simply do not understand how much it would cost to halve the error rate. From a certain level, reducing the error rate by half requires increasing the costs by an order of magnitude. Sometimes it is worth it, sometimes it is not.

Dear Sergey,
Thank you so much for your amazing example and comprehensive information, That means and is worth a lot to me. I'll study this

So could you please define a methodology for using the Cutwise to avoid these kinds of errors? (I mean how should I know in the last Single cut example if the 52% increase in the fire due to 0.10 degrees change is accurate or not? your answer matters)

 

[V_sh]

@Garry H (Cut Nut) Thanks for sharing your concerns and interests, firstly your field of work is a scientific one with few scientists in it; So please trust me that your article was helpful even 10 years ago but with all due respect to the diamond world/market, as a science researcher I found very few REAL scientists in this world; so as @Serg discussed before, scientific work has no worth if there is no researcher to read or work on them (Impact factor of your articles will be so low, not because of low quality but because few people care and read them)

Garry and Sergey I'm not really interested in understanding dirty diamonds as long as I think I couldn't understand the clean diamonds completely.
(and I don't understand people who don't clean their diamonds often and thoroughly, as they wash their cars toooooooo often)

But here are a few points to be highly considered:

_ Dirt on a diamond consists of complex organic and nonorganic film, so its interaction with light is far more complex than a simple RI; you may discuss this first (the dirt film on a diamond in a Tropical or arid region will be too different to be considered the same, let alone the impact of jewelry kind and setting differences and the owner)

_ If we expect the pavilion to be dirty and the crown is not the only impact of the dirt in diamond performance is in the area of leakage and patrial leakage, not the reflecting area, because when we have a total reflection from the pavilion the light don't go through the dirt behind the pavilion (can we track all kind of leakages during tilting and ignore total reflecting areas?)

_ should we suggest Ferrari make a special red color for those customers who don't wash their cars often?
(Trust me if they know you may drive their masterpieces dirty they won't even talk or sell to you, let alone fund R&D to make a special red color for you)

Does Paul Hung agree to design a diamond to be worn dirty? Please invite him to the threat if he is in the forum


_ Let's imagine we develop a diamond that will be the best when it becomes a little dirty and not really that good when totally clean; now we should sell a clean diamond to our new customers (imagine a bride) and tell them, because we know you won't clean your diamonds we develop a diamond that is good when it's dirty? (do you expect them to buy happily from us?)


@Garry H (Cut Nut) If you try to develop a system for fast simple cheap cleaning of jewelry it will make more sense. (Just like a supercar and high-quality car washing service)

In this case, I'll be happy to do research together and publish a good article with you, and maybe @Serg will accept to help you (But for optimizing a cut to be worn dirty, I would say that's not my thing)

What do you think Sergey? (Your answer is of great value, please)

 

[Garry H (Cut Nut)]

These IS images show that there is no difference between P41.25 and P40.25 in terms of light leakage under the table through dirty pavilion facets. So, what is the point of a shallow pavilion? A shallow pavilion reduces Fire, decreases DETAS, decreases Life, increase the negative effects of Head Obscuration,
but does not provide any real protection against contamination.

This shows a real world difference Sergey:

 

[Serg]

This shows a real world difference Sergey:

Garry,
This only shows that the diamond needs to be cleaned. Does anyone argue with that? However, the claim that P40.25 provides any real advantage for dirty stones compared to P41.25, and especially P40.75, has never been substantiated. There have been no photos, no videos, and no theories proving it. The theory and practice I know prove that dirt erases the differences between such closely related diamonds. Initially, you rejected RBC with P41.25 based on an IS image, as the IS showed a small leakage under the table. When it became clear that diamonds cannot be evaluated based on a single image, that not every leakage is harmful, and that for Stereo Vision, there is no difference* whether light is lost due to leakage or Head Obscuration, you started justifying the shift in HCA ratings towards shallow diamonds by claiming they look better when dirty.

*This is true for colorless diamonds in jewelry made of white metal. If the background behind the pavilion is colored, pavilion leakage can significantly alter the diamond's color. Many jewelers take advantage of this by placing Crushed Ice cuts of O-M color diamonds against a yellow metal background. This setting significantly colors the diamonds, making O-M color diamonds appear like fancy color diamonds.

I believe you genuinely believed that a shallow pavilion is better for dirty stones because it protected the wrong choice made 20-25 years ago. But you cannot objectively or scientifically prove the advantage of a shallow pavilion, neither through properly organized experiments nor through theory. It is obvious to me that diamonds with a dirty pavilion will have strong leakage under the pavilion, regardless of whether their crown is clean or dirty, and regardless of whether their pavilion angle is 40.25 or 40.75.

You yourself obtained and published IS images generated in Diamcalc that prove this. I can only repeat, abandon this idea, leave it in the past, and focus on creating something new and better.

 

[Serg]

So let's get down to the main topic. (please consider 3D virtual method I used)

I'll inform you what I did based on each step that I performed.

Based on what I saw It seems to me that for each light performance quality (Fire, Brilliance, etc) and for each cut there is a shifting point related to the facet(s) that cause that light property, some small changes like 0.05° may cause a big amount (10%) of decrease or increase in fire (I saw this in LG changing for RBC)

please check the following reports of the first step and let's talk about it.

do you know why small changes in angle make this difference in a single 8/8 cut?

EX Round, 1.00ct, D, IF, EX, EX, NON, +1.4%

EX Round, 1.00ct, D, IF, EX, EX, NON, +1.4%

cutwise.com

EX Round, 1.00ct, D, IF, EX, EX, NON, +1.4%

EX Round, 1.00ct, D, IF, EX, EX, NON, +1.4%

cutwise.com

My hypothesis turned out to be incorrect. The problem was not related to the threshold of what is considered fire; there was a simple(stupid) mistake in determining the size of the diamond in a photoreal image. It has been corrected, and now the metrics for these diamonds are very close.

Cutwise

cutwise.com

 

[Garry H (Cut Nut)]

Garry,
This only shows that the diamond needs to be cleaned. Does anyone argue with that? However, the claim that P40.25 provides any real advantage for dirty stones compared to P41.25, and especially P40.75, has never been substantiated. There have been no photos, no videos, and no theories proving it. The theory and practice I know prove that dirt erases the differences between such closely related diamonds. Initially, you rejected RBC with P41.25 based on an IS image, as the IS showed a small leakage under the table. When it became clear that diamonds cannot be evaluated based on a single image, that not every leakage is harmful, and that for Stereo Vision, there is no difference* whether light is lost due to leakage or Head Obscuration, you started justifying the shift in HCA ratings towards shallow diamonds by claiming they look better when dirty.

*This is true for colorless diamonds in jewelry made of white metal. If the background behind the pavilion is colored, pavilion leakage can significantly alter the diamond's color. Many jewelers take advantage of this by placing Crushed Ice cuts of O-M color diamonds against a yellow metal background. This setting significantly colors the diamonds, making O-M color diamonds appear like fancy color diamonds.

I believe you genuinely believed that a shallow pavilion is better for dirty stones because it protected the wrong choice made 20-25 years ago. But you cannot objectively or scientifically prove the advantage of a shallow pavilion, neither through properly organized experiments nor through theory. It is obvious to me that diamonds with a dirty pavilion will have strong leakage under the pavilion, regardless of whether their crown is clean or dirty, and regardless of whether their pavilion angle is 40.25 or 40.75.

You yourself obtained and published IS images generated in Diamcalc that prove this. I can only repeat, abandon this idea, leave it in the past, and focus on creating something new and better.

My last post on this topic Folks. Sergey and I have argued this point for about 15 years.
I was never referring to the pavilion leakage and never have (as you well know Sergey).
The topic is the dirt seen through the crown facets, which is apparent in the picture and also in the ray tracing posted earlier.
And here is the proof that I conducted about 15 years ago when Pete Yantzer was the lab Director at AGS:


I had my wife swap the diamond earrings from ear to ear every day to ensure they were equally dirty.

Dozens of people participated in this test and all agreed the very shallow stone appeared brighter and bigger. But when clean people with good eye sight preferred the Tolkowsky stone when holding them both in their hands.

"In 2005, I replaced one of my wife’s earring Ideal cut stones with a shallow
diamond. The shallow stone had a 59.5% table, 31.3° crown and 40.6°
pavilion with not very good symmetry. That equates to cut grades of GIA
Good or AGS 3 or 4. The remaining Ideal cut diamond had a 55.3% table,
34.9° crown and 40.75° pavilion with perfect optical symmetry (Hearts
and Arrows)."

This stone would probably be too shallow to be effective as a ring diamond, but in earrings or pendants it worked well.
The equivalent stone, if it had a 34.5 degree crown angle, would have a pavilion angle a shade under 40 degree.

 

[Serg]

My last post on this topic Folks. Sergey and I have argued this point for about 15 years.
I was never referring to the pavilion leakage and never have (as you well know Sergey).
The topic is the dirt seen through the crown facets, which is apparent in the picture and also in the ray tracing posted earlier.
And here is the proof that I conducted about 15 years ago when Pete Yantzer was the lab Director at AGS:


I had my wife swap the diamond earrings from ear to ear every day to ensure they were equally dirty.

Dozens of people participated in this test and all agreed the very shallow stone appeared brighter and bigger. But when clean people with good eye sight preferred the Tolkowsky stone when holding them both in their hands.

"In 2005, I replaced one of my wife’s earring Ideal cut stones with a shallow
diamond. The shallow stone had a 59.5% table, 31.3° crown and 40.6°
pavilion with not very good symmetry. That equates to cut grades of GIA
Good or AGS 3 or 4. The remaining Ideal cut diamond had a 55.3% table,
34.9° crown and 40.75° pavilion with perfect optical symmetry (Hearts
and Arrows)."

This stone would probably be too shallow to be effective as a ring diamond, but in earrings or pendants it worked well.
The equivalent stone, if it had a 34.5 degree crown angle, would have a pavilion angle a shade under 40 degree.

1. There was no control over the degree of dirt on the stones. It's possible the shallow diamond simply had less dirt than the diamond with Tolkowsky proportions.
2. The observation conditions and lighting were not described. It's possible the diamonds were compared under different observation conditions. As far as I remember, the first time I heard about this story from you, the diamonds were compared in earrings when they were in Drena's ears. Almost certainly, the lighting around Drena was not symmetrical, for example, there were windows on one side. The distance for observing the diamonds was not consistently ensured.
3. The diamonds differed significantly not only in pavilion angle.
4. Only one pair of diamonds was compared.

Any of these points is enough to disqualify your test as a scientific experiment. It resembles more of a restaurant entertainment.

 

[Garry H (Cut Nut)]

1. There was no control over the degree of dirt on the stones. It's possible the shallow diamond simply had less dirt than the diamond with Tolkowsky proportions.
2. The observation conditions and lighting were not described. It's possible the diamonds were compared under different observation conditions. As far as I remember, the first time I heard about this story from you, the diamonds were compared in earrings when they were in Drena's ears. Almost certainly, the lighting around Drena was not symmetrical, for example, there were windows on one side. The distance for observing the diamonds was not consistently ensured.
3. The diamonds differed significantly not only in pavilion angle.
4. Only one pair of diamonds was compared.

Any of these points is enough to disqualify your test as a scientific experiment. It resembles more of a restaurant entertainment.

Again selective hearing Sergey.
The test was conducted over months with many people in many lighting environments.
Drena swapped the stones from one ear to the other from time to time but never cleaning them.
The settings were identical.
Experts and non experts were asked for their opinion in daylight and dim restaurants (as with Pete Y).

• 3. The diamonds differed significantly not only in pavilion angle.

Common Sergey! Seriously? The crown pavilion relationship accounts for the equivalent of a very shallow pavilion angle if the crown was 34.5 degrees.

 

[Serg]

Again selective hearing Sergey.
The test was conducted over months with many people in many lighting environments.
Drena swapped the stones from one ear to the other from time to time but never cleaning them.
The settings were identical.
Experts and non experts were asked for their opinion in daylight and dim restaurants (as with Pete Y).

• 3. The diamonds differed significantly not only in pavilion angle.

Common Sergey! Seriously? The crown pavilion relationship accounts for the equivalent of a very shallow pavilion angle if the crown was 34.5 degrees.

The fact that Drena changed the position of the earrings from one ear to the other from time to time is not proof that the diamonds were equally dirty. There are many reasons why one stone could be much dirtier than the other, even if it was touched just once with very greasy fingers. You simply don't want to see how unreliable the results of such a study are. If there is no mechanism for precise and controlled contamination, at least 10 pairs of diamonds must participate in the experiment, worn by different people who are unaware of the reason for the experiment and exchange these earrings among themselves. The diamonds should also be observed under identical conditions, not just when men look at earrings in women's ears.

Regarding the differences between the diamonds, of course, I meant symmetry, not proportions. With the same success, your study could conclude that diamonds with poor symmetry handle dirt better. Why do you recommend only shallow diamonds and not shallow diamonds with low symmetry if the winning stone in your test had low symmetry?

 

[Garry H (Cut Nut)]

The fact that Drena changed the position of the earrings from one ear to the other from time to time is not proof that the diamonds were equally dirty. There are many reasons why one stone could be much dirtier than the other, even if it was touched just once with very greasy fingers. You simply don't want to see how unreliable the results of such a study are. If there is no mechanism for precise and controlled contamination, at least 10 pairs of diamonds must participate in the experiment, worn by different people who are unaware of the reason for the experiment and exchange these earrings among themselves. The diamonds should also be observed under identical conditions, not just when men look at earrings in women's ears.

Regarding the differences between the diamonds, of course, I meant symmetry, not proportions. With the same success, your study could conclude that diamonds with poor symmetry handle dirt better. Why do you recommend only shallow diamonds and not shallow diamonds with low symmetry if the winning stone in your test had low symmetry?

Who said only men were asked????
It was the only very shallow stone I had Sergey - a clients trade in. I never set out to test symmetry or have claimed it.

 

[Serg]

I had my wife swap the diamond earrings from ear to ear every day to ensure they were equally dirty.

Dozens of people participated in this test and all agreed the very shallow stone appeared brighter and bigger.

When we were traveling together in Europe, you also showed me Drena's earrings and asked which one was brighter. Did You count my response in favor of Shallow, even though I said I didn't see any difference.?

 

[Garry H (Cut Nut)]

When we were traveling together in Europe, you also showed me Drena's earrings and asked which one was brighter. Did You count my response in favor of Shallow, even though I said I didn't see any difference.?

Yes, no one preferred the Tolkowsky!

 

[Serg]

Yes, no one preferred the Tolkowsky!

There is a significant difference between "all agreed the very shallow stone appeared brighter and bigger" and "Yes, no one preferred the Tolkowsky!" . You cannot conclude that I believe the very shallow stone appeared brighter and bigger based on the fact that I didn't see any difference.

What was the exact number of participants in the tests? What percentage of the participants did not see any difference? What specific questions did you ask? How did you document the test results?

 

[V_sh]

at least 10 pairs of diamonds must participate in the experiment, worn by different people who are unaware of the reason for the experiment and exchange these earrings among themselves. The diamonds should also be observed under identical conditions

_ Dirt on a diamond consists of complex organic and nonorganic film, so its interaction with light is far more complex than a simple RI; you may discuss this first (the dirt film on a diamond in a Tropical or arid region will be too different to be considered the same, let alone the impact of jewelry kind and setting differences and the owner)

@Garry H (Cut Nut) Please provide us with your claims and opinions about the above two opinions.

Sergey is just asking you to conduct a vast scientific experiment and share the last results unbiasedly, my opinion is that you can not disagree with him it's the only way you can scientifically prove something.

You simply need more statistical population and firm controls and a published article at the end.

Please do not skip my post, your answers DO matter to me.

 

[V_sh]

My hypothesis turned out to be incorrect. The problem was not related to the threshold of what is considered fire; there was a simple(stupid) mistake in determining the size of the diamond in a photoreal image. It has been corrected, and now the metrics for these diamonds are very close.

Cutwise

cutwise.com

Appreciate Sergey for your consideration, you may wait for some days then we will discuss new pairs.

your support is of great value.