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GIA Triple EX - Do I really need to know more?

pyramid

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CBI are harnessing something, they have found the same way Whiteflash, have their look, used to be lots of fire (not whiteflash I
think). All Super Ideal Cut Hearts and Arrows diamonds are the same. You may notice something in your diamond but nobody else
will. We used to be told it was like a 1% difference from an Ideal Cut and you could not actually see it, now we get told you can :wall: . A vendor on the other board styled Hearts on Fire diamonds as Wallets on Fire because of that 1% invisible difference at the time this was being touted.

I would say all vendors on Pricescope inhourse hearts and arrows diamonds are the same, as being as good as each other. I don't
think I would see Blue Nile as the same but I may be wrong there.
 

pyramid

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Good Old Gold used to sell Isee2 diamonds Super Ideal Cut Hearts & Arrows which gave you a certificate showing the size of the rough the diamond was cut from and which mine it came from. Don't think they have that brand now as they have another name they promote. They also had their report no engraved on the table but it was so small you needed highter than 30 x magnification. All marketing.

Buy a Super Ideal if you want that level and be done with it.
 

pyramid

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Also back in 2004 I think, there will be posts if you search the archive, the AGS cut standards were changed a bit and some of the posters here who had bought Ideal diamonds found they no longer had Ideal 0 but Ideal 1 diamonds a grade lower. This was long before the GIA had a cut standard. So just remember what is ideal today may not be tomorrow. I am not worried by that as I am
not the person who upgrades to the latest technology, handbag etc but some people may be and not know that Cut grades can and
will change.
 

tristanking

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What does super ideal actually mean? I've heard the term used by a few different folks but don't know if there is a set standard a diamond must meet to get that name? Is it an AGS 000 or a GIA xxx?
 

ChristineRose

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There's no "official" definitions of superideal, although some labs and vendors have published their own definitions.

Ideal cut refers to the proportions of the diamond, and every lab has its own definition, e.g. AGS 0 and GIA X. Although they aren't identical they are at least close. The original ideal cut was defined by Marcel Tolkowsky in 1919 and used much simpler math than we can use today.

The Hearts & Arrows phenomenon is caused by perfectly symmetric alignment of major and minor facets. Some labs do grade H & A but neither GIA nor AGS does. Some vendors also do. The grading looks at minor features like whether there's a cleft between two sides of a heart, or whether the spaces between the bottom of the hearts and the little chevrons the hearts rests in are uniform. The graders will typically measure the sizes of these defects. If you buy one the branded stones you can assume a perfect hearts pattern.

So superideal could refer to Hearts & Arrows, or it could refer to a very strict definition of Hearts & Arrows. Some dealers use a very loose definition of H & A. At some point there is no visible difference, but if you really want to be sure you have the best, buy a branded stone from a respected dealer. Neither GIA nor AGS will let you know if it's a superideal.
 

gm89uk

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Just to add to the above, a diamond does not need perfect symmetry to be coined as an ideal cut. Ideal cut more refers to excellent light performance, such as AGS000 stones and some GIA xxx.

Ideal scopes and ASETs will help you tell if a diamond has great light RETURN but not necessary anything about fire or scintillation.

A hearts and arrow viewer will comment on symmetry. A super ideal as is understood here, is an ideal cut diamond that is precision cut (extra time taken to line up the facets) that exhibit excellent symmetry. Ideal cut diamonds can be very close to super ideal cut if you are selective and have a lot of patience, you can come across them, but a lot would not be able to compete in symmetry (seeing all the arrows evenly, evenly distributed flashes of light, generally accepted to make a more appealing diamond) .

It's often somewhat more straightforward to buy a super ideal brand straight away and be done with it, as usually comes great customer service, upgrade policy and representatives that are passionate for diamond cut.

Close tosuperideal by example would be true hearts by James Allen, which are stones that are not precision cut, but have very good optics and light reflectors ( some are better than others).

Is any super ideal better than the other? Only in the experience of some and not others, there are no confirmed studies to give you anything then a guess.
 

tristanking

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Thanks! I gotta admit, one of the most interesting / surprising things I heard on here was from wink when he said the way some AGS 000 were cut wouldn't hit the GIA XXX criteria. Seems so odd that the industry would have two of the leading grading entities with such unique standards that an ideal cut stone from cbi wouldn't be a XXX.
 

kb1gra

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The odds that a CBI stone wouldn't make GIA XXX are pretty slim.

There was one style of superideal cutting that removed any leakage at the girdle using painting, which GIA penalizes, but those stones would get AGS000 since the actual cut performance is evaluated, not the numbers/angles exclusively.
 

ChristineRose

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Just to expand on what kb1gra said: Light performance is itself a tricky term. It usually refers to face-up, white light return. The painted girdles they mention would increase white light return, but at the cost of scintillation and sparkle. That's why GIA put their proportions cutoff higher.

The AGS method also has the advantage that it can rank princess and cushion and other shapes by their white light return, but the flip side is that cuts like emerald which are charming in their own way but have inherently poor light return look bad.
 

Texas Leaguer

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tristanking|1477059140|4089238 said:
Thanks! I gotta admit, one of the most interesting / surprising things I heard on here was from wink when he said the way some AGS 000 were cut wouldn't hit the GIA XXX criteria. Seems so odd that the industry would have two of the leading grading entities with such unique standards that an ideal cut stone from cbi wouldn't be a XXX.

It's been alluded to already in this thread, but It's important to understand that the AGS and GIA cut grading systems are fundamentally different approaches. GIA elected to take a broad approach and create parameter based tables with grade categories based upon their research on light behavior combined with human surveys. They measure the diamond, average and round those measurements and look up on the table the corresponding grade. AGS elected to go with a system that directly ray traces a 3D model of the actual diamond for light performance. The results of 40,000 virtual light rays are mathematically calculated and individual values for light return, leakage, dispersion (fire), and contrast are calculated. The value for each factor is graded on a 0-10 scale. Combined deductions totalling more than .5 will drop the grade below 0 Ideal. Because the AGS system scientifically evaluates the contribution of all facets, parametric tables are essentially irrelevant.

Just a point about painting to clarify. Painting is traditionally used to retain a tiny bit of weight(which can be very valuable at a magic mark) and/or to camouflage some defects such as uneven girdle. It can be done on the crown or pavilion, or both. This should be penalized. But certain painting techniques can also be used to fine tune a diamond to maximize light return- potentially a good thing. Because the GIA system does not look at the actual light performance of the diamond, it cannot make that distinction. So it punishes the good and the bad equally. This is the main reason, from my experience, that you can have an AGS 0 that does not get GIA EX. The best example is one of the original super ideal brands called Eightstar that featured precision painting designed to eliminate all leakage. These extremely well crafted diamonds tend to fall into that crack in the GIA system.

Regarding the term super ideal, as already mentioned there is no universal definition. Generally it refers to a diamond that achieves the AGS light performance grade of 0-Ideal as a baseline, and then meets additonal criteria - in particular optical precision as demonstrated by hearts and arrows patterning. Some super ideal brands have a number of other criteria that must be met in order to qualify for their particular brand. Not all brands publish their qualifications and specifications.
 

WinkHPD

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tristanking|1477059140|4089238 said:
wink when he said the way some AGS 000 were cut wouldn't hit the GIA XXX criteria. Seems so odd that the industry would have two of the leading grading entities with such unique standards that an ideal cut stone from cbi wouldn't be a XXX.

Oh my goodness. I was not referencing CBI in that comment. Every CBI meets and far exceeds XXX, just as they do every major laboratory cut metric.

I was referencing the fact that GIA’s metric excludes some shallow-stones AGS will give 000 to. Anything with a 40.4 or 40.5 pavilion angle, for example, gets VG automatically regardless of crown specifics. This is because GIA XXX is centered higher, to allow steeper and deeper stones that let producers put more weight in the body.

Wink
 

denverappraiser

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#1 Diamonds do not come off the cutting wheel with a lab report. The lab is chosen and it’s chosen strategically. The AGS-000 is a harder target for the cutters to hit than GIA-xxx. One of the side effects of this is that when you see things with paperwork for AGS-000, it wasn’t an accident.

#2 As mentioned above, nearly all AGS-000’s meet the GIA-xxx standards. The reverse is definitely not the case. It’s actually unusual because GIA rewards some combinations that produce higher weights.

#3 AGS graded stones are considerably more difficult to find than GIAs. GIA outsells them by at least 50:1 in terms of lab output, and rather few non-AGS member stores carry them. It's not that they can't, they just don't understand the issues.

That means if you want to get a double graded stone, and you don’t want to start there as your spec, start with AGS and add GIA rather than the reverse.
 

tristanking

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Wink - so sorry for misinterpreting your post. Thanks for clarifying!
 

gm89uk

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Texas Leaguer|1477063191|4089263 said:
Just a point about painting to clarify. Painting is traditionally used to retain a tiny bit of weight(which can be very valuable at a magic mark) and/or to camouflage some defects such as uneven girdle. It can be done on the crown or pavilion, or both. This should be penalized. But certain painting techniques can also be used to fine tune a diamond to maximize light return- potentially a good thing. Because the GIA system does not look at the actual light performance of the diamond, it cannot make that distinction. So it punishes the good and the bad equally. This is the main reason, from my experience, that you can have an AGS 0 that does not get GIA EX. The best example is one of the original super ideal brands called Eightstar that featured precision painting designed to eliminate all leakage. These extremely well crafted diamonds tend to fall into that crack in the GIA system

Thank you for the informative post. Just a question, can 'good' painting maximise light return without compromising fire and scintillation?
 

Texas Leaguer

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gm89uk|1477132579|4089506 said:
Texas Leaguer|1477063191|4089263 said:
Just a point about painting to clarify. Painting is traditionally used to retain a tiny bit of weight(which can be very valuable at a magic mark) and/or to camouflage some defects such as uneven girdle. It can be done on the crown or pavilion, or both. This should be penalized. But certain painting techniques can also be used to fine tune a diamond to maximize light return- potentially a good thing. Because the GIA system does not look at the actual light performance of the diamond, it cannot make that distinction. So it punishes the good and the bad equally. This is the main reason, from my experience, that you can have an AGS 0 that does not get GIA EX. The best example is one of the original super ideal brands called Eightstar that featured precision painting designed to eliminate all leakage. These extremely well crafted diamonds tend to fall into that crack in the GIA system

Thank you for the informative post. Just a question, can 'good' painting maximise light return without compromising fire and scintillation?
That's a really good question.
Technically that bit of structured leakage around the perimeter can contribute to positive contrast and thus to scintillation. To what extent that impacts visual appeal is probably subjective. However, over time it seems that the eightstar style was not roundly adopted by the market, which might be evidence that removing that particular leakage is not beneficial visually.

So, from that narrow perspective I guess it could be argued that the penalty GIA puts on it is justified. Although certainly not to someone who appreciates the eightstar style and considering the cutting skill and precision necessary to produce one! Especially in light of some really questionable makes that get the GIA's top grade.
 

gm89uk

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Thanks a lot for that. Essentially, it may or may not do, to a minor degree; but what is fundamentally flawed is that the majority of GIAXXX in the market are not as well cut as an eight star yet make the excellent cut rating due to something that was penalised without consideration towards impact to diamond beauty.
 

tristanking

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Texas Leaguer - great stuff. do you work for White Flash? I see the company name in your profile.
 

FancyIntense

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Are you aware GIA and AGS are founded by the same person?

"The members of the American Gem Society felt that the industry, as well as the consumer, would benefit from a laboratory held to a stricter standard of diamond grading—with a founding tenet of consumer protection first and foremost". AGSL web site.

AGS was the first to assign cut grades. 10 years before GIA.
 

Serg

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Texas Leaguer|1477063191|4089263 said:
tristanking|1477059140|4089238 said:
Thanks! I gotta admit, one of the most interesting / surprising things I heard on here was from wink when he said the way some AGS 000 were cut wouldn't hit the GIA XXX criteria. Seems so odd that the industry would have two of the leading grading entities with such unique standards that an ideal cut stone from cbi wouldn't be a XXX.

It's been alluded to already in this thread, but It's important to understand that the AGS and GIA cut grading systems are fundamentally different approaches. GIA elected to take a broad approach and create parameter based tables with grade categories based upon their research on light behavior combined with human surveys. They measure the diamond, average and round those measurements and look up on the table the corresponding grade. AGS elected to go with a system that directly ray traces a 3D model of the actual diamond for light performance. The results of 40,000 virtual light rays are mathematically calculated and individual values for light return, leakage, dispersion (fire), and contrast are calculated. The value for each factor is graded on a 0-10 scale. Combined deductions totalling more than .5 will drop the grade below 0 Ideal. Because the AGS system scientifically evaluates the contribution of all facets, parametric tables are essentially irrelevant.

Just a point about painting to clarify. Painting is traditionally used to retain a tiny bit of weight(which can be very valuable at a magic mark) and/or to camouflage some defects such as uneven girdle. It can be done on the crown or pavilion, or both. This should be penalized. But certain painting techniques can also be used to fine tune a diamond to maximize light return- potentially a good thing. Because the GIA system does not look at the actual light performance of the diamond, it cannot make that distinction. So it punishes the good and the bad equally. This is the main reason, from my experience, that you can have an AGS 0 that does not get GIA EX. The best example is one of the original super ideal brands called Eightstar that featured precision painting designed to eliminate all leakage. These extremely well crafted diamonds tend to fall into that crack in the GIA system.

Regarding the term super ideal, as already mentioned there is no universal definition. Generally it refers to a diamond that achieves the AGS light performance grade of 0-Ideal as a baseline, and then meets additonal criteria - in particular optical precision as demonstrated by hearts and arrows patterning. Some super ideal brands have a number of other criteria that must be met in order to qualify for their particular brand. Not all brands publish their qualifications and specifications.

Bryan,

There is one more important the difference between GIA and AGS cut grading systems.

GIA used average results from diamonds survey research , they asked trade to compare diamonds.
AGS did not do such such research and use cyclops observer theoretical model.
It is explain the shift between central points of GIA EX and AGS000( Cr34.5 P41.2 and Cr34.5 P40.7 )
Each system has disadvantages and advantages , they are too different.
AGS did one half of necessary research, GIA did other half of research.
Nobody did full research and receive scientifically base cut grade.
May be PS community needs to stop mislead end consumers and start gives balanced information?
 

Texas Leaguer

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Serg|1477281099|4089907 said:
Texas Leaguer|1477063191|4089263 said:
tristanking|1477059140|4089238 said:
Thanks! I gotta admit, one of the most interesting / surprising things I heard on here was from wink when he said the way some AGS 000 were cut wouldn't hit the GIA XXX criteria. Seems so odd that the industry would have two of the leading grading entities with such unique standards that an ideal cut stone from cbi wouldn't be a XXX.

It's been alluded to already in this thread, but It's important to understand that the AGS and GIA cut grading systems are fundamentally different approaches. GIA elected to take a broad approach and create parameter based tables with grade categories based upon their research on light behavior combined with human surveys. They measure the diamond, average and round those measurements and look up on the table the corresponding grade. AGS elected to go with a system that directly ray traces a 3D model of the actual diamond for light performance. The results of 40,000 virtual light rays are mathematically calculated and individual values for light return, leakage, dispersion (fire), and contrast are calculated. The value for each factor is graded on a 0-10 scale. Combined deductions totalling more than .5 will drop the grade below 0 Ideal. Because the AGS system scientifically evaluates the contribution of all facets, parametric tables are essentially irrelevant.

Just a point about painting to clarify. Painting is traditionally used to retain a tiny bit of weight(which can be very valuable at a magic mark) and/or to camouflage some defects such as uneven girdle. It can be done on the crown or pavilion, or both. This should be penalized. But certain painting techniques can also be used to fine tune a diamond to maximize light return- potentially a good thing. Because the GIA system does not look at the actual light performance of the diamond, it cannot make that distinction. So it punishes the good and the bad equally. This is the main reason, from my experience, that you can have an AGS 0 that does not get GIA EX. The best example is one of the original super ideal brands called Eightstar that featured precision painting designed to eliminate all leakage. These extremely well crafted diamonds tend to fall into that crack in the GIA system.

Regarding the term super ideal, as already mentioned there is no universal definition. Generally it refers to a diamond that achieves the AGS light performance grade of 0-Ideal as a baseline, and then meets additonal criteria - in particular optical precision as demonstrated by hearts and arrows patterning. Some super ideal brands have a number of other criteria that must be met in order to qualify for their particular brand. Not all brands publish their qualifications and specifications.

Bryan,

There is one more important the difference between GIA and AGS cut grading systems.

GIA used average results from diamonds survey research , they asked trade to compare diamonds.
AGS did not do such such research and use cyclops observer theoretical model.
It is explain the shift between central points of GIA EX and AGS000( Cr34.5 P41.2 and Cr34.5 P40.7 )
Each system has disadvantages and advantages , they are too different.
AGS did one half of necessary research, GIA did other half of research.
Nobody did full research and receive scientifically base cut grade.
May be PS community needs to stop mislead end consumers and start gives balanced information?
Good points Serg. They clearly are very different approaches to reporting on cut quality. As you say, both have their strengths and weaknesses.

I don't think the PS community is attempting to mislead anyone. They are simply trying to get the most detailed lab report currently available of this most important aspect of diamond value. In this regard they are rightly drawn to a system that actually measures light performance (AGS), and one that has much stricter tolerances.

It's quite natural for shoppers to want both reports. Unfortunately this is generally impractical for a variety of reasons.

For the visitors here that might not know what you mean by 'cyclops', the fact that we look at diamonds with two eyes in stereoscopic vision, a real life view of a diamond (at close range) differs from the theoretical model used in the AGS system. This limitation was understood by AGS during development, but the computing power required at the time to fully account for this effect was deemed to be not practical.

My guess is that this would likely be an area of continued interest for the labs, as you have demonstrated brilliantly in your work.
 

kb1gra

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Stereostopic cut modeling software is currently available on the market. I believe GOG has access to it, and they may be one of the only companies in the market that does. So, in theory, the evaluation of light performance could also use this technology to once again verify that the light performance of an AGS0 stone is absolute.
 

gm89uk

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Serg said:
Bryan,

There is one more important the difference between GIA and AGS cut grading systems.

GIA used average results from diamonds survey research , they asked trade to compare diamonds.
AGS did not do such such research and use cyclops observer theoretical model.
It is explain the shift between central points of GIA EX and AGS000( Cr34.5 P41.2 and Cr34.5 P40.7 )
Each system has disadvantages and advantages , they are too different.
AGS did one half of necessary research, GIA did other half of research.
Nobody did full research and receive scientifically base cut grade.
May be PS community needs to stop mislead end consumers and start gives balanced information?

Serg, why do you think GIA found that 34.5/41.2 averaged best despite having reduced light performance? Did GIA take complimentary angles into account? do you think well facetes 34.5/41.2 can beat out the more traditionally accepted ideal angle cuts to a larger proportion of people? Several trade members here have stated their customers pick out their diamonds over GIA xxx stones. I'm just trying to understand how GIA found different conclusions to what is more widely accepted as better
 

Texas Leaguer

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kb1gra|1477323794|4090007 said:
Stereostopic cut modeling software is currently available on the market. I believe GOG has access to it, and they may be one of the only companies in the market that does. So, in theory, the evaluation of light performance could also use this technology to once again verify that the light performance of an AGS0 stone is absolute.
Yes, Serg and his research group have developed this capability. It's really interesting and I'm sure he will have more to say on the topic. :read:

I'm not sure we are ever going to achieve "absolute" in any grading system. ;-)
 

Serg

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gm89uk|1477325215|4090016 said:
Serg said:
Bryan,

There is one more important the difference between GIA and AGS cut grading systems.

GIA used average results from diamonds survey research , they asked trade to compare diamonds.
AGS did not do such such research and use cyclops observer theoretical model.
It is explain the shift between central points of GIA EX and AGS000( Cr34.5 P41.2 and Cr34.5 P40.7 )
Each system has disadvantages and advantages , they are too different.
AGS did one half of necessary research, GIA did other half of research.
Nobody did full research and receive scientifically base cut grade.
May be PS community needs to stop mislead end consumers and start gives balanced information?

Serg, why do you think GIA found that 34.5/41.2 averaged best despite having reduced light performance? Did GIA take complimentary angles into account? do you think well facetes 34.5/41.2 can beat out the more traditionally accepted ideal angle cuts to a larger proportion of people? Several trade members here have stated their customers pick out their diamonds over GIA xxx stones. I'm just trying to understand how GIA found different conclusions to what is more widely accepted as better

I do not see any good reason to discuss that is better : more wide or more narrow "ideal" cut group . It is wrong question because the reason of problem is in bounded cut group. the main problem is penalty approach . a penalty system and bounded groups will always create a problems : AGS0 rejects nice( may be best combination Fire and Brilliancy ) diamonds , GIA Ex includes diamonds with strong leakage . what is worse depends from your goals, priorities ,..


what is more important and interesting : AGS0 and GIA Ex is shifted . GIA EX has deeper pavilion angles.
Usually you will receive explanation on PS that GIA did it to increase motivation of cutters to send diamonds to GIA lab.
I know different the reason:
Cr34.5/P41.0 diamond has higher Fire and slightly higher Brilliancy than Cr34.5/P40.7 with same symmetry , size and any other proportions.
May be Cr34.5/P40.7 is more bright but Cr34.5/P41.0 has more brilliancy.
Cr34.5/P40.7 has better IS, ASET pictures, but Cr34.5/P41.0 has more "Life" for stereoscopic observer.
If you grade diamonds by mono images then you have to select Cr34.5/P40.7 as central of best group.
If you grade diamonds by human eyes then you have to shift you best diamond to slightly deeper pavilion.(Cr34.5/P41 ).
Also answer depends from your preferences for Brightness and Fire.
 

gm89uk

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Serg|1477333236|4090080 said:
I do not see any good reason to discuss that is better : more wide or more narrow "ideal" cut group . It is wrong question because the reason of problem is in bounded cut group. the main problem is penalty approach . a penalty system and bounded groups will always create a problems : AGS0 rejects nice( may be best combination Fire and Brilliancy ) diamonds , GIA Ex includes diamonds with strong leakage . what is worse depends from your goals, priorities ,..


what is more important and interesting : AGS0 and GIA Ex is shifted . GIA EX has deeper pavilion angles.
Usually you will receive explanation on PS that GIA did it to increase motivation of cutters to send diamonds to GIA lab.
I know different the reason:
Cr34.5/P41.0 diamond has higher Fire and slightly higher Brilliancy than Cr34.5/P40.7 with same symmetry , size and any other proportions.
May be Cr34.5/P40.7 is more bright but Cr34.5/P41.0 has more brilliancy.
Cr34.5/P40.7 has better IS, ASET pictures, but Cr34.5/P41.0 has more "Life" for stereoscopic observer.
If you grade diamonds by mono images then you have to select Cr34.5/P40.7 as central of best group.
If you grade diamonds by human eyes then you have to shift you best diamond to slightly deeper pavilion.(Cr34.5/P41 ).
Also answer depends from your preferences for Brightness and Fire.

Thanks a lot for your reply. I hadn't come across Brilliancy as a different characteristic to brightness before. Fire on HCA is graded less for a 34.5/41 combo compared to 34.5/40.7 and I always thought HCA was based on DiamCalc. What tool do you use to calculate fire or is this mainly in your experience?
 

Garry H (Cut Nut)

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gm89uk|1477350488|4090204 said:
Serg|1477333236|4090080 said:
I do not see any good reason to discuss that is better : more wide or more narrow "ideal" cut group . It is wrong question because the reason of problem is in bounded cut group. the main problem is penalty approach . a penalty system and bounded groups will always create a problems : AGS0 rejects nice( may be best combination Fire and Brilliancy ) diamonds , GIA Ex includes diamonds with strong leakage . what is worse depends from your goals, priorities ,..


what is more important and interesting : AGS0 and GIA Ex is shifted . GIA EX has deeper pavilion angles.
Usually you will receive explanation on PS that GIA did it to increase motivation of cutters to send diamonds to GIA lab.
I know different the reason:
Cr34.5/P41.0 diamond has higher Fire and slightly higher Brilliancy than Cr34.5/P40.7 with same symmetry , size and any other proportions.
May be Cr34.5/P40.7 is more bright but Cr34.5/P41.0 has more brilliancy.
Cr34.5/P40.7 has better IS, ASET pictures, but Cr34.5/P41.0 has more "Life" for stereoscopic observer.
If you grade diamonds by mono images then you have to select Cr34.5/P40.7 as central of best group.
If you grade diamonds by human eyes then you have to shift you best diamond to slightly deeper pavilion.(Cr34.5/P41 ).
Also answer depends from your preferences for Brightness and Fire.

Thanks a lot for your reply. I hadn't come across Brilliancy as a different characteristic to brightness before. Fire on HCA is graded less for a 34.5/41 combo compared to 34.5/40.7 and I always thought HCA was based on DiamCalc. What tool do you use to calculate fire or is this mainly in your experience?

The brilliancy concept is described in this article. Essentially when you look at a shiny object and one eye sees the shiny reflection or refraction of a bright light, while the other eye sees a darker dull area the dissonance in our mind from the two signals creates 'brilliancy'.
http://www.gem.org.au/ckfinder/userfiles/files/GAA_Journal_V25_No3_web2(1).pdf
When I built HCA I did not have quantitative tools for fire and I assessed images that were then able to be produced in DiamCalc. It is explained here: http://www.diamond-cut.com.au/12_fire.htm (and I just noticed a 15 year old typo).
 

Serg

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gm89uk|1477350488|4090204 said:
Serg|1477333236|4090080 said:
I do not see any good reason to discuss that is better : more wide or more narrow "ideal" cut group . It is wrong question because the reason of problem is in bounded cut group. the main problem is penalty approach . a penalty system and bounded groups will always create a problems : AGS0 rejects nice( may be best combination Fire and Brilliancy ) diamonds , GIA Ex includes diamonds with strong leakage . what is worse depends from your goals, priorities ,..


what is more important and interesting : AGS0 and GIA Ex is shifted . GIA EX has deeper pavilion angles.
Usually you will receive explanation on PS that GIA did it to increase motivation of cutters to send diamonds to GIA lab.
I know different the reason:
Cr34.5/P41.0 diamond has higher Fire and slightly higher Brilliancy than Cr34.5/P40.7 with same symmetry , size and any other proportions.
May be Cr34.5/P40.7 is more bright but Cr34.5/P41.0 has more brilliancy.
Cr34.5/P40.7 has better IS, ASET pictures, but Cr34.5/P41.0 has more "Life" for stereoscopic observer.
If you grade diamonds by mono images then you have to select Cr34.5/P40.7 as central of best group.
If you grade diamonds by human eyes then you have to shift you best diamond to slightly deeper pavilion.(Cr34.5/P41 ).
Also answer depends from your preferences for Brightness and Fire.

Thanks a lot for your reply. I hadn't come across Brilliancy as a different characteristic to brightness before. Fire on HCA is graded less for a 34.5/41 combo compared to 34.5/40.7 and I always thought HCA was based on DiamCalc. What tool do you use to calculate fire or is this mainly in your experience?

We use special software to calculate fire . Diamcalc metrics are good enough only for preliminary selection when you need in short time reject 99,99% really bad proportions from 1 million options.
If you want compare 34.5/41 and 34.5/40.7 then you need other level of instruments.

we have start developed these instruments when I many time received confirmation base on my own experience and opinions from other professionals that 34.5/41 at least is not worse than 34.5/40.7.
In attempt to understand why 34.5/41( and even 34.5/41.2) is not bad as it looks from IS, Mono calculation ,.. I found importance of Space, Temporal and Stereo rivalry in diamond beauty creation.

But current diamond market does not need it, and I am also not interesting more in any arguments, disputes. It will not helpful for diamond industry anymore. This Game is over.

Btw. In May 2015 Garry did comparison survey in Vegas. He compared 34.5/41.2 and 34.5/40.7. Ask him why he did not publish the result.
It is more interesting question for PS then the difference between 34.5/41 and 34.5/40.7.
 

Rockdiamond

Ideal_Rock
Trade
Joined
Jan 7, 2009
Messages
9,753
gm89uk|1477325215|4090016 said:
Serg said:
Bryan,

There is one more important the difference between GIA and AGS cut grading systems.

GIA used average results from diamonds survey research , they asked trade to compare diamonds.
AGS did not do such such research and use cyclops observer theoretical model.
It is explain the shift between central points of GIA EX and AGS000( Cr34.5 P41.2 and Cr34.5 P40.7 )
Each system has disadvantages and advantages , they are too different.
AGS did one half of necessary research, GIA did other half of research.
Nobody did full research and receive scientifically base cut grade.
May be PS community needs to stop mislead end consumers and start gives balanced information?

Serg, why do you think GIA found that 34.5/41.2 averaged best despite having reduced light performance? Did GIA take complimentary angles into account? do you think well facetes 34.5/41.2 can beat out the more traditionally accepted ideal angle cuts to a larger proportion of people? Several trade members here have stated their customers pick out their diamonds over GIA xxx stones. I'm just trying to understand how GIA found different conclusions to what is more widely accepted as better


Great discussion. From my perspective the disconnect isn't that PS "prosumers" are intentionally misleading people who come to ask questions.
The issue is that if you're not in the trade, and read a lot of PS, you can "learn" that one CR/PA combination is "better" than the other- not different, but better. No consumer coming here for advise wants to buy a diamond that performs "worse"- but they don't understand that performance is subjective. They may actually prefer the look of a diamond which gets knocked here for not performing well.
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
18,559
Serg|1477406277|4090395 said:
gm89uk|1477350488|4090204 said:
Serg|1477333236|4090080 said:
I do not see any good reason to discuss that is better : more wide or more narrow "ideal" cut group . It is wrong question because the reason of problem is in bounded cut group. the main problem is penalty approach . a penalty system and bounded groups will always create a problems : AGS0 rejects nice( may be best combination Fire and Brilliancy ) diamonds , GIA Ex includes diamonds with strong leakage . what is worse depends from your goals, priorities ,..


what is more important and interesting : AGS0 and GIA Ex is shifted . GIA EX has deeper pavilion angles.
Usually you will receive explanation on PS that GIA did it to increase motivation of cutters to send diamonds to GIA lab.
I know different the reason:
Cr34.5/P41.0 diamond has higher Fire and slightly higher Brilliancy than Cr34.5/P40.7 with same symmetry , size and any other proportions.
May be Cr34.5/P40.7 is more bright but Cr34.5/P41.0 has more brilliancy.
Cr34.5/P40.7 has better IS, ASET pictures, but Cr34.5/P41.0 has more "Life" for stereoscopic observer.
If you grade diamonds by mono images then you have to select Cr34.5/P40.7 as central of best group.
If you grade diamonds by human eyes then you have to shift you best diamond to slightly deeper pavilion.(Cr34.5/P41 ).
Also answer depends from your preferences for Brightness and Fire.

Thanks a lot for your reply. I hadn't come across Brilliancy as a different characteristic to brightness before. Fire on HCA is graded less for a 34.5/41 combo compared to 34.5/40.7 and I always thought HCA was based on DiamCalc. What tool do you use to calculate fire or is this mainly in your experience?

We use special software to calculate fire . Diamcalc metrics are good enough only for preliminary selection when you need in short time reject 99,99% really bad proportions from 1 million options.
If you want compare 34.5/41 and 34.5/40.7 then you need other level of instruments.

we have start developed these instruments when I many time received confirmation base on my own experience and opinions from other professionals that 34.5/41 at least is not worse than 34.5/40.7.
In attempt to understand why 34.5/41( and even 34.5/41.2) is not bad as it looks from IS, Mono calculation ,.. I found importance of Space, Temporal and Stereo rivalry in diamond beauty creation.

But current diamond market does not need it, and I am also not interesting more in any arguments, disputes. It will not helpful for diamond industry anymore. This Game is over.

Btw. In May 2015 Garry did comparison survey in Vegas. He compared 34.5/41.2 and 34.5/40.7. Ask him why he did not publish the result.
It is more interesting question for PS then the difference between 34.5/41 and 34.5/40.7.
There was a question about the cleanliness of the two diamonds. I sent them to an appraiser to be checked as I went on a vacation after the Vegas JCK show and was told that one of the two stones was dirty. However the dirty stone was not identified so we could not be sure of the results.
There is substance to Sergey's arguement, however from my experience the stereoscopic effect is stronger from close up inspection and less apparent in set diamonds than loose stones.
 

gm89uk

Brilliant_Rock
Premium
Joined
May 26, 2015
Messages
1,491
Serg|1477406277|4090395 said:
We use special software to calculate fire . Diamcalc metrics are good enough only for preliminary selection when you need in short time reject 99,99% really bad proportions from 1 million options.
If you want compare 34.5/41 and 34.5/40.7 then you need other level of instruments.

we have start developed these instruments when I many time received confirmation base on my own experience and opinions from other professionals that 34.5/41 at least is not worse than 34.5/40.7.
In attempt to understand why 34.5/41( and even 34.5/41.2) is not bad as it looks from IS, Mono calculation ,.. I found importance of Space, Temporal and Stereo rivalry in diamond beauty creation.

But current diamond market does not need it, and I am also not interesting more in any arguments, disputes. It will not helpful for diamond industry anymore. This Game is over.

Btw. In May 2015 Garry did comparison survey in Vegas. He compared 34.5/41.2 and 34.5/40.7. Ask him why he did not publish the result.
It is more interesting question for PS then the difference between 34.5/41 and 34.5/40.7.

I suppose the 34.5/41 diamond achieved the vote of confidence but that this cannot be validated as they didn't know which diamond was dirty.

@Rockdiamond & Sergy, people with your wealth of experience gives you ability to pick beautiful stones that don't fit the traditional bill. But for the regular consumer in this online e-ring world, there unfortunately is nothing measurable other than light performance with an Idealscope/ASET/AGS light performance, and to play it safe you would get what you can, best within available technology and resources. A well read consumer will not go for a 34.5/41 diamond vs a a 34.5/40.7 if buying blind (all else being equal), because with information available today, it is usually the superior 'looking' diamond, on paper at least...

Sergy if you were a consumer buying online (maybe you never would do such as a thing), you would be happy to consider a diamond with a 34.5/41 over a 34.5/40.7 if symmetry was good but there was a bit more leakage under table, based on your past experience?

I don't mean to probe, but I really do find this fascinating. It's teaching me a new way of thinking. Do these new devices work with stereopsis?

Is there anything that accurately measures dispersion (akin to the idealscope for light return)? Maybe a pure white scope with small leds and a camera that quantifies any colours?

And thanks for the clarification of brilliance Garry, will have a read
 
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