Proportions of a diamond and choices

[karsa]

I understand that going to see the actual stones using a loupe as well as by using the H&A viewer, idealscope viewer, ASET viewer is a better way to see the light performance and symmetrical performance of a diamond than just focusing on averaged out or rounded numbers on certifications like on the GIA report or AGS reports.

I would like to understand how certain differences in proportion will change the way the diamond reflects light internally and externally.
I have for you three examples where the diamonds have NO culet, NO flourescence, thin to slightly thick girdles, clarity grade that is VVS1 to IF, and are all GIA triple EX cuts.

In specific, for diamonds 1 and 3, they differ in depth. How does the depth being lower or greater in this case where all other factors including the crown angle and pavillion angle are constant affect light performance?

Moreover, for diamonds 2 and 3, how does having a pavillion angle in this case of 40.8 versus 41 as well as star facet length and lower girdle height make a difference in terms of light performance.

Furthermore, for diamonds 3 and 4, how does having a table width of 56% versus 54% under these constants, make a difference to the light performance of the diamonds.

Overall, which diamond would give the most balanced distribution of brilliance and fire out of these diamonds under the premise that these are the only constants and variables to consider (even though there are others)
1)
5.88/5.92/3.65
depth 61.9%, table 54%, crown angle 34.5, pavillion angle 40.8, star facet length 50%, lower girdle height 80%

2)
5.85/5.87/3.62mm
depth 61.8%, table 54%, crown angle 34.5, pavillion angle 41, star facet length 50%, lower girdle height 80%

3)
5.82/5.84/3.60mm
depth 61.7%, table 54%, crown angle 34.5, pavillion angle 40.8, star facet length 50%, lower girdle height 75%


4)
5.81/5.85/3.57mm
depth 61.3%, table 56%, crown angle 34.5, pavillion angle 40.8, star facet length 55%, lower girlde height 75%


I hope i have been clear with my question. In case there is any
thing that requires clarification, let me know. Thanks

 

[yssie]

The question is clear. The answer, however, is not, because the question you are asking represents a physical impossibility for which real models don't exist. The reason: a diamond model is not a linear equation. You can't change one variable and try to judge "effects" in a vacuum because that change necessitates other changes that will have other effects... assuming linear tests are meaningful descriptions of non-linear systems is a fundamentally terrible idea.

I am by no means an expert, hopefully some tradepeople will see this thread and give you their informed opinions, but the short version is that because a diamond is a physically bounded *thing*, when you change one proportion you've got to reconfigure that physical *thing* so that it always has a real shape and a real volume, and that re-configuring means other changes that will have other effects...

How does the depth being lower or greater in this case where all other factors including the crown angle and pavilion angle are constant affect light performance?
A: It doesn't. The depth is a function of crown, pav, girdle... What we can say is that since depth is a function that takes all those other parameters, by itself 61 vs. 62.5 vs 64 might be meaningless but an overly low or high depth would indicate that you'd better look over the other proportions because there's something funky going on!

Moreover, for diamonds 2 and 3, how does having a pavillion angle in this case of 40.8 versus 41 as well as star facet length and lower girdle height make a difference in terms of light performance.
First thing to note is that the GIA rounds the averaged pav up to 0.2deg, so that 41 might be a 40.9. The pavilion is the underside of the diamond from bottom edge of girdle to culet. There are two types of pavilion facets - the mains and the lower girdle facets. I highly recommend Karl's article and the GOG minor facets tutorial:
https://www.pricescope.com/journal/do_pavilion_mains_drive_light_return_modern_round_brilliant
http://www.goodoldgold.com/Articles/MinorFacets/
The pavilion angle noted on the GIA report is the averaged, rounded angle the mains take from the girdle plane (which is the normal to depth measurement), since the main facets extend all the way from girdle to culet. GIA reports LGF length: how far the LGFs extend unbroken from girdle toward culet as a percentage of total distance from girdle to culet (length of the mains). The longer the LGFs, the further they extend, the more surface area they take up, the thinner the mains (you see this as varying arrowshaft thickness face-up). LGFs are always steeper than the mains but the longer they are the shallower they are - back to Karl's article about what's actually leaking where when you read about about "rings of death" and other such calamities here on PS... Thicker mains = larger virtual facets = more readily visible IRL and permit larger, higher-energy refractions (bigger bolder flashes). Bigger stones have larger facets all 'round. Given two stones of the same diameter, same table, same crown height/angle/facets configuration, same girdle, and same reported LGF%, the one with higher pav angle must have longer mains and longer lower girdle facets by mm, which means light that refracts into the stone through the crown will hit the pavilion facets at different angles and reflect internally at different angles (if > critical angle of course)
...
You see where I'm going with this "everything's interwined" thing!

for diamonds 3 and 4, how does having a table width of 56% versus 54% under these constants, make a difference to the light performance of the diamonds.
Crown angle is angle of the kite facets from the girdle plane (because they extend unbroken from girdle to table). Given the same diameter and crown angle, a smaller table would yield a higher crown height and larger crown facets, and larger crown facets spaced further apart ups your odds of catching a single wavelength of an exiting dispersion (seeing "fire"). Given the same table size, a higher crown height indicates steeper crown angle. The GIA doesn't tell us about upper girdle angle, but overly steep UGFs (they'll always be more steeply angled than the kite facets) can cause more light escape at the girdle than you might like to see... and then cutters can tweak the girdle itself to manipulate the angles of crown and pavilion facets that meet the girdle - http://www.goodoldgold.com/4Cs/NewCutGrading/PaintingandDigging/
Some people also just like bigger or smaller tables for other reasons - more or less glare, for example, or the fact that a smaller table necessitates more tilt to see girdle reflection face-up under the table given a specific pav angle...


My honest advice? You aren't here to learn more just for the sake of learning more - you're trying to actually buy a stone. Given that priority, I think it's important to recognize that
A) there's currently a really big divide between how much you want to nitpick and the knowledge you have to nitpick with, and
B) there's currently a really big divide between how much you want to nitpick and the amount of info we have to help you nitpick with - and WE aren't the experts anyway!!
There's nothing wrong with (A) - we've all been there we all have a long way to go still! But the learning doesn't happen overnight - it takes time, and seeing lots of stones, and you're actually trying to buy a stone right now and you don't have indefinite time to bridge that gap. And I flat out refuse to address your questions in any specificity because of (B) - I can ramble in generalities all day long but to suggest that one can judge super-fine nuances with super-coarse inputs is at best completely useless, at worst wildly misleading.

I suggest a different buying tactic.
Choose a vendor that CAN help you with this sort of nitpicking. High Performance Diamonds sells the Crafted by Infinity line, Good Old Gold does all sorts of workups on their stones... WF and BGD can talk to you in-depth about their in-house stones... Make sure you trust your rep. Tell him/her your preferences and have him/her choose a stone for you. Have it shipped out and look at it with your own eyes. Take it to a local store and compare. And let your eyes call the final yes/no.
You're looking at four promising stones, given the info we have, but unfortunately without more detail absolutely no-one can give you the sort of detail you are looking for
ETA: Though there are undoubtedly a few on the Interwebz who would have you believe they have exactly that sort of extraordinary clairvoyance

ETA: date of issue on the reports?

 

[karsa]

The question is clear. The answer, however, is not, because the question you are asking represents a physical impossibility for which real models don't exist. The reason: a diamond model is not a linear equation. You can't change one variable and try to judge "effects" in a vacuum because that change necessitates other changes that will have other effects... assuming linear tests are meaningful descriptions of non-linear systems is a fundamentally terrible idea.

I am by no means an expert, hopefully some tradepeople will see this thread and give you their informed opinions, but the short version is that because a diamond is a physically bounded *thing*, when you change one proportion you've got to reconfigure that physical *thing* so that it always has a real shape and a real volume, and that re-configuring means other changes that will have other effects...

How does the depth being lower or greater in this case where all other factors including the crown angle and pavilion angle are constant affect light performance?
A: It doesn't. The depth is a function of crown, pav, girdle... What we can say is that since depth is a function that takes all those other parameters, by itself 61 vs. 62.5 vs 64 might be meaningless but an overly low or high depth would indicate that you'd better look over the other proportions because there's something funky going on!

Moreover, for diamonds 2 and 3, how does having a pavillion angle in this case of 40.8 versus 41 as well as star facet length and lower girdle height make a difference in terms of light performance.
First thing to note is that the GIA rounds the averaged pav up to 0.2deg, so that 41 might be a 40.9. The pavilion is the underside of the diamond from bottom edge of girdle to culet. There are two types of pavilion facets - the mains and the lower girdle facets. I highly recommend Karl's article and the GOG minor facets tutorial:
https://www.pricescope.com/journal/do_pavilion_mains_drive_light_return_modern_round_brilliant
http://www.goodoldgold.com/Articles/MinorFacets/
The pavilion angle noted on the GIA report is the averaged, rounded angle the mains take from the girdle plane (which is the normal to depth measurement), since the main facets extend all the way from girdle to culet. GIA reports LGF length: how far the LGFs extend unbroken from girdle toward culet as a percentage of total distance from girdle to culet (length of the mains). The longer the LGFs, the further they extend, the more surface area they take up, the thinner the mains (you see this as varying arrowshaft thickness face-up). LGFs are always steeper than the mains but the longer they are the shallower they are - back to Karl's article about what's actually leaking where when you read about about "rings of death" and other such calamities here on PS... Thicker mains = larger virtual facets = more readily visible IRL and permit larger, higher-energy refractions (bigger bolder flashes). Bigger stones have larger facets all 'round. Given two stones of the same diameter, same table, same crown height/angle/facets configuration, same girdle, and same reported LGF%, the one with higher pav angle must have longer mains and longer lower girdle facets by mm, which means light that refracts into the stone through the crown will hit the pavilion facets at different angles and reflect internally at different angles (if > critical angle of course)
...
You see where I'm going with this "everything's interwined" thing!

for diamonds 3 and 4, how does having a table width of 56% versus 54% under these constants, make a difference to the light performance of the diamonds.
Crown angle is angle of the kite facets from the girdle plane (because they extend unbroken from girdle to table). Given the same diameter and crown angle, a smaller table would yield a higher crown height and larger crown facets, and larger crown facets spaced further apart ups your odds of catching a single wavelength of an exiting dispersion (seeing "fire"). Given the same table size, a higher crown height indicates steeper crown angle. The GIA doesn't tell us about upper girdle angle, but overly steep UGFs (they'll always be more steeply angled than the kite facets) can cause more light escape at the girdle than you might like to see... and then cutters can tweak the girdle itself to manipulate the angles of crown and pavilion facets that meet the girdle - http://www.goodoldgold.com/4Cs/NewCutGrading/PaintingandDigging/
Some people also just like bigger or smaller tables for other reasons - more or less glare, for example, or the fact that a smaller table necessitates more tilt to see girdle reflection face-up under the table given a specific pav angle...


My honest advice? You aren't here to learn more just for the sake of learning more - you're trying to actually buy a stone. Given that priority, I think it's important to recognize that
A) there's currently a really big divide between how much you want to nitpick and the knowledge you have to nitpick with, and
B) there's currently a really big divide between how much you want to nitpick and the amount of info we have to help you nitpick with - and WE aren't the experts anyway!!
There's nothing wrong with (A) - we've all been there we all have a long way to go still! But the learning doesn't happen overnight - it takes time, and seeing lots of stones, and you're actually trying to buy a stone right now and you don't have indefinite time to bridge that gap. And I flat out refuse to address your questions in any specificity because of (B) - I can ramble in generalities all day long but to suggest that one can judge super-fine nuances with super-coarse inputs is at best completely useless, at worst wildly misleading.

I suggest a different buying tactic.
Choose a vendor that CAN help you with this sort of nitpicking. High Performance Diamonds sells the Crafted by Infinity line, Good Old Gold does all sorts of workups on their stones... WF and BGD can talk to you in-depth about their in-house stones... Make sure you trust your rep. Tell him/her your preferences and have him/her choose a stone for you. Have it shipped out and look at it with your own eyes. Take it to a local store and compare. And let your eyes call the final yes/no.
You're looking at four promising stones, given the info we have, but unfortunately without more detail absolutely no-one can give you the sort of detail you are looking for
ETA: Though there are undoubtedly a few on the Interwebz who would have you believe they have exactly that sort of extraordinary clairvoyance

ETA: date of issue on the reports?

Wow. I will have to do a lot of reading I appreciate your input.
I will get back to this after I absorb the explanation.

Report numbers for the diamonds under my comparison is: GIA
1159527673 july 23rd, 2013
6147761623 june 22, 2012
1156262683 february 15th 2013