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Why did this GIA diamond receive an excellent cut grade?

RockBrat

Shiny_Rock
Joined
Feb 22, 2016
Messages
116
Hello! I'm new here! This is my second thread with a head scratching question I'm hoping to get some help on.

Why did this diamond receive an excellent cut grade from gia? What is the certificate missing that gia graders saw in person ? The diamond's dimensions are listed below. At gia, don't 3 graders look at each diamond? So I assume at least 2 people thought excellent was the correct grade. When I plug it into the facetware software on gia's website and use their charts it comes up as very good. Also, AGS it comes up as good. It is a very beautiful diamond, the inclusions are twinning wisps, SI1 grade. But it's not sitting right. Any input is greatly appreciated thank you!

2.26 ctw
Depth 62.7%
Table 57%
Crown 36.5 / 16%
Pavilion 41.0 / 43.5%
Girdle med to slightly thick 3.5%

I have tried to research it and the only think I can think is the numbers on the cert are rounded so are actually different. Or that gia likes the percentages of the crown and pavilion section. What am I missing? I want to rely on the excellent grade but a borderline grade stresses me out.

Also, this diamond only scores 4.9 on the HCA. I think this is one of the most beautiful diamonds I have ever seen. What's wrong with it? Where would it technically leak light? What types of light would I see? Thank you!
 

ChristineRose

Brilliant_Rock
Premium
Joined
Aug 5, 2012
Messages
926
It's right on the edge of the GIA Excellent box (you can see it when you run the HCA). So rounding error is probably why it drops out.

A lot of stones are cut to be on the edge of the excellent category.

It would leak light under the table. If you got an Idealscope of this diamond the "doughnut" around the culet would be a paler pink than the rest of the stone.

Stones like this can be better looking than stones with a lower HCA number. The HCA doesn't take into account nearly as many factors as does the GIA. It doesn't look at minor facets for example. If the minor facets on the 2.0 HCA stone are a mess, then the stone will not be an excellent and will not look good.

Assuming though you were comparing it to a stone with all the minor facets in good order, this stone will be less bright, but it might make up for it by having good contrast and more fiery flashes. That's why it gets an excellent--some people GIA tested liked stones in this range as much, or more, as stones in the HCA 2.0 range.

The best advice would be to find an AGS 000 perfect hearts and arrows stone and to observe this stone and the "perfect" stone in a variety of light situations. You may or may not like this one as well under real-life conditions. Jewelry stores pick their light to make everything look good.
 

RockBrat

Shiny_Rock
Joined
Feb 22, 2016
Messages
116
Thanks for the great input! It helps me to better understand cut factors and feel better about the stone's cut grade. Is it possible in the future it could be downgraded to a very good just based on it's stats alone? If I compared it to the one below, how would they essentially be different? What would be the difference between the fire/scintillation/ angles? What would someone see in stone 1 vs. stone 2?

2.17 ctw
Depth 60.5
Table 56
Crown 34/ 14.5%
Pavilion 40.6/ 43%
Girdle thin to medium 3%

This one scores 0.5 excellent within TIC range on the HCA.

What would the difference be that one might see between the two if compared side by side?

Thank you!
 

RockBrat

Shiny_Rock
Joined
Feb 22, 2016
Messages
116
Can anyone please refer me to threads or photos or let me know what to search for so I can research the diamond in my first post? I'm having a difficult time figuring out what kind of affect those angles will have on brilliance, etc. Thank you!
 

queradas

Rough_Rock
Joined
Jan 11, 2016
Messages
50
RockBrat|1456263285|3994574 said:
Can anyone please refer me to threads or photos or let me know what to search for so I can research the diamond in my first post? I'm having a difficult time figuring out what kind of affect those angles will have on brilliance, etc. Thank you!
Can you post the actual listing and grading report number with AGSL then we can hopefully pull the full report and find out if it is a platinum, gold or other report.
 

queradas

Rough_Rock
Joined
Jan 11, 2016
Messages
50
RockBrat|1456180026|3994149 said:
Hello! I'm new here! This is my second thread with a head scratching question I'm hoping to get some help on.

Why did this diamond receive an excellent cut grade from gia? What is the certificate missing that gia graders saw in person ? The diamond's dimensions are listed below. At gia, don't 3 graders look at each diamond? So I assume at least 2 people thought excellent was the correct grade. When I plug it into the facetware software on gia's website and use their charts it comes up as very good. Also, AGS it comes up as good. It is a very beautiful diamond, the inclusions are twinning wisps, SI1 grade. But it's not sitting right. Any input is greatly appreciated thank you!

2.26 ctw
Depth 62.7%
Table 57%
Crown 36.5 / 16%
Pavilion 41.0 / 43.5%
Girdle med to slightly thick 3.5%

I have tried to research it and the only think I can think is the numbers on the cert are rounded so are actually different. Or that gia likes the percentages of the crown and pavilion section. What am I missing? I want to rely on the excellent grade but a borderline grade stresses me out.

Also, this diamond only scores 4.9 on the HCA. I think this is one of the most beautiful diamonds I have ever seen. What's wrong with it? Where would it technically leak light? What types of light would I see? Thank you!
GIA cut grading has nothing to do with human graders or subjective observations. It is numerical based and takes into account primarily the average pavilion and crown angles (average of the 8 mains) and the table facet from a sarin scan. GIA does not take into account the minor facets in its cut grading.
 

RockBrat

Shiny_Rock
Joined
Feb 22, 2016
Messages
116
queradas|1456263443|3994576 said:
RockBrat|1456263285|3994574 said:
Can anyone please refer me to threads or photos or let me know what to search for so I can research the diamond in my first post? I'm having a difficult time figuring out what kind of affect those angles will have on brilliance, etc. Thank you!
Can you post the actual listing and grading report number with AGSL then we can hopefully pull the full report and find out if it is a platinum, gold or other report.
Hi thank you!! The attached is all I have unfortunately but hopefully there is something on it that will help me understand better what's going on with this stone. It's a gia report, I just used AGS's online tools and charts to see how they would potentially grade the stone.

20160223_162001-1.jpg
 
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