Diamond Depth and Width/Pavillion Angles

[preetam]

HI,
I have been learning about diamonds and have made a couple of purchases in the past - all BN. While surfing on their site for rounds i realized that diamonds within the following ranges are more expensive than others of similar sizes.

Depth - < 60.3
Width - < 58
Pavillion Angle < 40.8
Crown Angle < 34.5

Again there are stones which are outside these ranges for similar sizes and still manage to get excellent on the GIA certificate. I understand GIAs excellent is a range and any stone that falls within that range is excellent.

I also used Garys Cut Advisor and stones with the above numbers seem to be closer to 0 (the sweet spot for brilliance i guess).

My question is - can you make a decision about the cut of a stone just based on the above numbers ?


Thanks,
Preetam.

 

[Ellen]

Date: 3/11/2009 5:38:06 PM
Author:preetam

My question is - can you make a decision about the cut of a stone just based on the above numbers ?


Thanks,
Preetam.

Hi Preetam,

To answer your question, no. You need all the info a grading report gives, and preferably an ASET or IS pic. And I'm not sure if I misunderstood what you were actually saying about GIA Ex's, but that grade does not always ensure a really well cut diamond. Some are great, some not so much.

And about the HCA, shooting for zero is not the goal. Any stone that scores under 2, ideally with the x falling in the AGS/GIA overlap, or close to, deems it worthy of more info. (assuming you don't already have pics, Sarin, etc) Gary states many people find the 1-2 range very pleasing.

There are many numbers/specs that can make up a beautiful stone, so we can't just give you a set of numbers. They all work together in their own way!

 

[Lorelei]

Date: 3/11/2009 7:30:36 PM
Author: Ellen

Date: 3/11/2009 5:38:06 PM
Author:preetam

My question is - can you make a decision about the cut of a stone just based on the above numbers ?


Thanks,
Preetam.

Hi Preetam,

To answer your question, no. You need all the info a grading report gives, and preferably an ASET or IS pic. And I''m not sure if I misunderstood what you were actually saying about GIA Ex''s, but that grade does not always ensure a really well cut diamond. Some are great, some not so much.

And about the HCA, shooting for zero is not the goal. Any stone that scores under 2, ideally with the x falling in the AGS/GIA overlap, or close to, deems it worthy of more info. (assuming you don''t already have pics, Sarin, etc) Gary states many people find the 1-2 range very pleasing.

There are many numbers/specs that can make up a beautiful stone, so we can''t just give you a set of numbers. They all work together in their own way!

Ditto all the above!

 

[preetam]

Hi Ellen,
Thanks a ton for your reply. I think i know what an ASET pic is, what is an IS pic? Also what are the other numbers/specs that make a stone beautiful ? Is there some online resource you can point me to where i can educate myself about these specs. When i am looking at stones online (and i dont have Sarin, ASET info) how can i short list stones ? What I do today is look at the GIA report and then enter the numbers in the Cut Advisor and see if the stone falls in the AGS/GIA overlap.

Thanks again.
Preetam.

 

[stone-cold11]

Date: 3/12/2009 10:37:19 AM
Author: preetam
Hi Ellen,

Thanks a ton for your reply. I think i know what an ASET pic is, what is an IS pic? Also what are the other numbers/specs that make a stone beautiful ? Is there some online resource you can point me to where i can educate myself about these specs. When i am looking at stones online (and i dont have Sarin, ASET info) how can i short list stones ? What I do today is look at the GIA report and then enter the numbers in the Cut Advisor and see if the stone falls in the AGS/GIA overlap.

Thanks again.
Preetam.

IS is the a simpler reflector tech than ASET, only involving 2 light zones instead of 3 of the ASET.

The HCA = cut advisor is the tool. Use that to short list stones without access to ASET/IS. If ASET/IS are available, those imagess would trump whatever grades given by HCA if taken correctly.

 

[Lorelei]

Date: 3/12/2009 10:37:19 AM
Author: preetam
Hi Ellen,
Thanks a ton for your reply. I think i know what an ASET pic is, what is an IS pic? Also what are the other numbers/specs that make a stone beautiful ? Is there some online resource you can point me to where i can educate myself about these specs. When i am looking at stones online (and i dont have Sarin, ASET info) how can i short list stones ? What I do today is look at the GIA report and then enter the numbers in the Cut Advisor and see if the stone falls in the AGS/GIA overlap.

Thanks again.
Preetam.

Here is a very useful tutorial which explains both for you. Basically the Idealscope determines light leakage or lack of. The ASET breaks the light reflecting through a diamond down into coloured zones so it is easier to interpret the quality of the light return.

http://www.highperformancediamonds.com/index.php?page=education-performance

I will post some numbers many of us use as a guide to find a well cut diamond.

Your method of using the HCA is fine, there are various configurations which do not fall within GIA/ AGS area which can also make great looking diamonds. The HCA is used for elimination only, not selection.

Here are the numbers.

depth - 60 - 62% - although my personal preference is to allow up to 62.4%
table - 54- 57%
crown angle - 34- 35 degrees
pavilion angle - 40.6- 41 degrees
girdle - avoid extremes, look for thin to slightly thick, thin to medium etc
polish and symmetry - very good and above

note - with crown and pavilion angles at the shallower ends ( CA 34- PA 40.6) and steeper ( CA 35- PA 41) check to make sure these angles complement in that particular diamond - eyeballs, Idealscope, trusted vendor input - check as appropriate!

As the above implies, configurations depend on each other. A little give here can still work with a little take there.

From expert John Pollard ( slight edit).

With that said, here's a "Cliff's Notes" for staying near complementary angles with GIA reports (their numbers are rounded): A crown angle of 34.0, 34.5 or 35.0 is usually safe with a 40.8 pavilion angle. If pavilion angle = 40.6 lean toward a 34.5-35.0 crown. If pavilion angle = 41 lean toward a 34.0-34.5 crown.

GIA "EX" in cut is great at its heart, but it ranges a bit wider than some people prefer, particularly in deep combinations (pavilion > 41 with crown > 35).

 

[Ellen]

You''re welcome preetam, and it appears all your other questions have been covered!

 

[preetam]

Thanks for your replies. the link was helpful and i should get the ASET .

Googled and found two vendors selling em, Kassoy and gem appraisers.com. The handheld ASET looks different at both these places. Can you guys recommend where i should buy it from?

THanks,
Preetam.

 

[vfrhokie]

I got mine here.

http://www.ideal-scope.com/