Member Recommended Proportions?

[anniversary40]

Hello! Newbie to this forum and would welcome clarification on info found here. I read that “when pavilion angle is 40.8 and crown angle is 35, lower halves need to be 80%. I’m looking at several diamonds (including a JA Harts & Arrows and WhiteFlash Cut Above) with these pavilion & crown angles with lower halves st 75%. What am I missing? Thanks!

 

[Karl_K]

If you have is/aset images you can ignore the rule of thumb.
The gia gross rounding can stack on the good side but often doesn't.

 

[tyty333]

Just FYI...and you may already know that JA H&As arent in the same category as ACAs.

 

[anniversary40]

Thank you both for your input! It was easier for me to rely on “numbers” to narrow down options. Now I have to do the hard work of learning how to read visual images for signs of light leakage, etc.

 

[freddyboston]

one trick for eyeballing the lower's - the higher you go the skinnier the arrows...

Also most of the 35/40.8 most likely fall in the 77 ~ 78 but because of GIA rounding would either be called 75 or 80 despite the fact there is only 1% difference

Facets Explained: Understanding the Lower Halves

Within robust diamond proportion sets, the lower girdle facets have great influence on the life and character of a diamond, particularly if the diamond has good patterning (optical symmetry or ‘Hearts & Arrows’ diamonds).

www.whiteflash.com

 

[anniversary40]

What a cool trick! Thanks!

 

[tyty333]

Thank you both for your input! It was easier for me to rely on “numbers” to narrow down options. Now I have to do the hard work of learning how to read visual images for signs of light leakage, etc.

Not that I'm pushing ACAs but they are already vetted to have the best light return and they have all the images to prove it.
So...no need to look at anything as far as ACAs (except to learn what a nice stone looks like).

With JA H&A some are decent but some are not.
Good...

https://www.jamesallen.com/loose-diamonds/round-cut/1.05-carat-g-color-vs2-clarity-true-hearts-cut-sku-21748485

Not good enough (IMO)

https://www.jamesallen.com/loose-diamonds/round-cut/1.00-carat-f-color-vs2-clarity-true-hearts-cut-sku-16146981

https://www.jamesallen.com/loose-diamonds/round-cut/1.03-carat-g-color-vvs2-clarity-true-hearts-cut-sku-16727621

To me, it seems like JA only evaluates the H&A but not everything else while Whiteflash evaluates every aspect of the
stone.

Edit...you can read here about ACAs to see what WF looks for in a stone. (They have their own stones cut.)

A CUT ABOVE® Diamonds Specifications and Qualifications

Uncover the diamond specifications and qualifications that make up the Whiteflash A CUT ABOVE® diamonds. The most carefully crafted diamonds in the world.

www.whiteflash.com

 

[anniversary40]

I can’t thank you enough for providing details and links to help me learn about the subtleties of H&A vs ACA’s. Everyone on this thread has been extraordinarily helpful!