Diamond %s and Angles?

[phaketrash]

Hello all,

This forum has been really enlightening thus far, so I was just curious about a few things:

I see all these %'s and numbers and angles...and outside of GIA Ex cut/polish/symm or AGS Ideal 0, I don't really know what those numbers mean -- in the sense that I have no idea what is good versus what is bad. I plug things into the HCA calculator, and I've heard lower the number the better, with scores under 1 being kinda the same. Is this right? What else do people who are very knowledgeable about diamonds (such as y'all) look for when diamond shopping? Thanks! --referring to round brilliants btw

 

[slg47]

the most important thing is that the angles are complementary...the HCA is a tool that can help you decide this. there are some 'cheat sheets' on PS but in general they are restrictive and may eliminate some diamonds with perfectly fine proportions.

You can use this chart as a cheat sheet in order to help you find a well cut round diamond.


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!

here is the 'cheat sheet' but again I would not automatically eliminate diamonds that do not fall directly on these angles if they work well on HCA/have good idealscope image/etc.

 

[tyty333]

For HCA just look for scores under 2 (1.1 not better than 1.7). Diamonds that score under 2 are worth further
investigation.

 

[phaketrash]

For HCA just look for scores under 2 (1.1 not better than 1.7). Diamonds that score under 2 are worth further
investigation.

thanks. but what do you mean by further investigation, i.e. how would you further investigate?

 

[phaketrash]

the most important thing is that the angles are complementary...the HCA is a tool that can help you decide this. there are some 'cheat sheets' on PS but in general they are restrictive and may eliminate some diamonds with perfectly fine proportions.

You can use this chart as a cheat sheet in order to help you find a well cut round diamond.


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!

here is the 'cheat sheet' but again I would not automatically eliminate diamonds that do not fall directly on these angles if they work well on HCA/have good idealscope image/etc.

i know you said dont eliminate if it misses the cheat sheet, but would table % of 58-59% then be noticeably bad? assuming 61% ish depth %. id imagine the diamond, from the top, would look a tad bigger, though lose a little shine? assume GIA Ex/Ex/Ex.

 

[slg47]

no I think you will be fine with a slightly larger table. it will just have a different look although not necessarily bigger...for that check the diameter measurement. there are many 'flavors' of excellent cut diamonds.

when we say 'further investigation' we generally mean checking out in person, requesting idealscope images from vendor, etc.

 

[tyty333]

For HCA just look for scores under 2 (1.1 not better than 1.7). Diamonds that score under 2 are worth further
investigation.

thanks. but what do you mean by further investigation, i.e. how would you further investigate?

Further investigation...post a link to the GIA/AGS report so others can evaluate the stone. Depending on the
numbers it may be a good idea to get an ideal scope (IS) image.