Question about GIA cuts

For cut, take note of every number. Most importantly for round, as GIA does not grade cut for other shapes, table, depth, crown and pavilion angle and girdle variation. Ex in cut does not automatically imply great cut, GIA Ex allows some combination that are bad.

So how should I identify a excellent Cut grade is the real ideal cut? thanks.

Input the numbers into here. http://www.pricescope.com/cutadviser.asp

Score below 2 is worth futher consideration, getting IS/ASET image, checking if eye-clean, hearts and arrow images. Post here and we can review the result for you.

EDT:
Generally, safe numbers are

depth: 58.5-62.7%.
table: 53-58%.
Crown: 33.5-35 degree.
Pavilion: 40.6-41 degree.
girdle: thin - sl tk range.

The crown and pav angles has a inverse relationship, lower crown angle require higher pav angle and vice versa.

play with the numbers on the cut adviser and you will see.

http://diamonds.pricescope.com/round.asp

thanks, what about the chart in the link above? Can I also use it as reference?

Date: 6/30/2009 2:34:31 PM
Author:lwan123
I am looking for a excellent cut, polish, and symmetry stone.
When I look at GIA report, should I also pay attention to the depth and table of the diamond even it says excellent in all cut, polish, and symmetry?
OR once it says excellent in all cut, polish, and symmetry, the stone should be in some range of % for depth, girdle, table, and so on?
Thanks in advance.

Hi iwan,

GIA Excellent are not created equal, this grade can allow for some steep angled combos which won''t be the best performers and can leak light.

The best thing to do is to note down the following info on the diamonds you are interested in and post it here, then we can look it over for you.  This is the info needed.

depth%
table%
crown and pavilion angles
girdle thickness
polish and symmetry grades
diameter measurement
star %
lower girdle facet %
fluorescence if applicable.

If you get the following info on each one then we can go from there.  You can use the HCA certainly but it is really used as an elimination tool and for selecting you might find some diamonds which need further evaluation of the <2 scorers so best to post the info here.

Yap, you can. But the range available to you for a 1A cut is smaller than if you just plug in the numbers into the cut adviser.

EDT:
Lorelei, all yours. :P

Date: 6/30/2009 2:52:37 PM
Author: lwan123
http://diamonds.pricescope.com/round.asp

thanks, what about the chart in the link above? Can I also use it as reference?

You can use the chart and also these numbers as a guide.

depth - 60 - 62% - although my personal preference is to allow up to 62.4% - don't go too far past this or you can lose face up size and the diamond will look small for the weight.
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!

From expert John Pollard.

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

With that said, here's a "Cliff's Notes" for staying near Tolkowsky/ideal 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)."

 

Date: 6/30/2009 2:49:32 PM
Author: Stone-cold11
Input the numbers into here. http://www.pricescope.com/cutadviser.asp

Score below 2 is worth futher consideration, getting IS/ASET image, checking if eye-clean, hearts and arrow images. Post here and we can review the result for you.

EDT:
Generally, safe numbers are

depth: 58.5-62.7%.
table: 53-58%.
Crown: 33.5-35 degree.
Pavilion: 40.6-41 degree.
girdle: thin - sl tk range.

The crown and pav angles has a inverse relationship, lower crown angle require higher pav angle and vice versa.

play with the numbers on the cut adviser and you will see.

Where did you get these numbers from SC?

lol!

Just the range of numbers that I prefer when I search. Mixed from your notes, AGA range. :P

Date: 6/30/2009 2:54:26 PM
Author: Lorelei

Date: 6/30/2009 2:34:31 PM
Author:lwan123
I am looking for a excellent cut, polish, and symmetry stone.
When I look at GIA report, should I also pay attention to the depth and table of the diamond even it says excellent in all cut, polish, and symmetry?
OR once it says excellent in all cut, polish, and symmetry, the stone should be in some range of % for depth, girdle, table, and so on?
Thanks in advance.

Hi iwan,

GIA Excellent are not created equal, this grade can allow for some steep angled combos which won''t be the best performers and can leak light.

Given all the useful pointers from Lorelei and Stone-Cold, you might like to see the article written by John Pollard which has great pictures of different combinations of GIA Ex diamonds compared so that you can see what Lorelei and Stone-Cold here are referring to.

Laboratory Cut Grades:  What the report doesn’t show

http://journal.pricescope.com/Articles/72/1/Laboratory-Cut-Grades-What-the-report-doesn%e2%80%99t-show.aspx

by John Pollard