H&A RB Proportion Questions

[JeBri31508]

Hello everyone...I apologize if this question has already been beat into the ground, but I keep on getting different answers when I use the search tool. I am going to be looking for an upgrade (I am wanting at least a 1 carat RB) at a local wholesale jewelry store here in OK. The thing is, they use GIA grading system. Now, I have heard several things on PS about GIA letting diamonds be "steep/deep" and that these diamonds can be considered EX by the grading system. I am wanting to know a basic "proportion" of what would be considered the most ideal, brilliant diamond I can buy (depth, table, angels, etc). I would also like to know exactly what constitutes a steep/deep diamond (i.e. the numbers), so that I do not accidentally buy one of these!

I also ordered an idealscope, so I''m hoping that will help out with my search as well. I''ve just read a lot about the steep deep thing with GIA and now I''m scared that I will unknowingly get one...but that''s what I have all of you here for, to educate me lol. TIA!

 

[Lorelei]

Date: 1/15/2010 4:24:37 PM
Author:JeBri31508
Hello everyone...I apologize if this question has already been beat into the ground, but I keep on getting different answers when I use the search tool. I am going to be looking for an upgrade (I am wanting at least a 1 carat RB) at a local wholesale jewelry store here in OK. The thing is, they use GIA grading system. Now, I have heard several things on PS about GIA letting diamonds be 'steep/deep' and that these diamonds can be considered EX by the grading system. I am wanting to know a basic 'proportion' of what would be considered the most ideal, brilliant diamond I can buy (depth, table, angels, etc). I would also like to know exactly what constitutes a steep/deep diamond (i.e. the numbers), so that I do not accidentally buy one of these!

I also ordered an idealscope, so I'm hoping that will help out with my search as well. I've just read a lot about the steep deep thing with GIA and now I'm scared that I will unknowingly get one...but that's what I have all of you here for, to educate me lol. TIA!

Hi jebri

If I post the ' cheat sheet' for you which some of us use as a guide to finding a well cut round stone, it might be helpful.

Also concerning steep deeps and conversely the shallow proportion combos, the Holloway Cut Advisor will help with that, generally for ring stones look for ones which score between 1 and 2 on the HCA, that should weed out the steep deeps and shallower stones which can be prone to obstruction. Obstruction is the visible darkening of the diamond which can occur with shallow proportioned diamonds due to the head/ body of the viewer blocking the light to the diamond if the stone is viewed closely.

Steep deep - crown and pavilion angles of around 35/41 and above are entering the steep deep zone.

Shallow shallows ( prone to obstruction) crown and pavilion angles of less than 34/40.6

Also watch out for pavilion angles of much over 41 degrees and less than 40.6 to avoid light leakage and obstruction respectively as well as other potentially undesirable issues.

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.

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).

Thats great you have ordered an Idealscope, they are simple to use and it will be very helpful to you. Especially as you may have read about GIA rounding issues, this means that the crown and pavilion angles might be shallower or steeper than on the report, so especially with borderline angle combos such as the steep deeps for example, an Idealscope will help you evaluate any of these should you encounter them so you can judge how effectively the proportions work together.

 

[JeBri31508]

This is awesome--a cheat sheet is exactly what i''ve been needing! Thank you so much, I think that I''ve got a handle on this proportion thing now

 

[Dreamer_D]

Can''t add much to that!

 

[Lorelei]

Date: 1/16/2010 1:54:40 AM
Author: dreamer_dachsie
Can''t add much to that!

LOL!!!

JeBri - you are most welcome, very glad to be of help to you