Triple Ex GIA with "fair" HCA

[deborah1830]

Why would a Triple EX Gia diamond only have a fair fire and scintillation and only good Light Performance? This is the parameters of the diamond:

GIA
0.91 I Si2
Depth: 62.1
Table: 57
Crown: 34.5
Pavillion: 41.4
Culet: None

Should I stay away from this diamond and focus on another? I do not have any other information besides actually looking at it. The price is around $6100.

 

[Gypsy]

Because the angles aren't complimentary.
Yes, you should keep looking. But I can look for you, what do you want and what is your budget.

And here, please STUDY (click on the links and read) this:
The entire purpose of faceting a diamond is to reflect light.
How well or how poorly a diamond does this determines how beautiful it is.
How well a diamond performs is determined by the angles and cutting. This is why we say cut is king.
No other factor: not color, not clarity has as much of an impact on the appearance of a diamond as its cut. An ideal H will out white a poorly cut F. And GIA Ex is not enough. And you must stick to GIA and AGS only. EGL is a bad option: [URL='https://www.pricescope.com/community/threads/egl-certification-are-any-of-them-ok.142863/']https://www.pricescope.com/community/threads/egl-certification-are-any-of-them-ok.142863/[/URL]
So how to we ensure that we have the right angles and cutting to get the light performance we want?
https://www.pricescope.com/wiki/diamonds/diamond-cut
Well one method is to start with a GIA Ex, and then apply the HCA to it. YOU DO NOT USE HCA for AGS0 stones.
https://www.pricescope.com/wiki/diamonds/holloway-cut-advisor
The HCA is a rejection tool. Not a selection tool. It uses 4 data points to make a rudimentary call on how the diamond may perform.
If the diamond passes then you know that you are in the right zone in terms of angles for light performance. Under 2 is a pass. Under 2.5-2.1 is a maybe. 2.6 and over is a no. No score 2 and under is better than any other.
Is that enough? Not really.
So what you need is a way to check actual light performance of your actual stone.
That's what an idealscope image does. https://www.pricescope.com/wiki/diamonds/firescope-idealscope
It shows you how and wear your diamond is reflecting light, how well it is going at it, and where you are losing light return. That is why you won't see us recommending Blue Nile, as they do not provide idealscope images for their diamonds. BGD, James Allen, GOG, HPD, ERD and WF do.

The Idealscope is the 'selection tool'. Not the HCA.
So yes, with a GIA stone you need the idealscope images. Or you can buy an idealscope yourself and take it in to the jeweler you are working with to check the stones yourself. Or if you have a good return policy (full refund minimum 7 days) then you can buy the idealscope, buy the stone, and do it at home.


Now if you want to skip all that... stick to AGS0 stones and then all you have to do is pick color and clarity and you know you have a great performing diamond. Because AGS has already done the checking for you. That's why they trade at a premium.

 

[SirGuy]

Hi Deborah,

The pavilion angle is too deep on that one. GIA "ex/ex/ex" for cut, polish, and symmetry can be a little misleading. GIA grades cut by rounding the angles in a proportion-based metric. Furthermore, stones graded by GIA can have crown and pavilion angles that are each "within the range" still achieve an excellent score, even if they don't complement each other.

Another reputable lab Gypsy mentioned, AGS, uses a 3D ray tracing map for light performance for all of the stones' facets working together. An AGS0 score (for light performance, polish, and symmetry) is a tighter margin than GIA "triple excellent."

Certain branded stones, such as Whiteflash's A Cut Above (ACA) and Crafted By Infinity (CBI, dealt by Wink Jones at High Performance Diamonds) are cut within more narrow specifications even within that AGS0 window.

GIA's highest cut score still allows what we refer to as "steep/deep" diamonds, referring to the crown and pavilion angles. Cutters are tempted (and rightly so) to maximize weight retention if they can still send a stone to GIA and receive the "ex/ex/ex" grade. They do this because wasting rough costs money, and because most consumers believe a GIA "ex/ex/ex" is automatically ideal. (It is not.)

Cutters who emphasize ideal cut above all else waste more material, and therefore the stones cost more to the consumer.

Cut is king. Nothing affects a stone's light performance and liveliness as much as cut.

If you're going to look at GIA stones, "triple excellent" is a good place to start; it's not a good place to finish your decision. Knowledge is power. Education takes time. Ignorance, however, is more expensive.

Read through the materials here and ask questions as you are. We'll do our best to help you make an informed decision.

 

[krisjon]

You've received some great feedback. Such are the perils of GIA Triple Excellent. You can find some great stones in the mix, but in general, the parameters are just too wide for them to be a sure bet/guarantee of a well-cut stone.

 

[Gypsy]

Great post Sir Guy!

 

[deborah1830]

Great information!! Thank you so much! They did have an ASET scope in which I looked through. There was a lot of red in there. Not sure if there can be too much red or not.

 

[SirGuy]

Hi Deborah,

Red in an ASET signifies light coming from higher on the horizon around the stone (if we consider the plane of the girdle the horizon). Green means light lower on the horizon. Blue means obstructed light (like, your head!) and paler colors usually can mean leakage (light that doesn't reflect as well through the table back to your eyes).

Here is one of my favorite education pages for how to use and interpret Ideal-Scope and ASET, and their images: http://www.highperformancediamonds.com/index.php?page=education-performance

Hope that helps!

 

[Lorelei]

Why would a Triple EX Gia diamond only have a fair fire and scintillation and only good Light Performance? This is the parameters of the diamond:

GIA
0.91 I Si2
Depth: 62.1
Table: 57
Crown: 34.5
Pavillion: 41.4
Culet: None

Should I stay away from this diamond and focus on another? I do not have any other information besides actually looking at it. The price is around $6100.

Hi Deborah,

The others have given you good feedback regarding the flags with this stone, namely the deep pavilion angle could well be problematic. I would also like to add another important potential issue with such a deep pavilion that hasn't been mentioned, colour entrapment. This might not be a problem in a colourless stone, but in an I colour, the pavilion could hold more warmth from the I colour grade and make the stone look more tinted that it might otherwise appear if the pavilion angle was less deep.

I would keep looking personally, if you give us an idea of your budget, the team here will be pleased to find some alternatives for you.

 

[Lorelei]

Hi Deborah,

Red in an ASET signifies light coming from higher on the horizon around the stone (if we consider the plane of the girdle the horizon). Green means light lower on the horizon. Blue means obstructed light (like, your head!) and paler colors usually can mean leakage (light that doesn't reflect as well through the table back to your eyes).

Here is one of my favorite education pages for how to use and interpret Ideal-Scope and ASET, and their images: http://www.highperformancediamonds.com/index.php?page=education-performance

Hope that helps!

That I believe is the one of the best educational pages to help others with ASET, thank you for posting it Sir! You deserve a shout out SG for your very helpful posts, you have got off to a flying start here!

 

[SirGuy]

Ah, thank you very much, Lorelei! Your kind words mean a lot to me. I've always appreciated the enthusiasm, candor, and gentle guidance you give others in your posts. So right back at ya! (Also, ladies, if you haven't seen my new thread in SMTB, I'd love for you to check it out! Shows the same journey as yours, Deborah, with a payoff at the end! )

 

[Lorelei]

Ah, thank you very much, Lorelei! Your kind words mean a lot to me. I've always appreciated the enthusiasm, candor, and gentle guidance you give others in your posts. So right back at ya! (Also, ladies, if you haven't seen my new thread in SMTB, I'd love for you to check it out! Shows the same journey as yours, Deborah, with a payoff at the end! )

Awww.....now you are making me blush.... Thank you Sir, I appreciate your kind words! I am going to your thread right now to have a peekerooney at your purchase....

 

[diamondseeker2006]

In case this hasn't already been said, if you are looking at stones with a 34-35 crown angle (which is the range ideal cut diamonds most often are), then you want the pavilion angle to be between 40.6-41.0. You will find that stones in those ranges generally will fall in the ideal cut area (assuming good table and depth) and will have a better HCA score. I would avoid a 41.4 pavilion angle because it is more likely to have leakage in the center.

 

[deborah1830]

HUGE thanks to all of you (SirGuy, Gypsey, Lorelei, DiamondSeeker! The feedback is extremely helpful. Lorelei, that is so interesting that you mentioned the color entrapment. I didn't know that at the time I looked at the diamond but I did notice the stone having a little more warmth to it. The setting does have side stones so I am concerned with the center diamond matching the rest of the ring. I am going through Helzberg b/c I have a trade in/trade up deal. They are not my first choice as they mark up their diamonds. I am really nervous picking the right stone, but I feel with your feedback I am able to make an educated decision, so your suggestions and feedback mean ALOT to me.

 

[Lorelei]

HUGE thanks to all of you (SirGuy, Gypsey, Lorelei, DiamondSeeker! The feedback is extremely helpful. Lorelei, that is so interesting that you mentioned the color entrapment. I didn't know that at the time I looked at the diamond but I did notice the stone having a little more warmth to it. The setting does have side stones so I am concerned with the center diamond matching the rest of the ring. I am going through Helzberg b/c I have a trade in/trade up deal. They are not my first choice as they mark up their diamonds. I am really nervous picking the right stone, but I feel with your feedback I am able to make an educated decision, so your suggestions and feedback mean ALOT to me.

It's not widely known but colour entrapment can definitely be a pitfall, interesting that you noticed it Deborah, you have a good eye! It's good to know these things first off, it can save those horrible little after purchase niggles where you might notice something is a little ' off' but you aren't sure why...

Here is a cheat sheet I made with the help of expert John Pollard some years back, it has been of help to many buying diamonds and it might be useful to get you within the ball park of the better proportioned diamonds. If you use the advice below as a guide, you should avoid potentially ' unsafe' proportion configurations that can cause light leakage and colour entrapment. Then, try to keep your centre stone and side stones within 2 colour grades of each other, that should avoid any discernible difference colour wise. You are going to find a great stone Deborah, I am quite confident you will with the questions you have asked, just ask again as and when you have further queries.


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!

From John Pollard himself.


''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).''

 

[deborah1830]

Thanks Lorelei. I am printing this info out and will keep it close while I'm looking at the diamond selection.

 

[John P]

They did have an ASET scope in which I looked through. There was a lot of red in there. Not sure if there can be too much red or not.

Two questions if I may, deborah: First, when you viewed the diamond was it in an ASET viewer or a H&A viewer? I know Helzberg has adopted ASET use (which is great!) but sometimes the two scopes can get mixed. Second question: Was it a backlit setup, showing leakage as white...or a non-backlit setup, showing leakage as black? No problem if you don't recall, just seeking info as I try to keep up with what's happening in the showroom scene at-large.

Finally: I think you're getting great input from some dedicated first-class community leaders here.