Obsessions with Cut Proportions. Be all end all?

[leakinglight]

Hello,

I'm in the market to purchase a diamond. I narrowed it down to one that has excellent cut proportions:

GIA Triple EX (though reading the forum, AGS is better for Cut)
Table Size: 56 %
Crown Angle: 34.5%
Pavilion Angle: 40.8%
Crown Height: 15.0%
Star Facet: 55%
Lower Girdle: 75%
Depth: 61.6%


Yet, when looking at the Ideal Scope images for this diamond, I'm met with this:



Am I crazy in believing that numbers are the only thing that matter? In every article and guide, these numbers seem to point to an ideal cut. Could it be this vendor does not provide good images and this is why there is "light leakages" under the table?

Please help a math person out!

 

[Dancing Fire]

IMO, This is a nice stone with well balanced specs.

 

[Karl_K]

The back lighting is to bright on the image.
Anything darker than the center is not significant leakage.
The best of the best have it.
Super bright back lighting only of a computer generated perfectly "cut" with cherry proportions "diamond".

 

[lovedogs]

This diamond is great, don't worry!

 

[leakinglight]

The back lighting is to bright on the image.
Anything darker than the center is not significant leakage.
The best of the best have it.
Super bright back lighting only of a computer generated perfectly "cut" with cherry proportions "diamond".

Thanks for the analysis Karl.
Are you saying its the way the image was taken, in this case? And that this diamond has no significant leakage problems?

 

[Karl_K]

Numbers dont tell much of the story especially gia numbers which are rounded averaged then grossly rounded but that is a whole nuther long story.

 

[Karl_K]

Thanks for the analysis Karl.
Are you saying its the way the image was taken, in this case? And that this diamond has no significant leakage problems?

Yes, back light is to bright.
No significant leakage problems.

 

[Diamond_Hawk]

You've obviously done some great work and you have certainly come up with a good starting place (the numbers).

No matter what numbers you utilize, remember that you are, ultimately, operating in a 'wire frame' world with these numbers.

Each angle on the lab report is an average of several different measurements that are then rounded. Why is that important? Because two diamonds that have a lab report with identical carat, color, crown, pavilion, table and depth could have differing light performance due to the rounded averages. Now - carat, color, and clarity as graded by any reputable lab will vary only rarely. With cut it is a different matter:

On a GIA report the rounded averages can be impactful. There are 57 facets, each one is a separate measurement and all of them are, essentially, mirrors reflecting light. The number for crown angle, for example, is a rounded average of 8 separate measurements which gets changed to the nearest half degree. So a 34.5 means the average was 34.3, or 34.4, or 34.5, or 34.6, or 34.7 (the average!) on a report showing "34.5" - that's a lot of variables. Now take that same process and apply it also to Pavilion angle, Lower Halves and Stars... I hope you see where this is going.

NOTE: Pavilion Angle is rounded to the nearest .2 - but is a VERY important number on the report. So if you have, say 8 measurements that average to 30.9 in one diamond and that average to 40.1 in another, the report will still say "PA 40.0"- but the 'mirrors' will treat the light differently in the two diamonds - and produce different results.

So, how do you know what diamond to choose if the numbers on the report do not automatically mean it is a top performer?

Once you have found a diamond (or 3) that pique your interest, insist on light-performance images (Ideal-Scopes and ASETs) and/or in-person inspection. Use the numbers for sure, but the real differentiation begins after you've found the diamonds that fit those parameters.

 

[leakinglight]

You've obviously done some great work and you have certainly come up with a good starting place (the numbers).

No matter what numbers you utilize, remember that you are, ultimately, operating in a 'wire frame' world with these numbers.

Each angle on the lab report is an average of several different measurements that are then rounded. Why is that important? Because two diamonds that have a lab report with identical carat, color, crown, pavilion, table and depth could have differing light performance due to the rounded averages. Now - carat, color, and clarity as graded by any reputable lab will vary only rarely. With cut it is a different matter:

On a GIA report the rounded averages can be impactful. There are 57 facets, each one is a separate measurement and all of them are, essentially, mirrors reflecting light. The number for crown angle, for example, is a rounded average of 8 separate measurements which gets changed to the nearest half degree. So a 34.5 means the average was 34.3, or 34.4, or 34.5, or 34.6, or 34.7 (the average!) on a report showing "34.5" - that's a lot of variables. Now take that same process and apply it also to Pavilion angle, Lower Halves and Stars... I hope you see where this is going.

NOTE: Pavilion Angle is rounded to the nearest .2 - but is a VERY important number on the report. So if you have, say 8 measurements that average to 30.9 in one diamond and that average to 40.1 in another, the report will still say "PA 40.0"- but the 'mirrors' will treat the light differently in the two diamonds - and produce different results.

So, how do you know what diamond to choose if the numbers on the report do not automatically mean it is a top performer?

Once you have found a diamond (or 3) that pique your interest, insist on light-performance images (Ideal-Scopes and ASETs) and/or in-person inspection. Use the numbers for sure, but the real differentiation begins after you've found the diamonds that fit those parameters.

Thanks for the info! Based on the Ideal-Scope images, what do you think?

 

[sledge]

Numbers are gorgeous but as @Diamond_Hawk and @Karl_K pointed out, they are just the starting point.

But in this case you have an IS and hearts image to evaluate. As already pointed out the IS is good. The pinkish white you see is just overly bright backlighting.

For me, the hearts image is also interesting. While it isn't a true H&A stone, the symmetry is very good which helps provide warm fuzzies.

I think this is a good choice and would order it for evaluation with my eyes.

Nice find!

 

[gm89uk]

No problems with the IS, looks magnificent.

Now you have to change your name!

 

[kmoro]

Thanks for the info! Based on the Ideal-Scope images, what do you think?

The experts have already chimed in ... but both the numbers and the images indicate this is a great stone.

You did good!

 

[Diamond_Hawk]

Thanks for the info! Based on the Ideal-Scope images, what do you think?

Forum rules prevent me from giving specific opinions on specific diamonds, but the data provided and the opinions of experts on this thread do seem to agree, in my judgement.

 

[diamondseeker2006]

Beautiful stone which happens to also have great numbers!

 

[arkieb1]

Numbers aren't the whole diamond story, you also have to look out for things that can negatively impact a diamond like surface and internal graining, certain types of inclusions and fluorescence which can have a negative impact ie make a diamond look cloudy in a small number of diamonds.