GIA symmetry need not mean much

[Garry H (Cut Nut)]

This group of pictures show a stone with "good" GIA symmetry. The stone actually has excellent symmetry as you can see for yourself. The problem comes about because the table has a 0.65 degree tilt and this causes the pavilion measurements to vary from 40.1 to 41.4 degrees (as was first noted by Sergey).

Actually the pavilion is nearly perfectly symmetrical, but because the table is used by Sarin and Ogi systems as the reference plain - it appears the stone has been dowwn graded by GIA for this reason.

Does anyone use their eyes?
Do they look at diamonds?

We will work on a system to make it possible for you to view GemAdviser images online for dealers who own Sarin equipment. It is still early days for all this stuff - but it is possible for you to then view a virtual diamond before you make any commitment.

We will continue on this website to bring you amazing new developments to make buying diamonds easier.

PS the file was too big - click the little note just below here to seee the file.

 

[pricescope]

here is the picture

 

[oldminer]

Garry;

I see what you are describing and it is an advance in the understanding of what is taking place between grading and reality.

How do you define "symmetry"? Is is possible that the GIA graded the stone "good" because of the tilted table plane? What you are showing demonstrates the stone is a very good one for light, but also highlights something wrong with the symmetry in some way, too.

Am I missing something?

 

[Garry H (Cut Nut)]

Dave he tilted table has virtually no impact on the cut quality of the diamond, yet it makes the Sarin #'s look lousy.

This stone has excellent symmetry, not good symmetry.
This is what I call the features / benefit conflict.
GIA and most labs measure features that can be defined with rules.
Those features may (and often are) unrelated to benefits that the market prices (as discounts) into the notation of these features.

Am i making sense?
It is late here.

 

[oldminer]

Garry;

I know you are saying the diamond is a great performer. I know you are saying that the tilt in the plane of the table is not making the diamond a poor performer.

These things aside, the word "symmetry" has to do with equal lengths and angles. A stone with a tilted table is less than symmetrical. That is why, possibly, the GIA gave it "good". Why else?

What you are proving is that the symmetry grade from GIA may be irrelevant on some diamonds. That's a great and innovative point...I understand that. However, that does not make the stone symmetrical. This is a word that is as clearly defined as "none" when it comes to no UV fluorescence.

Not every last thing the GIA does is objectively correct or totally relevant. They do what they do. They teach what they teach. We think and create and sometimes we get to some new facts and truths... I think you have shown us something new here in a visible way that is going to make some of us think about the value of GIA symmetry ratings.

 

[mrmarius]

This is why I can't see myself buying a diamond over the Internet, sight unseen and going purely on the numbers. Why pay more for a diamond that has been graded to have excellent symmetry when there are stones like the above out there?

Same thing goes for clarity... I am sure I can find a stone that that was graded on a day the grader was in a bad mood, and gave the stone a SI1 when it should really have been a VS2.

I know many people do it, but I can't imagine dropping 8 or 9K on a diamond that I haven't seen with my own eyes. Garry, Dave, Leonid, and whoever else, what do you guys think about buying sight-unseen?

Marius

 

[pricescope]

I think there are ways to buy sight unseen especially if it'll save you some $$ and time.

E.g if VS2 in the internet would cost you less than SI1 in B&M store (all other factors kept equal) why bother with seeing it?

If you can buy super ideal H&A in the web for the price of the regular goods in the mall, why bother with checking them yourself?

You also can request Sarin data from the internet vendors to plug into HCA and try to find a good performer outside traditional ideal range.

Finaly, you can get the stone shipped to David to get professional analysis of your final candidate(s).

 

[mrmarius]

It's fun to check them myself!

What is that they say, a little knowledge is a dangerous thing?

Seriously, that isn't the best of reasons. Actually, I live near dirtcheapdiamonds, so I could probably get to see them, the best of both worlds!

I also checked out Dave Atlas' website and it turns out one of his recommended appraisers works in the building next to mine.

 

[pricescope]

Sounds like win-win situation M.


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It's fun to check them myself!
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Be carefull - it is very adictive