What''s the relationship between graded symmetry and H&A?

[glitterata]

Can you have GD sym and still have H&A, or does the symmetry have to be VG or EX before you get hearts and arrows? Or are hearts and arrows related to the angles rather than the symmetry?

What are they looking at, anyway, when they rate a stone GD or VG or EX or whatever for symmetry?

 

[Magnum]

"What are they looking at, anyway, when they rate a stone GD or VG or EX or whatever for symmetry?"

The tutorial on Niceice's website does a nice job of explaining it verbally, and the tutorial on goodoldgold's website does a nice job drawing examples of different types of symmetry variations.

Niceice

goodoldgold

 

[glitterata]

Thanks--those links were helpful.

I still wonder how the symmetry grade affects H&A patterns.

 

[Garry H (Cut Nut)]

http://www.gemology.ru/cut/english/symmetry/
or www.gemology.ru/cut/english/symmetry/
will give you a full and good bedtime read on what labs grade and why it is no longer relevant for the purposes that most people think symmetry is all about.
Edited - someone needs to teach me how to ut links in

Just copy and paste this to your broswer
www.gemology.ru/cut/english/symmetry/

 

[Magnum]

----------------
On 5/22/2004 8:16:13 PM glitterata wrote:

Thanks--those links were helpful.

I still wonder how the symmetry grade affects H&A patterns.----------------

I'm sure one of the experts can explain it better, but I'll throw in my two cents. As far as the H&A pattern, it's an optical symmetry that is dependent on several factors, a very small one being the external symmetry that is graded by the major labs. The standard answer is that they are not related at all, but I think that if the symmetry variations the labs measure were large enough, it could affect the H&A pattern. The H&A effect is created by the relationship of the diamond's facets, and if you had a big enough symmetry variation, like a culet or table way off center, or crown facets totally misshapen, then I think it could adversely affect the H&A pattern. Now at what symmetry level these variations become large enough to effect the H&A pattern is a harder question. With symmetry grades of Ideal, excellent, or very good, any small variations in symmetry should have practically no noticeable effect on the H&A pattern. I'm pretty sure that you should be ok with a grade of Good, as well, but I could be wrong about that. I don't think there is a hard and fast answer, as every diamond's own H&A pattern should be examined individually. If anything I've said is incorrect, hopefully one of the experts can point it out.

 

[Rhino]

Hrm... just up taking a late night ... snack.

Yes ... that's it.




Simply put ... symmetry as graded by the labs has absolutely nothing to do with what has come to be called *optical or 3-dimensional symmetry* (or optical design). In reality you can have many different types optical symmetry patterns but there are relatively few and limited diamonds that have the proper combinations of *both proportions & symmetry* to produce the H&A phenomena. Just becuase a diamond is an H&A however does not always guarantee the best light performance. We've seen them run the gamut and frequently get in stones being advertised as H&A that simply are not and we've also tested diamonds that were not even ideal cut that had better light performance than some H&A's. H&A however is the first step in the right direction towards getting one of the most beautiful of stones.

 

[mdx]

Optical or dimensional symmetry can determine if the H&A pattern is visible. The pattern however can be distorted by at least 8 of a possible 16 symmetry deviations.

As Rhino points out not all Hearts and Arrows are Ideal Cuts and not all Ideal cuts display Hearts and arrows

Johan

 

[glitterata]

So can you have an H&A that gets just "good" symmetry? Can you have an H&A that gets "fair" symmetry?

What proportion of diamonds with H&A get high marks (Excellent and above) for symmetry? What proportion get Very Good?

 

[Garry H (Cut Nut)]

I think fair = bloody orrible