GIA grading.

[rusty_5620]

GIA has given this diamond an [excellent] symmetry rating and yet some diamond experts would say this diamond is out of round.
Does anybody know why there is this contradiction.

6.83 x 6.94 x4.21 round brilliant.


Regards,
Rusty

 

[yssie]

GIA has given this diamond an [excellent] symmetry rating and yet some diamond experts would say this diamond is out of round.
Does anybody know why there is this contradiction.

6.83 x 6.94 x4.21 round brilliant.


Regards,
Rusty

Grade is assigned based on both proportions and physical facet/facet-meet configurations (how well they line up, etc.).. more info in the links below but they include but they include details that aren't noted on the report.

Basic GIA summary on sym/pol: http://www.gia.edu/diamondcut/pdf/polish_and_symmetry.pdf
GIA article on symmetry: http://www.gia.edu/diamondcut/pdf/WN11A3.pdf
Analysis: http://www.gemology.ru/cut/english/symmetry/index.htm

 

[SVerma]

The final cut grade is given on three parameters proportions, polish and symmetry. Actually in GIA grading system the final grade for Symmetry and polish are given one grade higher than their actual grades. Suppose the Polish and symmetry grade is VG, then the final grade that is assigned to it is one grade higher that is Excellent. While for proportions it is considered as it is, that is final grade is the actual grade.
Out of round is a symmetry problem, which when considered to other symmetry issues may be more prominent in your case and would have lowered the initial/actual grade to VG. While polish may be having initial grade as VG or Excellent, since you do not mention any major polish issues i consider as Excellent. And as there is no grade higher than excellent so final grade for polish will be Excellent only.

Now considering the proportions, Since in case of proportions no higher grade is assigned as final grade, and since you mention that they have given final cut grade as Excellent, so that bring down to fact that proportions are Excellent.

So We have following Assigned grades And final grades-
Assigned Grade Final Grade
Proportions Excellent Excellent
Polish Excellent Excellent
Symmetry VG( as it is out of round) Excellent

So when we give final Cut grade we only consider the final grades of proportions, polish and symmetry so Its Excellent. Even though its out of round.

I hope you got what i mean, as i am not expert in expressing things especially through written communication. Incase if its not clear feel free to write and i will then try my best again.

Thanks
Saurabh
GD (GIA), DGI (coloured stones)