The Symmetry rating on a diamond grading report refers to the precision with which the facets of a diamond are aligned with each other and the consistency of facet shape and size per given section. The symmetry rating reflected on a diamond grading report is not an indication of the proportions of a diamond.
Most laboratory issued diamond grading reports rate symmetry on a scale which might include ratings such as Poor, Fair, Good, Very Good, and Excellent or Ideal. In general, determining factors of each grade are as follows:
GIA Excellent or AGS Ideal: No misshapen or misaligned facets are visible when the diamond is viewed under 10x magnification. High magnification, such as 30x may be used to locate any misaligned or misshapen facets. The brilliance of a diamond with Excellent Symmetry will be noticeably superior to that of a diamond with a symmetry rating of Good.
Very Good: Represents diamonds that contain one or two minor symmetry characteristics that can be found under 10x magnification. Higher magnification will again be used by the grader to locate these areas easily. The degree of brilliance between a diamond graded as Very Good in Symmetry and one graded as having Good Symmetry is still noticeably different; however, it is practically impossible for the average consumer to distinguish between Very Good and Excellent or Ideal Symmetry without a lot of coaching and high levels of magnification.
Good: Numerous inconsistencies of facet alignment and shape are visible under 10x magnification. As a bare minimum, we recommend that a round brilliant cut diamond have a symmetry rating of Very Good or better. However, it is important to note that most fancy shape diamonds only have polish and symmetry ratings of good. It drives us nuts, but you learn to accept it after awhile if you ever want to find an acceptable fancy shape diamond.
Fair: Numerous inconsistencies in facet shape and alignment. Luster is below average and unimpressive.
Poor: A significant amount of the facets are misaligned and misshapen. Luster is minimal and the diamond lacks life.
The American Gem Society Laboratory (AGS) uses a numerical system to represent the Symmetry Grade of the diamonds that they evaluate. The numerical grades and associated degree of visibility of the Symmetry Characteristics are as follows:
We recommend you purchase a diamond with a Symmetry Rating of either AGS Ideal or GIA Excellent. At the very least, the Symmetry Rating of the diamond you select should be Very Good. It goes without saying that a diamond with a Symmetry Grade of AGS Ideal or GIA Excellent is going to cost a little more than a diamond with comparable characteristics and a Symmetry Rating of Very Good simply because it takes more time to achieve. However, there is also a significant difference in the visual performance of the diamond. We consider a true “Ideal Cut” to be a diamond with AGS Ideal Cut Proportions and a Symmetry Rating of Very Good, Excellent, or Ideal depending on which laboratory issued the grade. Remember, there are four categories to consider when determining a diamond’s overall cut rating:
It is important to realize that is highly unlikely that the average consumer will be able to detect a difference between the Symmetry Grades of Very Good, Excellent, and Ideal without assistance. However, most of our enlightened customers have been able to easily detect a dramatic difference in brilliance between diamonds rated as Good versus those rated as Excellent in symmetry.