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Symmetry is the equality in measurement (angles, lengths, etc.) between corresponding parts of a stone.

Good symmetry contributes to light return because the various facets of a diamond can work better together when they are properly aligned. In addition, a symmetrical diamond is, quite simply, better looking than one which is not.

Below are some common symmetry variations of a brilliant round diamond.

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GIA Symmetry Grading

GIA grades symmetry on the following scale. Most other labs use a similar scale:
• Excellent
• Very Good
• Good
• Fair
• Poor

AGS Symmetry Grading

AGS, on the other hand, has a more granular numerical grading scale as follows:

0 - Extremely difficult to locate under 10x
1 - Very difficult to locate under 10x.
2 - Difficult to locate under 10x.
3 - Relatively easy to see under 10x, not visible to unaided eye.
4 - Easy to see under 10x, extremely difficult to to see with unaided eye.
5 - Very easy to see under 10x, very difficult to see with unaided eye.
6 - Obvious to see under 10x, difficult to see with unaided eye.
7 - Relatively easy to see with unaided eye.
8 - Easy to see with unaided eye.
9-10 - Obvious to see with unaided eye.

Never buy a diamond with a symmetry grade below 'Very Good' (on the GIA scale) or 2 (on the AGS scale). Diamond cutting technology is so advanced today that there is no excuse for cutting diamonds with poor symmetry.

Take note that GIA and AGS grades symmetry based on the observable symmetry variations above. They do not consider the optical symmetry (which is the observable cut 'pattern') of the diamond.

AGS and GIA do consider a diamond's pattern only as a contributor to light return because the pattern contributes to contrast, fire and scintillation. However, they do not grade the aesthetic quality of the pattern as well as how well and symmetrical these patterns are formed as a result of fine craftsmanship. For example, whether a diamond possess Hearts & Arrow optical symmetry is irrelevant when AGS and GIA determine their cut grades. Therefore, it is advisable to examine these patterns yourself or rely on a vendor who can assess these patterns, so that you may buy the diamond with the pattern you prefer. It is foolish to leave the patterning to chance if you care for it. We will talk more about these pattern when we discuss the scintillation of a diamond later on.

A very popular pattern is the Hearts and Arrows pattern. Do read up on the Hearts and Arrows diamond if you would like to get a diamond with super symmetry. Personally, I think you should consider Hearts and Arrows diamond for your proposal ring because they are more aesthetically pleasing, and it affects a diamond's scintillation, which we will discuss later.


Next: Proportions...