Diamond Symmetry

2018-11-25T21:31:37+00:0024th November 2018|Education|

The modern world welcomes the charm in the abstract, the offbeat, and the asymmetrical. But the classic beauty standard has always been perfection!

Symmetry is soothing to the eye simply because we all want harmony. Many forms of art deem perfection as intricate mastery, and diamonds are no different! While the Cut Proportions are behind a diamond’s light performance, gemological labs also grade symmetry and polish, and these factors impact the overall cut grade.

You’ll find GIA’s guidelines on how they influence the cut grade here. But if you want to know the nitty-gritty, read on as we’re going in-depth with Diamond Symmetry. Because even though the diamond cut is the maker and breaker of brilliance, knowing how symmetry works can help you pick a better diamond that can potentially save you money!

What is Diamond Symmetry?

It’s basically the symmetrical arrangement and even placement of the facets of the diamond. A symmetrical diamond should have perfectly aligned and shaped facets.

And if it’s not, it may bear off center culets, wavy girdles, or misplaced tables. With poor symmetry, the diamond could lead the light that enters to wrong angles, and thus, lessen the diamond’s supposed sparkle.

Which Symmetry Grade to Choose:

Excellent Symmetry: There are no symmetry flaws visible under 10x magnification.

Very Good Symmetry: Minute defects are difficult to see under 10x magnification.

Good Symmetry: Noticeable flaws can be viewed under 10x magnification.

Fair Symmetry: Flaws are noticeable under 10x magnification and may also be seen by the naked eye. Usually not offered by diamond shops.

Poor Symmetry: Flaws are visible to the naked eye. Usually not offered by diamond shops.

A diamond with an Excellent Cut has to have Excellent or at least Very Good Symmetry characteristics. GIA has found that a Very Good Symmetry grade does not impact an Excellent Cut grade negatively whereas a Good Cut grade can.

Here’s a pro tip: Excellent symmetry is more significant in VVS2 Clarity and beyond because the minute flaws that comes with a Good or Fair symmetry will be more evident.

I would, therefore, only recommend choosing a diamond with a Very Good Symmetry grade. Such diamonds include flaws that can only be seen face-up at 10x magnification. Diamonds with only Good Symmetry grades, on the other hand, might exhibit symmetry flaws that can be viewed with the unaided eye. Such diamonds will never receive an Excellent Cut grade.

Of course, you can still find a stone with only a Good Symmetry grade that doesn’t impact the light performance in a negative way, and it would be 10%-15% cheaper than a diamond with Excellent Symmetry, but it would be more of a gamble.

Factors that Influence the Symmetry Grade of a Diamond

1. Out-of-Round

An out-of-round diamond deviates from the normally round diamond shape insofar as the width differs from the length. While a perfectly round diamond would have the exact amount of mm both in width and in length.

For “Excellent” symmetry, GIA allows a deviation of 0 – 0.9% in the width-length variance. And a deviation of more than 0.9% will be reason enough to classify the diamond into “Very Good” symmetry. This flaw might have a negative impact on all the other facets of a diamond.

2. Table Off-Center

The table is considered off-center if one table edge is further away from the table center than another table edge. Gemologists measure the direct distance between the table center and the outline center and then compare it to the average diameter. So, for a diamond to fall within an “Excellent” symmetry grade, the deviation must be under 0.6%. Otherwise, the grade will be reduced to “Very Good.”

3. Culet Off-Center

A culet is considered to be off-center when the culet deviates from the central position of the pavilion. And a diamond with a culet that is off center to the naked eye should be disregarded.

If the direct distance between the culet center and the outline center projected into any horizontal plane such as the table deviates more than 0.6% from the average diameter, it will only receive a “Very Good” symmetry grade.

4. Table/Culet Alignment

The Table/Culet alignment flaw refers to the misplacement of the table facet and culet in the opposite direction.

It is measured as the direct distance between the table center and the culet center projected into the table plane as a percentage of the average diameter. If the distance is more than 0.9% of the average diameter, the symmetry grade will be downgraded to “Very Good.”

5. Crown Height Variation

A crown height variation refers to differing crown height measurements. In a perfect diamond, the crown height should always be the same. However, due to a wavy girdle or the table and girdle not being parallel to each other, crown heights vary.

6. Crown Angle Variation

The crown angle variation refers to the crown angles being unequal. Such a crown angle variation is usually the result of an off-center table.

It’s simply measured as the difference between the maximum and minimum crown angle values in degrees. If the difference is more than 1.2 degrees the diamond’s symmetry grade will be downgraded to “Very Good.”

7. Pavilion Depth Variation

The pavilion depth variation refers to differing pavilion depth measurements. Usually, such differing measurements are a strong indicator of a wavy girdle. It’s measured as the difference between the maximum and minimum pavilion depth values. If this difference surmounts 1.2% of the average diameter, the grade will be downgraded to “Very Good.”

8. Pavilion Angle Variation

The pavilion angle variation refers to the pavilion angles being unequal. This is usually related to the diamond’s culet being off-center.

If the difference is more than 0.9 degrees the diamond’s symmetry grade will be downgraded.

9. Girdle Thickness Variation

A girdle thickness variation refers to a variation of the girdle thickness at bezel positions. The bezel position is to be found where the crown of a diamond meets the girdle.

It is measured by the difference between the minimum and maximum girdle thickness values measured at bezel positions. If the difference is more than 1.2% of the average diameter, it will be downgraded to “Very Good.”

10. Table Size Variation

The table size variation refers to differing table size measurements. This is due to the table not being octagonal.

It is measured by the difference between the minimum and maximum table size values. If this difference surmounts 1.2% of the average diameter, the stone’s symmetry grade will be downgraded.

Conclusion

All things considered, the overall cut grade is still the main factor when choosing a diamond. If you can’t decide between two Excellent cuts with ideal proportions, you may use symmetry as a deciding factor but never the sole determinant.

And if your budget is on the line, ask yourself if the pricier “excellent symmetry” is worth the small bump in the diamond’s light performance. But if you’re mainly interested in symmetry for ideal purposes, then go for excellent – heck, even a hearts and arrows diamond to suit your perfectionist eye.