Diamond Polish & Symmetry: 6 Points You Should Know

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You can’t go far in learning about diamond grades without coming across the 4Cs. Cut, color, clarity, and carat weight are of course the most crucial aspects for grading a diamond. However, there are other criteria that have a large impact on a diamond’s grade. Two of these criteria are diamond polish and symmetry. Here are six questions you should know the answers to if you want to understand your diamond’s polish and symmetry grades.

What are the scales for grading polish and symmetry?

Diamond graders use a fairly simple scale to evaluate the quality of a diamond’s polish and symmetry. The scale for both criteria runs: Excellent, Very Good, Good, Fair, and Poor.

Why are diamond symmetry and diamond polish so important?

Polish and symmetry influence cut grade, and cut grade has the greatest impact on a diamond’s price. The difference between Excellent and Very Good polish and symmetry can translate to a 10-12% difference in a diamond’s price. They also affect the appearance of a diamond. Polish and symmetry can either greatly enhance or detract from a diamond’s sparkle.

What is diamond symmetry?

The symmetry a diamond grader is looking for is a perfect alignment of the crown (top) and pavilion (bottom) of a diamond where they meet at the girdle.

A chart of asymmetrical diamonds. Photo credit: GIA
A handy chart for recognizing different types of asymmetrical diamonds. Photo credit: GIA.

While diamond symmetry may not be easily apparent to the naked eye, it has an important effect on a diamond’s internal structure. Think of diamond symmetry like a piece of IKEA furniture or an origami box. They both might look fine on the outside, but a lack of structural integrity can cause them to collapse from the inside.

The same goes for a diamond; if a diamond is asymmetrical, its facets “collapse” in on themselves. This causes the stone to lose a great deal of sparkle, because an asymmetrical diamond won’t reflect light as well as a diamond with an Excellent symmetry grade.

How are diamonds polished, and who polishes them?

Polishing occurs during the diamond cutting process. For the majority of polish jobs, a diamond cutter uses a polishing wheel, which is somewhat like a sander. Instead of sandpaper, though, a polishing wheel uses finely ground industrial-grade diamonds to “sand” the loose diamonds to a polish.

Diamond cutting process

In some cases a diamond cutter will use a hand polish rather than a polishing wheel. This occurs when a diamond is already in position to have exceptional grades across the 4Cs, and thus the potential to be especially high value.

Is an Excellent diamond polish grade difficult to achieve?

Yes, diamond polishing is an incredibly difficult skill to master. The table is where polishing mistakes happen most often; it is also the flattest and most visible part of a diamond. A diamond cutter must try to achieve the best and most even polish possible without polishing down too much of the stone’s table.

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The difference between a 1 carat diamond and  a 0.99 carat diamond can happen during a polish, so the pressure is on when a diamond cutter needs to polish a diamond that is already high value.

Can you tell a diamond’s polish or symmetry grade just by looking at it?

If you are looking at a diamond without magnification and under artificial light, it can be difficult to tell how it ranks for polish and symmetry. If you take your diamond outside into natural light, though, you’ll have a better chance of seeing the nuances of its facets and sparkle. You can also use a magnifying loupe of 10x or more to take a closer look at your diamond’s symmetry and polish.

Diamond polishing wheel marks

You can feel the quality of your stone’s polish grade better than you can see it. Flaws in a diamond’s polish are felt as small ridges, raised streaks, or indentations on the table. Once again, a magnification of 10x or more will reveal any polish anomalies on your diamond.

Polish and symmetry are instrumental in determining a diamond’s appearance, price, and grade. Do you want to know your diamond’s polish and symmetry grades? You can find them under the “Additional Grading Criteria” section on any GIA report. Feel free to share any additional questions and photos of your well-polished diamonds in the comments below!