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When you’re evaluating a diamond, there are two important characteristics that make up a diamond’s finish. One is polish and the other is symmetry.

Polish has to do with the overall condition of a diamond’s surface (i.e. smoothness). Symmetry refers to the diamond’s proportions. It encompasses things like exactness of shape, placement and alignment of facets and overall outline of the diamond.

What You Didn’t Know About Symmetry

Its definition is straightforward enough, but here’s what you didn’t know: A diamond’s symmetry is a behind-the-scenes predictor of its cut quality. So if you see a diamond with an “excellent” or “ideal” cut, it must also have “very good” or better symmetry, according to GIA standards.

If all other parameters indicate that a diamond should be designated “excellent cut,” but its symmetry is “good,” that diamond will be labeled as “very good” instead of “excellent.” This is how important symmetry is to a diamond’s overall value. A diamond can only ever receive a cut grade that is one level above its symmetry.

Is Excellent Symmetry Perfect?

When you’re evaluating a diamond, remember that some flaws are a sign of its natural beauty. Just like people, all diamonds are flawed in one way or another. An excellent symmetry rating means that your diamond has some very minor flaws that are barely detectable.

What You Should Know About Symmetry Flaws

Because diamonds are cut to exacting specifications, it’s easy to believe that symmetry flaws are a sign of a poorcut. This is almost never the case. In fact, cutting mistakes are extremely rare.

To understand symmetry flaws, we must first understand that every diamond cutter’s goal is to extract the maximum value from every rough diamond. Sometimes, you must sacrifice a bit of symmetry to get more value from the stone. These are very calculated decisions.

You may prefer a diamond with “excellent” cut and someone else may prefer a larger carat size. There is demand for diamonds of all shapes, sizes and symmetries. This is why diamond cutters may focus on carat size for one cut and symmetry for another. Diamond cutters may also sacrifice symmetry for a more marketable diamond. There is more value in a 1.00 carat diamond with “good” symmetry than a 0.96 carat diamond with “excellent” symmetry.

There are essentially two categories of symmetry flaws.

  • Proportional – Proportional flaws affect the alignment and balance of a diamond’s facet structure. These flaws impact the diamond’s overall appearance and include flaws like:
    • Off-center culet – The area where pavilion mains meet is off center
    • Off-center table – The table facet does not appear centered
    • Table/culet alignment – Table and culet aren’t properly positioned
    • Crown angle variation – There’s significant variation in the crown angles
    • Pavilion angle variation – There’s significant variation in the measured pavilion angles
    • Girdle thickness variation – There are variations in girdle thickness around the rim
    • Out of round girdle outline – A round diamond may have squared-off area
    • Wavy girdle –The girdle takes on a wavy appearance.
    • Facet-Related Flaws – These flaws have to do with the normalization of individual facets. When there’s a facet-related flaw, similar facets may not be cut to equal sizes and regularity. Some examples of facet-related flaws include:
      • Missing or extra facets – Facets are placed or removed without regard to symmetry to remove inclusions
      • Misshapen facets – Facets are of unequal shape and/or size
      • Truncated facets – The facet’s points don’t end properly at the girdle
      • Table not a regular octagon – Table facet is unequal
      • Non-pointing – Facets don’t meet at a single point
      • Misalignment of crown and pavilion facets – Bezel and pavilion mains are in the wrong places, which may or may not cause a wavy girdle

Diamond symmetry is one of many factors to evaluate when deciding on a diamond. Once you understand how diamond symmetry is graded, you can determine which grades are acceptable for your diamond.

GIA Symmetry Ratings Explained

  • Excellent – No or minute flaws that are difficult to detect under 10x magnification
  • Very Good – Minor flaws that can be found in the face-up view under 10x magnification
  • Good – Noticeable flaws under 10x magnification
  • Fair – Obvious symmetry issues under 10x magnification
  • Poor – Obvious symmetry issues that you can see without magnification

 

 

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