diamond polish and symmetry | certified diamonds | GemTrove

Diamond's Polish & Symmetry

While not seen as important as the diamond 4 C’s, the polish and symmetry of stone are vital in both the appearance and pricing of any jewellery item. Polish is the smoothness of each, individual facet found in the stone, while symmetry is the degree to which the shape itself is geometrically perfect. If these two are of poor quality, the diamond’s visual brilliance will severely impact.

Diamond Polish

During the polishing process, the stone fixed into one place, then smoothed over with a polishing wheel. If not taken with the utmost care, this wheel can drag picked up crystals (similar to wood grains when using sandpaper) along the edge of the stone. These will leave scratch marks, professionally known as a defect, and in some cases, can also leave pits and cavities, if severe enough.

The Gemological Institute of America has graded the quality of the diamond polish into five categories, ranging from excellent to poor. A polish condition that is deemed excellent will show no defects at all under 10x magnification, while a poor quality polish will have defects that you do not require magnification to see. Many jewellery outlets, such as Gemtrove, refuse to offer stones that fall into the poor category.

While fair polished diamonds may contain traces of defects that you can see, these often attributed to low-quality stones with several inclusions. Due to this, a stone that falls into the fair category of polishing can sometimes have the defects masked due to the inclusions present. An example of this is black diamonds, where a large number of inclusions that create its distinctive colour easily hide the polishing defects.


The theory behind diamond symmetry has been engineered to reflect both how the facets line up and how it best reflects light back into the eye. Ideally, the light should enter and exit at direct and opposite points of the table of the diamond. A diamond without perfect symmetry may slightly angle the exiting light or completely refract it through the other side, similar to a prism. The light reflection, known as brilliance, is one factor in determining the price-per-carat of a stone.

Symmetry is graded similarly to polish - excellent, very good, good, fair, and poor - and is also based on obvious defects visible under 10x magnification. This is one of the many reasons why both symmetry and polish are linked. However, it is quite common to find exceptional clarity diamonds with fair or poor symmetry grades. It is recommended that symmetry only is considered for those seeking fire and brilliance as a priority.

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