When a person buys diamonds, he looks for many things. The overall finish of the diamonds can attract or distract the buyer and thus symmetry of the diamond become one of the most important factors. The exactness of shapes and the way of arrangement of facets is what is referred to as ‘symmetry’. The natural, extra, tables, culets, and misshapen facets are included in this. The person who does not know about the symmetry will never be able to make out the difference between a symmetrical and an asymmetrical diamond. If you are buying lower grade diamonds, the symmetry will not be a big concern.
When buying higher-grade diamonds, symmetry plays an important role. Just like the polish grades, the grades for symmetry are Excellent, Very Good, Good and Poor. People most often purchase the diamonds that have Good symmetry grade. This is due to the beautiful appearance of these diamonds. You should avoid buying the diamonds that have symmetry from fair to poor.
When the diamonds are sent to the labs for grading, they are checked with the help of microscopes to see if the facets have perfect symmetry or not and then grading is done. The highly skilled cutters also make mistakes and end up creating diamonds that are not symmetrical. Very few diamonds are excellently symmetrical.
The placement of the table (the largest facet on a diamond) should be centered at the top of the stone and needs to be parallel to the girdle. If the table is off-center or not parallel with the girdle this can cause uneven crown angles from one side to the other. In this example we see the unbalanced appearance that occurs from an off-center table.
To check if the culet is centered, look at the diamond in the face-up position. You’ll see the lower girdle facets through the table. If the lines formed by them look like a perfect square, the culet is centered. If the cross bends one way or the other, the culet is not centered. In this example we see what an off-centered culet might look like.
Table & Girdle Not Parallel
Here we see another example of what occurs when the table is not parallel with the girdle. As you see, the crown angle is much more steep on one side versus the other. From the top view you may have noticed an off-center table.