While cutting and finishing a diamond two factors play a major part of the finish: Polish and symmetry. Symmetry is the arrangement, size, and shaping of diamond's facets. Diamonds are cut in various flat planes along the surface. These are called facets. It is because of the placement of the facets that a diamond sparkled and shine. Symmetry is angles and lines that form the placement of the facets. Precision is the most important aspect.
In today’s time, diamonds are cut to the point of accuracy using advance equipment. However, at times the diamond cutter might make a slight symmetry imperfection during the finishing of the diamond so as to avoid another kind of inclusion. Being a subset of diamond cut grade, symmetry is also graded. These grades are scaled considering how accurately and cleanly diamond facets have been cut and placed in relation to each other. Low symmetry grades can have a negative effect on a diamond’s sparkle and its ability to hide inclusions. Though symmetry is only a subset, it can still hinder the visual appearance of the diamond.
Symmetry can have and impact of around 10 to 15% on the diamond’s pricing.
Similar to other attribute, even symmetry is graded on a scale standardised by GIA. The grades are as follows:
Excellent: This implied perfect symmetry and alignment of the facets in relationship to the location of the girdle, crown, culet, table etc.
Very Good:For this grade the proportions and alignment is near perfect. There might be a slight alignment error which is unnoticeable.
Good: Here the size or location of characteristics and facets are slightly disproportionate, that might hinder the appearance and the sparkle of the diamond.
Fair:Here the disproportions are more apparent and can be visually detected. It is recommended to avoid these diamonds.
Excellent symmetry grades carry higher premium. Though there is only a slight difference between excellent and very good and good each grade difference can impact the price by 5% to 10%.
Types of Symmetry Defects:
- Out of round: Circle of the round cut is not perfect and ratio of length to width is 1.10 and more.
- Table off centre: Table facet is slightly off centre moving towards the corners.
- Culet off centre: The tapering bottom of the diamond is not aligned with the center.
- Table Culet Alignment are dis proportionate
- Crown and pavilion is not aligned properly.
- Wavy girdle: Girdle is not is straight alignment which can affect the evenness of the diamond.