How Optical Symmetry Differs from Physical Symmetry
Symmetry is one of those things that can cause your diamond flower band ring to appear flawless, and so it is a desirable trait in any stone you get. There are 10 different symmetry parameters for diamonds as recognized by GIA.
- Girdle thickness variation
- Out-of-round
- Culet off-center
- Table off-center
- Table size variation
- Table/culet alignment
- Crown angle variation
- Crown height variation
- Pavilion angle variation
- Pavilion depth variation
Physical and Optical Symmetry
It is easy to think that if all of the above symmetry parameters were perfect, then the diamond would look symmetrical. However, there is another thing called the azimuth, where more defects can sometimes be found.
If the diamond’s azimuth shifts, this would come up as a twist in the facets. A ‘twisted’ diamond will be able to pass the above tests and still look asymmetrical when you look at it from a hearts & arrows viewer.
The twisting mentioned here is also called ‘yaw’, and it happens when the cutter has to take off material unevenly. This is usually done in order to cover up other defects, which would harm the physical symmetry of the stone. Among cutters, this is often called ‘cheating’ the lab test.