Cut is often classified in the 4 C’s as the shape such as a Round Brilliant, Pear, Oval, Princess, Asscher, Emerald etc. This is only the foundation of understanding the cut of a diamond. When referring to a Round Brilliant, there are recognized proportions that are considered to be more desirable than others. This is how “Cut” can add value to the diamond. It is often said that Cut is the most important ‘C’ of all because this will ultimately dictate how the light moves within the diamond. The best way to understand how cut can affect a diamond’s performance is to look at the diamond facet as a series of windows and mirrors and that a beam of light is being bounced around inside the diamond. A well cut diamond will be able to keep the light within the diamond until it is finally shot straight up through the top of the diamond to the viewers eye. This is what causes the diamond to sparkle. A poorly cut diamond will lose light out the bottom of the diamond and not reflect it back through the top, thus leading to less light performance.

The correct terms for what the viewer sees or the ‘sparkle’ can be categorized in the following ways: Brilliance: the light reflected from the diamond, Fire: The dispersion of light or the rainbow color the view sees in the reflection, and Scintillation: the flashes of light or sparkle when the diamond is moved.

If a diamond is poorly cut, these attributes will not be as strong.  In a well cut diamond, the viewer will see lots of bright light being reflected back to the eye. This is also important when setting a grade for the diamond cut. The highest grade for a diamond cut is an “Excellent”. The cut grade scale is Excellent, Very Good, Good, Fair, Poor.

Diamond Cuts are graded on the following criteria:

Proportions: Proportions refer to the standard Round Brilliant diamond. Round Brilliants are the only cut of diamond that has industry standards in terms of proportions. Fancy cut diamonds such as Oval, Pear, Asscher, Emerald, Princess and the like do not have a standard proportion to grade upon, so they do not follow the industry standard criteria for Fancy Cut diamonds.

Polish: As most people know, diamond is the hardest material on earth. This means that diamonds can hold a polish like no other known substance. The quality of the craftsmanship of the diamond cutter will determine how well polished each and every facet on the diamond is and thus will affect the light performance of the diamond. An easy way to remember the polish is to think of each facet as a window. Think of how differently light passes through a freshly cleaned window versus a frosted window. A well polished diamond will reflect light and/or pass light at the most pristine transparency and reflection any substance on earth can.

Symmetry: Symmetry is very basic to understand. A Round Brilliant diamond has 57 or 58 facets. (58 if it has a culet). It is round and is fashioned in order to reflect the most light up through the table as possible. If a diamond is not symmetrical (all sides equal), it can be lop sided, heavy in the middle or deep in the pavilion and will not reflect the light beams back through the top as desired. If the symmetry of the cut is off, the diamond will not sparkle much as it would it was symmetrical.