When you are planning to purchase a diamond it is important that you know as much as possible about how diamonds are classified. Today, the 4Cs of diamond quality is the universal method for assessing the quality of any diamond, anywhere in the world. Moreover, there's the "Fifth C" : Certificate

When it comes to grading diamonds, the "cut" is a grade of diamond's reflective qualities- not the diamond's shape.

A good cut gives a diamond its brilliance, which is that brightness that seems to come from the very heart of a diamond. Thus, Diamond cut is perhaps the most important of the 4Cs. Precise artistry and workmanship are required to fashion a stone so its proportions, polish and symmetry deliver the dazzling and magnificent return of light that is only possible in a diamond. GIA calculates the proportions of the facets that influence the diamond's face-up appearance; these proportions allow diamond graders to evaluate how successfully a diamond interacts with light to create desirable visual effects such as;

Brightness:
Internal and external white light reflected from a diamond.


Fire:
The scattering of white light into all the colors of the rainbow.


Scintillation:
The amount of sparkle a diamond produces, and the pattern of the light and dark areas caused by reflections within the diamond.


Grades:

- Excellent
Cut Reflects nearly all light that enters the diamond. An exquisite and rare cut.


- Very Good
These diamonds reflect most of the light that enters them, creating a good deal of brilliance. With these diamonds, the cutters have chosen to stray slightly from the preferred diamond proportions in order to create a larger diamond.


- Good
Diamonds that reflect much of the light that enters them. Their proportions fall outside of the preferred range because the cutter has chosen to create the largest possible diamond from the original rough crystal. Represents roughly the top 25% of diamond quality based on cut. Reflects most light that enters. Much less expensive than a very good cut.


- Fair & Poor
A diamond’s graded as fair or poor when it reflects only a small proportion of the light that enters it. Typically these diamonds have been cut to maximize the carat weight over most other considerations.