Cut
A diamond’s cut is the most important factor to be considered when purchasing a diamond. It not only refers to the diamond’s shape, but also to how effectively the diamond returns light back to the viewer’s eye. It is the quality that causes the diamond to sparkle and fire. A well-cut diamond will appear very brilliant and fiery, while a poorly cut diamond can appear dark and lifeless. Even if a diamond has a perfect clarity and color grade, if it has a poor cut, it may appear dull.
GIA has created a Diamond Cut Grading System for standard round brilliant diamonds. Each cut grade is based on a relative scale from Excellent to Poor considering the following components: brightness (the total light reflected from a diamond), fire (the dispersion of light into the colors of the spectrum), scintillation (the pattern of light and dark areas and the flashes of light, or sparkle, when a diamond is moved) weight ratio, durability, polish, and symmetry.

 

 

Color
Another important component taken into consideration when buying a diamond is color, as it is visible to the naked eye. A diamond's color has a significant impact on its value; the less color, the higher their value. Colorless diamonds are the rarest, so they are the most valuable. Diamond’s colors range from colorless to light yellow, to brown.  Color is graded on a scale from D-Z, with D being colorless and Z being light yellow.


Clarity
The term clarity refers to the internal characteristics diamonds contain, called inclusions or blemishes. The fewer and less visible the inclusions, the higher the clarity grade. In order to attain the most value in your diamond, it is suggested to purchase diamonds that are “eye clean,” where no internal flaws are visible to the naked eye. This includes diamonds that are graded VS2 or higher. The GIA Diamond Grading System assigns a clarity grade to a diamond that ranges from flawless (FL) to diamonds with obvious inclusions (I3).
Flawless (FL) - No inclusions or blemishes are visible to a skilled grader using 10× magnification
Internally Flawless (IF) - No inclusions and only blemishes are visible to a skilled grader using 10× magnification
Very, Very Slightly Included (VVS1 and VVS2) - Inclusions are difficult for a skilled grader to see under 10× magnification
Very Slightly Included (VS1 and VS2) - Inclusions are minor and range from difficult to somewhat easy for a skilled grader to see under 10x magnification
Slightly Included (SI1 and SI2) - Inclusions are noticeable to a skilled grader under 10x magnification
Included (I1, I2, and I3) - Inclusions are obvious under 10× magnification and may affect transparency and brilliance.

 

Carat Weight
Carat is a term that refers to the weight of a diamond. The carat is subdivided into 100 equal parts called “points.” One point equals 0.01 carat or 1/100 carat. A half‐carat diamond is 50 points and a one carat diamond equals 100 points. It's important to note that a diamond's carat weight does not equal size. When comparing diamond carat sizes, take a diamond's cut into consideration as well. A high-carat diamond with a poor cut grade may look smaller than a diamond with smaller carat weight and a better cut.