Diamonds are easiest to understand by breaking down its features into four C's: clarity, color, cut, and carats.
Clarity refers to tiny, natural imperfections, usually not visible to the unaided eye, that occur in all but the finest diamonds.
FL, IF • Flawless, Internally Flawless
Flawless: No internal imperfections.
Internally Flawless: No internal or external imperfections.
VVS1, VVS2 • Very, Very Slightly Included
Very difficult to see imperfections under 10x magnification. An excellent quality diamond.
VS1, VS2 • Very Slightly Included
Imperfections are not typically visible to the unaided eye.
SI1, SI2 • Slightly Included
Imperfections are visible under 10x magnification, and may be visible with the unaided eye.
I1 • Included
Minor inclusions that may be visible to the unaided eye.
After cut, color is the second most important feature to consider when purchasing a diamond. The human eye detects the diamond's sparkle first, and the color second. The less color a diamond has, the higher the color grade.
DIAMOND CUT & SHAPE
A diamond's cut determines how much it will sparkle. Diamond shapes are available in a variety of cut grades, ranging from Ideal to Poor. A very good cut will reflect light that enters the diamond, while a poor cut would be a shallow or narrow diamond that will lose light.
The 58-facet round brilliant cut is the most popular because of its fire and brilliance, which is due to precise mathematical calculations.
The cut of a diamond refers not only to the shape of the diamond and number of facets, but also to the quality of the cut. A diamond with uneven or poorly proportioned facets won't be given the same grade of cut as an ideally proportioned and masterfully cut stone.
A diamond's weight is measured in carats. Diamonds can range in size from a fraction of a carat to several carats. Given the rarity of large stones, however, the price of a diamond will quickly increase with size. It is rare to find a very large diamond with good color and clarity. To understand diamond size, consider carat weight and the diameter of the stone across the top (mm) and the diamond's cut grade.