Diamond grading in order to assess overall diamond quality uses the standards as set by the GIA’s “4 C’s”: Color, Clarity, Carat, and Cut.
Color: Diamond color actually refers to the absence of color. The less color present, generally the higher the value of the diamond. Most diamonds have some color due to chemical impurities within the crystal structure of the stone. These colors are usually yellow, gray, or brown, though rare trace elements can cause fancy colors, such as blue. The scale at which diamond color is sorted is: D, E, F = Colorless; G, H, I, J = Near colorless; K, L, M = Faint color; N, O, P, Q, R = Very light, S, T, U, V, W, X, Y, Z: Light; Beyond Z = Fancy, with varying degrees dependent on hue, tone, and saturation.
Clarity: Diamond clarity is measured by the absence or presence of inclusions, with consideration given to their size, nature, position, color or relief. Because diamonds are creations of nature it is important to remember that the parameters represent a range. The rarest and highest clarity is Flawless (FL), in which no inclusions or blemishes are visible at 10x magnification. Internally Flawless (IF), is the next range in which no inclusions and only blemishes are visible. Very, Very Slightly Included (VVS1 & VVS2) represents diamonds in which inclusions are very difficult to see. Very Slightly Included (VS1 & VS2) have inclusions that are minor and may range from difficult to somewhat easy to see. Slightly Included (SI1 & SI2) have noticeable inclusions. Lastly, the lowest clarity range is considered Included (I1, I2, & I3) in which inclusions are obvious and may even obstruct transparency and brilliance.
Carat: Refers to the weight of the stone. It is measured by 100 points to a carat. Generally speaking, all other factors equal, the higher the carat weight, the higher the value of the stone.
Cut: Refers to the quality of the faceted style of the diamond, with considerations are taken to the measurements and proportions that ultimately affect how light enters and exits the stone. Cut directly affects the patterns of light and dark areas in the diamond as observed by the brilliance, scintillation, and fire of the stone. The grading categories are: Excellent, Very Good, Good, Fair, and Poor.