Diamonds can have internal characteristics known as inclusions or external characteristics known as blemishes. Diamonds without inclusions or blemishes are rare; however, most characteristics can only be seen with magnification.
A stone is said to be flawless if, under 10-power magnification, no internal flaws (clouds, feathers, pinpoints) and no external imperfections (scratches, pits, nicks) are visible. Absolutely flawless diamonds are exceedingly rare and priced accordingly. Gem-grade diamonds are given a clarity rating based on an industry-standard scale.
The clarity scale of the Gemological Institute of America ranges from Fl (flawless) to I3 (many inclusions visible without magnification.)
Clarity, like color, is a measurement of rarity, not beauty. And in the absence of magnification, the less rare SI1 is visually identical to the higher clarity grades, but significantly less expensive, so…
The precise shape and positioning of a diamond’s facets—determines the stone’s general appearance and its beauty. Gem diamonds are properly proportioned and cut to achieve the ideal balance of brilliance, dispersion and scintillation.
Of all the 4Cs, cut has the greatest effect on a diamond’s beauty. In determining the quality of the cut, the grader evaluates the cutter’s skill in the fashioning of the diamond. The more precise the cut, the more captivating the diamond is to the eye.
“Carat” denotes the weight of a diamond. One carat equals 0.20 grams
There are five carats in a gram, and a “point” is 1/100th of a carat. For example, a 50- point diamond is half a carat. As a general rule, larger diamonds are rarer and therefore more valuable. But size does not determine beauty and brilliance. Two stones of the same carat weight can have very different values. Color and Clarity are also measurements of rarity, and Cut is extremely important when it comes to beauty.
Diamonds are graded on the color scale from D (colorless) to Z (light yellow). The most expensive diamonds are found at either end of the scale, due to their rarity. But don’t confuse rarity with beauty. Colorless is rare. Highly colored is more rare, and consequently, more valuable. Diamonds with a trace amount of color are just as beautiful, but less rare, making them a better value.