Because cut is so important, several grading methods have been developed to help consumers determine the cut of a particular diamond. In general, these grades are: ideal, premium, very good, good, fair and poor.
Most diamonds contain some inner flaws, or inclusions, that occur during the formation process. The visibility, number and size of these inclusions determine what is called the clarity of a diamond. Diamonds that are clear create more brilliance, and thus are more highly prized, and priced.
Diamonds are graded for clarity under 10x loupe magnification. Grades range from flawless (diamonds which are completely free of blemishes and inclusions), to included 3 (diamonds which possess large, heavy blemishes and inclusions that are visible to the naked eye).
Colorless diamonds are the most desirable because they allow the most refraction of light (sparkle). Off white diamonds absorb light, inhibiting brilliance.
When jewelers speak of a diamond’s color, they are usually referring to the presence or absence of color in white diamonds. Color is a result of the composition of the diamond, and it never changes over time.
Because a colorless diamond, like a clear window, allows more light to pass through it than a colored diamond, colorless diamonds emit more sparkle and fire. The formation process of a diamond ensures that only a few, rare diamonds are truly colorless. Thus the whiter a diamond’s color, the greater its value.
Diamonds graded G through I show virtually no color that is visible to the untrained eye.
Fancy color diamonds do not follow this rule. These diamonds, which are very rare and very expensive, can be any color from blue to green to bright yellow. They are actually more valuable for their color.
To grade ‘whiteness’ or colorlessness, most jewelers refer to GIA’s professional color scale that begins with the highest rating of D for colorless, and travels down the alphabet to grade stones with traces of very faint or light yellowish or brownish color. The color scale continues all the way to Z.