Tipsheet: Know Your Rocks
Diamonds are priced according to four major factors: color, cut, clarity, and carat weight, known as "the four C's."
Color: Colorless diamonds are graded on a scale of D to Z, ranging from truly colorless to barely yellow. The highest grades, D, E, and F, are genuinely colorless. G to J are near-colorless, K to M are faint yellow, and N to Z are very light yellow. Prices drop accordingly until you get to Z. (Note: Even the lowest-grade diamonds will look colorless to the untrained eye, especially under incandescent light; daylight and special diamond lamps are more revealing.) After Z-grade stones, you move into a completely different category: diamonds with truly noticeable color (like fancy yellow diamonds or J.Lo's pink rock), which are the rarest kind of diamond and are very expensive. Jewelers like Tiffany will not sell colorless diamonds with a grade lower than I, but most dealers stock stones through grade L.
Cut: Cut refers to the faceting of a diamond, which is calculated to produce maximum brilliance. When the cut is ideal, all light that enters a stone is refracted from facet to facet and through the top, and no light is lost. Emerald- and cushion-cut stones do not have as many facets as the "brilliant" cuts (round, princess, heart, oval), so they sparkle less.
Clarity: Almost all diamonds have natural flaws or inclusions. The highest-clarity grade is "flawless," but as soon as a stone is set, minor imperfections appear on its surface, and it becomes "internally flawless." Very, very slight imperfectionsgraded VVS1 and VVS2are extremely difficult to see under ten-power magnification. Ones that are very slightVS1, VS2are easier to detect under magnification. Slight inclusionsSI1, SI2are defects you can just about see (with magnification). But remember: All these flaws are often hard to spot when a diamond is set, except on I1 or I2 stones, which have fairly obvious inclusions.
Carat: A carat is one fifth of a gram. Each carat is in turn divided into 100 parts, called points. Small side-stones are often described in terms of points.
From the 2003 New York Wedding Guide