Every diamond is unique, reflecting the story of its arduous journey from deep inside the earth to a cherished object of adornment. Yet all diamonds share certain features that allow us to compare and evaluate them. These features are called the 4Cs.
One carat equals 0.2 grams. For diamonds under a carat, each carat is divided into 100 points, similar to pennies in a dollar. For instance, 0.75ct. = 75 points and 1/2 ct. = 50 points.
The GIA Clarity Scale includes eleven clarity grades ranging from Flawless to I3. Because diamonds form under conditions of tremendous heat and pressure, internal inclusions and external blemishes are common and help gemologists identify individual stones. The Clarity Scale also helps separate natural diamonds from synthetics and simulants.
The GIA Color Scale extends from D (colorless) to Z (light yellow or brown). Although many people think of diamonds as colorless, most diamonds used in jewelry have subtle tints of yellow or brown. Each letter grade represents a range of color and is a measure of the degree of color within the diamond, all measured by comparing the diamond to a set of master stones.
A polished diamond's proportions affect the performance and interplay of light which, in turn, affects its beauty and desirability. Brightness is the combination of all white light reflecting from both the surface and interior of a diamond. Fire describes the colored flashes that can be seen in a diamond. And scintillation is the sparkle of light you see and the overall pattern of bright and dark areas when you look at a diamond face-up. The design and craftsmanship of a diamond also affect its cut quality, and these factors are considered in determining a diamond's GIA Excellent-to-Poor Cut Grade.
Many diamonds emit a visible light, called fluorescence, when exposed to ultraviolet radiation.