The GIA Colour Scale extends from D (colourless) to Z (light yellow or brown). Although many people think of gem quality diamonds as colourless, truly colourless diamonds are actually very rare. Most diamonds used in jewellery are nearly colourless with tints of yellow or brown.
The GIA Clarity Scale includes eleven clarity grades ranging from Flawless to I3. Because diamonds form under tremendous heat and pressure, it is extremely rare to find a diamond that lacks any internal and external characteristics. These characteristics are a by-product of its formation and help gemologists separate natural diamonds from synthetics and simulants, and identify individual stones.
The GIA Cut Scale ranges from Excellent to Poor. GIA provides a cut quality grade for standard round brilliant diamonds that fall in the GIA D-to-Z colour range.
A polished diamond’s beauty lies in its complex relationship with light; how light strikes the surface, how much light enters the diamond, and how, and in what form light returns to your eye.
The result is a magnificent display of three attributes. Brightness is the combination of all white light reflecting from the surface and the interior of a diamond. Fire describes the “flares” of colour emitted from a diamond. Scintillation describes the flashes of light you see when the diamond, the light, or the observer moves.
One carat equals 200 milligrams in weight. For diamonds under one carat, each carat is divided into 100 points – similar to pennies in a dollar. 0.75ct. = 75 points, ½ ct. = 50 points.