Diamond Cut Color
Diamond cut, color, clarity and carat comprise the four "C"s for rating diamonds.
Diamond cut should maximize brilliance. If the diameter of the cut diamond is 100, the face should be cut to 53-62 and the diamond height cut to 60. Cut as such, light entering the face of the diamond makes two 90 degree turns and exits the face of the diamond ("ideal cut" on the right). If the diamond cut is too deep, the light reflects at an angle too obtuse and exits through the side ("deep cut"). If the diamond cut is too thin, the light passes through without reflecting ("thin cut").
Diamond colors use the alphabetic characters from D to Z to rate the lack of yellowish tint. Diamond colors visibly yellow are rated S to Z, with Z being the darkest, even though all of them are called, "light yellow". Lighter yellowish diamond colors are rated N to R and called "very light yellow", while diamond colors whose yellowish tint is barely noticeable are rated K to M and called, "faint yellow".
All other clear diamonds appear completely colorless to the naked eye, yet are still rated. Diamond colors that appear slightly yellow under magnification are rated G to J and called, "near colorless", while those that appear colorless even under magnification are called "colorless" but still rated D to F.
Diamonds' sizes are measured in carats, which is actually a unit of weight; 1 carat is equal to 0.2 grams (0.007 ounces). The size of diamonds for rings start under 1 carat and the price rises exponentially after the first carat or so.