Purity is the measure of the number and size of the small imperfections that may occur in most diamonds, many of which are microscopic and do not significantly affect the beauty of a daimond. The diamonds with the least number of imperfections receive the higher grades.
Colour refers to a diamond's lack of colour, grading the whiteness of a diamond. A colour grade of D is the highest possible, while Z is the lowest. Taking the GIA colour scale comparison, D represents the higher possible grade, while Z the lowest.The colour in the diamond is a light yellow, thus the least colour is visible, the highest the grade.
Cut is a diamond's most important characteristic. It has the greatest overall influence on a diamond's beauty. It determines what we generally think of as sparkle. Of the Four Cs, no other characteristic has a greater influence on a diamond's appearance. When a diamond is cut with the right proportions, light is returned out of the top of the diamond (which gemmologists refer to as the table). If it is cut too shallow, light leaks out of the bottom; too deep and it escapes out of the side.
Carat is the the unit of weight for diamonds and it's equals to 0.200 grams.I IA diamond's cut grade should also be considered because, as we noted in the cut grade section, when a diamond is cut with the proper proportions, the maximum amount of light (or sparkle) is returned out of the top of the diamond. Thus, when a diamond is well cut, the light reflected out of the top makes it appear larger. In addition, much of the weight of a poorly cut diamond, for example, may be "hidden" in the base of the diamond, making the diamond appear smaller than its carat weight would imply.