Used to describe size and number of inclusions in a diamond. Most cannot be seen by the naked eye and require magnification to become apparent. Large inclusions interfere with the dispersion of light and therefore the diamond's brilliance. The larger or more numerous the inclusions the less valuable the diamond. The fewer the inclusions, the rarer the stone. VVs, Vs and Si inclusions are not visible to the naked eye, they are only visible through magnification.
While many diamonds appear colorless, or white, they may actually have subtle yellow or brown tones that can be detected when comparing diamonds side by side. Diamond color grades start at D and continue through the alphabet. The closer a diamond is to being colorless, the rarer and more valuable it is. Although the presence of color makes a diamond less rare and valuable, some diamonds come out of the ground in colors - well defined reds, blues, pinks, greens, and bright yellows.
The weight of a diamond is measured in carats. One carat is divided into 100 "points" so that a diamond of 25 points is described as a quarter of a carat or 0.25 carats. The larger the diamond the more expensive per carat it will be. The Carat measurement of a diamond is actually a measurement of the Diamond's weight rather than its size or diameter. This is important to remember as depending upon the proportions of the Cut of the diamond. Diamonds are sometimes cut in shallow proportions.
The cut gives each diamond its unique sparkle and brilliance. Diamonds may be cut in different shapes with the most common shapes being round. When a diamond is cut to ideal proportions, light is reflected from one facet to another and then dispersed through the top of the stone. If a diamond is cut too deep, some light escapes through the opposite side of the pavilion. If the cut is too shallow, light escapes through the pavilion before it can be reflected.