A good cut enables a diamond to make the best use of light. A fully cut diamond has 58 facets, which are small, flat, polished surfaces cut into a diamond. When a diamond is in proper proportion, light is reflected from one facet to another and then dispersed through the top of the stone. Cuts that are too deep or too shallow allow light to escape before reflecting through the top of the stone.
A diamond is the only stone in which the absence of color makes the stone more valuable. A colorless diamond acts as a prism to form a rainbow of colors, commonly called “fire”. The scale below shows the color range from colorless to a degree of yellow tint. Visible differences between one grade of color and the next grade are very subtle.
Diamonds can be found in all shapes and sizes. The size of a diamond is determined by its weight in carats. A carat is divided into 100 points, so a diamond of 75 points is .75 carats or 3/4 carat. Larger diamonds are more rare, and command a higher price. While size is an obvious factor in determining the value of a diamond, bigger is not necessarily better, all 4 “C’s” should be considered.
Most diamonds contain inclusions. Inclusions are natural birthmarks and considered nature’s fingerprints on the diamond. A diamond’s clarity is determined under 10 power magnification by a trained eye, taking into account the number, size, type, and location of the inclusions. The fewer inclusions in a diamond, the more valuable it is.
Read more about "The Four C's" at The GIA