After sorting, the diamonds are cut and polished. In ancient times, diamonds were left uncut and mounted into their settings, which gave each piece a dark, deep, mysterious look. In the 1400's diamonds started to be cut and polished, which gave them their telltale sparkle and brilliance.

Currently cutting and polishing take place in southern Africa, Belgium, China, India, Israel, Russia and the US, among other countries. Cutting a rough diamond takes great skill. A well-cut diamond reflects light within itself, from one facet to another, as well as through the top of the diamond, bringing out its spectral brilliance. The most popular cut is the 57 facet round brilliant.

After a stone has been cut, it is then polished and classified again, this time by its cut, color, clarity and carat weight, also known as the "Four Cs."

Cut: The art of polishing a diamond is to maximize its brilliance and fire (dispersion). A diamond that is cut too deep or too shallow will be less brilliant and ultimately, less valuable. The cut is the only factor of a polished diamond's value that is controlled by human hands.

Color: With diamonds, even the smallest variation in color can make a big difference. Colorless diamonds are the most popular, but nature has also created diamonds in all colors of the rainbow. All other 'Cs' being equal, the rarer the color, the more valuable the diamond is.

Clarity: Most diamonds contain naturally occurring inclusions, which developed while they were forming in the earth. The number, type, size, position and brightness of these inclusions can affect the clarity of a diamond, although most are too small to affect the beauty or brilliance of a stone.

Carat: As with all precious stones, the weight – and therefore the size – of a diamond is expressed in carats. One carat (equivalent to 0.2 grams) can be divided into 100 'points'.