The fewer imperfections or irregularities, the greater the diamond's value. A diamond's imperfections are usually microscopic and invisible to the naked, untrained eye. Carat is the weight of the stone. A carat is equal to 200 milligrams, and there are 142 carats to an ounce. The cost of a diamond increases significantly when it reaches the full, one-carat weight since larger stones are more rare and limited in supply.
Color is the natural hue of the stone.
Truly colorless diamonds are extremely rare and, therefore, the most expensive. Most diamonds have a trace of yellow or brown, although this is normally very subtle. Stones are graded by color on a scale from D to Z, with D being colorless and the most valuable. If you're buying a fine diamond over one carat, you should make sure you receive a diamond grading report, or certificate, which is normally issued by the Gemological Institute of America. This report not only certifies the stone's genuineness, but provides a rating of each of the critical factors affecting quality and value.