Anyone wanting to make an informed purchase of diamond jewelry needs at least a cursory understanding of the Four C's. These are the standards by which diamonds are graded, and ultimately determine their value. They are Cut, Color, Clarity and Carat weight. What follows is a brief description to acquaint diamond shoppers with these essential benchmarks. CARAT WEIGHT - Contrary to popular belief, a large stone alone does not a valuable diamond make! While bigger can be better, it's not the only.