The value of a diamond is determined by 4 quality factors. these were established in Amsterdam in 1975, during the congress of the World Federation of Diamond Bourses (WFDB) and the International Diamond Manufacturers Association (IDMA). It became known as the system of the 4 C’s, after the words Carat, Color, Clarity and Cut.
The larger the diamond and the finer the color, the higher its value is. The greater the clarity, the more beautifully and better cut, the more perfect it is.
Prices of diamonds are kept stable by regulating what flows into the market. The world stock is supposedly large enough to provide a cupful of diamonds for every inhabitant of the USA.