Of the all gemstones found in the nature the diamond is perhaps the most popular and desired gemstone. Four criteria determine the value of a diamond. And these are known in the trade as four Cs: Color, Clarity, Cut and Carat. A diamond should be colorless or deeply colored; it should be free from flaws and inclusions; it should be cut according to the dimensions that give it the best luster and be without scratches; and the greater its weight, the more expensive it becomes. These considerations also determine in general, the value of any precious gemstone.
The ever increasing demand for gems has often resulted in imitation being sold as genuine. Modern science has also developed techniques to synthesize gemstones, thereby doing in a few hours or days, what nature took several thousands of years to accomplish. Besides, treatment techniques to improve the appearance of poor quality gems have been perfected, so increasing the trade and its payback. The possibility of making large profits by substituting an imitation or cheap synthetic stone in place of a real gem has encourage crime. To assure the customer that he is not being cheated, trade associations have devised many sophisticated tests to identify a genuine stone and thought it is somewhat difficult to know if a gem has been improved by present day sophisticated processes. This can be done with some degree of certainty. Such tests are expensive and so are used mainly on large and expensive gemstones where the cost of testing is small compared to the value of the stone itself.