Buying a significant diamond is likely to be one of the most important and expensive purchases you will make in your life. It is also a grand gesture of love, so it is natural to want the process to be as enjoyable as possible. You will no doubt encounter many different explanations and opinions on what to look for in a diamond but the essential rules you need to know are quite simple: diamonds are always graded to specific criteria. These are commonly known as "The 4C's" - this refers to: Cut, Colour, Clarity and Carat weight.