The diamond certificate guarantees the authenticity of the diamond. In other words: the document confirms that the stone described is indeed a natural diamond and not an imitation or a synthetic. The certificate furthermore contains a complete quality description of the diamond. These quality, characteristics determine the value of the stone.
The certificate mentions: shape, weight, clarity grade, flourescece, colour grade, measurements, proportions and finish grade, and additional comments if applicable. It also contains a drawing of the stone on which the most important characteristics are shown. The main quality characteristics are reffered to as the 4 C's: Carat, Clarity, Colour and Cut.