Abstract: The thermal or mechanical damage to diamond occurs possibly during the various stages of cutting and polishing. The mechanical damage to diamond is related to the internal stress-induced fissure under the high temperature. The different styles of anomalous birefringence can be observed in diamond with internal strain. Those diamonds can be picked out under the polarized microscopy so that they are cut specially. During the stages of cutting and polishing, heat accumulation can lead to burn marks on the surface of diamond. This kind of thermal damage can be prevented by using supersaturated solution of borax in the process of diamond cutting.