A diamond certificate is the documented inspection and evaluation by an independant third-party, not the diamond buyer nor the seller.
Certification laboratories such as the internationally acknowledged GIA (Gemmological Institute of America), HRD (HRD Antwerp) and in Australia, GSL (Gem Studies Laboratory) are all independant laboratories who grade precious gemstones and diamonds.
During their inspection, the diamonds are given a Colour and Clarity Grading along with specific information noted about the Cut including measurements and Carat weights. In addition there is a diagram of the diamond which indicates any inclusions within the stone along with proportional measurements drawn to scale.
Any diamond, good or bad can be certified, and the majority of diamonds in Australia are in fact certified. It also has to be said that we may come across an amazing diamond from time to time that has not been certified. In this case we, as gemmologists can assess the stone and arrange for an independant certification to be completed on request.
Sample of GIA Diamond Report: