Diamond certificates, or certs, as they are known in the diamond industry, are often called the fifth C, in addition to the well-known 4Cs of diamond stones: carat weight, cut, colour, and clarity.
Several well-known grading agencies in the United States and Europe have high reputations:
Gemological Institute of America (GIA)
European Gemological Laboratory (EGL)
Diamond High Council (HRD, which is an abbreviation of the Dutch “Hoge Raad voor Diamant”)
International Gemological Institute (IGI)
GIA, based in the United States, is considered to be the industry standard and is the most widely used and trusted name in the diamond trade. HRD, EGL, IGI and BGI are not as well known in the United States as their American brethren, but certificate from any of these agencies is a solid proof that you the diamond is what it says it is.
GIA certificate explained:
Different company’s certificates contain the same information but some have more information than others. The most extensive certificate is the GIA certificate and this explains the terms and information given on the cert.