WHAT IS DIAMOND CERTIFICATE ? Diamond certificate can check details of diamonds, including diamond color, carat, clarity, and its cut grade. You should never buy a diamond without a certificate. Laboratories with more well known, including the Gemological Institute of America (GIA), International Gemological Institute (IGI). Diamond Certficate Diamond certificate can check details of diamonds, including diamond color, carat, clarity, and its cut grade. You should never buy a diamond without a certificate. Laboratories with more well known, including the Gemological Institute of America (GIA), International Gemological Institute (IGI). The value of diamonds will be priced according to their quality, and that is the public awareness of 4Cs, color, Clarity , cut and carat weight. Relations between four quality properties is used to determine the value of a diamond. Four of them, carat weight affects the price more than the rest of the color, clarity and cut.