If the diamond is not certified, there is a good chance you may be buying a stone that is one or more grades below stated values in terms of carat weight, color, clarity, or cut. Without a certificate, issued by a reputable agency, such as GIA, AGS, or EGL, or HRD, a buyer relies on a jeweler’s integrity that the diamond’s 4C parameters are accurate and not overstated.
A lack of a certificate may be a clue that the diamond has been “enhanced” and the jeweler knows an inspection would reveal the diamond’s true condition, as well as indicate how the compromised diamond might erode.
Several well-known grading agencies in the United States and Europe have high reputations:
Gemological Institute of America (GIA)
American Gemological Society (AGS)
European Gemological Laboratory (EGL)
Diamond High Council (HRD, which is an abbreviation of the Dutch “Hoge Raad voor Diamant”)
International Gemological Institute (IGI)
International Confederation of Jewelry, Silverware, Diamonds, Pearls, and Stones (CIBJO)