The laboratory of the Gemological Institute of America (GTL GIA) and its branches in New York and Los Angeles (USA) are the most respectable centers. Moreover, well-known centers include:

  • International Diamond Council (HRD), Antwerp, Belgium;

  • Gemological Association Laboratory (GAGTL), London;

  • European Gemological Laboratory (EGL);

  • International Gemological Institute (IGI), Belgium, USA, etc.;

  • Laboratory of the American Gemological Society (AGS), Las Vegas;

  • Israel Gemological Laboratory (IDI, former GILI), Ramat Gan.

   Many countries have cetrification centers and gemological laboratories. For example, according to certificate a stone can be graded in terms of the GIA system, but in a Japanese laboratory. Most of the laboratories use one of the following three grading systems:

  • GIA System

  • HRD System

  • CIBJO System

   Each of the systems is based on a specific method and employs specific nomenclature. The back side of a certificate often contains the tables of conversion of one grading system into another. Such conversion is easy since the boundaries of all color and clarity ranges used in these systems coincide. However, different laboratories can derive different grades for the diamond quality.

   Diamond certificates issued by one or another laboratory are variously rated in different countries and even by different dealers. As a rule, a diamond is certified one time only, therefore, it is important to choose a proper certification organ. The cost of certificaiton depends on the authority of the laboratory and commonly ranges within 1-5% of the diamond value. Thus, the price of a certified diamond is higher than that of a noncertified one. At the same time, liquidity of a certified diamond is also higher. There is no reason for certification of small diamonds and cheap ones. A certification laboratory usually receives stones more than 0.47 ct (GIA more than 0.21 ct). Big wholesale lots and mounted diamonds are rarely certified. Synthetic, treated, and composite diamonds are not certified. Specimens of GIA and IGI Certificates.