Grading of Precious Stones

the last two decades there has been a proliferation of certification for gemstones. There are a number of laboratories which grade and provide reports on diamonds. As there is no universally accepted grading system for colored gemstones, only one laboratory, AGL (see below) grades gemstones for quality using a proprietary system developed by the lab.

International Gemological Institute (IGI), independent laboratory for grading and evaluation of diamonds, jewellery and colored stones.

Gemological Institute of America (GIA), the main provider of education services and diamond grading reports

American Gemological Society (AGS) is not as widely recognized nor as old as the GIA.

American Gem Trade Laboratory which is part of the American Gem Trade Association (AGTA) a trade organization of jewelers and dealers of colored stones.

American Gemological Laboratories (AGL) which has been taken over by "Collector's Universe" a NASDAQ listed company which specializes in certification of collectables such as coins and stamps

European Gemological Laboratory (EGL).

Gemological Association of All Japan (GAAJ), aka Zenhokyo, Japan, active in gemological research

Gemmological Institute of Thailand (GIT) is closely related to Chulalongkorn University

Asian Institute of Gemmological Sciences (AIGS), the oldest gemological institute in South East Asia, involved in gemological education and gem testing

Swiss Gemmological Institute (SSEF), founded by Prof. Henry Hänni, focusing on coloured gemstones and the identification of natural pearls

Gübelin Gem Lab, the traditional Swiss lab founded by the famous Dr. Eduard Gübelin. Their reports are widely considered as the ultimate judgement on high-end pearls, coloured gemstones and diamonds

Each laboratory has its own methodology to evaluate gemstones. Consequently a stone can be called "pink" by one lab while another lab calls it "Padparadscha". One lab can conclude a stone is untreated, while another lab concludes that it is heat treated. To minimise such differences, seven of the most respected labs, i.e. AGTA-GTL (New York), CISGEM (Milano), GAAJ (Tokyo), GIA (Carlsbad), GIT (Bangkok), Gübelin (Lucerne) and SSEF (Basel), have established the Laboratory Manual Harmonisation Committee (LMHC), aiming at the standardisation of wording on reports and certain analytical methods and interpretation of results. Country of origin has sometimes been difficult to find agreement on due to the constant discovery of new locations. Moreover determining a "country of origin" is much more difficult than determining other aspects of a gem,

Gem dealers are aware of the differences between gem laboratories and will make use of the discrepancies to obtain the best possible certificate