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The Gemological Institute of America, short GIA, generates certificates for diamonds and gemstones that are accepted worldwide. Since 1931, the institute has been active in the research, teaching and grading of gemstones. In addition to its headquarters in California, the GIA has another 14 offices worldwide. Based on the institute, the 4 C's (colour, clarity, cut, carat) were developed and defined for the classification of diamonds. These are now used worldwide to classify gemstones. The Institute was founded by the jeweller Robert M. Shipley, given that most jewellers had little knowledge of diamonds and only traded on the basis of trust and experience. Through research, gemological instruments and education, the founder wanted to professionalise the industry. The GIA certificate for diamonds gives information about the cut shape, the measurements in millimetres, the weight in carats and the colour using the introduced scale of D-Z. The certificate also gives information about the clarity and the size of the diamond. It also provides information on the polish (evenness of the surface) and symmetry. The certificate for coloured gemstones, in contrast, only provides information on the weight, dimensions, cut, colour and transparency, as well as whether the stone is natural or artificial.

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