Valuable coloured gemstones come with a certificate that confirms all of the important details of the stone, such as colour, weight, shape, cut and proportions, including proof of whether it has a natural colour (NTE) or not. Rare or valuable coloured stones have a certificate that confirms their origin. Certificates that are not issued by a known institute are meaningless. Laboratories of worldwide acclaim include: the GIA (Gemmological Institute of America) in Carlsbad California, the SSEF (Swiss Gemmological Institute) in Basel, the Gübelin in Luzern and the GRS (Gem Research Swiss Lab).