The National Association of Goldsmith (N.A.G.) was established in 1894 to serve and support the Jewellery Industry of Great Britain and Ireland. The Association promotes high professional standards among its membership to inspire consumer confidence and t
Testing a gemstone on a refractometer prism, when the stone has a greater refractive index than the measuring prism of the device, or higher than the refractive index of immersion liquid used for optical contact, the scale of refractometer remains dark an