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The Gemological Institute of America (GIA) is a nonprofit institute based in Carlsbad, California. It is dedicated to research and education in the field of gemology and the jewelry arts. [1] Founded in 1931, GIA's mission is to protect buyers and sellers of gemstones by setting and maintaining the standards used to evaluate gemstone quality.
Diamond color grading chart. Refers to a grading scale for diamonds in the normal color range used by internationally recognized laboratories (GIA, IGI, & GCAL by Sarine for example). The scale ranges from D which is totally colorless to Z which is a pale yellow or brown color.
Gem identification is basically a process of elimination. Gemstones of similar color undergo non-destructive optical testing until there is only one possible identity. Any single test is nearly always only indicative. For example: The specific gravity of ruby is 4.00, glass is 3.15–4.20, and cubic zirconia is 5.6–5.9 . So one can easily ...
By the 1970s, the GIA Gem Trade Laboratory staff was examining large numbers of gemstones, including the grading of diamonds and the identification of colored stones and pearls. Sensing the need for a group of scientists who would focus on the many emerging technical challenges in gemology, Liddicoat formally established the current GIA ...
International Gemological Institute (IGI) is a gemological organization which certifies diamond, colored stone and jewelry. It was established in 1975 in Belgium. [1] On May 21, 2023, Blackstone Group announced their acquisition of IGI. [2]
Clarity grading in coloured gemstones is based on the eye-clean standard, that is, a gem is considered flawless if no inclusions are visible with the unaided eye (assuming 20/20 vision). [29] The Gemological Institute of America classifies tanzanite as a Type I gemstone, meaning it is normally eye-clean.
It is advised to check the references for photos of reaction results. [1] Reagent testers might show the colour of the desired substance while not showing a different colour for a more dangerous additive. [2]
When using the chart, it is important to remember these tips: Isotropic and opaque (metallic) minerals cannot be identified this way. The stage of the microscope should be rotated until maximum colour is found, and therefore, the maximum birefringence. Each mineral, depending on the orientation, may not exhibit the maximum birefringence.