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U Edit 6 terms found

U
A grade in GIA’s Color Grading System…. at the beginning of the “Light Yellow” category.
Ultraviolet Fluorescence
The property in diamonds that makes them glow in ultraviolet light. Also known as photoluminescence. Ultraviolet light is high frequency, short wavelength electromagnetic radiation, between visible light and X-rays.
Uncut or Unpolished Diamonds
Diamonds that are usually referred to as “rough” or “diamond rough”… diamonds are they are found in the earth. It applies to all diamonds that have not been cut and polished yet.
Uni-Directional Rotating Bezel
Introduced in the 1980s, this elapse time bezel is often found on divers’ models, and only moves in the counterclockwise direction. Thus, protecting the diver from an erroneous (and potentially dangerous) reading when measuring decompression times, since any accidental movement could only err on the side of safety.
Unmounted
A faceted diamond which is loose, not set into a piece of jewelry.
Upper Girdle Facets
These are 16 triangular shaped facets, that are located on the crown just above the girdle.