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Ultrasonic Cleaning - this is a method used by jewelers to clean jewelry. The tank or ultrasonic bath is filled with a liquid cleaning solution and employs ultrasonic vibrations which breaks up the dirt/film on the jewelry.
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Ultra Violet Light - electromagnetic radiation having wavelengths which range from just beyond the violet end of the visible spectrum at roughly 380 nm down to the longest X-ray wavelengths at around 20 nm. Because of the visible emission peaks in the mercury discharge lamps and low-pressure mercury vapor lamps used to reduce UV light for gem testing, thes lamps are filtered to produce light at 365 nm (LW UV) and 254 nm (SW UV).
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Unakite - a type of granite rock containing quartz, pink feldspar and green epidote, usually cut in cabochon form or tumbled.
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Upper Girdle Facets - the triangular facets adjacent to the girdle on the crown (upper portion) of a brilliant-cut stone.
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Uranium Glass - a yellow glass, also called canary glass, sometimes used as a gemstone simulant.