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optical flint

noun
  1. an optical glass of high dispersion and high refractive index containing lead oxide. They are used in the manufacture of lenses, artificial gems, and cut glassAlso called: flint glass
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012