Brown-photochromic glasses

摘要

This invention is directed primarily to a composition for a photochromic glass which is essentially colorless in the undarkened state consisting essentially, expressed in terms of weight percent, of -SiO2 54-58 TiO2 0-2 PbO 0-0.8 -B2O3 18-22 ZrO2 2-4.5 Sb2O3 0-0.2 -Al2O3 7-8 Ag 0.155-0.175 Er2O3 0-0.5 -Li2O 3.75-4.5 Cl 0.3-0.4 Au 0-5 ppm -Na2O 0-1 Br 0.08-0.11 Pd 0.8-1.2 ppm -K2O 5.5-7.5 CuO 0.0065-0.01 - wherein the mole ratio Li2O:Na2O>/=9:1, said glass at a thickness of 2 mm exhibiting a coloration in the fully darkened state corresponding to the chromaticity coordinates, in accordance with the 1931 C.I.E. trichromatic colorimetric system, falling within area IJKLI in the appended drawing.