| 摘要 |
An optical crown glass of low dispersion and a refractive index within the range 1.53-1.68 comprises up to 78% (preferably 14-78%) boron orthophosphate, 6-84% barium and/or strontium pyrophosphate, and up to 48% (preferably 2-48%) of an oxide component selected from one or more of alkali or alkaline earth metal oxides and the oxides of Al, Zn, Cd, La, As, Sb, Pb, and Bi. The purified raw materials are melted at a temperature within the range 1200-1300 DEG C. Many examples of the composition are given.
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