Lightweight, high refractive index glasses for spectacle lenses

摘要

A glass having a high refractive index, preferably 1.77, and a low specific gravity, preferable 3.8, is provided for utilization as spectacle lenses. The glass consists essentially of 80 mol percent or more of light cationic oxides with the remainder being cationic oxides having a greater molecular weight. It has a high crystallization stability in a viscosity range 200 poises and an expansion coefficient 10.sup.7 between 20-300 C. of . ltoreq.100. Sufficiently light in weight to be well-suited for use as spectacle lenses, the glass can be continuously produced, as it has no pronounced tendency toward crystallization. The resulting corrective optical lenses have relatively high dioptric values, even with small center and edge thicknesses.