US Patent 7585801 Gray glass composition

A glass composition that includes a base glass composition including: SiO2 from 65 to 75 weight percent, Na2O from 10 to 20 weight percent, CaO from 5 to 15 weight percent, MgO from 0 to 5 weight percent, Al2O3 from 0 to 5 weight percent, K2O from 0 to 5 weight percent and BaO from 0 to 1 weight percent, and a colorant and property modifying portion including total iron from 0.5 to 0.8 weight percent, Er2O3 from 0.05 to 0.5 weight percent, Se from 1 PPM to 4 PPM, and CoO from 1 PPM to 15 PPM, wherein the glass composition has a redox ratio ranging from 0.25 to 0.35.