A glass composition is provided. The glass composition includes: 25-40 wt % SiO.sub.2; 2.5-10 wt % B.sub.2O.sub.3; 0-10 wt % Al.sub.2O.sub.3; 0-15 wt % Li.sub.2O; 0-16 wt % of Li.sub.2O, Na.sub.2O, and K.sub.2O in total; 10-25 wt % CaO; 0-15 wt % BaO; 0-5 wt % MgO; 0-5 wt % SrO; 10-30 wt % CaO, BaO, MgO, and SrO in total; 0-7 wt % ZnO; 2-10 wt % ZrO; 2-15 wt % TiO.sub.2; 5-25 wt % Nb.sub.2O.sub.5; 0-5 wt % Ta.sub.2O.sub.5; 5-25 La.sub.2O.sub.3; and 0-5 wt % Y.sub.2O.sub.3. The glass composition has a refractive index from about 1.74 to about 1.80, a density from about 3.5 g/cm.sup.3 to about 4.0 g/cm.sup.3, a critical cooling rate from about 1° C./min to about 50° C./min, and a liquidus viscosity greater than 25 Poises.

Methods of processing glass-based substrates to reduce birefringent defects and glass-based substrates are disclosed. In one embodiment, a method for processing a glass-based substrate includes rolling a glass-based material to form the glass-based substrate, and heat treating the glass-based substrate by increasing a temperate of the glass-based substrate, holding the temperature at a maximum temperature for a hold period, and then decreasing the temperature at one or more cooling rates, wherein after the heat treating, the glass-based substrate has a retardance over thickness of 5 nm/mm or less at locations outside of and including 5 mm from any corner of the glass-based substrate and outside of and including 5 mm from any edge of the glass-based substrate.

Methods of processing glass-based substrates to reduce birefringent defects and glass-based substrates are disclosed. In one embodiment, a method for processing a glass-based substrate includes rolling a glass-based material to form the glass-based substrate, and heat treating the glass-based substrate by increasing a temperate of the glass-based substrate, holding the temperature at a maximum temperature for a hold period, and then decreasing the temperature at one or more cooling rates, wherein after the heat treating, the glass-based substrate has a retardance over thickness of 5 nm/mm or less at locations outside of and including 5 mm from any corner of the glass-based substrate and outside of and including 5 mm from any edge of the glass-based substrate.

A glass composition is provided. The glass composition includes: 25-40 wt % SiO.sub.2; 2.5-10 wt % B.sub.2O.sub.3; 0-10 wt % Al.sub.2O.sub.3; 0-15 wt % Li.sub.2O; 0-16 wt % of Li.sub.2O, Na.sub.2O, and K.sub.2O in total; 10-25 wt % CaO; 0-15 wt % BaO; 0-5 wt % MgO; 0-5 wt % SrO; 10-30 wt % CaO, BaO, MgO, and SrO in total; 0-7 wt % ZnO; 2-10 wt % ZrO; 2-15 wt % TiO.sub.2; 5-25 wt % Nb.sub.2O.sub.5; 0-5 wt % Ta.sub.2O.sub.5; 5-25 La.sub.2O.sub.3; and 0-5 wt % Y.sub.2O.sub.3. The glass composition has a refractive index from about 1.74 to about 1.80, a density from about 3.5 g/cm.sup.3 to about 4.0 g/cm.sup.3, a critical cooling rate from about 1 C./min to about 50 C./min, and a liquidus viscosity greater than 25 Poises.