Patent ID: 6878652

Claim:
A glass composition, comprising: a. SiO 2 70 to 75 weight percent b. Na 2 O 12 to 15 weight percent c. K 2 O 0 to 5 weight percent d. CaO>9 weight percent e. MgO<4 weight percent f. Al 2 O 3 0 to less than 1.6 weight percent g. SO 3 0 to 1 weight percent h. Fe 2 O 3 0 to less than 0.65 weight percent wherein SiO 2 +Al 2 O 3 ≧70 weight percent Na 2 O+K 2 O 12 to 15 weight percent CaO+MgO 12 to less than 13.4 weight percent CaO/MgO 2.33 to 5 wherein the glass composition has a log 2 viscosity in the range of about 2570° F. to about 2590° F. (1410° C. to 1421° C.) and a log 4 viscosity in the range of about 1850° F. to about 1894° F. (1010° C. to 1034° C.).