Patent ID: 8763429

Claim:
A method for producing alkali-metal free glass sheets by a downdraw process comprising selecting, melting, and fining batch materials so that the glass making up the sheets comprises SiO 2 , Al 2 O 3 , B 2 O 3 , MgO, CaO and BaO, and, on an oxide basis, comprises: (i) a MgO content greater than or equal to 2.0 mole percent; (ii) a CaO content greater than or equal to 3.0 mole percent; (iii) a BaO content greater than or equal to 1.0 mole percent; and (iv) a SiO 2 content greater than or equal to 64.0 mole percent; wherein: (a) the glass satisfies, and said mole percent contents are limited by, the relationships: (i) a Σ(MgO+CaO+SrO+BaO)/(Al 2 O 3 ) ratio greater than or equal to 1.15, and (ii) [MgO]:[CaO]:[SrO+BaO]=1±0.15:1±0.15:1±0.15, where Al 2 O 3 , MgO, CaO, SrO, and BaO represent the mole percents of the respective oxide components; (b) the fining is performed without the use of substantial amounts of arsenic; and (c) a population of 50 sequential glass sheets produced by the downdraw process from the melted and fined batch materials has an average gaseous inclusion level of less than 0.10 gaseous inclusions/cubic centimeter, where each sheet in the population has a volume of at least 500 cubic centimeters.