Patent ID: 8640498

Claim:
A method for producing alkali-free glass sheets by a downdraw process comprising: (A) 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, and CaO, and, on an oxide basis, has: (i) a Σ[RO]/[Al 2 O 3 ] ratio greater than or equal to 1.0, where [Al 2 O 3 ] is the mole percent of Al 2 O 3 and Σ[RO] is the sum of the mole percents of MgO, CaO, SrO, and BaO; and (ii) a MgO content greater than or equal to 1.0 mole percent; (B) producing the glass sheets from the melted and fined batch materials; wherein: (a) on an oxide basis, the glass making up the glass sheets comprises at most 0.005 mole percent As 2 O 3 ; (b) on an oxide basis, the glass making up the glass sheets comprises at most 0.005 mole percent Sb 2 O 3 ; (c) SnO 2 is used in the fining and the glass making up the glass sheets has an SnO 2 content which in mole percent on an oxide basis satisfies the relationship: 0.01≦SnO 2 ; and (d) the glass making up the glass sheets has a liquidus viscosity that is greater than or equal to 100,000 poise.