glass t liq is the highest temperature above which no crystalline phases can coexist in equilibrium with the glass in another aspect the viscosity corresponding to the liquidus temperature of the glass is greater than about 150 000 poise more preferably greater than 200 000 poise and most preferably greater than 250 000 poise in another aspect the disclosed glass is characterized in that t 35 k u2212 t liq gt 0 25 t 35 k u2212 225 u00b0 c this ensures minimum tendency to devitrify on the forming mandrel of the fusion process in one aspect the substantially alkali free glass comprises in mole percent on an oxide basis sio 2 50 85 al 2 o 3 0 20 b 2 o 3 0 10 mgo 0 20 cao 0 20 sro 0 20 bao 0 20 where al 2 o 3 mgo cao sro bao represent the mole percents of the respective oxide components in a further aspect the substantially alkali free glass comprises in mole percent on an oxide basis sio 2 68 74 al 2 o 3 10 13 b 2 o 3 0 5 mgo 0 6 cao 4 9 sro 1 8 bao 0 5 where al 2 o 3 mgo cao sro bao represent the mole percents of the respective oxide components in one aspect the disclosed glass includes a chemical fining agent such fining agents include but are not limited to sno 2 as 2 o 3 sb 2 o 3 f cl and br and in which the concentrations of the chemical fining agents are kept at a level of 0 5 mol or less chemical fining agents may also include ceo 2 fe 2 o 3 and other oxides of transition metals.