Patent ID: 8127572

Claim:
A method of making a glass article comprising: melting a batch material comprising at least one multivalent oxide compound to form a glass melt having a total concentration of reduced multivalent oxide compound(s) and a water content; flowing the glass melt through a vessel comprising a platinum group metal, an atmosphere in contact with an outside surface of the vessel comprising a partial pressure of hydrogen pH 2 ; forming a glass article from the glass melt, the glass article comprising a concentration of a reduced multivalent oxide compound, a water content expressed as β OH, and a number of blisters per pound of glass; calculating a blister index (I b ), from the reduced multivalent oxide compound concentration, the β OH concentration and the partial pressure of hydrogen according to the equation: I b =(√pH 2.in −√pH 2.out )−KΣa i [M i b1+ ] where pH 2,in is the H 2 partial pressure in the melt, pH 2,out is the H 2 partial pressure in contact with the non-glass contacting side of the platinum group metal, and KΣa i [M i bT+ ] is the equivalent molar concentration of reduced multivalent oxide compounds capable of adsorbing O 2 wherein [M i ] is the concentration of reduced multivalent oxide i, a i is the number of moles of O 2 that can be adsorbed by one mole of the reduced multivalent oxide i, and K is a constant determined experimentally; repeating the melting, the flowing, the forming, and the calculating steps over a range of one or more process variables selected from the group consisting of the water content of the glass melt, the partial pressure of hydrogen in the atmosphere in contact with an outside surface of the vessel, and the total concentration of reduced multivalent oxide compounds in the glass melt; determining a relationship between the number of blisters per pound of glass and the blister index (I b ) to thereby calculate a critical value of the blister index (I bc ) over the range of process variables; and maintaining the blister index (I b ) below the critical value of the blister index (I bc ) by controlling the multivalent oxide compound in the batch material, the water content in the glass batch, and the partial pressure of hydrogen, or a combination thereof according to the determined relationship.