Abstract: A method of controlling blister formation in a glass melt flowing through a system comprising one ore more refractory metal vessels by developing a blister index and determining the critical blister index value. The critical value of the blister index may be used to control the principal variables responsible for blister formation, including the water content of the melt, the concentration of reduced multivalent oxide compounds in the melt, and the hydrogen partial pressure of an atmosphere in contact with the outside surface of the refractory metal vessel. Also disclosed is a minimum partial pressure of hydrogen necessary to produce an essentially blister-free glass article in a glass essentially free of arsenic and antimony.