High static fatigue alumina isopipes

Isopipes (13) for making a glass or a glass-ceramic using a fusion process are provided. The isopipes are made from an alumina material which has a higher static fatigue than existing alumina materials intended for use as isopipes. In particular, the alumina materials have times-to-failure (static fatigues) of greater than one hour at 1200°C at an applied stress of 10,000 psi. These high levels of static fatigue allow alumina isopipes to replace zircon isopipes in the manufacture of high performance glass sheets by the fusion process, including glass sheets which are incompatible with zircon isopipes but compatible with alumina isopipes, e.g., chip and scratch resistant glass sheets which have high alkali contents.