Milling time during the fine grinding of fused mullite and mullite-corundum powders in a vibromill instead of a ballmill can be reduced by a factor of five. The addition of sulfite lye or ethyl silicate in amounts of 0.1% reduces by a factor of 12–18 the vibromilling time, but iron pickup is increased. Grinding in a jet mill causes the specific surface to be much less than milling in a vibromill; the capacity for sintering such powders is impaired.