A rotating mold has a plurality of air channels that communicate with a cavity formed in the mold. Silica grain is deposited in the rotating mold and then formed into the shape of a crucible having a lower portion that comprises a substantially uniformly thick wall. An upper portion of the grain is formed into a substantially narrowed wall portion about the perimeter of the formed shape. The silica grain is heated, and a pump draws gas through the air channels while the silica fuses. There is a pressure drop across the narrowed wall portion. After fusing, the upper portion of the crucible, including the narrowed wall portion, is cut off.