n 2 he ar etc cf 4 or any other f dopant may also be added to the input if fluorinated sio 2 is desired it has been demonstrated that sio 2 powder can be delivered to a burner by flowing a carrier gas through a container of powder assuming a capture efficiency of about 30 passing 3333 grams of soot through the burner will generate 1000 grams of high purity fused silica glass typically 6 grams per minute of sio 2 powder is delivered to the burner about 2 hours is allowed to pre heat the furnace 40 and 9 3 hours of laydown time 3333 grams 6 grams min for a total run time of about 11 3 hours as the sio 2 powder contained in the nitrogen soot stream passes through the burner and enters the flame envelope it is heated to the point where it will vitrify immediately as it is deposited in a pre heated cup 42 supported on a turntable base 48 as shown in the drawings the burner is mounted on the furnace crown 44 the furnace further includes a ring wall 45 vent 47 and furnace frame 49 the burner is lit and the furnace is pre heated by conventional means not shown to at least 1625 deg c crown temperature before the n2.