Abstract: An improved purified vitreous silica body is made at high temperature by applying a polarizing potential across the boundary surfaces of the vitreous silica body or vessel to cause migration of impurities of ions away from one of the boundary surfaces thereof while the silica body is held at 1000 degrees centrigrade and during the cooling until the body is less than 800 degrees centrigrade whereby alkali ions move to one boundary of the silica body.