crucible can be heated with an induction coil 6 the outer crucible 1 is suspended on a water coded flange 7 the inner crucible 2 is suspended on a tubular shaft 8 which in accordance with an advantageous embodiment is rotatable as indicted by corresponding arrows by means of a shaft suspension 9 which is adjustable in height the shaft and the inner crucible can be adjusted with respect to their height relative to the outer crucible in this way it is possible to adjust the distance of the nozzle 10 of the outer crucible relative to the nozzle 20 of the inner crucible the crucibles can be loaded through glass rods 30 40 these glass rods which for example have a diameter of 4 mm to 10 mm are slowly inserted into the crucibles the glass rod 40 is inserted into the inner crucible through the tubular shaft 8 the crucible nozzles can be closed off by means of a seal not illustrated as soon as the glass melts have been brought to the drawing temperature this seal is removed so that a light conducting fiber 11 can be drawn a drawing drum 15 is provided for this purpose a thickness measuring device 12 can.