Experimental evidence has been obtained which shows that, in certain instances, it may be preferable to use a high-voltage arc in lieu of the conventional flame for sealing in hard glass T-6 1/2 bulbs and stems. By use of this arc-sealing technique it is possible to heat a highly restricted area of glass, at the periphery of the part being sealed, to its working temperature in an extremely short period of time, thereby limiting the total quantity of heat used and, consequently, reducing the maximum temperature within the tube structure. This technique, therefore, offers the dual advantages of reduced oxidation and heat distortion of the internal structure as well as elimination of contamination often introduced by flame-combustion products.