Abstract :
ALTHOUGH glass can be ground, sawed, and drilled in the solid state, its hardness is such that many operations are performed most easily on glass which has been reheated to a plastic state. From early antiquity, fire and heat have been used for sealing, moulding, and joining glass parts together. Flame heating applications are limited by inherent disadvantages — flame heating is surface heating; steep temperature gradients occur which sometimes boil away volatile constituents; and flame heating is difficult to restrict into sharply localized paths without excessive sacrifice in heat.
