 Glass welding is a common practice during glassblowing . It is used very often in the construction of lighting , neon signs , <unk> , scientific equipment , and the manufacture of dishes and other glassware . It is also used during glass casting for joining the halves of glass molds , making items such as bottles and jars . Welding glass is accomplished by heating the glass through the glass transition , turning it into a thick , <unk> , liquid mass . Heating is usually done with a gas or oxy @-@ gas torch , or a furnace , because the temperatures for melting glass are often quite high . This temperature may vary , depending on the type of glass . For example , lead glass becomes a weldable liquid at around 1 @,@ 600 ° F ( 870 ° C ) , and can be welded with a simple propane torch . On the other hand , quartz glass ( fused silica ) must be heated to over 3 @,@ 000 ° F ( 1 @,@ 650 ° C ) , but quickly loses its viscosity and formability if overheated , so an <unk> torch must be used . Sometimes a tube may be attached to the glass , allowing it to be blown into various shapes , such as bulbs , bottles , or tubes . When two pieces of liquid glass are pressed together , they will usually weld very readily . Welding a handle onto a pitcher can usually be done with relative ease . However , when welding a tube to another tube , a combination of blowing and suction , and pressing and pulling is used to ensure a good seal , to shape the glass , and to keep the surface tension from closing the tube in on itself . Sometimes a filler rod may be used , but usually not . 
