Fourcault process the pit must be "heated back" and then the process can continue anew. Glass chemistry has a huge impact on the process since it controls the melting, forming and annealing temperatures, liquidus temperature (point where various chemicals that make up the glass start to crystallize out of the glass) and rates of change of characteristics of the glass itself. Occasionally the ribbon will break or crack, leading to failure of the drawing process. Such breaks, known as "checks" can be alleviated by using proper operating parameters. Sometimes an expedient measure, using a portable source of heat, can be used to
Glass-ceramic-to-metal seals equivalents including more refractory behaviour, in addition to their ability to seal successfully to many different metals and alloys. They have been used in electrical feed-through seals for such applications as vacuum interrupter envelopes and pyrotechnic actuators, in addition to many applications where a higher temperature capability than is possible with glass-to-metal seals is required, including solid oxide fuel cells. In the formation of a glass-ceramic-to-metal seal, the parts to be joined are first heated, normally under inert atmosphere, in order to melt the glass and allow it to wet and flow into the metal parts, in much the same