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-to-metal seal glass on the metal. If the contact angle is low (good wetting) the surface of the glass is everywhere under compression stress like an enamel coating. Ordinary soda-lime glass does not flow on copper at temperatures below the melting point of the copper and, thus, does not give a low contact angle. The solution is to cover the copper with a solder glass which has a low melting point and does flow on copper and then to press the soft soda-lime glass onto the copper. The solder glass must have a coefficient of thermal expansion which is equal or a