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 knife Glass knife A glass knife is a knife with a blade composed of glass. The cutting edge of a glass knife is formed from a fracture line, and is extremely sharp. Glass knives were used in antiquity due to their natural sharpness and the ease with which they could be manufactured. In modern electron microscopy, glass knives are used to make the ultrathin sections needed for imaging. Beginning in the Stone Age, glass knives (and other tools, such as arrowheads) were produced through a process known as knapping or lithic reduction. Although such bladed tools were often made of stone,