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
Building insulation cavities like the attic. This is beneficial in an actively cooled or heated building, but can be a liability in a passively cooled building; adequate provisions for cooling by ventilation or radiation are needed. Fibrous materials are made by tiny diameter fibers which evenly distribute the airspace. The commonly used materials are silica, glass, rock wool, and slag wool. Glass fiber and mineral wool are two insulation materials that are most widely used in this type. Cellular insulation is composed of small cells which are separated from each other. The commonly cellular materials are glass and foamed plastic like polystyrene,