When glass is heated above 1200 degrees it becomes as soft as taffy.With more heat glass softens to a honey-like consistency as parts liquefy and fuse together into a singular form.
Fusing is, at its most basic, stacking two or more layers of glass in a kiln and heating the glass until it is blended or joined into a single unit. It is then cooled down through an annealing process.
Different effects or levels of fusing are achieved by adjusting the temperature and length of time the glass is in the kiln. However in order to fuse successfully, the glass pieces must be compatible with one another, meaning the glass will expand and contract at the same rate when it is heated and cooled. This is known as the
co-efficient of expansion (COE)