Fused glass

Fused glass is glass that has been fired (heat-processed) in a kiln at a range of high temperatures from 593 °C (1,099 °F) to 816 °C (1,501 °F). There are 3 main distinctions for temperature application and the resulting effect on the glass.

Firing in the lower ranges of these temperatures 593–677 °C (1,099–1,251 °F) is called slumping. Firing in the middle ranges of these temperatures 677–732 °C (1,251–1,350 °F) is considered "tack fusing". Firing the glass at the higher part of this range 732–816 °C (1,350–1,501 °F) is commonly described as a "full fuse".

All of these techniques can be applied to one glass work in separate firings to add depth, relief and shape.

While the precise origins of glass fusing techniques are not known with certainty, there is archeological evidence that the Egyptians were familiar with techniques ca. 2000 BCE. Although this date is generally accepted by researchers, some historians argue that the earliest fusing techniques were first developed by the Romans, who were much more prolific glassworkers. Fusing was the primary method of making small glass objects for approximately 2,000 years, until the development of the glass blowpipe. Glassblowing largely supplanted fusing due to its greater efficiency and utility.

While glass working in general enjoyed a revival during the Renaissance, fusing was largely ignored during this period. Fusing began to regain popularity in the early part of the 20th century, particularly in the U.S. during the 1960s. Modern glass fusing is a widespread hobby but the technique is also gaining popularity in the world of fine art.

Disparate pieces of glass must be compatible in order to ensure they can be fused properly. It is a common misconception that glasses having the same coefficient of expansion (COE) will be compatible. Coefficient of expansion is one indicator that glasses may be compatible, but there are many other factors that determine whether glasses are compatible. If incompatible glasses are fused together, it is unlikely that the fused piece will be able maintain structural integrity. The piece may shatter during the cooling process, or develop stress originating from the point of contact between the incompatible glasses over time, leading to fractures within the glass, and eventually breakage.

Generally, kiln-glass manufacturers will rate their glasses for compatibility with other glasses they make. In order to be certain that the glasses they use will be compatible, many glass fusers will adopt one manufacturer’s glasses to use exclusively.

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Wikipedia