Fused glass is a term used to describe glass that has been fired (heat-processed) in a kiln at temperatures of 700 C to 900 C. Firing at lower temperatures is called slumping.

History

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While the precise origins of glass fusing techniques are not known with certainty, there is archeological evidence that the Egyptians were familiar with rudimentary techniques ca. 2000 BCE Gil Reynolds: The Fused Glass Handbook. Hidden Valley Books; Scottsdale, Arizona 1987, ISBN 0915807025. Although this date is generally accepted by all researchers, some historians argue that the earliest fusing techniques were first developed by the Romans, who were much more prolific glassworkers Boyce Lundstrom: Kiln Firing Glass. Vitreous Publications; Colton, Oregon 1983, ISBN 0961228237. 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 as well. 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 not widely used for large scale glass production.

Techniques

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Most contemporary fusing methods involve stacking, or layering thin sheets of glass, often using different colors to create patterns or simple images. The stack is then placed inside the kiln (which is almost always electric, but can be heated by gas or wood) and then heated through a series of ramps (rapid heating cycles) and soaks (holding the temperature at a specific point) until the separate pieces begin to bond together. The longer the kiln is held at the maximum temperature the more thoroughly the stack will fuse, eventually softening and losing its original shape. Once the desired effect has been achieved the kiln is vented briefly to stop the fusing process, then allowed to cool slowly over a period of 12 - 24 hours.

Finished products

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While fused glass techniques are generally used to create glass art and jewelry, the annealing process (which tempers the glass) allows the creation of larger, functional pieces like dishes, bowls, plates and ashtrays. Producing functional pieces generally requires 2 or more separate firings; one to fuse the glass and a second to shape it.

Since the 1970s, more hobbyists have focused on using kiln-fused glass to make beads and components for jewelry. This has become especially popular since the introduction of dichroic glass.

References

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Glass art