Fused glass consists mainly of silica. 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 . 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.  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.

(from Wikipedia)