Fused glass is referred to as warm glass, since it is cooked in a kiln at temperatures ranging from 1100 to 1500 degrees F. Okay, that is hot but not as hot as blown glass, which goes into a furnace and is heated to around 2100 degrees. Stained glass, since heat isn’t needed to make the pieces, is called cold glass. The specific origins of glass making are lost to history, but there is evidence that glass fusing began at least 4000 years ago in Mesopotamia and was subsequently perfected by the Egyptians. With the development of glass blowing approximately 2000 years ago, fusing fell out of favor and was pretty much ignored until late in the 20th century. In the US, particularly in the 60s, the growth of the studio glass movement generated renewed interest in fusing. With the establishment in the 80s of fusing glass manufacturers, which provided artists with readily available and consistent materials, interest in fusing grew quickly.
Today, glass used in fusing is manufactured in sheets that are about 20-22 inches wide by 30-35 inches tall. These sheets are made when the ingredients for the glass (including, for some colors, gold – it’s expensive to buy and make) are heated and poured by hand from a huge ladle onto a conveyor belt – it’s an awesome procedure to see! Window glass (or float glass, as it’s called) can be fused but incompatibility can be a problem. If the glass doesn’t expand and contract at the same rate during the heating and cooling process, you can end up with a broken mess. For glass to be fused successfully, the pieces have to have the same coefficient of expansion (COE). As my favorite high school teacher used to say, “It all boils down to physics.”
I cut these glass sheets by hand to the shapes I want, depending on my designs. Typically, for a full fuse, I start with two layers of cut glass stacked in an electric kiln. Sometimes I add frit (ground glass bits), thin rods of glass and certain metals or other inclusions in my designs. The glass is heated to melt the pieces together and then cooled slowly – a process called annealing — so the piece doesn’t cool unevenly and break. The result is a flat piece of glass. If I want a textured effect, I may add smaller pieces of glass and fire again at a lower temperature. In order to form the glass into a plate or bowl, a technique which is called slumping, another firing at a lower temperature is required. Pendant lights are made in a process called draping, which is trickier than slumping. Each of these processes can take 20 or more hours of kiln time, depending on factors such as glass thickness and effects desired. Needless to say, my local power company loves me.