Warm Glass - Hot Stuff: Fused Glass Art

The term warm glass refers to the art of heating glass with a torch or in a kiln until the glass becomes tacky enough to stick to other glass and soft enough to be shapable. This happens at temperatures of 1,100 degrees F. to 1,700 degrees F.

This is in contrast to hot glass, which refers to processes of heating the glass up to temperatures of over 2,000 degrees, enough to make it molten.


Photo by Emerald Isle Designs

Artists can use this technique to create jewelry, sculpture or practical items like vases, platters and bowls. The introduction of reasonably-priced mini-kilns into the consumer market has fueled an explosion in the popularity of fused glass. In particular, many have chosen to make fused glass jewelry, as a hobby or to sell, because of the relatively small initial investment and small work space needed.

Photo by Emerald Isle Designs

PLAN - Decide what you want to make. Plan colors and patterns. You can layer pieces of glass to create patterns or pictures.

CUT - Using standard cutting tools common in the stained glass studio, cut out the glass pieces you need.

PLACE AND GLUE - After washing the glass to remove dirt and oils, carefully attach the glass pieces, with a tiny dot of glue,in an arrangement on a base piece of glass. You can stack glass pieces two or more layers high. At this time, you might also add other inclusions like bits of wire or metal pieces. Usually, but not always, place a clear piece of glass over your glass pieces.

FUSE - This is when it starts getting really fun. Carefully place the whole glass arrangement in a prepared kiln. You are going to heat the glass so that it sticks together or until it sinks into the layer below it. Because of the nature of glass and heat, this process takes MANY hours. AND you can't open the kiln until it has cooled to room temperature. NO CHEATING or the glass will crack and the whole project will be ruined.

SLUMP - After your fused piece has cooled, place it on a slumping mold and put it back into the kiln again. As the glass heats, gravity will pull it down to form the shape of the mold. Cool, huh? After it cools completely again, you have your very own piece of kiln-formed artwork. The photo of the bowl with triangles at the top of this section shows my first fused glass project ever.
Photo by Emerald Isle Designs

ANNEAL - It's really important that the glass cools at the same rate throughout the piece. If a thicker portion cools more slowly than a thinner section, the glass will develop stress and eventually will crack. Annealing is resting the glass at a certain temperature long enough for the entire piece to come to the same temperature. There are certain temperatures at which this is critical and others it doesn't matter so much. You should know those critical temperatures and plan to anneal your glass, although seeing an object shatter from stress can be pretty spectacular.

COE - This means coefficient of expansion. Different kinds of glass expand at different rates. If you are fusing pieces of glass together, it's very important to make sure they have the same COE. We call them compatible. Glass manufacturers sell special glass for fusing with the COE labelled. You can also fuse with sheet glass from the hardware store, if you make sure the entire project is made from the same sheet of glass (therefore, the same COE).

FUSE - To heat the glass pieces enough to make them stick together or sink into the lower layer. Also, what blows when your electric kiln overwhelms your home's electrical system.

KILN - A really hot oven used for fusing and slumping glass. Some kilns are made for both glass and clay, but not at the same time. The really cool kilns have programmers on them, so you can tell it how fast to heat, how long to stay at a temperature, and how fast to let everything cool. Not recommended for baking bread.

SLUMP - To heat the glass on some kind of mold that softens the glass enough to allow gravity to shape it. Also, what you do when you couldn't wait until the piece cooled completely to room temperature in the kiln before looking at it, and you realize that the shock of cold air hitting the warm glass just made it crack (also see "swear").

TACK - To heat the glass pieces just long enough for them to stick together, but not for the glass pieces to change shape at all or begin to sink into each other.

Photo courtesy of Flickr and Periwinkle Studio