What is Fused Glass?


Fused glass is a term used to describe how 2 separate pieces of glass can be joined into one solid piece. It is also known as Warm glass or Kiln-formed glass. Both pieces of glass MUST be of the same COE (coefficient of expansion) to avoid stress and/or unstableness. Using 2 different glass coe’s will result in the glass cracking during the cooling process. In order to join two pieces of glass into one solid piece they must be heated up to a temperature range of 593 °C (1,099 °F) to 816 °C (1,501 °F). This heated process is accomplished in a kiln designed for high firing of glass. There are 3 main temperature ranges that have different effects on the glass.


Slumping is the term used for heating glass to temperatures in the range of 593–677 °C (1,099–1,251 °F). Another term used when firing glass at these temperatures is known as Draping. When slumping you shape the glass on the inside of the mold. When draping, you shape the glass over the mold. These temperatures allow a solid piece of glass to take on a special form or shape without affecting any other characteristics on the glass. The use of ceramic or stainless steel molds and forms are used to achieve a particular shape, for example a colour flashlight shape.

Tack fusing is a term used when heating glass in temperature ranges of 677–732 °C (1,251–1,350 °F). When glass is heated to these temperatures the glass surface becomes tacky and will cause the two pieces of glass to remain stuck together. The edges on the glass will soften and round out creating a clean polished appearance.

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


Annealing is the process by which fused glass is cooled at a controlled rate. Depending on the thickness and size of the glass will determine how fast to heat and cool it. Heating glass too fast will cause the glass to stress and crack. In the same manner cooling the glass too fast can also cause stress in the glass and it can crack. Sometimes the stress may not be visible immediately but in time it can appear and crack.