What is Kiln Formed glass?  

If you apply heat to glass, it will soften.  If you continue to apply heat, the glass will become more fluid and flow together. 

Kiln Formed, or Fused, glass was first developed in Mesopotamia and Egypt 4000 years ago. Fused glass fell out of use about 2000 years ago with the development of blown glass because it was a slower and more restrictive method of forming glass.

Modern kiln forming typically takes place at temperatures between 1100 and 1700 degrees Fahrenheit.  Heating the glass in this range allows it to respond much like a liquid -- it sags, flows, or blends and the surface softens and smoothes.  At high enough temperature two or more pieces of glass will stick (or "fuse") to each other.  When the appropriate glass is heated and then cooled properly, the resulting fused glass piece will be solid and stable.

Kiln formed glass responds to heat slowly and the character of a finished piece depends quite a bit on the time it spends at working temperature. Even a simple piece could spend 20 hours in a kiln before it is finished. Larger and more complex pieces require days, sometimes weeks, of very slow heating and cooling to achieve the artist's vision.