Glass Fusing 101

BlueDeepScatterWhat is Glass Fusing?

Glass fusing is simply the process of stacking two or more layers of “compatible” glass together to make a design, and then placing the stacked glass into a kiln, where it melts (fuses) together.

What is Glass “Compatibility?”

Glass expands when it is heated and contracts when it cools. All glass has a distinct rate at which it expands and contracts, generally referred to as the Coefficient of Expansion (C.O.E.). You cannot fuse glasses with differing C.O.E. rates together — breakage will result! This is why choosing a family of glass products should be the first step in fusing.


Most manufacturers of fusing glass test their own products consistently to assure compatibility within their own lines. The phrase “Tested Compatible” is often used to assure a specific family of products will correctly fuse together well.

“Firing” Glass — Fusing and Slumping

After cut, or nipped pieces of compatible glass are stacked/assembled, the project is placed in a kiln. The kiln will heat the glass slowly from room temperature up to fusing temperatures (1300º-1500º Fahrenheit) and slowly back down again according to the Firing Program or Schedule selected. Different effects — how smooth, or dimensional the finished surface of the fused piece will be — can be created through controlling the firing program.


The finished fused piece can be displayed as a flat decorative piece that can be enjoyed as it is, or put back into the kiln and shaped into a 3-dimensional piece such as a bowl, vase, or other artistic shape through a second firing – this type of glass kiln-forming is called “slumping.” Glass is slumped at lower temperatures than fusing (1225º – 1250º F) and is shaped using kiln-washed molds of various types.

Getting Started

Once you have chosen which family of compatible glass products to use, it is best to consult the glass manufacturer for recommended firing schedules, and other information. There are also many classes available to help you learn about, and explore the numerous and exciting possibilities of kiln-fired glass. Look through the links on this site to learn more.SparklerAndRetro

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