About Fused Glass

About Fused Glass

Fused glass differs from the traditional stained glass in the method of assembly. The Egyptians and Romans were highly skilled in the art of fused glass, and it was the main art glass techique until around 500 AD. Fused glass more or less faded into the background as the development of blown glass and sheet forming techniques for stained glass flourished. In the last century, fused glass has undergone a long overdue and almost explosive renaissance. The art of fusing glass has become the technique of choice for many glass artists. Glass fusing is sometimes referred to as "warm glass".

Hand cut pieces of glass are layered on top of one another and fused together in a kiln. In general the glass is heated to a temperature where it sticks together or flows together in a limited way. The major difficulty in fusing glass is that the different pieces must be "compatible" by having the same thermal expansion rate, or "coefficient of expansion". That is they must expand and contract at the same rate. If the glass is not compatible, it will crack as it cools. A number of art glass manufacturers now make lines of glass that are pre-tested for compatibility. The colour choices for fused glass are somewhat more limitied than with stained glass because of this need for compatibility. Additional colours can sometimes be obtained by layering different colours of glass together.

The kilns used for fusing glass are usually broad and flat with elements in the walls and lid. The temperatures used range from about 1100 to 2000 degrees F. The glass is heated to fusing temperatures over about 3 hours, but the cooling cycle takes another 6 to 24 hours in order for the glass to "anneal" properly. Large or multilayered pieces can take much longer. The heating and cooling must be done slowly to prevent the glass from breaking due to thermal shock.

The design possibilities for fused glass are extensive and different from those that can be achieved with other glass techniques. Fused glass has a very pleasing smooth surface and a sparkle that cannot be matched by traditional stained glass.