Wednesday, May 13, 2009

Fused Glass – History and How It’s Made


Fused Glass is a term that describes glass that has been layered or stacked and then fired / melted in a kiln in temperatures between 1100 degrees F to 1500 degrees F. You may also have seen it referred to as kiln-fired glass, warm glass, slumped glass, or dichroic glass. It is a beautiful, innovative art form that combines all the sparkling qualities of stained glass but without the lead lines. Warm glass and slumped glass are explained below. Dichroic glass is what you may have seen in some glass jewelry, where the piece looks very glittery and changes colors. It is a specific type of coating for the glass that was originally made for the space program and now has been adopted by fused glass enthusiasts.

Its applications can be seen in jewelry, window decorations, bowls and platters, as well as decorative art pieces such as wall hangings, clocks, vases and other creations.

My career as an artist started out with stained glass because I love the colors, textures, and sparkle of glass. I gravitated towards fused glass after seeing some of the process and becoming fascinated with the seemingly endless ways to create with glass.


The exact origin / discovery of how to fuse glass is not known for certain, though some scholars believe the ancient Mesopotamians were the first to use the glass fusing and kiln casting techniques beginning from around 2000 to 2500 BC. The Egyptians were thought to have built upon the basic techniques of the Mesopotamians.


These “warm” glass techniques continued to be used and improved by the Greeks and the Romans through the third century BC until the birth of Christ. An important discovery was how to create core formed vessels, which was done by wrapping glass around a core vessel and then heating it to form mosaic and other patterns.

Soon after this time the technique of glassblowing (or “hot glass”) was discovered, which involved forming a vessel by using a long, hollow tube (called a blow-pipe) to shape the molten glass that had been heated in a furnace. Because this technique became more popular due to its efficiency, repeatability, and lower cost, the fused glass techniques all but died out.

It wasn’t until the 19th century AD that the glass-working techniques were rediscovered in Europe, though glass fusing itself was still largely ignored. However, fusing began to regain popularity in the 20th century, especially during the 1960’s until now.

As mentioned above, glass fusing (or “warm glass”) is formed by layering thin pieces of different colored compatible glass and then placing the stack inside a kiln, which is then heated through a series of ramps (rapid heating cycles) until the pieces begin to bond or fuse together. The longer the kiln is held at the maximum temperature, the more thoroughly the glass will fuse.

Glass is considered compatible when all the pieces and layers will expand and contract at the same rate, thereby safeguarding the final piece from shattering or cracking in the kiln or later.

There are basically three temperature ranges:

1) 1100 degrees F to 1250 degrees F is called “slumping” and is the temperature for molding and shaping a flat sheet of glass to a form, like a plate or bowl.

2) 1250 degrees F to 1350 degrees F is the temperature where glass pieces become “tack fused” , i.e. the pieces are attached permanently but you can still see the outlines of the individual pieces and layers. This creates some contours and textures.

3) 1350 degrees F to 1500 degrees F is considered “full fusing” temperature, where the glass is so thoroughly melted together it appears as one solid piece of glass.

Baroque Iridized Vase

Once the desired effect of the glass is attained, the temperature of the kiln is brought down very rapidly to about 1000 degrees F, after which it enters into the phase known as annealing. This is a slow cooling period which allows the glass to “soak” at various temperatures in order to prevent uneven cooling and subsequent breakage, to relieve stress in the superheated glass, creating a strong finished product.

The entire firing process can take up to 20 to 24 hours per firing, depending on the size and thickness of the pieces and the size of the kiln. Creating smaller pieces for jewelry, for example, can be done in a tabletop kiln and the firing stages can go a lot more quickly. I am able to complete such a firing in about 6 hours or less.

Of course, there are many, many specific techniques for the designing and creation of various fused glass art pieces, and this is a simplified overview only.

It is fun to do, sometimes getting unexpected results. It is always exciting to have pieces firing in the kiln and then finally to be able to open the kiln the next day to see the results!

I hope you enjoyed this post, and I am happy to answer any questions you may have. If you are interested in more detailed instructions, post a comment and let us know what you are interested in.

Spirit Essence Art


Creations With Heart said...

Very informative article! Fused Glass is so pretty! That's something I'd love to try!