Tip #54: Firing Glass (in your ceramic kiln)
Have you ever wondered about firing glass in your kiln?
Kiln fired glass, or warm glass as it is also called, is typically done in an electric kiln at temperatures lower than ceramic temperatures. 1300-1500 degrees F is typical. (For reference, Cone 04 is about 1900 degrees F and Cone 10 is about 2350.)
Because of the lower temperatures involved, all ceramic kilns are capable of firing glass. However, electronic controllers are particularly useful for glass firings, as the temperatures have to be controlled precisely during certain stages of firing.
Glass kilns usually have an element in the lid. This is especially important for glass fusing, where different pieces of glass are combined into a single agglomeration by heating them to the point where they soften, and a flow of material occurs across each piece. During fusing, the lid element is turned on high so even heating occurs across the glass piece.
If you're doing small pieces of glass, a lid element is not crucial for fusing. If you're making jewelry for example, the small tabletop kilns without lid elements work fine. But the larger your pieces get, the more difficult it gets to do without a lid element.
It also is extremely useful to see inside glass kilns, so windows are a great help.
Slumping (melting the glass into a mold) does not need the element to be in the lid. So if all you're doing is slumping, such as wine bottles or already fused sheets of glass, any ceramic kiln will be fine.
Using a ceramic kiln for firing glass
If you plan to do a fair amount of glass and ceramic work, then your best option for a kiln would be a dual-media kiln which is designed for both. These are the most popular.
If you are a serious glass artist, you probably will want a separate kiln for ceramic and glass. This will allow you to optimize features for each one. Paragon is the most popular brand of glass kiln, and has a variety of styles to choose from.
For more information
The website www.WarmGlass.com has a lot of great information.
We also have a number of new books on kiln formed glass, including:
A fun glass project
A fun project is to take a beer or wine bottle and slump it into a "spoon rest". Make sure you have a lot of kiln wash on your shelf. I personally would try this first inside a ceramic bowl, just to be safe. Make sure you have the bottle where you can see it through your spy hole. Heat the kiln at about 250 degrees F per hour. The bottle will probably start to slump at 1000-1100 degrees F, and be pretty flattened by 1200 degrees F. You can also add a lump of clay (dry greenware or bisque) beneath the neck of the bottle, and it will form over the lump and make a nice handle. Cooling the kiln fast down to about 850 degrees F will probably result in the clearest glass. Then cool very slowly
Here is an image of a bottle slumped into a serving tray. To give proper credit, this nice looking item is sold at a web site called She-Works.com. Item # G-901.