Firing Glass

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.

It also is extremely useful to see inside the glass kiln, so good spy holes or even a glass panel are a great help.

Another major process in kiln formed glass is stretching, sagging or slumping. This involves melting glass into, over, or through molds so they deform into shapes. Molds are coated with release agents (often called separators) to keep the glass from sticking

Using a ceramic kiln for firing glass

As I have said, glass can be fired in any ceramic kiln, although top elements are useful and an electric controller or pyrometer is crucial. Generally the smaller the piece you are working with, the more forgiving it is. If you want to experiment with making small pieces of jewelry, go for it! You are likely to get good results with a little bit of research.

If you plan to do a fair amount of glass and ceramic work, then your best option for a kiln would be an Olympic ceramic kiln with an optional heating element in the lid. The lid would be left off while firing ceramics, and only used when necessary during glass fusing. The lid element adds less than $200 to the cost of the kiln.

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:
* Dictionary of Glass
* Glass, An Artists Medium
* Techniques of Kiln Formed Glass

In addition we have new books on making glass beads, stained glass, and glass painting.

Check the book index

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

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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.

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