Common Questions About Glass Kilns

Can I use a ceramic kiln for glass?

Yes – but not easily except for small projects like jewelry.

There are two big differences between firing clay and glass:

• Even heating is critical for glass, less so for clay.
   
• Glass requires precise control over heating and cooling rates.  These requirements change throughout the firing.

Because of the need for even heating, glass kilns almost always have heating elements in the lid.  Ceramic kilns do not.   To avoid heating the edges of the glass too quickly, ceramic kilns must heat much more slowly than glass kilns when firing glass. 

To ensure the required control over the glass firing schedule, most glass kilns have a computerised controller.  Many ceramic kilns (especially the older ones) do not need a controller – instead they use a simple mechanism called a "kiln sitter" that simply turns off the kiln when it reaches a specified temperature.

How expensive is firing glass?

Less than you may think.

Even though kilns draw a lot of electricity, they do not draw it continually.  Over the course of a typical glass firing the kiln’s elements are only on a fraction of the time.

Newer kiln controllers allow you to enter your cost per kilowatt hour for electricity and they will report back the cost of the firing.  A recent pattern bar firing at our studio, in a 240 volt (40 amp) kiln with 3.3 cubic feet interior (about as big as most home users will ever get) lasted about 20 hours and used less than $4 worth of electricity.

Are kilns safe?

When used with common sense and according to the manufacturer’s instructions, kilns are very safe.

The heating elements in a kiln are managed by the kiln controller.  In the event of a controller failure – where the elements are left powered – the kiln will continue to heat until to the elements exceed their rated temperature and fail.  At this point the kiln will cool naturally.

During such a failure, the largest risk is that the overheated kiln will start a fire.  You can significantly minimize this risk by keeping sufficient space between the kiln and all other objects and by making sure the kiln is on a non-flamable surface.

Do you have other questions you’d like us to answer?  If so, please leave a comment below.