How to Reduce the Chance of Thermal Shock in the Kiln

There are a number of things we can do to ensure more even heating – and lower chance of breaking – of glass in a kiln.

Here are some of the easiest and most effective methods.

Slow down:

The slower the kiln heats, the more time the heat has to disperse evenly throughout the glass. This is always the first and best line of defense against thermal shock.

Slow down:

Yes, I’ve listed this one twice because it is really, really important.

Use a kiln with lid elements:

Heating the glass from above tends to heat more evenly because the entire surface is (usually) the same distance from the elements. Kilns with just side elements (like ceramic kilns) present some real challenges for kilnforming glass artists.

Position the glass for even heating:

The best place to put your work is the center of the kiln shelf. The kiln shelf should be as low as possible while still leaving space between it and the floor of the kiln for air circulation.

If you are firing multiple pieces at one, consider which one(s) are most likely to thermal shock and place those near the center.|

Baffle side heat:

Sometimes it isn’t possible to put as much space as you would like between the glass and the side heating elements. When that’s the case, you can baffle the heat with kiln furniture, fiber board, strips cut from an old kiln shelf or fire brick.

Baffling heat is easy – simply position the kiln furniture (or whatever you are using) around the glass on the shelf like this:

heat damn in kiln


Here’s a close-up:

heat dam

How does this help? The heat from the nearby elements now needs to travel farther to reach the glass. The farther the heat travels the more time it has to disperse and the more evenly it hits the glass.

One note on this technique – it is important that there are no gaps in your baffle since that can contribute to the uneven heating.

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