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Kiln Pointers

Preventing Glass from Cracking

Most problems in fusing are caused by rushing the firing. The glass must heat slowly during the critical temperature range of 100 – 500 degrees F.

The second critical temperature range is annealing, which is the cooling range of 950 – 750 degrees F average. Cool the glass slowly in this range so the stress in the glass will have time to dissipate.

If you become impatient after the glass has fused and you crack open the lid of the kiln for a few seconds to peek inside, you may hear a “ping,” which is the sound of glass cracking. Avoid the temptation to open the lid. Wait until the kiln has cooled to room temperature. Some artists schedule their fusing so that it is completed before they go to bed. That way they will be asleep while the glass cools and they won’t be tempted to open the lid.

After each firing, examine the shelf. Recoat if the kiln wash is chipped. When glass sticks to a bare section of the shelf, the glass cracks.

If the cracks appear along the edge lines of glass pieces that are fused together, then the cracking may be due to incompatible glass. This may happen if you fuse different brands of glass.

If the edges of cracks are rounded, then the glass probably cracked as it heated up. If the edges of cracks are sharp, then the glass probably cracked during cooling.


For a change of pace, I will share a kiln story with you from time to time. Last week I shared the story of the kiln that fell off a truck and survived. Here's another one:

In 1985, we produced a magazine ad announcing a new freight-free program. The ad showed a Paragon kiln on a railroad track.

A Paragon employee named Morris helped me place the kiln on the railroad track, which was across the road from the Paragon factory. I was setting up the camera on a tripod and Morris was polishing the kiln when we heard an approaching train. Morris and I quickly moved the kiln off the track. The train came roaring past us, shaking the earth as it went. Morris and I set up the kiln again, and I shot the photo.

Morris, always gentle and polite, has since passed away. And Paragon still has the freight-free program. (You can order a kiln freight-free from participating dealers.)

I would enjoy reading your kiln stories.

With best wishes,

Arnold Howard Paragon Industries, L.P. - Better Designed Kilns 2011 South Town East Blvd. Mesquite, TX 75149-1122 Voice: 972-288-7557 & 800-876-4328 / Fax: 972-222-0646 /

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