glass breaking in kiln--help??

annj · Post by **annj** » Tue May 13, 2003 10:33 pm

I have a question about fusing glass and kilns..

I bought the new "bigger" (13" top loading) kiln and I keep having glass explode in it-- well not explode, but break up.

It's got the very same automatic controller as my little kiln so I (think) I know how to use it. I have tried going up slower, but that doesn't seem to work.

The only difference I can see is the ceramic shelf and the size of the Kiln. In the little kiln I fire for a full fuse to 1550 (if it's accurate). Might the big kiln be hotter for some reason and would that cause glass to break? The other thing is that the thin fire paper seems to break up (turn to dust) more in the big kiln whereas in the little kiln it stays in sort of delicate sheet consistency.

Ann Jones

Brad Walker · Post by **Brad Walker** » Tue May 13, 2003 10:38 pm

What's your firing schedule? What do the breaks look like (smooth, sharp, curved or straight, how many pieces)?

Stuart Clayman · Post by **Stuart Clayman** » Wed May 14, 2003 12:30 am

Annj,
Is your smaller kiln a quick fire that goes up fast? If so, then the air in the kiln gets hotter that the glass. In a larger kiln when it gets hotter slower then the glass is closer to the air temp. That is why you have to fire hotter in a quick kiln than in a larger kiln.

Stuart

Lynne Chappell · Post by **Lynne Chappell** » Thu May 15, 2003 12:56 am

You're going from a pretty small kiln to a bigger kiln. Are the pieces you're firing also bigger? If so, then you have to change your firing schedule.

If the glass is breaking on heat up then you need to slow down the rate of firing. A 12" piece 1/4" thick should be OK if heated at 400F per hour as long as it isn't too close to the elements.

If it's breaking on cool down, then your annealing schedule isn't adequate.

There's also the possibility that the new kiln isn't reading the temperature correctly. With a little more info, we could maybe help more.