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Wonder what I am doing wrong. I was trying to slump a single layer 2 to 3mm peice of Bullseye Confetti glass. This has not been tested for compatibility but I have fused it and slumped it in the past. This has happened to me a 3 times, with different glass but always the same mold and always the same kind of break (only has happened with CoE untested glass). I thought you could slump just about any glass!

The mold is 8 inches across and is square. I was ramping up at 580 per hour to 1320, coming down the same and annealing at 960 for 30 minutes. Is that too fast? The break is always a single break, about 1/3 of the way across, and is curvy.

I never reach a full slump before I find that it has broken. This last time the kiln was at about 1200 when I peeked and it was already broke.

Karon

you're heating it much too fast. try 250/hr for a ramp up.

kbarbour wrote:Wonder what I am doing wrong. I was trying to slump a single layer 2 to 3mm peice of Bullseye Confetti glass. This has not been tested for compatibility but I have fused it and slumped it in the past. This has happened to me a 3 times, with different glass but always the same mold and always the same kind of break (only has happened with CoE untested glass). I thought you could slump just about any glass!

The mold is 8 inches across and is square. I was ramping up at 580 per hour to 1320, coming down the same and annealing at 960 for 30 minutes. Is that too fast? The break is always a single break, about 1/3 of the way across, and is curvy.

I never reach a full slump before I find that it has broken. This last time the kiln was at about 1200 when I peeked and it was already broke.

Karon

Thermal shock. Slow down to 300 DPH or less, and you should be fine. You don't even have to go as hot as 1320, try 1150-1200. Brock

Confetti is particularly sensitive, and wants to be coddled much more than most glasses. The problem is the thickness differential where the shards are. It can be half as thick in some areas as others, and that makes for very uneven heating. I ramp up three times as slowly for Confetti.

Thanks so much for all the great info. I have to go back and read my charts for firing. I must be reading them wrong.

Karon