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Author Topic: Glass craked on cooling down.  (Read 1082 times)
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Laura S
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« on: June 04, 2016, 06:12:41 AM »

Hi
I slumped a 6mm thick panel on a batt washed hump mould, that I've used about half a dozen times before. The panel had no visible bubbles and had been properly annealed on it's first firing. It split in two whilst cooling down. I am totally baffled as to why this happened. I used the same schedule that I've used before (175d to 606d 15mins, Full to 482d 1hour, then 83d to 399d) without any problems.  I fired in a Skutt Firebox 14. Any ideas would be much appreciated.

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qwirkyglass
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« Reply #1 on: June 04, 2016, 05:28:50 PM »

My gut feeling is thermal shock, how fast did you bring it down at the end?
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silkworm
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« Reply #2 on: June 05, 2016, 04:45:08 AM »

I have a Firebox 14 and find that I need to be very careful with slumping anything deeper that the very gentlest of curves. My problem is more often it breaking on the way up rather than down though. I still tend to use the preset programs for slumping and found that by using the slowest one I had less problems, one glass worker I spoke to suggested slowing it even further to heating and cooling at 50 degrees per hour!
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Mary
Laura S
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« Reply #3 on: June 05, 2016, 06:42:40 AM »

I don't think it can be thermal shock. From the target temperature I cooled on full to 482d , to anneal, and then 83d to 399d. I think there must have been a fault in the glass I wasn't aware of.
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flame n fuse
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« Reply #4 on: June 05, 2016, 02:38:07 PM »

you're saying that it split on the way down. Was this because the edges of the break were sharp?
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Laura S
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« Reply #5 on: June 06, 2016, 10:48:44 AM »

Yes, the edges were sharp.
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