Why did my plate break?

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Michael Hyland
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Joined: Fri Sep 28, 2012 11:26 pm

Why did my plate break?

Post by Michael Hyland »

photo2.JPG
I am trying to make a plate, and I ran into a problem fusing it. The plate is 9" X 9". All glass is System 96.
The firing schedule I used was:
Ramp at 300 deg/hr to 1150 deg
hold for 30 min
ramp at 400 deg/hr to 1350
hold forever
ramp down as fast as possible to 950
hold 60 min
...

The plate consists of a single thickness (1/8") red piece, covered by a single thickness clear piece, topped with a black figure surrounded by clear frit.
The break occurred while ramping up somewhere below 1320 degrees. Only the red glass broke.
I'm wondering what would make the glass separate so violently. Also, the kiln (supposedly) never got hotter than 1340 or so. The plate looks like it is close to a full fuse, which, according to Spectrum, should happen about 1460 deg. Is it possible that my kiln controller is measuring temps inaccurately? How could I test this?
I'd appreciate any pointers the board could give me. Thanks!
carol carson
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Re: Why did my plate break?

Post by carol carson »

Your schedule is too fast, you need to slow it down a lot.
Michael Hyland
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Joined: Fri Sep 28, 2012 11:26 pm

Re: Why did my plate break?

Post by Michael Hyland »

Thanks, Carol. I based the schedule on the firing schedule on the System 96 web site (skipping step 2, as they suggest you may do). How much is a lot, as in slow down schedule "a lot"?
carol carson
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Re: Why did my plate break?

Post by carol carson »

I would not ramp up @300° per hour, you should go no more then 100° on the way up to 1150°.
twin vision glass
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Re: Why did my plate break?

Post by twin vision glass »

I toooo feel it was too quick and I never go faster than 100 deg. per hour unless tiny pieces. I even go 50 deg. per hour with thick work. Les
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bob proulx
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Re: Why did my plate break?

Post by bob proulx »

Your piece was uneven in thickness, in that case as everyone mentioned you must slow it down.
Bob
Michael Hyland
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Re: Why did my plate break?

Post by Michael Hyland »

Thanks, everyone, for the suggestions. I'll take it a lot slower next time.
David Jenkins
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Re: Why did my plate break?

Post by David Jenkins »

Breakage aside, I'm pretty impressed by the black figure. Did you cut that yourself?
Dave Jenkins
Glass at Harbor Gates
Cypress, TX
Michael Hyland
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Joined: Fri Sep 28, 2012 11:26 pm

Re: Why did my plate break?

Post by Michael Hyland »

Yes, David, I cut it on a Taurus II ring saw. It was pretty time-consuming. BTW, the piece is an Albanian flag. The guy who requested the plate wanted it as a present to his girl friend's parents, who are Albanian. After sawing out that eagle, I wish his girl friend was Japanese!
David Jenkins
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Re: Why did my plate break?

Post by David Jenkins »

Wow. Are the tongues stringer? Or did you actually manage to cut those as part of the larger piece?
Dave Jenkins
Glass at Harbor Gates
Cypress, TX
Tony Smith
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Re: Why did my plate break?

Post by Tony Smith »

Just to be clear, there are lots of cases where a 300 deg/hr rate will be acceptable. With the black, irregular figure on top, this isn't one of those cases.

Tony
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Michael Hyland
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Joined: Fri Sep 28, 2012 11:26 pm

Re: Why did my plate break?

Post by Michael Hyland »

David Jenkins wrote:Wow. Are the tongues stringer? Or did you actually manage to cut those as part of the larger piece?
The tongues are cut from separate pieces of plate glass. I couldn't figure out how to cut the whole figure in one piece.
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