Cracking during slump

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Doug Zawodny
Posts: 33
Joined: Wed Feb 28, 2007 8:30 pm
Location: Sacramento California

Cracking during slump

Post by Doug Zawodny »

Got an Olympicgf314etlc last July. All my firings went fine fuse,slump,melts. A couple months ago using the same slumping schedule I always use. 300 to 1200 hold 20 afap to 900 hold 60 100 to 700 no hold afap to room temp. The piece cracked on heatup ( edges were not sharp) from edge to edge in the middle of the piece. The piece was 18 in.in diameter. I fired another piece that was 14in. diameter. I changed the schedule to 200 to 1200, 250 to 900, the rest the same. It didn’t crack. I fired another 18in piece at the new schedule and it cracked on heatup, edge to edge in the middle of the piece. Since the smaller diameter piece didn’t crack (I’m presuming its distance from the side elements is the reason) Im thinking my top elements aren’t firing properly hence the sides of the larger pieces are getting hotter than the middle and cracking. Im heartbroken at ruining these great pieces on the final firing. Any ideas out there?
Brad Walker
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Re: Cracking during slump

Post by Brad Walker »

Got a photo of the break?

I'm a bit puzzled by your comment that the edges cracked and were not sharp. If your top temperature was only 1200F, then that shouldn't be hot enough to round the edges.

Also, a description of the mold you used would help.
Doug Zawodny
Posts: 33
Joined: Wed Feb 28, 2007 8:30 pm
Location: Sacramento California

Re: Cracking during slump

Post by Doug Zawodny »

The mold was a shallow bowl 18x3 bullseye. For some unknown reason I cannot post a pic to this site. The inside edges of the cracks are not that sharp, the side facing the mold has sharp edges. It did not crack at element lines but across all.
Doug Zawodny
Posts: 33
Joined: Wed Feb 28, 2007 8:30 pm
Location: Sacramento California

Re: Cracking during slump

Post by Doug Zawodny »

Trying tp post photos[
D39BB27A-3CF8-45F6-A570-DBC2FCDE1CB1.jpeg
C0A607F3-8753-4743-86E7-88183628C983.jpeg
Brad Walker
Site Admin
Posts: 1489
Joined: Fri Mar 07, 2003 9:33 pm
Location: North Carolina, USA
Contact:

Re: Cracking during slump

Post by Brad Walker »

Is the piece conforming to the mold or is it still flat? Is the piece split in two (or three) or just cracked down the middle? Curved crack? Can't tell from the photos, since they're just partial pics.

Round bowl mold? (Have the BE number?) Was the mold on the shelf or just on posts? How close are you to all the elements (top and side)?

There is a limit to the size of the photos you can post (1000 MB), so that could be your problem with posting. Or they could be a format the software doesn't support. You can always send photos to me and I'll get them up for you.
Doug Zawodny
Posts: 33
Joined: Wed Feb 28, 2007 8:30 pm
Location: Sacramento California

Re: Cracking during slump

Post by Doug Zawodny »

I had to shrink the photos to get them down to the permitted size. Brad, all previous firings in the same mold height ect. Worked. Everything is the same state that previously slumped properly. Thats the mystery. The shelf placement, mold, schedule all worked before. In this kiln I’ve fired dozens of slumps in the same mold, same schedule and they were successful
The shelf is on posts, top of the shelf is aligned with the bottom side elements The edge of the shelf is about 1in from the sides. Again I don’t think its the setup. The piece is fully slumped into the mold. The shelf is 2in above the kiln floor.
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