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I full fused this piece (see photo) in our pottery kiln. I programed a slump with 3 other bowls. All bowls were fine- but this one- It was thinner than the other 3 bowls. It looks like it slumped at the edge of the mold and the edge of the lower shelf. When did it break?? I am new to fusing. I used the System 96 published programs.

What a shame. Such a cute bowl. It obviously happened on the way up. What as your schedule? What kind of kiln. Knowing that is the only way we can help!

Skutt kiln used mostly for pottery. Here's the schedule I used for slumping taken from System 96 booklet.
Ramp > Goal temp > Hold Time
150> 300> 15'
300> 1100> 20'
150> 1235> 15'
9999*> 950> 60'
150> 800> 10'
300> 100> 0

Was the blank circular to start with? Were you slumping over the mold, or into it?

David- From the photo it was into the mold.
Amy- Scrap the published program- there's no need for a hold at 300 and the rates up are too fast. (The annealing looks problematic too.) You can use the Bullseye schedules on Spectrum- just anneal at 950 instead of 900- I think they're a lot more careful.
Have you got Brad's book?

Amy,

You mention "It looks like it slumped at the edge of the mold and the edge of the lower shelf." By "lower shelf", do you mean you were slumping various different items on various stacked shelves in the same kiln load? If so, I think that's where most of the problem may lie. While your schedule is not optimal, I think it's more likely that the temperature differences from one part of the kiln to another may have been too great for your glass to endure. The distance between the two sections of glass indicates to me that there was a fairly large desparity in temperature between one section of the glass and the other.

Richard

From the photo it looks like she had the piece set on top of the mold and the thermal shock on the way up broke the glass with enough force to separate the pieces and send the one on the right side of the mold off the edge where it proceeded to slump down to the shelf.

Your witness.....

Like Marty said. You can use Multi shelves but you need to go slow. I also try and keep shelves at least 3" above the top of the mold. R.

In a side element kiln, placement can be critical. If the glass edge "sees" the element, it can heat shock it. You could try raising or lowering the shelf height. Side kilns must be ramped up slower than top fired kilns, simply because the heat is not as evenly distributed. The good news is that you can use the same anneal schedules as other kilns. As others said, slow down.

I hate to be so dense, but I'm still not clear on the original arrangement/layout of the slump.

Marty, your first post implies that it's obvious from the photo that she was slumping into the mold, but I asked my original question because that was not obvious to me, at all. Your later post indicates that the blank was on top of the mold, which kind of implies (or at least I infer) that the slump was to be a kind of a drape. That's the way I saw it, too.

At any rate the picture confuses me in the way a convex/concave illusion confuses.

Thank you everyone for your input. To answer a few questions: (1) the piece was circular to begin with (2) it was being slumped INTO a 10" bowl mold (3) I had 4 molds in the kiln, 1 mold per half shelf, stacked in a Skutt pottery kiln. I had done this before with no problems. (4) I do have Brad's book. So I gather that I need to raise the temperature very slowly for the slumping. Do you feel that is also needed for the FULL Fuse? Could this happen during the full fuse as well as the slump? I fear so from what you are saying and from what I have read.
Bottom line: Should I keep the temp ramp at 150 until I reach the critical temp to slump and then hold?
Thanks again!

Yes unless 150dph f is too fast.