I have been getting severe marks on the underside of the glass in my slumping runs. They look like stretch marks or wrinkles. All the pieces are 2 layer BE transparents, all were fired to fuse on the same Bulls Eye kilnwashed shelf in one fire. the kiln wash was not fresh, but I always do multiple firings on the same wash until I get scratches or nicks. I was using a fairly aggressive schedule for the first piece (650F p/h to 1225), so I slowed way down for the next (150F p/h to 1225), so I rewashed the mold and tried somewhere in between (400F p/h to 1300). All three have undersides totally covered with the texture. Pretty frustrating, any thoughts? I know this has been addressed before but most of the tips in the archives were to adjust firing schedules and that's not doing it here.
lissa.
Slump stretch marks again
Moderators: Brad Walker, Tony Smith
Re: Slump stretch marks again
What are you slumping on? You mentioned shelves, but not molds. I wouldn't go as hot, for one thing. Try slumping at 1150 with a hold. Brock
Yeah, I finish my shelves very carefully and there is almost no discernable texture left on the glass. I was wondering more if it is some sort of contamination, like I said, this has never happened in the past, even going to 1225 at ~350F p/h. I'll see what happens today, this glass is from a freshly washed shelf. Four pieces got it and I am having to change my design ideas to incorporate a blasted back. It'll keep me on my toes.
thanks for your help.
lissa.
thanks for your help.
lissa.
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Cynthia
Lissa, for what it's worth, I bend 1/4" x 20" pieces in BE ball molds with this schedule.
250 dph to 100 no hold. Ooops. I did indeed mean 1000 F. thanks for pointing that out Jim.
100 dph to 1200 no hold.
Then cool with anneal as usual. this works well for two reasons. I get full slump with differing depths of ball molds in the same firing and it's such a cool and slow bend that there are no "stretch marks" or mold marks created. The back of the piece retains the texture it had from full fuse.
Top firing fiber kiln with the pieces sitting 6" to 8" below the elements.
250 dph to 100 no hold. Ooops. I did indeed mean 1000 F. thanks for pointing that out Jim.
100 dph to 1200 no hold.
Then cool with anneal as usual. this works well for two reasons. I get full slump with differing depths of ball molds in the same firing and it's such a cool and slow bend that there are no "stretch marks" or mold marks created. The back of the piece retains the texture it had from full fuse.
Top firing fiber kiln with the pieces sitting 6" to 8" below the elements.
Last edited by Cynthia on Fri Jan 09, 2004 7:43 pm, edited 1 time in total.
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jim simmons
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Hmmm . . . there's a couple of things you could try.lissa wrote:It happened again. I ramped up at 200F to 1150, 45 min. hold. It did not slump completely, which is fine, but got the texture, not fine. All these pieces have BE clear as the bottom layer, could I have gotten an 'off' sheet? This has never been a problem. Arg.
lissa.
If your blank is the same size as the mold, (in other words, if your blank is suspended by the very rim of the mold) make it a little smaller, so the the blank rests against the interior side walls of the mold, not the rim.
If you have the equipment, grinder, or preferably, wet belt sander, put a SMALL bevel on the bottom edge of your blank. It doesn't have to be much, a 1/16" is enough. This will help the glass "slide" down the mold.
Brock
Aha! Very interesting. I used a lap wheel to finish these edges before slumping, so it's a pretty sharp edge on the surface of the mold. They are sitting inside the mold completely, but the sharp edge really holds them in place, it is hard to move the glass to get it level. So, maybe it is holding onto to its original position in the mold and resisting settling into the slump. I bet that's it. Hope so. Thanks for the aha moment.
lissa.
lissa.