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Air Bubble in large panel when slumping.
Posted: Thu Mar 07, 2013 2:29 am
by Richard Carder
Hi, when slumping a large panel 8" x 15" on a wave mould I always get a large air bubble in the middle of the piece. I have air holes in the mould. The only thing I can think that is causing it is that panel is slight thickness differences in the panel.
Re: Air Bubble in large panel when slumping.
Posted: Thu Mar 07, 2013 6:01 am
by bob proulx
Is your mould raised up off of your kiln shelf, if not that could be the problem.
Bob
Re: Air Bubble in large panel when slumping.
Posted: Thu Mar 07, 2013 8:42 am
by Richard Carder
Yes, I have raised it off the kiln floor to let the air escape through the air holes.
Re: Air Bubble in large panel when slumping.
Posted: Thu Mar 07, 2013 9:15 am
by Bert Weiss
You could try fiber paper on the mold, or lowering your slump temp. The first solution allows air to escape through the porous paper. The second keeps the glass too stiff for the bubble to be able to expand the glass. I am assuming the bubble is coming from under the glass.
Re: Air Bubble in large panel when slumping.
Posted: Thu Mar 07, 2013 10:24 am
by Mary Lou
What is your schedule and how thick is the piece?
Re: Air Bubble in large panel when slumping.
Posted: Thu Mar 07, 2013 12:04 pm
by Richard Carder
Hi, the firing schedual is in cent, 85,538,20,85,633,5,465,716,12,Full,488,60,20,445,10,215,150
Re: Air Bubble in large panel when slumping.
Posted: Thu Mar 07, 2013 12:05 pm
by Richard Carder
Oh yes, the thickness is 3mm with fused frit on top.
Re: Air Bubble in large panel when slumping.
Posted: Thu Mar 07, 2013 2:26 pm
by Bert Weiss
Richard Carder wrote:Oh yes, the thickness is 3mm with fused frit on top.
Do not fire at full speed up to your top temp. 3mm glass picks up heat very quickly. Your fast firing up to top temp is making the glass get too hot and soft. Working with glass thinner than 6mm requires quite a bit of sensitivity.
I'd think about trying 85 633, 170 716 5 Your soaks are a waste of time unless you know something I don't, like glass broke without them. The 5 minute soak can be shortened or extended, as required, to get the job done. If that schedule results in a bubble, either slow down or lower temperature.
Re: Air Bubble in large panel when slumping.
Posted: Thu Mar 07, 2013 2:35 pm
by Laurie Saukko
I had been getting a pesty and persistent air bubble on one piece and I slowed my slump right down and it finally came out brilliant!
Re: Air Bubble in large panel when slumping.
Posted: Thu Mar 07, 2013 2:40 pm
by Richard Carder
Thanks everyone.
Re: Air Bubble in large panel when slumping.
Posted: Thu Mar 07, 2013 3:46 pm
by Laurie Spray
Recently i have changed my standard slumping schedule to
300 / 1100. No hold (Slower for thick or tack fused etc)
50 / 1250 then to anneal
Everything has been coming out more evenly slumped and perfect.
I think it all about slowing down at the top.
Re: Air Bubble in large panel when slumping.
Posted: Fri Mar 08, 2013 12:11 pm
by rosanna gusler
and is the bubble a 'bubble' or a lump resulting from the glass being so soft that is sliding/stretching down into the mold? r.
Re: Air Bubble in large panel when slumping.
Posted: Fri Mar 15, 2013 7:54 am
by Richard Carder
Just open kiln and my panel is perfect. Thanks everyone for advice.