I hate to even ask it but... huge bubble

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Lauralei
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I hate to even ask it but... huge bubble

Post by Lauralei »

rats, I was doing so well, then bam ! huge bubble in my 22" platter, the 8 " center of white BE surrounded by black BE, AND with a silk screened design on it when blooey.
I did try to do my homework and seach for reasons why but I may have done something extrodinarily stupid - that's never been tried before..
Fired once as blank , no problems
sandblasted design (i know - wrong)
Fired 2nd time & slumped with silk screened dry paradise paint - too matte
Fired 3rd time - still in slump mold ( could that be the key to my madness?) to bring the paint to glossy red.
Result - enormous flying crane over mt Kilamanjaro...

before I create a pattern bar with this - Wha happened? All jeers will be accepted with constructive criticism...

(last fire - 350 to 1250 hold 15, 350 to 1350 hold 15, afap 960 hold 45, 200 to 700 - off.

thanks ! :-({|=
Lauralei
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Brock
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Post by Brock »

Tell us about your mold. Brock
My memory is so good, I can't remember the last time I forgot something . . .
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Barbara Muth
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Post by Barbara Muth »

And was the last firing to 350 for 15 minutes done in the slumping mold?
Barbara
Check out the glass manufacturer's recommended firing schedules...
LATEST GLASS
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Lauralei
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Hi Brock!

Post by Lauralei »

Your Effervescent student from Corning ( who had to leave early...)
it was a BE ceramic slump mold with a very shallow curve...
Much bigger bubble than the one in the black plate blank... where did I go wrong...
Lauralei
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Brock
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Re: Hi Brock!

Post by Brock »

Lauralei wrote:Your Effervescent student from Corning ( who had to leave early...)
it was a BE ceramic slump mold with a very shallow curve...
Much bigger bubble than the one in the black plate blank... where did I go wrong...
Hi Laurelei - I'm kinda stumped. If it slumped on the mold the first time, then you refired hotter to get the PP shiny, I don't see why you would get a bubble. It had already conformed to the mold. Where did the air come from?
My memory is so good, I can't remember the last time I forgot something . . .
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charlie
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Post by charlie »

did you move the mold? was it on stilts the first time and not the second? could something have plugged the holes in the bottom? are there holes in the bottom? could it have not slumped all the way down the first time, but sealed on the edges, and the 2nd time the air pocket expanded since it had no where to go?
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Lauralei
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Post by Lauralei »

I can't figure where it came from either, Brock .... the 2 pin holes at the slump bottom was clear.. nothing else in the kiln etc... it's ready for a pattern bar now - but I wanted to see how I could avoid in the future..
I didn't wash the plate before I refired, I checked for level with the bubble level.. Maybe some air got trapped at the bottom? but what could have made a difference? firing it without the mold and letting it get flat and reslumping? I did have the 2 kiln side vents open, as Avery said the Reds didn't like to be with out oxygen. Could the vents have pulled in too much outside air to cause that? or am I hoping for little green men?

Barbara - thanks for your assistance - but I think the firing schedule is misread as 350 for 15 min - thats the "ramp rate" for the 1st 2 ramps.. any advise is welcome ..
Lauralei
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Lauralei
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Post by Lauralei »

Charlie, what do you mean? Yes I think it slumped all the way down the first time .. so what are you saying ? that if so whatever air was below the edge got caught and couldn't get out of the 2 pin holes? Not clogged by the way .. not on stilts first or second time...
Lauralei
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Steve Immerman
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Re: I hate to even ask it but... huge bubble

Post by Steve Immerman »

Lauralei wrote:Fired 3rd time - still in slump mold ( could that be the key to my madness?) to bring the paint to glossy red.
Result - enormous flying crane over mt Kilamanjaro...
Did you take it out of the mold after the 2nd firing, and then put it back into the mold again? Or just leave it in and refire?

Steve
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Brad Walker
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Post by Brad Walker »

Is there any chance that you fired too high and the piece slid down the edges of the mold, leaving what looks like a bubble on the bottom? I've had this happen once or twice when I fired above 1300 trying to quickly fire polish with the piece in a mold.

Got a photo of the bubble?
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Cynthia

Post by Cynthia »

I've had bubbles with BE ball surface molds and the square slumper. I've not left a peice in the mold and taken it up to higher temps than required for bending...but what I believe happens with the bending bubbles is that the glass reaches the base and covers the vent holes before the sides conform to the mold, trapping air and not allowing the piece to fully seat to the shape of the mold leaving a raised bubble like shape where the glass couldn't bend.

It's possible that this is what happened to you, but in a less obvious way. Some small pocket of air space was still between the mold and the glass...then you fired it at a high enough temp for the air to expand and push up a bubble in the glass...

1350 is hot enough for that to happen...

Something to consider.
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Tony Serviente
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Post by Tony Serviente »

I've had bubbles in bowl forms, sometimes with dramatic results, always a result of overfiring. Once had a batch of 8" diameter rimmed forms (with the requisite holes in the bottom) sprout mushrooms in the center! Was very cool looking, but left something to be desired as a piece of functional glassware. The little glass fungi were about 2" tall with very thin stalks, but pretty substantial crowns. Air holes got plugged with glass, and the trapped air in the center did some extemporaneous glass blowing.
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Lauralei
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Post by Lauralei »

Thanks Everybody for your insight - that's all something for me to think about ... Yes Brad - I do have a picture - I'll post the mold and the big bubble tomorrow when I get it out of the camera. I really appreciate your help in trying to understand how to avoid this in the future! thanks
Steve - yes I took it out of the mold after the 1st time and then re-leveled it for the 2nd fire. I look forward to what y'all have to see after you see it - it's HUGE !
Lauralei
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Steve Immerman
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Post by Steve Immerman »

Lauralei wrote:Steve - yes I took it out of the mold after the 1st time and then re-leveled it for the 2nd fire. I look forward to what y'all have to see after you see it - it's HUGE !
I think that if you take something out of a mold, put it back in the mold and refire - that the relationship of the glass to the mold changes, particularly if the glass is rotated with respect to it's original position. There can be air trapped between the glass and the mold that just may not find it's way to the holes - resulting in a bubble.

Just a theory - but it has happened to me- and that's how I've been able to explain it.

Steve
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charlie
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Post by charlie »

Steve Immerman wrote:
Lauralei wrote:Steve - yes I took it out of the mold after the 1st time and then re-leveled it for the 2nd fire. I look forward to what y'all have to see after you see it - it's HUGE !
I think that if you take something out of a mold, put it back in the mold and refire - that the relationship of the glass to the mold changes, particularly if the glass is rotated with respect to it's original position. There can be air trapped between the glass and the mold that just may not find it's way to the holes - resulting in a bubble.

Just a theory - but it has happened to me- and that's how I've been able to explain it.

Steve
i would expect this to occur if the mold wasn't exactly symetric, which is probably pretty common for slip poured molds.
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Lauralei
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Post by Lauralei »

Well - here it is - my huge bubble - thanks again to everybody !
I'll be interested to see if any of the diagnosis change after you've seen the patient...
Image
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Lauralei
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Post by Lauralei »

[img]<img%20src="http://img.villagephotos.com/p/2003-11/ ... t=680>[img][/img]
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Lauralei
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Post by Lauralei »

http://img.villagephotos.com/p/2003-11/ ... bubble.JPG
Lauralei
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Lauralei
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Post by Lauralei »

http://img.villagephotos.com/p/2003-11/ ... bubble.JPG

sorry - i think i've got it now....
Lauralei
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Brock
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Post by Brock »

Lauralei wrote:http://img.villagephotos.com/p/2003-11/ ... bubble.JPG

sorry - i think i've got it now....
We call that trapped air. Does that mold have hole(s) in the side? Was it directly on the shelf? Did you check the vent holes before you re-slumped?Do you live under a big black cloud? Were you very bad as a child? Brock
My memory is so good, I can't remember the last time I forgot something . . .
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