'Trying to fire a large plate, at least 20" across, two layers of clear, plus decoration... I called Bullseye, and got another firing schedule, that goes up 300° an hour to 1250, then up to 1500°.. Annealing 3 hours, and reducing 60° an hour to 700°... I'm using five coats of Bullseye kiln wash, letting it dry in the sun, and heating it up in the kiln before firing.. My shelf is new, but was purchased from a ceramic store.
I've been teaching glass art for over 20 years, and I'm stumped.
HELP!
Large bubble on my 20" diameter piece
Moderators: Brad Walker, Tony Smith
Martycom --
I just completed, though with some bubbling problems on the slump (that have now been flattened and is re-slumping now with more holes in the mold) a 20" round piece. It had two layers of clear as a base (UB glass) and tiles stacked up as many as five layers on top. It varied. I had no problem with firing it and this is the fourth time now, and I believe it will make it through this too. I was extremely conservative because I had spent so much time and effort on the piece. I constantly remember what some wise glassie once said, that now is not the time to get impatient after you have spent so much time and energy making the piece.
My schedule (on thinfire) was:
50 dph set 1100 hold 30 minutes
100 dph set 1450 hold 30 minutes
AFAP set 960 hold 3 hours
60 dph set 700 hold 30 minutes
Cool to room temp without peeking or venting
It made it!! Hope this helps.
Aimee
aka
anea
I just completed, though with some bubbling problems on the slump (that have now been flattened and is re-slumping now with more holes in the mold) a 20" round piece. It had two layers of clear as a base (UB glass) and tiles stacked up as many as five layers on top. It varied. I had no problem with firing it and this is the fourth time now, and I believe it will make it through this too. I was extremely conservative because I had spent so much time and effort on the piece. I constantly remember what some wise glassie once said, that now is not the time to get impatient after you have spent so much time and energy making the piece.
My schedule (on thinfire) was:
50 dph set 1100 hold 30 minutes
100 dph set 1450 hold 30 minutes
AFAP set 960 hold 3 hours
60 dph set 700 hold 30 minutes
Cool to room temp without peeking or venting
It made it!! Hope this helps.
Aimee
aka
anea
Martycom --
I just completed, though with some bubbling problems on the slump (that have now been flattened and is re-slumping now with more holes in the mold) a 20" round piece. It had two layers of clear as a base (UB glass) and tiles stacked up as many as five layers on top. It varied. I had no problem with firing it and this is the fourth time now, and I believe it will make it through this too. I was extremely conservative because I had spent so much time and effort on the piece. I constantly remember what some wise glassie once said, that now is not the time to get impatient after you have spent so much time and energy making the piece.
My schedule (on thinfire) was:
50 dph set 1100 hold 30 minutes
100 dph set 1450 hold 30 minutes
AFAP set 960 hold 3 hours
60 dph set 700 hold 30 minutes
Cool to room temp without peeking or venting
It made it!! Hope this helps.
Aimee
aka
anea
I just completed, though with some bubbling problems on the slump (that have now been flattened and is re-slumping now with more holes in the mold) a 20" round piece. It had two layers of clear as a base (UB glass) and tiles stacked up as many as five layers on top. It varied. I had no problem with firing it and this is the fourth time now, and I believe it will make it through this too. I was extremely conservative because I had spent so much time and effort on the piece. I constantly remember what some wise glassie once said, that now is not the time to get impatient after you have spent so much time and energy making the piece.
My schedule (on thinfire) was:
50 dph set 1100 hold 30 minutes
100 dph set 1450 hold 30 minutes
AFAP set 960 hold 3 hours
60 dph set 700 hold 30 minutes
Cool to room temp without peeking or venting
It made it!! Hope this helps.
Aimee
aka
anea
Re: Large bubble on my 20" diameter piece
new shelf: have you checked it for flatness? put a straightedge across it at many different angles to see if there's any gaps under the edge.Martycom wrote:'Trying to fire a large plate, at least 20" across, two layers of clear, plus decoration... I called Bullseye, and got another firing schedule, that goes up 300° an hour to 1250, then up to 1500°.. Annealing 3 hours, and reducing 60° an hour to 700°... I'm using five coats of Bullseye kiln wash, letting it dry in the sun, and heating it up in the kiln before firing.. My shelf is new, but was purchased from a ceramic store.
I've been teaching glass art for over 20 years, and I'm stumped.
HELP!
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Steve Immerman
- Posts: 208
- Joined: Sun Mar 09, 2003 4:55 pm
- Location: Eau Claire, Wisconsin
- Contact:
I agree with Charlie. I've been through this myself. I think, particularly with a large piece, that a shelf with a uneven surface or uneven internal density is most likely the culprit if the bubble is between the shelf and the glass.
If that is where the bubble is next time try firing in thinfire paper. Otherwise, try a different shelf. Bullseye sells shelves that are supposed to be perfectly flat.
If the bubbles are between layers, than it may be how you have your glass laid out in the kiln, or you're firing too fast.
Steve
If that is where the bubble is next time try firing in thinfire paper. Otherwise, try a different shelf. Bullseye sells shelves that are supposed to be perfectly flat.
If the bubbles are between layers, than it may be how you have your glass laid out in the kiln, or you're firing too fast.
Steve
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Cynthia
What Charlie and Steve said except that I would add one other factor into the mix for your consideration.
If your kiln has side firing elements as well as top, or instead of top...you may just well be getting your perimeters hotter and softer before the rest of the glass. This can create a situation where the glass seats against the shelf before the air has had a chance to escape, even if your shelf is flat.
Shelf paper will work, or baffling your side elements with fiber board, or slowing down your schedule from the upper strain point to full fuse. I don't fire rapidly from 1000 to full process temps anymore, but ramp at 100 dph from 1150 to 1250, then 500 dph to full fuse. No bubbles between shelf and glass and fewer bubble troubles between the glass. If your shelf is warped, flip it and see if the other side is useable. Replace it as soon as is feasible, but these other approaches are a help
If your kiln has side firing elements as well as top, or instead of top...you may just well be getting your perimeters hotter and softer before the rest of the glass. This can create a situation where the glass seats against the shelf before the air has had a chance to escape, even if your shelf is flat.
Shelf paper will work, or baffling your side elements with fiber board, or slowing down your schedule from the upper strain point to full fuse. I don't fire rapidly from 1000 to full process temps anymore, but ramp at 100 dph from 1150 to 1250, then 500 dph to full fuse. No bubbles between shelf and glass and fewer bubble troubles between the glass. If your shelf is warped, flip it and see if the other side is useable. Replace it as soon as is feasible, but these other approaches are a help
Cynthia.... I think you're on to something, as there are more burners on the sides than a kiln that I use at the College where I teach......
I noticed that the bubbles appear in relatively the same places.
I have extra bricks that I use for making thick blocks of glass. Are you suggesting that I place something around the perimeter of the shelf to keep it cooler there?..........I think I have a sense of what you're describing, but would you elaborate more? Thanks
I have several kiln shelves, so will look for the flattest one.
No wonder those large pieces are expensive!
I noticed that the bubbles appear in relatively the same places.
I have extra bricks that I use for making thick blocks of glass. Are you suggesting that I place something around the perimeter of the shelf to keep it cooler there?..........I think I have a sense of what you're describing, but would you elaborate more? Thanks
I have several kiln shelves, so will look for the flattest one.
No wonder those large pieces are expensive!
Marty, I took a look at the piece this afternoon and found another golfball size bubble after the second firing. This bubble was closer to the center, but occured where there were only two layers rather than three. Talked to two glass artist, one suggested 1500 was too hot, bring down to 1450 and soak, also lower shelf away from side heating elements. Other lady suggested heating more slowly below 1200 to allow air to escape. It also looked like several other bubbles had formed and then collapsed since some spots were thinner and a slightly different texture.
- Mara
- Mara
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Cynthia
Yes, I am suggesting that you place some strips of mullite or fiberboard around the perimeter of the piece to shield it from getting direct heat from the side elements. You could also slow down your schedule from 1000 F to your upper process temp. It's often better (dependent upon the end result you are looking for) to fire up more slowly and use lower temps to fire the glass than to ramp AFAP to 1500 and soaking. You can create a way for trapped air to escape by firing on a fiberpaper which would make it so you don't have to baffle, or worry so much if your shelf is flat or not. It provides it's own set of issues though. Pick your poison.Martycom wrote: Are you suggesting that I place something around the perimeter of the shelf to keep it cooler there?..........I think I have a sense of what you're describing, but would you elaborate more? Thanks
I have several kiln shelves, so will look for the flattest one.
No wonder those large pieces are expensive!
Hi there
We regualrly fuse up to three layers of bullseye without bubbling.
We always dam with fibre board, with clear glass we occaisionally use thin fire paper, although we are still on our stock of the old stuff which shrinks when fired and which corroded the finish of irids if fired face down
We have found that elevating our shelf helps, Putting it on stilts or kiln bricks.
We also fire our shelves after applying the kiln wash to ensure there is no moisture.
We have tried making the bowls diametre slightly larger than we need and using compatible frit around the edges to elevate the glass and then very slowly bring the glass through the slumping range to allow the air to escape. we then go back after the fusing to belt down the edge to eliminate the bulges from the frit.
Hope some of this helps,
Bill
We regualrly fuse up to three layers of bullseye without bubbling.
We always dam with fibre board, with clear glass we occaisionally use thin fire paper, although we are still on our stock of the old stuff which shrinks when fired and which corroded the finish of irids if fired face down
We have found that elevating our shelf helps, Putting it on stilts or kiln bricks.
We also fire our shelves after applying the kiln wash to ensure there is no moisture.
We have tried making the bowls diametre slightly larger than we need and using compatible frit around the edges to elevate the glass and then very slowly bring the glass through the slumping range to allow the air to escape. we then go back after the fusing to belt down the edge to eliminate the bulges from the frit.
Hope some of this helps,
Bill
Bill Jamieson
Vitreous Designs, Mayne Is, B.C.
Vitreous Designs, Mayne Is, B.C.
Thank you Cynthia, Steve and Bill.... This has been great.
I checked the shelf and it was level with one of the burners, so I will put it on higher posts..... I have some bead blankets that I will cut into strips and place them around the perimeter of the bowl.
Bill, great idea of the frit around the edge.... But I don't understand why you would make the piece slightly bigger. Does the piece contract with the frit?
I'm printing all of this out, and will try to fire another piece next week....
Then, I'm out of here for a nice month in Europe. I hope to visit Nancy and see all of that beautiful glass again...(Daum glass)....
Thanks again... Marty
I checked the shelf and it was level with one of the burners, so I will put it on higher posts..... I have some bead blankets that I will cut into strips and place them around the perimeter of the bowl.
Bill, great idea of the frit around the edge.... But I don't understand why you would make the piece slightly bigger. Does the piece contract with the frit?
I'm printing all of this out, and will try to fire another piece next week....
Then, I'm out of here for a nice month in Europe. I hope to visit Nancy and see all of that beautiful glass again...(Daum glass)....
Thanks again... Marty
Hey Marty;
The frit leaves distortions, or bumps which can distract from you pattern. I have found that it was better to cut or belt my border to remove the "bumps". I always end up firing the pieces again for slimping, or after extensive sand blasting, so I get my firepolished edge. Another thing we do is we will create a rim or border of fibre board with strips of the kiln paper to keep our edges uniformly thick. we have to belt any distortions after firing, but it keeps our work uniform.
We have also fired on 1/8" or 1/4" hard board (sorry, I can't remember the technical name for it) on our kilnshelf. it is porous enough to allow air trapped under the first piece of glass to escape.
Ciao, enjoy Europe.
Bill
The frit leaves distortions, or bumps which can distract from you pattern. I have found that it was better to cut or belt my border to remove the "bumps". I always end up firing the pieces again for slimping, or after extensive sand blasting, so I get my firepolished edge. Another thing we do is we will create a rim or border of fibre board with strips of the kiln paper to keep our edges uniformly thick. we have to belt any distortions after firing, but it keeps our work uniform.
We have also fired on 1/8" or 1/4" hard board (sorry, I can't remember the technical name for it) on our kilnshelf. it is porous enough to allow air trapped under the first piece of glass to escape.
Ciao, enjoy Europe.
Bill
Bill Jamieson
Vitreous Designs, Mayne Is, B.C.
Vitreous Designs, Mayne Is, B.C.
Thanks Bill....... I'll print this out too. I'm actually putting together a little notebook on the 20" bubble.
When you talk about fireboard, I used to fire on an asbestos type board back in "the day"...... The new, nonasbestes boards, warped after the first couple of firings...... Is this what you're talking about?
I have a sandblaster in my studio, so will be able to smooth out any of the imperfection left by the frit.....
I wanted to mention that I have successfully fired the large plates with recycled glass, particularly the glass with the bottle ring designs. I'm curious if that glass starts to get viscous at a higher temperature. When I think about it, it is filled with irregular designs, off the shelf, so is probably doing what the frit does.. HUM?
Again... thanks for the good information.... Marty
When you talk about fireboard, I used to fire on an asbestos type board back in "the day"...... The new, nonasbestes boards, warped after the first couple of firings...... Is this what you're talking about?
I have a sandblaster in my studio, so will be able to smooth out any of the imperfection left by the frit.....
I wanted to mention that I have successfully fired the large plates with recycled glass, particularly the glass with the bottle ring designs. I'm curious if that glass starts to get viscous at a higher temperature. When I think about it, it is filled with irregular designs, off the shelf, so is probably doing what the frit does.. HUM?
Again... thanks for the good information.... Marty
Hi Marty;
The board is a fibre material, not asbestos, and because I slump my work after my several fusings are completed, It doesn't matter to me if the board is perfectly flat. It ends up curved anyway, so if your piece ends up needing to be flat, it probably isn't a good idea to use it.
I too have a sandblast booth. Tyring to flatten a bump through sandblasting is a painful and ultimately futile process. It never gets flat, besides, you end up blasting away your top color trying to even out the bump.
We use a lot of float and recycled glass also for other aspects of our work, It has it's own headaches.
Best wishes,
Bill
The board is a fibre material, not asbestos, and because I slump my work after my several fusings are completed, It doesn't matter to me if the board is perfectly flat. It ends up curved anyway, so if your piece ends up needing to be flat, it probably isn't a good idea to use it.
I too have a sandblast booth. Tyring to flatten a bump through sandblasting is a painful and ultimately futile process. It never gets flat, besides, you end up blasting away your top color trying to even out the bump.
We use a lot of float and recycled glass also for other aspects of our work, It has it's own headaches.
Best wishes,
Bill
Bill Jamieson
Vitreous Designs, Mayne Is, B.C.
Vitreous Designs, Mayne Is, B.C.
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Stuart Clayman
- Posts: 224
- Joined: Mon Mar 31, 2003 12:35 pm
- Location: Virginia
- Contact:
Marty,
We were having a problem with the new paper at the studio. We solved it. The new paper is flatter and seems to be firing things hotter. We slowed the ramp up to allow for the air to escape. We were only getting the bubble in gthe kiln that fires the fastest of them. The suspision is that since the paper is flatter (and may more dense), and the kiln raqmps up fast it was traping air where it was not happening in the slower kilns. The reason that I said that they items seem to be firing hotter is that we are using the same program settings that we have been using for years and with the new paper it looks like the thin items that we are making are cooking a little more.
Hope this helps,
Stuart
We were having a problem with the new paper at the studio. We solved it. The new paper is flatter and seems to be firing things hotter. We slowed the ramp up to allow for the air to escape. We were only getting the bubble in gthe kiln that fires the fastest of them. The suspision is that since the paper is flatter (and may more dense), and the kiln raqmps up fast it was traping air where it was not happening in the slower kilns. The reason that I said that they items seem to be firing hotter is that we are using the same program settings that we have been using for years and with the new paper it looks like the thin items that we are making are cooking a little more.
Hope this helps,
Stuart