i cast some frit and other elements on top of a 10" disk of BE opal salmon last week, and the result was about a half inch thick. i must have been a little hasty to take it out of the kiln, because later on the blank cracked in half.
when this project was firing, the bottom sheet of salmon cracked, evidently on the way up (Y-shaped crack). i wasn't going up very fast, either, maybe 300dph. (can't lay my hands on the schedule unfortunately ... must've gotten thrown away).
i've put the thing back together, with a band of fiber paper around the outside to hold it together. it wouldn't fit back into the stainless steel ring. i've added some more elements, so it'll be a little thicker. here's the schedule i put together, but i'm just guessing and trying to be conservative. i dont suppose it would crack again going up since it's already got a big crack down the middle, but anyway, here's my plan:
150dph to 500, H 30
150dph to 1000, H 30
250dph to 1235, H 30
300dph to 1550, H 20
AFAP to 960, H 90
57dph to 815
114 dph to 725
570 dph to 90
there are a zillion little pieces of stuff on this blank, so i thought i should go up slowly. the 30 minute holds are to let the temperature stabilize thru the thick piece. i opted for a 90 minute hold at 960 because the piece is probably over 1/2" thick, so i went for the H recommended for 3/4" thick pieces. the descent is from BE annealing chart.
any advice, corrections, adjustments would sure be welcome. THANKS.
Re-Fire of Thick Piece - Schedule Advice Please
Moderators: Brad Walker, Tony Smith
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Cynthia
Re: Re-Fire of Thick Piece - Schedule Advice Please
Following a schedule for 1/2" thick glass according to Graham Stones schedules...this is what I would do. This is a guideline, so make adjustments according to what you know about your kiln. I'd baffle the sides as well.
250 dph to 1470, hold if necessary
AFAP to 960 with a 30 minute soak
30 dph to 940
60 dph to750
320 dph to 130 then off
You don't need all those soaks you have in your schedule. Your ascent in temp. is so slow that the glass can keep up and heat evenly. In the schedule I gave you, the 30 minute soak is ample to allow the glass to equalize in temp, and the descent through the annealing range is slow enough to allow even cooling = annealing.
Slow the ramp up if you feel it necessary for your kiln. This schedule has never failed me to date, knock wood, and I have fired the same panels, 1/2" and thicker, multiple times without problems. Now watch. I've probably just jinxed it.
You are going so slowly up to processing temps and hanging in that devit range for so long, that you might want to consider using an overglaze to prevent devit...or change the schedule to ramp up more rapidly from 1000 to full fuse temps to get in and out of that range faster.
250 dph to 1470, hold if necessary
AFAP to 960 with a 30 minute soak
30 dph to 940
60 dph to750
320 dph to 130 then off
You don't need all those soaks you have in your schedule. Your ascent in temp. is so slow that the glass can keep up and heat evenly. In the schedule I gave you, the 30 minute soak is ample to allow the glass to equalize in temp, and the descent through the annealing range is slow enough to allow even cooling = annealing.
Slow the ramp up if you feel it necessary for your kiln. This schedule has never failed me to date, knock wood, and I have fired the same panels, 1/2" and thicker, multiple times without problems. Now watch. I've probably just jinxed it.
You are going so slowly up to processing temps and hanging in that devit range for so long, that you might want to consider using an overglaze to prevent devit...or change the schedule to ramp up more rapidly from 1000 to full fuse temps to get in and out of that range faster.
i ended up soaking the piece for 90 minutes at 960, and used the descent cynthia offered. around 300 i heard the piece PING from the kiln. it cracked.
i've never had this happen before, but this piece is thicker than i most of my previous projects. do you think i should slow the descent down even more after the soak at 960?
this piece broke in half after the first firing, sitting on a table, not exposed to any air conditioning or sunlight. it was in a dim room. maybe it has some inherent problems that can't be resolved. i'm considering sawing it up into pieces for future pattern bars ... or throwing it away.
always interested to hear what others think. sometimes things just don't work out the way we plan.
i've never had this happen before, but this piece is thicker than i most of my previous projects. do you think i should slow the descent down even more after the soak at 960?
this piece broke in half after the first firing, sitting on a table, not exposed to any air conditioning or sunlight. it was in a dim room. maybe it has some inherent problems that can't be resolved. i'm considering sawing it up into pieces for future pattern bars ... or throwing it away.
always interested to hear what others think. sometimes things just don't work out the way we plan.
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Cynthia
Well. Hmmm.
What shape is the crack? Does it run in the same place as the first time? Could it be you've got incompatible glass in there, or the compatibility shifted? Or do you believe it's an annealing problem?
I know Jackie Beckman uses scads of differnt colors of glass in her work, and she fires very conservatively. Perhaps she has some advice.
Sorry it didn't work.
C.
What shape is the crack? Does it run in the same place as the first time? Could it be you've got incompatible glass in there, or the compatibility shifted? Or do you believe it's an annealing problem?
I know Jackie Beckman uses scads of differnt colors of glass in her work, and she fires very conservatively. Perhaps she has some advice.
Sorry it didn't work.
C.
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Barbara Muth
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What I learned is that my ramp up of 200 dph for a 1/4 inch piece that was smooth but did have both black and white in it was too fast. Apparently, even though it had worked before, I had always been skating on thin ice, and it finally cracked. I would go up even more slowly than what you are suggesting with a piece that thick, especially because of the texture in the piece. After all you have invested in the piece, better to ramp up more slowly and waste time than to ramp up not quite slow enough and have to redo it again....
Once I have fired some new work I'll let you know if new schedules are working for me.
Kitty, I strongly recommend a few tests of your kiln. If your kiln isn't heating evenly, you could be introducing more stress during the annealing. BE has a great test of evenivity that I ran a few weeks ago on my kiln when I was looking at why my pieces were breaking. http://www.bullseyeconnection.com/pdfs/ ... tes_01.pdf
Slowing down on ramp up and down is not a bad thing. good luck!
Barbara
Once I have fired some new work I'll let you know if new schedules are working for me.
Kitty, I strongly recommend a few tests of your kiln. If your kiln isn't heating evenly, you could be introducing more stress during the annealing. BE has a great test of evenivity that I ran a few weeks ago on my kiln when I was looking at why my pieces were breaking. http://www.bullseyeconnection.com/pdfs/ ... tes_01.pdf
Slowing down on ramp up and down is not a bad thing. good luck!
Barbara
Last edited by Barbara Muth on Tue Aug 05, 2003 9:49 am, edited 1 time in total.
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Jackie Beckman
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Hi Kitty,
I agree with Phil that the rate from 750 down to room temp should have been slower. Had it been only a two layer piece, I still would have gone slower during the final cool down, but I am ultra conservative when it comes to my schedules. I probably would have gone no faster than 100dph until I got to 300 with a piece that thick, then turned off the kiln and not opened it until about 100, then let sit there on the shelf a while even still.
Jackie
I agree with Phil that the rate from 750 down to room temp should have been slower. Had it been only a two layer piece, I still would have gone slower during the final cool down, but I am ultra conservative when it comes to my schedules. I probably would have gone no faster than 100dph until I got to 300 with a piece that thick, then turned off the kiln and not opened it until about 100, then let sit there on the shelf a while even still.
Jackie
barbara muth -- i did do an evenity test on this kiln about six months ago, and all seemed well, but i'll do it again. that's a good suggestion.
jackie -- thanks. i'll re-fire it with slower cooling, and let it "set a spell" before taking it out.
i've noticed in the last few months a number of posts here talking about much more conservative firing schedules. i think i'm beginning to understand why.
thanks, everybody.
jackie -- thanks. i'll re-fire it with slower cooling, and let it "set a spell" before taking it out.
i've noticed in the last few months a number of posts here talking about much more conservative firing schedules. i think i'm beginning to understand why.
thanks, everybody.
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Barbara Muth
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Brian and Jenny Blanthorn
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Re: Re-Fire of Thick Piece - Schedule Advice Please
Yo KittyKitty wrote:i cast some frit and other elements on top of a 10" disk of BE opal salmon last week, and the result was about a half inch thick. i must have been a little hasty to take it out of the kiln, because later on the blank cracked in half.
when this project was firing, the bottom sheet of salmon cracked, evidently on the way up (Y-shaped crack). i wasn't going up very fast, either, maybe 300dph. (can't lay my hands on the schedule unfortunately ... must've gotten thrown away).
i've put the thing back together, with a band of fiber paper around the outside to hold it together. it wouldn't fit back into the stainless steel ring. i've added some more elements, so it'll be a little thicker. here's the schedule i put together, but i'm just guessing and trying to be conservative. i dont suppose it would crack again going up since it's already got a big crack down the middle, but anyway, here's my plan:
150dph to 500, H 30
150dph to 1000, H 30
250dph to 1235, H 30
300dph to 1550, H 20
AFAP to 960, H 90
57dph to 815
114 dph to 725
570 dph to 90
there are a zillion little pieces of stuff on this blank, so i thought i should go up slowly. the 30 minute holds are to let the temperature stabilize thru the thick piece. i opted for a 90 minute hold at 960 because the piece is probably over 1/2" thick, so i went for the H recommended for 3/4" thick pieces. the descent is from BE annealing chart.
any advice, corrections, adjustments would sure be welcome. THANKS.
On this type of fire up
U gota a few things going on
Cracks in the glass not broke ?
Thick big glass
Partly bafled
New stuff on top again part baffle
On this kinda set up I would go slow over night
Say 50 or even 20 c hour till well above aneal
Keep vents closed if U can or only open 1 due 2 thermal shock
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Brian and Jenny Blanthorn
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Kitty wrote:brian, i can't understand exactly what you mean about the baffling. it's a top firing kiln. please explain. thanks!
OK the use of a baffle is usually 2 achive evenivity of temp
But in ur set up, the side dams that will cover the sides of the glass n give unevenivity
+ U got glass on top again causing unevenivity
Hence the more cautious slow schedule
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Cynthia
I apologize Kitty. Huge error on my part for the 300 to room temp. That's what the book says, but I always just turn my kiln off after 700 and allow it to cool naturally...which is incredibly slow. I should have altered the schedule I gave you to reflect that instead of the one in the book. Did you actually vent to cool at that rate? As my neighbor kid would say..."My bad".
I still wonder about a compatibility shift since your crack showed up in the same location, but that isn't to suggest that thermal shock isn't a possibility if not a probability.
I still wonder about a compatibility shift since your crack showed up in the same location, but that isn't to suggest that thermal shock isn't a possibility if not a probability.
well, i thought that seemed kinda fast, based on BE chart, but what do i know? it's a learning thing.
i have to make some things to put on this piece before re-firing it, in hopes of the next firing being the last one. i'm kinda busy with other stuff right now, and this little problem piece has been set aside, on it's kiln shelf, to wait. i dont want to move it and find out how deeply the crack runs thru it.
i'll report back later when i've revisited the project. kitty.
i have to make some things to put on this piece before re-firing it, in hopes of the next firing being the last one. i'm kinda busy with other stuff right now, and this little problem piece has been set aside, on it's kiln shelf, to wait. i dont want to move it and find out how deeply the crack runs thru it.
i'll report back later when i've revisited the project. kitty.