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pizzuti_

Up to what temp can I vent?

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I have a paragon XL. I've blown up a couple of pieces in the past so now I'm venting and doing a mirror test but I was just curious as to what temp I can vent to?  When do I know for sure it's safe to shut the lid?

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Pieces can look dry on the surface but not be fully dry all the way through, and can be tricky to determine if you're in a humid environment. How a piece feels (ie cool to the touch) can be a better indicator. If a piece is particularly thick, like with some sculptural work, you need to allow for more time for the water to work its way fully out of a piece. Water vapour that is escaping a piece too rapidly in the early part of the firing is what causes explosions, not anything else. You vent a kiln to prolong element life, and to keep the atmosphere in the kiln clean to allow for proper burnoff of organic materials so your pieces don't black core. Venting won't have an effect on wether or not a piece blows up.

As to when you can stop venting for the sake of conserving energy, it depends on the conditions your kiln is firing under.  My kiln is outdoors and in a shed, and has no other vent fan.  I leave one peep unblocked until the firing is done (mostly because I'm lazy), and then block it completely to cool. Someone with a venting system will likely do things differently. 

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12 minutes ago, Callie Beller Diesel said:

Pieces can look dry on the surface but not be fully dry all the way through, and can be tricky to determine if you're in a humid environment. How a piece feels (ie cool to the touch) can be a better indicator. If a piece is particularly thick, like with some sculptural work, you need to allow for more time for the water to work its way fully out of a piece. Water vapour that is escaping a piece too rapidly in the early part of the firing is what causes explosions, not anything else. You vent a kiln to prolong element life, and to keep the atmosphere in the kiln clean to allow for proper burnoff of organic materials so your pieces don't black core. Venting won't have an effect on wether or not a piece blows up.

As to when you can stop venting for the sake of conserving energy, it depends on the conditions your kiln is firing under.  My kiln is outdoors and in a shed, and has no other vent fan.  I leave one peep unblocked until the firing is done (mostly because I'm lazy), and then block it completely to cool. Someone with a venting system will likely do things differently. 

Thank you, that was helpful. I am in a very damp, humid area. And I don't have peep holes so I just propped the lid a bit.

Most of my work is pretty thick because it is all sculptures and I like them solid, it took forever for me to hollow them, I just don't like hollow sculptures. The one I'm firing today is thick. I was going to leave it solid but ended up hollowing a bit before I fired it. It seemed dry, not cool at all. I candled it yesterday and then had it vented up to 750 today. No steam on the mirror, fingers crossed.

 

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I also have an electric which I bisque in a little (more gas bisquing)I leave the lid cracked until 800-900 degrees-then all water is gone so I close the lid-if the work is bone dry I do not crack the lid.750 should be fine to close up at.

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Yeah, leaving sculptures solid will definitely cause you a lot of loss in the kiln. To leave pieces solid, you'd need months for something to dry thoroughly, particularly if you're somewhere humid. I think learning to love hollow sculptures will make your life infinitely easier. Building on packed paper or other removable armatures could be less nerve wracking, if you don't like cutting pieces apart and putting them back together.  

I think venting to 750C is probably just right, particularly if your just propping the lid open.  

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I won't even let someone fire a piece of sculpture that hasn't been hollowed out in my kilns.   You just end up with a messy kiln.     Denice

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1 hour ago, Mark C. said:

I also have an electric which I bisque in a little (more gas bisquing)I leave the lid cracked until 800-900 degrees-then all water is gone so I close the lid-if the work is bone dry I do not crack the lid.750 should be fine to close up at.

Well we'll see in the morning.... :)

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1 hour ago, Callie Beller Diesel said:

Yeah, leaving sculptures solid will definitely cause you a lot of loss in the kiln. To leave pieces solid, you'd need months for something to dry thoroughly, particularly if you're somewhere humid. I think learning to love hollow sculptures will make your life infinitely easier. Building on packed paper or other removable armatures could be less nerve wracking, if you don't like cutting pieces apart and putting them back together.  

I think venting to 750C is probably just right, particularly if your just propping the lid open.  

Yeah, I'm working on adapting to hollowing out pieces. It bothers me but I did it on this last one. Hopefully I did enough.

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40 minutes ago, Denice said:

I won't even let someone fire a piece of sculpture that hasn't been hollowed out in my kilns.   You just end up with a messy kiln.     Denice

That's why God made vacuum cleaners! :)

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You shouldn't leave any part of the sculpture more than 1/2 inch thick. Any thicker and you run the risk of steam explosions unless you fire very slowly. The explosions will happen when the water in the clay turns to steam. In a thick piece in a typical firing schedule, the kiln may reach 250C before the inside of the piece reaches 100C and the explosions start. If you're firing with a manual kiln, I suggest just turning on the bottom switch to low and letting it sit for 12-24 hours with the lid propped to make sure the pieces are dried out completely. Then fire very slowly for the first several hundred degrees. If you're firing a digital kiln, then program a long preheat segment, holding at 90C.

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54 minutes ago, neilestrick said:

You shouldn't leave any part of the sculpture more than 1/2 inch thick. Any thicker and you run the risk of steam explosions unless you fire very slowly. The explosions will happen when the water in the clay turns to steam. In a thick piece in a typical firing schedule, the kiln may reach 250C before the inside of the piece reaches 100C and the explosions start. If you're firing with a manual kiln, I suggest just turning on the bottom switch to low and letting it sit for 12-24 hours with the lid propped to make sure the pieces are dried out completely. Then fire very slowly for the first several hundred degrees. If you're firing a digital kiln, then program a long preheat segment, holding at 90C.

Thanks, that's helpful. I have pieces that are more than 1/2" thick. The one I just fired is probably an inch thick in a few spots. I heated him at 200 for a few hours yesterday with the lid propped up a bit. Just fired him we'll see if he made it tomorrow...

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I wonder how you will feel about vacuuming a kiln after you have been firing for 45 years.  The person who made the work doesn't stick around and I have seen a blown piece break another one that is near by.   Denice

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4 hours ago, Denice said:

I wonder how you will feel about vacuuming a kiln after you have been firing for 45 years.  The person who made the work doesn't stick around and I have seen a blown piece break another one that is near by.   Denice

I was kidding..

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Sounds like you'd rather find out for yourself than do things the usual way. There's nothing wrong with making solid sculpture essentially as long as you're willing to have it destroyed when it's fired, and only blowing up your own work and damaging your own kiln for no particular reason, being that there are better ways to do it that were discovered thousands of years ago. I'm wondering why you're asking questions about it if you're so sure it will work? It seems like a lot of wasted effort when you could be focusing on sculpting instead of things blowing up. 

 I too enjoy pushing the boundaries and generally have to see things to believe them, but in my old age I've learned actually taking advice lets me move forward faster, (note my signature, if you like). But, my bit of advice is to make sure things are bone dry. Not just think they look dry. You can get away with a lot if it's simply bone dry. Solid sculpture is going to take a long, long time to fully dry, hence the hollowing. Air doesn't expand much, steam does. 

Question for you: What is the head sculpture you use for your icon made of? 

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58 minutes ago, yappystudent said:

Sounds like you'd rather find out for yourself than do things the usual way. There's nothing wrong with making solid sculpture essentially as long as you're willing to have it destroyed when it's fired, and only blowing up your own work and damaging your own kiln for no particular reason, being that there are better ways to do it that were discovered thousands of years ago. I'm wondering why you're asking questions about it if you're so sure it will work? It seems like a lot of wasted effort when you could be focusing on sculpting instead of things blowing up. 

 I too enjoy pushing the boundaries and generally have to see things to believe them, but in my old age I've learned actually taking advice lets me move forward faster, (note my signature, if you like). But, my bit of advice is to make sure things are bone dry. Not just think they look dry. You can get away with a lot if it's simply bone dry. Solid sculpture is going to take a long, long time to fully dry, hence the hollowing. Air doesn't expand much, steam does. 

Question for you: What is the head sculpture you use for your icon made of? 

I'm not exactly sure what you are talking about but the piece I referenced in this post was already in the kiln by the time anyone responded and it came out just fine, over an inch think in places so I guess it was completely dry.  I've only blown up two pieces, not really a big deal, it's not like I can't make another one.

My icon is porcelain.

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37 minutes ago, pizzuti_ said:

I'm not exactly sure what you are talking about but the piece I referenced in this post was already in the kiln by the time anyone responded and it came out just fine, over an inch think in places so I guess it was completely dry.  I've only blown up two pieces, not really a big deal, it's not like I can't make another one.

My icon is porcelain.

Is the porcelain head sculpture in your icon hollow, or solid? 

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22 minutes ago, pizzuti_ said:

I'm not exactly sure what you are talking about but the piece I referenced in this post was already in the kiln by the time anyone responded and it came out just fine, over an inch think in places so I guess it was completely dry.

This is Hülda, a maquette I made for a project I never completed. She is loosely based on paleolithic figures.

Hulda.jpeg.d70c7fcd4f5b25eedadc823398e68af2.jpeg

Sorry for the appalling photograph!

Anyway, she is about 8 inches high, and at her broadest, perhaps 2 inches by 1 inch. And she is solid, deliberately so, because I love the weight of a solid sculpture. Hülda wouldn't be Hülda if she were hollow. The weight - the solidity, the nature of the material - is part of her identity.

The clay is a porcelain paper clay. I had no fear of her exploding, having fired this clay at similar thicknesses many times before. The key is to know the limits of your material. I would be happy to fire much thicker than this, with an appropriate schedule. People panic too much.

 

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1 hour ago, Sputty said:

This is Hülda, a maquette I made for a project I never completed. She is loosely based on paleolithic figures.

Hulda.jpeg.d70c7fcd4f5b25eedadc823398e68af2.jpeg

Sorry for the appalling photograph!

Anyway, she is about 8 inches high, and at her broadest, perhaps 2 inches by 1 inch. And she is solid, deliberately so, because I love the weight of a solid sculpture. Hülda wouldn't be Hülda if she were hollow. The weight - the solidity, the nature of the material - is part of her identity.

The clay is a porcelain paper clay. I had no fear of her exploding, having fired this clay at similar thicknesses many times before. The key is to know the limits of your material. I would be happy to fire much thicker than this, with an appropriate schedule. People panic too much.

 

Thank you. :) I feel the same, hollow is not my thing.

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Well try is for sure the answer here.

However....an old potter had a solid piece which had sat in her studio then in her lounge room by her backdoor back into the corridor In her house..

FOR YEARS

 

Her kiln long gone she asked me to fire it.

I nursed it up a long long slow fire, like a new brick kiln...over 24 hrs electric kiln filled with other sculpted pieces  student work. Nothing else blew

So do what you like but  folk gave great advice

 

Head blew apart. Discussion re moisture or air ensued...moisture.

Can "get away" more often by inserting skewers from base up to allow moisture to evaporate out....

Sputty That's not a big sculpture. You know how to fire.

Edited by Babs
Emphasis

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1 hour ago, yappystudent said:

Is the porcelain head sculpture in your icon hollow, or solid? 

Solid, almost all of my work is solid with the exception of two busts where I hollowed out the chest a bit but all the heads are solid. This piece I was talking about in this post was a commission.

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6 minutes ago, Babs said:

Well try is for sure the answer here.

However....an old potter had a solid piece which had sat in her studio then in her lounge room by her backdoor back into the corridor In her house..

 

Her kiln long gone she asked me to fire it.

I nursed it up a long long slow fire, like a new brick kiln...over 24 hrs electric kiln filled with other sculpted pieces  student work. Nothing else blew

So do what you like but  folk gave great advice

 

Head blew apart. Discussion re moisture or air ensued...moisture.

Can "get away" more often by inserting skewers from base up to allow moisture to evaporate out....

i am not unwilling to take advice, that is why I asked.  I just like solid pieces better. Sculpture is different than pots and bowls, it has a life to it, being hollow affects it, I know that probably sounds strange but that's how I feel.

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Not strange at all but heed the ambient humidity,  where your piece is placed in your kiln , slow drying of piece. If the surface dries quickly or unevenly it can seal the clay to the point that moisture cannot escape from the interio thus the skewering from base up into the interior.

This becomes more severe in the firing.

Drying off the base , rotate surfaces which are exposed to sure during drying. Wrap in plastic and dry SLOWLY etc etc.

Fire on could of clay or a layer of fine grog to allow heavy sculpture to move as it shrinks.

All the best 

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So I just checked and the largest piece I have that was fired solid is the head on my Happy Chinese Man. He's porcelain and his head measures 2.75 x 2.75 x 2.5. I did not fire him. He was fired in a gas kiln by a woman in Brooklyn that did work for the Met, so an expert firer (is that a word?).  She had like 20 kilns. Really nice woman. Anyway, I can't remember him drying that long either, a few weeks at the most. I was in a sublet and only there 4 weeks, but it was during winter and the heat was full blast so the room was very, very dry.

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