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Fertilizers For Pit Firing


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#21 firefly

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Posted 10 October 2013 - 04:00 PM

Jayne, My "technique" for pit firing? Simple: drive to Colorado and sign up for a pit firing session with Sumi von Dassow at Washington Heights Arts Center in Lakewood, CO. I am embarrassed to say that as I was mainly interested in techniques that I could bring to trash can/sawdust firing, I didn't pay very much attention to the actual pit construction. I've tried to find photos from the trip for you but it appears that my computer has eaten them. I SEEM to remember that the pipes had slashes cut in them rather than holes, but I could be mistaken. And the blower looked very much like a large leaf blower, but it would have to have been one with an on/off switch, not a trigger-type start. What I did learn and remember that has helped my firings is to stop using porcelain (I switched to Laguna cone 5 B-mix), lower my bisque temp to cone 010, and add copper carbonate rather than just copper sulfate (found in MiracleGro). She recommends the use of terra sigillata, but I prefer just to burnish my pieces.

 

As to why Bonnie Staffel would use Pet Litter, I am just guessing that she is referring not to cat litter but to the wood shavings used as bedding for many pets. It's larger than sawdust, won't pack as densely, and will therefore fire hotter and quicker, vaporizing your chemicals better without just smoldering and producing mainly shades of black and gray like fine sawdust. I go to a feed and grain store here in Kansas City and buy aspen wood shavings. It may be my imagination but I think I get better colors with the aspen rather than cedar shavings.

 

My apologies if I've gone on too long, but as someone who has lurked on this forum for well over a year, it's nice to be able to share, if only a little bit.

 

Jean



#22 Bob Coyle

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Posted 10 October 2013 - 08:43 PM

Bottom line is this...as always. Ceramics is 90% art 10% science, even for a chemist like me. Read up on what you want to do. Check out references on the internet then experiment with what you want to have happen. Come up with YOUR method with YOUR chemicals with YOUR process and tweak it till it gives you what you want.Half of what you read and see about pit firing has nothing to do with chemical fact. It is folklore. Seaweed, dung, bark, oak leaves all will give a certain effect SOMETIMES or maybe NOT.

 

The methods people use and the variables are too diverse to really duplicate from one situation to the next. I guarantee your firing will be different from any other you have read about or seen.

 

Controlled kiln firings with commercial glazes show variations from one kiln to the next. No way is any pit firing going to be reproducible from one to another. You can use chemicals and firing conditions to push the pit fire result one way or another but don't rely on other persons experience to tell you what the result will be. Just go for it and be aware of what works and doesn't work for you and take joy in the fact that you are participating in a tradition that spans at least 8000 years or more.



#23 Isculpt

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Posted 11 October 2013 - 01:08 AM

Jayne, My "technique" for pit firing? Simple: drive to Colorado and sign up for a pit firing session with Sumi von Dassow at Washington Heights Arts Center in Lakewood, CO. I am embarrassed to say that as I was mainly interested in techniques that I could bring to trash can/sawdust firing, I didn't pay very much attention to the actual pit construction. I've tried to find photos from the trip for you but it appears that my computer has eaten them. I SEEM to remember that the pipes had slashes cut in them rather than holes, but I could be mistaken. And the blower looked very much like a large leaf blower, but it would have to have been one with an on/off switch, not a trigger-type start. What I did learn and remember that has helped my firings is to stop using porcelain (I switched to Laguna cone 5 B-mix), lower my bisque temp to cone 010, and add copper carbonate rather than just copper sulfate (found in MiracleGro). She recommends the use of terra sigillata, but I prefer just to burnish my pieces.

 

As to why Bonnie Staffel would use Pet Litter, I am just guessing that she is referring not to cat litter but to the wood shavings used as bedding for many pets. It's larger than sawdust, won't pack as densely, and will therefore fire hotter and quicker, vaporizing your chemicals better without just smoldering and producing mainly shades of black and gray like fine sawdust. I go to a feed and grain store here in Kansas City and buy aspen wood shavings. It may be my imagination but I think I get better colors with the aspen rather than cedar shavings.

 

My apologies if I've gone on too long, but as someone who has lurked on this forum for well over a year, it's nice to be able to share, if only a little bit.

 

Jean

Jean, thanks for sharing your experiences with me.  I have my feelers out for a workshop a bit closer to SC, although I'd love a workshop with Summi!  Long before I had heard of her, I was visiting Taos, NM, and found and bought a decoratively fired sculpture of a woman holding a pot.  I asked the gallery owner for the artist's name, and the gallery owner went one better -- she called Summi while I waited and asked Summi to email artist info to me.  Later on when I became interested in clay as a maker rather than just a buyer, I was thrilled to find her name in reference books and articles. 

 

Y'know, about that pet litter -- I figured it meant shavings, too.  So to test my assumption I googled "pet litter" -- and all I found were references to cat litter!!!  But I'm sure you're right!!

 

Jayne



#24 Isculpt

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Posted 11 October 2013 - 01:41 AM

Bottom line is this...as always. Ceramics is 90% art 10% science, even for a chemist like me. Read up on what you want to do. Check out references on the internet then experiment with what you want to have happen. Come up with YOUR method with YOUR chemicals with YOUR process and tweak it till it gives you what you want.Half of what you read and see about pit firing has nothing to do with chemical fact. It is folklore. Seaweed, dung, bark, oak leaves all will give a certain effect SOMETIMES or maybe NOT.

 

The methods people use and the variables are too diverse to really duplicate from one situation to the next. I guarantee your firing will be different from any other you have read about or seen.

 

Controlled kiln firings with commercial glazes show variations from one kiln to the next. No way is any pit firing going to be reproducible from one to another. You can use chemicals and firing conditions to push the pit fire result one way or another but don't rely on other persons experience to tell you what the result will be. Just go for it and be aware of what works and doesn't work for you and take joy in the fact that you are participating in a tradition that spans at least 8000 years or more.

Bob, thanks for the advice; I know it is heartfelt.  But the reason I'm asking for help is not because I don't want to bother with experimenting or researching -- I've done a great deal of both.  I've done a number of trash can firings and I've been present when my Native American husband fired his pots on the ground in the manner of his tribe, whose pottery tradition is believed to be an unbroken 5-6,000 year old tradition.  I know first-hand how varied the results can be, but I can't help believing that having some grasp of the chemistry involved will help to reduce the incidence of specific undesirable results.  And those are the facts and specifics that I've had a hard time finding, despite having read, viewed videos, and discussed pit firing & trash can firing for several years now.  Information like "extreme reduction = solid black pots" or "a fire that isn't hot enough = greyed and muddy pots instead of pots with bold carbon markings" can help us to diagnose the problems we're having instead of randomly altering different aspects of the firing.  If you get certain results without understanding why you got them, it's hard to know which aspects of the process to tweak. Particularly frustrating is watching my husband use the same materials that his grandmother and great-great grandmother used, yet getting the same results only occasionally.   Thanks to folks on the Forum, I now know how to avoid some of the unsuccessful results he has gotten in his coil-built pots and I have gotten in my sculptures. 

 

Jayne



#25 Marcia Selsor

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Posted 11 October 2013 - 06:47 AM

You can check out Peipenberg video on saggar firing, He mixes salt and copper carbonate in layers of newspaper, wood and sawdust.
He fires in an oil drum with a few holes to help the burn along. Also Bet Thomas has some interesting work in the Alternative Firing book.

Marcia

#26 Isculpt

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Posted 12 October 2013 - 02:44 AM

You can check out Peipenberg video on saggar firing, He mixes salt and copper carbonate in layers of newspaper, wood and sawdust.
He fires in an oil drum with a few holes to help the burn along. Also Bet Thomas has some interesting work in the Alternative Firing book.

Marcia

thanks, Marcia, I'll pursue those avenues as well....



#27 JBaymore

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Posted 12 October 2013 - 10:58 AM

Half of what you read and see about pit firing has nothing to do with chemical fact. It is folklore.

 

BINGO!

 

Good one, Bob.

 

best,

 

....................john

 

PS:  One of the BIG things I stress in my ceramic materials classes at the college is understanding Scientific Method.  I spend a lot of time on the concept of identifying and controlling variables before making cause and effect conclusions.


John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com




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