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Firing Clay Experiments Going Wrong, Please Help


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#1 AndreaHeilotes

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Posted 20 May 2014 - 04:38 PM

When you look the phrase "starving artist" up on google, the first result is a link to my resumé, portfolio and facebook page. I can't afford a kiln, but I am in love with clay right now. So I've got all these pieces laying around that need either bisque firing or glaze firing. So I think to myself, "humans from before civilization have been firing clay without electricity virtually no problem, why can't I?

 

Presumably, the answer is because I'm the product of thousands of  years of devolution since pre-historic man. I can't figure puit firing out on my own and with the great resource of the almighty interwebz, I still can't figure it out.

 

My first attempt was to essentially grill the bone dry clay test tiles, I stacked bricks to create a grill structure with either a wood fire or charcoal briquet fire going underneath. My clay wasn't as bone dry as I thought, it exploded. but the broken pieces did not bisque fire. I tried placing a tin can over the broken pieces to trap heat, still no luck. I then assummed i wasn't getting the fire hot enough, I put a fan in front of the fire to oxydize the wood or charcoals. No results.

 

My second experiment was to lay down brush in a pit, lay my test tiles on top, cover my work with more brush and wood, light on fire. No results.

 

My best guess is that I'm not getting things hot enough. My clay should bisque at cone 4-5, according to the box. Apparently I'm not hitting those kind of temperatures.

 

I was hop[ing that I was at least hitting glaze fire temperatures, so I tried the above with tiles that were underglazed. Still no luck.

 

What am I doing wrong? Are there any ways I can fire my work without dropping a ton of money that I don't have on a kiln?



#2 Benzine

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Posted 20 May 2014 - 05:55 PM

Pit fire temperatures, just aren't hot enough, to reach Cone 5, though you shouldn't be bisquing that high anyway. Bisque firing is generally done between Cone 06 and Cone 04.

In regards to the explosions, you ran into the same issue I did, the first time I tried to pit fire, small bits of the wares blew out. The issue is that, even if you fully air dry the wares, you still have to ramp up the temperature slow, so that the chemical water in the clay can move out of the clay slowly, otherwise you can still have explosions.
While it is possible to completely fire a ware, in a pit, many bisque their wares in a traditional kiln first, then use the pit firing for the surface effects it offers.

If you want to fire things you have made, your best bet is to find someone in the area, who has a kiln you can share, like a community studio.
"Anything worth believing, is worth questioning"

#3 Mark C.

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Posted 20 May 2014 - 06:20 PM

Use the grill for food and then you will not be a starving artist

Get sone funds together and buy or salavage some bricks and then you can woodfire those clay things

Mark


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#4 jrgpots

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Posted 20 May 2014 - 07:22 PM

When I was about 4 y/o, Our family went to the Yuba river in Northern CA. We kids knew we could swim because our favorite TV show was "The Aquanauts." That summer we had watched all of the episodes, so naturally we knew all about swimming. They made swimming look so easy. Unfortunantly, we had nevergotten our feet wet, much less learned to swim. I wish my mother had had a movie camera as my father dragged out of the water 4 half-drownd water-logged kids.

My point is that this forum is like The Aquanauts...One can learn all about clay. There are people here that make it look so easy. BUT, we all start at the same point...by getting our feet wet.

So, the water is warm. Welcome to the beach. It's a bit rocky at first.

Jed

#5 Benzine

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Posted 20 May 2014 - 08:29 PM

Jed, in the forum version of your story, John B. is the father dragging the kids out of the water.....
"Anything worth believing, is worth questioning"

#6 alabama

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Posted 20 May 2014 - 09:20 PM

Hey,

 

You didn't say what kind of clay you're using, but to do what you think you want to do, you'll need to find a source of clay along the river bank.

Clay intended for the wheel is too dense.  For water and humidity to exit the clay body, it has to be porous.  Any moisture is going to expand

1,700 times its volume, and if it happens to be anywhere in your clay body the results is a spall/explosion.  Pottery fired too soon spalls.

If you're putting out a house fire, you need the water to expand, but if you're making pottery you don't.

 

Good luck,

Alabama



#7 Marcia Selsor

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Posted 20 May 2014 - 09:42 PM

one thing anthropologists say about pottery communities is that they are extremely stationary like fishing villages. They stay with what they know and that has been built upon for generations. Clay, local resources, predominant winds etc.
Someone on a forgotten hilltop did not develop pottery on his own. Sorry, but that is a myth.
Look up Anna O. Shepherd's book, Ceramics for the Archeologist or Fred Matson's Ceramics and Man.Both are excellent references for early beginnings in clay.

Open pit fires which is what the second experiment sounds like, usually takes several hours of keeping the blaze going strong, not with brush but with wood. You may get into the bisque range doing that method.
In the photo, the Paco is firing his mother's work in a "Celtic" style kiln made of granite rocks. The structure is complex with spokes radiating from a stone pillar. The spokes are made of clay and support the load above the fire box. Primitive by most of our standards but they produce some beautiful pots.The kiln fires full blast for 5 hours after Alista, the otter stokes it for preheating during the day.The pile on the right is a variety of scrub oak and brush used at specific times. So brush is useful.


This is what I did on my year in Spain on a Fulbright. I visited traditional potters and documented how they fired, made clay etc.

Marcia

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#8 schmism

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Posted 20 May 2014 - 11:07 PM

electric kilns in my area re $200-$500 on CL depending on condition and size. I can find a dozen within 300 miles of me.

#9 Stellaria

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Posted 21 May 2014 - 05:54 AM

I second the suggestion to find another potter or a community arts center that can fire for you. As others have said, pit firing kind of requires that you build/throw for that purpose. And finding another person or group with a kiln means making more friends! Yay!

#10 Marcia Selsor

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Posted 21 May 2014 - 09:43 AM

I agree. There is a benefit in working with others.
Especially if you can access equipment that they know. You mat have to prove your clay will go to their preferred temperature before you put it in the kiln.

Marcia

#11 Up in Smoke Pottery

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Posted 22 May 2014 - 03:05 AM

If you want to continue the pit fire experience, you will need to pre warm your pieces to dry them out before firing.  This can be done by building your fire and setting your pieces outside the fire, but close enough to warm the pots.  Be certain to keep rotating the pots so all sides get dried out.  Once your initial fire is down to coals you can start to build you pit fire, be careful the coals are still warm.  This should work for small firings.  Marcia is right you need wood, good hardwood, avoid plywood and painted boards.    there are many ways to do it, we do not add wood during the fire, just pile it on prior to ignition.  Pit fire temps range from 900-1400 F on average. 

 

I agree, find another potter, studio, school, art resource to pair up to use kiln space.  I have rented mine in the past for a few fellow potters that were in a bind.  Your clay supplier may also fire pieces as well.

 

Best of luck, if I can answer any other questions let me know.  Also read Sumi Von Dassow's books, or there is a new one by Dawn Whitehand featuring 25-30 artists with technique overviews for other suggestions.


Chad

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#12 timbo_heff

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Posted 22 May 2014 - 12:09 PM

Also, not sure if you realize, but pit firing is really not for functional work like cups and bowls:  they will be pretty but so underfired that they will be leaky etc.

You probably will make progress faster with a craiglist electric kiln.as suggested above:

Get cone 6 clay and glazes and you will up and running.

 

You don't have to sell very many bowls to pay off a $400 kiln!



#13 Isculpt

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Posted 24 May 2014 - 01:34 AM

It's all well and good to tell someone that they can buy a used kiln for $400, but if they have no means to wire it, or if they can't put their hands on $400, other solutions can be found.

 

If you will Google "Youtube Pit firing" you will find dozens of videos showing the many ways that other people make pottery without a kiln.  You can certainly make pottery without a kiln, but you will need to use a strong clay, with grit.  Raku clay is designed to withstand thermal shock, so it's a good choice.  It is certainly more difficult than firing in a kiln, and the losses are much greater due to cracking in the fire, but it can be done and has been done for millennia.

 

My husband's tribe uses no kilns, but they do warm their pots in an electric stove, a modern version of setting the pots around the fire, then moving them closer and closer until they are warm enough to be placed into the ashes and embers of that first fire. Using the electric stove, they slowly raise the temperature from the stove's lowest setting, keeping the temperature below 200 for the first few hours.  But then over a matter of 4 or 5 hours the temperature is slowly raised to get to the maximum heat setting, usually 500 degrees.  Then the pots are loaded in a towel-lined basket or even a cooking sheet and quickly moved to the ember and ash-filled remains of a fire that was built when the pots went into the oven, and that has since burned down.  That fire was built from brush topped with roughly 2" diameter branches or split dried wood.   Whatever bits of wood are left in the fire "pit" are pushed to the sides, the pots are laid into the ashes and then split dried hardwood or branches are laid over the pots.  The wood quickly catches fire from the embers and ashes, which raises the temperature of the pots further, and tree bark is immediately laid over the pots to cause reduction.  This is only one method; many other variations are available on Youtube.  But as mentioned before, these pit-fired pots are fragile and meant to be decorative items only; they will not hold water. 

 

Jayne

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#14 Benzine

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Posted 26 May 2014 - 01:56 PM

Jayne,

Those pieces of your husband's look great. Quite a nice smooth sheen in the surface.

In regards to the original poster using the pit firing method, the big problem I see is that they currently have work laying around, that needs to be fired. Unless they happened to use a Raku body, or something similar, that can take the shock, pit firing is still not a viable solution.
"Anything worth believing, is worth questioning"

#15 Isculpt

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Posted 27 May 2014 - 10:08 PM

Benzine, I bow to your knowledge about clays.  I am a rank beginner with a grain of knowledge and a lot of good intentions!  But when I first started working with clay 4 or 5 years ago, I used white earthenware.  Sometimes I used smooth earthenware, sometimes I used earthenware with just a little bit of grog.  Not knowing that I couldn't or shouldn't, I pit fired these ladies without a kiln, and they survived.  Was the success of that firing sheer beginner's luck?  I don't use that clay anymore, but you've made me curious! 

Jayne

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#16 Benzine

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Posted 27 May 2014 - 10:17 PM

Jayne, as with your other sculptures, I am a fan of those ladies. I love your style.

I too used a low fire white, for the first pit fires I did. The first, as I mentioned, was with greenware, which went terribly. But the bisqued low fire survived quite well, because the temperature increase and decrease was gradual. If a person was to try and fire from green in a pit, I would definitely recommend a Raku-type body.

Also, don't let me fool you, I am still learning just like you. I've been working with clay for a little over ten years, and my goal, is just to know more and get better than I was before, then pass that information on to all who want it....Or in the case of my students, whether they want the information or not!
"Anything worth believing, is worth questioning"

#17 Up in Smoke Pottery

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Posted 28 May 2014 - 01:37 AM

Jayne, your sculptures turned out amazing! Thanks for sharing.


Chad

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#18 Isculpt

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Posted 30 May 2014 - 02:47 AM

Chad and Benzine, thanks for the compliments.  I have to say that I haven't had great success with pit firing or trash can firing since those early attempts.  Chad's website is full of helpful information offered in an entertaining way.  Chad's site lists a number of potential colorants, with the usual suspects like banana peels. I always hear that banana peels are good for color in a pit fire but I can't help wondering how a person stockpiles enough banana peels to make a difference!  As for the other colorants -- Well, Chad, I'm just not sure I'm ready to start stockpiling road kill!!  :wacko:

Jayne :P



#19 Up in Smoke Pottery

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Posted 30 May 2014 - 04:44 AM

Jayne, one of our "secret" sources to get a lot of bananas is to contact a local day care/ child care facility.  they are notorious for serving bananas on a regular basis, and typically only 1-2 people peel them for the younger ages.  Ask them to bag them up for you, I try to pick them up that day or one of the ones i used would freeze them and I picked them up weekly.  It will not take long to get boxes full.  Bribery with handmade coffee cups doesn't hurt either.  My wife will not let me do roadkill,...Yet. 


Chad

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