Question About Alternative "Pit" Firing Technique

[picasso_of_lonliness]

After several years of working exclusively with electric kilns, I finally find myself with an opportunity to try some alternative firing methods. (I live in the city, so finding a place where I can burn a smoky fire without attracting the cops, or worse, the ire of neighbors is a challenge.)

In addition to attempting a "pit" firing in a barrel (as seen in many instructional videos/guides), I was intrigued by a method for creating rich blacks outlined here (https://www.swkiln.com/non-traditional-black-black-firing-jo-ann-weldon), in which a reduction atmosphere is created inside an upside down metal can lined with sawdust/wood shavings (and filled with pottery) by burning a fire around the outside of the can. In the post linked above, the author mentions that using too little sawdust will result in some areas of the pots staying white/grey. I am wondering if it would be possible to achieve a colored surface if I were to use this method with only a little sawdust mixed with colorants -- or perhaps with only colorants (seaweed, banana peels, copper carbonate, etc.) and no sawdust at all. I am a complete novice when it comes to any sort of alternative firing (and the chemistry involved, for that matter, so I have no idea if this might work -- or if it's a stupid question).  I'm also wondering about coating the pots with ferric chloride and firing using this method with limited fuel inside the pot. 

My assumption is that there needs to be enough organic material in the kiln to consume all the available oxygen, but basically I am wondering if colorant-laden fuel alone would yield colorful pots. Or would they be likely to come out black either way?

Thanks in advance for any advice -- as always, I'm grateful for those willing to share their experience and expertise with a newbie like me. 

[hitchmss]

The barrel upside down over another barrel, with your pots inside, is essentially a saggar firing. A saggar is an chamber which is inside of a heated space which contains your pots and "added materials". The inner chamber acts as a reduction zone; like you stated, organic materials consume the oxygen in the inner chamber, providing the reduced atmosphere, and thus change in colors of your coloring agents. Saggars come in all shapes, sizes, and made from all kinds of materials. A saggar can be made from clay, aluminum foil, old metal barrels, old kiln shelves/clay in a raku kiln.....The style of saggar will impact your finished product, as much as the type of combustibles/colorants you use.

While there is a lot of information on how to perform saggars or other alternative firing techniques, because there is SO much variety in how you construct and perform your firing, there really isnt a "tried and true" method for achieving certain results. Essentially a lot of experimenting is in play here to find the surface you want. Do you use fine saw dust, which takes a long time to combust/burn off and may provide richer tones, but maybe not as hot of temps? Do you use wood chip bedding (like the kind for gerbils, etc) which is looser, and burns more rapidly, providing more heat, but maybe less carbon? Is it a mixture? Is it hardwoods, or softwoods? Are you using pine cones, pine needles, straw soaked in sodium.................? Are you allowing some oxygen into your chamber via holes in your can, or none at all?

If you go to use actual colorants, not solely materials which contain trace amounts of colorants (seaweed, bannana peels, etc) you will need to reach higher temperatures to ascertain volatilization of those materials; Copper begins to volatilize around 1100 degrees, which is definitely in the range of "camp fires", but maybe not if you arent building a big/hot, or long enough firing. Remember, the inner chamber will take longer to reach those temps, so an hour or two long fire may not produce those temps.

If you do go into playing around with more toxic and caustic materials like ferric chloride, metallic salts, etc be aware of the dangers, and take appropriate measures to protect yourself. Be cautious of the fumes which come off the kiln/fire, as well as handling and applying these materials. General rule of thumb; lots of ventilation!

My advice would be to pick up some books(tons out there) on these processes, and do some good research; limit your initial experimentation to a few sources of colorants/materials so you can begin to grasp what each element provides to your surface, and how you can utilize this information to your advantage. Make a small chamber/kiln so you can fire regularly and not require large amounts of pots/materials for each firing. The clay body you use for these firings should be less sensitive to thermal shock, but that is not to say porcelains and stoneware clay bodies cant be used, just takes a little more care than a groggy raku or sculpture body.

These pots will of course be non functional, and the surfaces can be smudged if not careful, so some treatment following the firings is usually necessary to prevent smudging of your surface; a lot of folks like spray on acrylics, but other sealants can be used too.

Best of luck, and have fun! Lots of fun experimentation to be had!

[picasso_of_lonliness]

1 hour ago, hitchmss said:

The barrel upside down over another barrel, with your pots inside, is essentially a saggar firing. A saggar is an chamber which is inside of a heated space which contains your pots and "added materials". The inner chamber acts as a reduction zone; like you stated, organic materials consume the oxygen in the inner chamber, providing the reduced atmosphere, and thus change in colors of your coloring agents. Saggars come in all shapes, sizes, and made from all kinds of materials. A saggar can be made from clay, aluminum foil, old metal barrels, old kiln shelves/clay in a raku kiln.....The style of saggar will impact your finished product, as much as the type of combustibles/colorants you use.

While there is a lot of information on how to perform saggars or other alternative firing techniques, because there is SO much variety in how you construct and perform your firing, there really isnt a "tried and true" method for achieving certain results. Essentially a lot of experimenting is in play here to find the surface you want. Do you use fine saw dust, which takes a long time to combust/burn off and may provide richer tones, but maybe not as hot of temps? Do you use wood chip bedding (like the kind for gerbils, etc) which is looser, and burns more rapidly, providing more heat, but maybe less carbon? Is it a mixture? Is it hardwoods, or softwoods? Are you using pine cones, pine needles, straw soaked in sodium.................? Are you allowing some oxygen into your chamber via holes in your can, or none at all?

If you go to use actual colorants, not solely materials which contain trace amounts of colorants (seaweed, bannana peels, etc) you will need to reach higher temperatures to ascertain volatilization of those materials; Copper begins to volatilize around 1100 degrees, which is definitely in the range of "camp fires", but maybe not if you arent building a big/hot, or long enough firing. Remember, the inner chamber will take longer to reach those temps, so an hour or two long fire may not produce those temps.

If you do go into playing around with more toxic and caustic materials like ferric chloride, metallic salts, etc be aware of the dangers, and take appropriate measures to protect yourself. Be cautious of the fumes which come off the kiln/fire, as well as handling and applying these materials. General rule of thumb; lots of ventilation!

My advice would be to pick up some books(tons out there) on these processes, and do some good research; limit your initial experimentation to a few sources of colorants/materials so you can begin to grasp what each element provides to your surface, and how you can utilize this information to your advantage. Make a small chamber/kiln so you can fire regularly and not require large amounts of pots/materials for each firing. The clay body you use for these firings should be less sensitive to thermal shock, but that is not to say porcelains and stoneware clay bodies cant be used, just takes a little more care than a groggy raku or sculpture body.

These pots will of course be non functional, and the surfaces can be smudged if not careful, so some treatment following the firings is usually necessary to prevent smudging of your surface; a lot of folks like spray on acrylics, but other sealants can be used too.

Best of luck, and have fun! Lots of fun experimentation to be had!

 

Wow, thank you so much for the detailed response -- this is so, so, helpful. It makes a lot of sense to think of the barrel in this method as a saggar, and for whatever reason, thinking of it that way helps clarify the process a bit (in my mind, at least). 

I am definitely hoping to try this a couple different ways, perhaps even using more than one "saggar" (with different combustibles in each) in a larger fire . I figure that might improve the odds of the blaze getting up to a high enough temp. For now, I am using a white stoneware clay body, but I plan to try this out with sturdy, relatively small pieces  to see what kind of results I get. Hopefully at least a handful survive, but even if they don't, I think even shards will still provide a good learning opportunity. 

One follow-up question: I wasn't planning on cutting any air holes in the saggars. Do you -- or does anyone else -- have an instinct as to whether or not cutting a hole or two is a good idea? I have been laboring under the (perhaps misguided) assumption that a "true" reduction would be most effective here, but maybe letting a little oxygen flow through would be good. And I could always try to devise a safe way to plug them midway through the firing. Any thoughts?

Thank you again for your advice -- I really do appreciate it. I'll bring a bunch of pots and a bunch of materials with me, and see what I get. Fingers crossed I stumble across something cool. 

-I

[neilestrick]

A simple, less toxic way of getting color in your pit firings is to soak your combustible material (wood shavings work well) in salt water and let them dry before using them in the pit. Google 'low fire salt fuming' and you'll find good examples. Paul Soldner did some great work. HERE is a good article.

A pit is different from post-firing reduction. In a pit, the pots are in direct contact with the burning material, and color effects can be obtained by putting different materials in there. In post-firing reduction, the purpose is to create smoke/carbon which is taken into the pot to turn it black. Or in raku firing, the lack of oxygen in post-firing reduction causes copper-rich glazes to flash colors. You don't need much combustible material to make that happen.

[hitchmss]

2 hours ago, picasso_of_lonliness said:

perhaps even using more than one "saggar" (with different combustibles in each) in a larger fire

When the Chinese traditionally (and still do to some extent) would fire their pots in wood kilns, especially for copper reds, each pot in the kiln had a saggar made just for itself. They would stack; the copper red pot fit inside of the larger saggar (which the inside was coated with a wash of copper carb), and the saggar which would sit on top, the foot of it, would be made to fit the galley of the saggar beneath it, essentially acting like a lid. This kept fly ash from ruining the surfaces, but also helped to trap the volatilizing copper which is easy to "burn off". There is absolutely no reason that you couldnt fire 6-10 small saggars, each with a different material/pot inside, in a single larger saggar, or just inside your kiln/fire. I wouldnt suggest burning off a lot of organic materials in your electric kiln; the organics can shorten the lifespan of the bricks and elements, but if you have a raku kiln, or gas kiln, it would be easy enough to throw them in there and fire em off.

In some senses firing them in a saggar, in a gas kiln, offers you more control over the firing, which may make it easier to reproduce results; Not to say you cant do it in a pit out in the yard, but you'll have to understand the fire to be able to replicate...kind of a "wax on....wax off" zen like state you will master.

I believe in the Lark book "Alternative Firing Techniques" there was an example of a clay saggar which was made which had a number of plugs built into it which allowed the user to add oxygen if desired, or to slowly cool the chamber down. The addition of oxygen in your chamber is a choice which mainly depends on what surfaces you want; the ash and carbon will still build up black colors in oxidation, but maybe not as heavily as if in reduction. A part of this, is that if you are adding oxygen, then you are increasing the odds of combusting the materials in the saggar, rather than allowing them to smoke, and produce that heavy reduction. Copper carb in a glaze in oxidation firings tends to yield greens/blues, but in reduction it yields reds/purples (and a variety of other colors too, but for discussions sake); the choice to add oxygen comes down to that. As well, the reduction atmosphere not only interacts with the surfaces you apply, but also with the clays in your clay body; lack of reduction means you might not get those atmospheric flashing that a lot of folks look for.

It does seem however that most of the western raku and saggar firings I see are heavy on the reduction. I dont do much saggar/raku myself, so maybe someone who does a lot can tell you further about their experiences between oxidizing and reducing in regards to their surfaces.

If you do make a hole in your metal barrels/clay saggars, they could easily be plugged with a handful of kaowool.

[Marcia Selsor]

Robert Peipenberg had a short video of trash can smoke firing using sawdust , wooden sticks , charcoal briquettes, newspaper, copper carb, etc. Holes in the sides at strategic places. Picasso of Loneliness mentioned the upside down can.. I had a guest artist, Tom Fresh, demonstrate this about 30+ years ago He said the magic ingredient for the black was a chunk of horse manure.

Meanwhile, I think your goals are sawdust saggar firing like Peipenburg did. One woman whose sagger-fired work  I admire is Sinead Fagan of Ireland.

http://www.sineceramics.com

Another is Judith Motzkin who will be on our panel at NCECA http://www.motzkin.com/ceramics.htm

 

[TougeiBoy]

Hi from Japan. I am not sure where to post this question: I wonder if there is anyone at this site with experience using various types of manure for their firing. I am familiar with cow dung firing (recalling one memorable incident being chased by a bull while I was gathering fuel in his field... Just made it over the fence with a pile of "stuff" under my arm), but I wonder about the chemical aspects of using, say, chicken manure, etc.  Thank you for your time, and I look forward to any enlightenment you can send my way (including advice on where else I might post this query).

[liambesaw]

47 minutes ago, TougeiBoy said:

Hi from Japan. I am not sure where to post this question: I wonder if there is anyone at this site with experience using various types of manure for their firing. I am familiar with cow dung firing (recalling one memorable incident being chased by a bull while I was gathering fuel in his field... Just made it over the fence with a pile of "stuff" under my arm), but I wonder about the chemical aspects of using, say, chicken manure, etc.  Thank you for your time, and I look forward to any enlightenment you can send my way (including advice on where else I might post this query).

I think cow manure burns so well because it's full of fiber.  Chicken poop not so much.

[TougeiBoy]

Is there any effect when combined with sawdust?