Logan Oplinger on tue 30 jan 01
Vince,
I will have to disagree to some extent with what you say about "garbage can firing"
---- you wrote:
>...The wares are bedded in
> sawdust, which is ignited from the top and smolders down through over twelve
> hours or so (ideally). But the sawdust smoking process never reaches even
> minimal sintering temperatures, and the wares must be bisque-fired first.
I use a scaled down version, making a firing container out of a large coffee can (6"d x7"h). The sawdust I use is coarse (> 1/16") with most of the fines (< 1/16") removed by screening out. In testing, both earthenware and stoneware clays were fired to very low red heat (pulled & observed during test firing, near end of firing). The size of the pieces were beads no more than 3/8" thick and 1.5" long. Soaking the beads in water several hours after firing did not produce any deterioration.
The coffee can has the bottom removed & saved. A square piece of 1/8" wire mesh is attached to the bottom w/ four pieces of bailing wire. The bailing wire is wrapped around the can rim and the wire mesh. The container is set on 3 small rocks inside a barbecue pit or other suitable outdoor location where nothing will catch fire. To load, sawdust is placed in the coffee can up to the first ring, and a layer of beads place on the sawdust at 1/2" spacing. The loading is continued the same for each ring. The last layer of sawdust to the top of the can has no beads placed on top.
To light, the TOP SURFACE ONLY of the sawdust is wetted with charcoal lighter fluid, and ignited. Flames are allowed to burn out, and a piece of aluminum window screen is placed over the top of the can to prevent sparks from flying out. If there is a breeze blowing, the saved bottom of the coffee can is is used as a damper by placing it over the top of the can to control the rate of burn. The whole firing process is somewhat variable taking about four hours, depending upon packing, type of sawdust, and air movement.
The coffee can process described may be reaching a higher temperature because air may have better access to the sawdust to produce more efficient combustion. A fine sawdust does not burn as well as the coarse, and produces beads with more carbon coloring.
Submitted for comment.
Logan Oplinger
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vince pitelka on tue 30 jan 01
> I use a scaled down version, making a firing container out of a large
coffee can (6"d x7"h). The sawdust I use is coarse (> 1/16") with most of
the fines (< 1/16") removed by screening out. In testing, both earthenware
and stoneware clays were fired to very low red heat (pulled & observed
during test firing, near end of firing). The size of the pieces were beads
no more than 3/8" thick and 1.5" long. Soaking the beads in water several
hours after firing did not produce any deterioration.
Logan -
Your smoking process sounds interesting, and I expect you might be
increasing the temperature considerably as a result of the particular
arrangement you use, but I still cannot see how smoldering sawdust can bring
clay up to minimal sintering temperatures. I have never seen it happen in
the sawdust smoking process. Can you carve into the "fired" product with a
tool? That might be a better test.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
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