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In the spring of 2002 a pottery class from The Pottery School in the Pioneer Square neighborhood of Seattle attempted their first pit fire. The results were disappointing, but it was a fun experience and piqued our interest in this firing method. A smaller group of potters decided to try again. We did some research, and most of the articles we found described large scale firings. We wanted to try something smaller. So, over the next summer, we did several smaller firings, each achieving better and better results. We are continuing to learn more and refine our technique with every firing. These pages describe what we've discovered.
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The Pottery |
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Most of the pieces we have pit fired have been made with cone 6 stoneware clays. Since the fire temperature will not be too high, low fire clays could also be used. Since the low fire clays will be more vitrified they will be stronger, but they will also be less porous so they may not take up the colors as readily. We haven't experimented much with low fire clays, so aren't sure how different the results would be.
We have achieved the best results with well burnished pieces; they take up the colors better than rougher surfaced pieces. It is good to start off with a piece which has a fairly smooth surface, so keep this in mind when throwing a piece destined for a pit fire. You can create a clean, smooth surface using a flexible metal or rubber rib during shaping, or just as a last step before removing the piece from the wheel.
 Some people like to begin burnishing by rubbing with a polished rock or the back of a spoon. If the piece is fairly smooth to begin with, you can probably skip this step, or just concentrate on spots that need a little extra attention. One method of getting a good shine is using Terra Sigillata, a very thin slip. Apply a thin layer of the terra sig to a small part of a bone dry piece and allow to dry a bit (a few seconds). Then rub it with a small bit of thin plastic (grocery bag weight). It may take a few coats to get a good shine. However, if too much terra sig is applied it may craze (crackle) or even flake off when bisqued, or in the pit. The crazing can be a nice effect, but the flaking almost always looks bad.
There is a trade off between strength and shine in choosing a bisque temperature. A cooler bisque will retain more of the shine, but will result in a weaker finished product. Hotter bisques will strengthen the piece, but result in loosing some of the shine. Most of us choose to bisque somewhere between cone 010 and 06.
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Preparing the Pottery for the Pit |
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Much of the colors from the pit fire come from materials wrapped around the pots before they are put into the pit. You want to keep the materials as close to the piece for as long as possible. To do this you can tie them down with string or twine, wrap the piece with newspaper, and bind the piece with more twine or wire.
Materials to try:
- String/twine/grasses soaked in salt water then dried (can also add copper carbonate or other chemicals)
- Seaweed (dried is better)
- Thin copper wire
- Wire mesh (i.e. chore boy scrubber)
- Steel wool
- Banana peels
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Preparing and Loading the Pit |
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We have had very successful pit fires using fire pits provided on the beach. These are usually between two and three feet deep and three to five feet in diameter and made of either metal or concrete. Between 30 and 50 pots will fit into a pit this size.
 First clean out the pit a bit if needed and smooth it out flat. If there are vents toward the bottom of the pit, expose them to improve air flow. Line the bottom of the pit with a layer of sawdust between two and four inches deep. Then sprinkle the sawdust layer with copper carbonate. Copper carbonate gives a blush color to the pots. You can sprinkle rock salt and/or epsom salt on the sawdust as well. We have found that the salt often results in a dark, rough, crusty finish to the pieces.
Now it's time to add the pots. You can the place the pots on top of the sawdust layer, or dig them in a little. The parts of the pot which are in contact with the sawdust will likely turn black. We have found that a single layer of pots produces the best results. If possible, avoid putting pots at the edge of the pit since the fire is cooler there. More copper carbonate can be sprinkled top of and around the pots if desired. Add a layer of crumpled newspaper on top of the pots. This helps in getting the fire started, and it gives the pots a cushion from the heavier wood. The next layer should be small kindling, followed by larger pieces of wood. Hardwoods burn hotter, but any wood will do fine.
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Firing |
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 We have experimented with various firing lengths and found that a good raging fire going for about three hours is enough. Just keep adding more wood as needed to keep it going strong. Put the wood on gently to avoid breaking the pots below. Fireplace or raku tongs are helpful when the fire is going strong. You may also need to 'stir' the fire a bit on occassion. Put the last piece of wood on about three hours after starting the fire. Then just let the fire burn down to ashes (stiring when needed).
The longer you can wait to remove the pots the better. When pots are taken out hot they are more likely to crack. Expect some cracking even if you remove them when they are cool. We usually have a few that are badly cracked, so don't be disappointed if you end up with some cracked or shattered.
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Finishing the Pieces |
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Often the pieces just need a rinse to remove the ashes and they look great. Some people like to polish them using a paste wax (floor wax). Since the clay wasn't fired as hot as it would be in a modern kiln, the pots are still fairly porous. So, if you have a vase you might want to use dried flowers, or put a container inside to hold the water.
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Pit Fire Gallery |
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This gallery has a sample of pieces we have created. |
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Other Online Resources |
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