What is pit-firing?
Pit firing is a primitive, low-tech method of firing pots. Traditionally a pit was dug into the earth, and pots were fired in this pit with wood and other organic materials, such as dried dung, used as fuel. Cultures around the world used this method of firing pottery before the introduction of kilns, which allowed for a hotter fire. Some indigenous cultures continue to pit fire all of their wares.
Today pit firing has come to mean different things, but the basic gist is that pots are fired at a relatively low temperature using organic materials to produce atmospheric affects and various colors. Some people use 50 gallon drums, some people dig a giant pit, and some build a little kiln out of bricks (like what I did in my backyard). Where the pots are placed in relation to one another and what combustible materials are in the kiln affect the surfaces of the pots, so no pot is like any other and no firing is like the last. It is a constantly evolving process and you learn a little from each firing.
Forming and preparing the pots
I form my pots using very basic techniques of pinching and coil building, and I use a white midrange clay body. When my pots are bone dry I apply a white terra sigillata to the surface and burnish it to a silky sheen. Terra sigillata is a fine particle slip that translates to "earth seal."
I then bisque my pots to cone 08, a relatively low temperature. The terra sigillata helps to seal the surface of the pots, but with the low bisque temperature, the pots are still very porous. The porosity allows the surfaces to accept the smoke and fuming from the pit fire.
Pit-firing is an ongoing experiment! Different organic materials produce a variety of colors and effects. I start gathering some of my organic materials (compost and beach items) ahead of time because they need time to dry out.
- Wood - To make the fire, you need wood, so I try to just gather small branches all the time. I also save wooden pallets to break down and use as fuel.
- Sawdust - At the base of the pit, I always put a layer of sawdust an inch or two thick. Anywhere the pots are touching the sawdust will turn black.
- Organic materials from the beach - seaweed, seagrass, sponges, etc. Salts make great colors! I just gather things from the beach and dry them out ahead of time.
- Compost - You can try anything, but so far I've had the best results with dried banana peels and corn husks.
- Copper carbonate - Copper makes reds. I sprinkle this on the sawdust around the pots. I also make a copper carb wash that I brush on the pots.
- Household items - Miracle Gro, kitty litter with crystals-- Some household items have all kinds of organic color-producers in them, such as potassium, copper, manganese, salts.
Loading the pit
I start with a layer of sawdust a couple of inches thick. For some pots, I make a little pouch out of aluminum foil. I place the pot as well as some materials (like a banana peel or miracle gro) into the foil pouch and then place the whole pouch into kiln.
I brush a copper carbonate wash onto the remaining pots and place them on top of the sawdust. Once all of pots are placed, I sprinkle some copper carbonate onto the sawdust around the pots. Sometimes I also sprinkle red iron oxide. Like I said before, it's an ongoing experiment. I place all of the organic materials- dried banana peels, corn husks, sea stuff- around, under, and on the pots.
Next comes little sticks and balled up newspaper or dried leaves or more sawdust. After the little sticks, bigger sticks until I've reached the top of the kiln. I light the fire and try to keep it going pretty good for a couple of hours, adding more wood when necessary. Once the fire has died down, I cover the surface of the kiln with sheet metal and let the fire smolder. I leave it covered overnight and then unload the next day.
Unloading, cleaning, and polishing the pots
This is the really exciting part! Once the kiln has cooled, I take the lid off and start unloading the ash-covered pots to find the magical results (hopefully!). I brush each one off and then rinse and lightly scrub off any debris. The surfaces are delicate, so you can't scrub too hard.
My pots already have a sheen because of the burnished terra sigillata, but I do opt to polish them once more. I apply a small amount of paste wax and buff/burnish it with an old t-shirt. This just protects the surface a bit more and makes the pots easier to dust quite honestly.
At the time of this writing, I have only fired in my "pit" twice. And, I actually had to rebuild the kiln between firings because we needed the original bricks to finish a walkway. I expect that each firing will be unique, producing some great pots and some duds. With each firing, I hope to learn something new that I can apply to the next round!
If you want to see the rest of the results, click here.