How to Fire Pottery Without a Kiln
An electric pottery kiln is a convenient tool but making art without the use of modern technology is fun and gives a sense of connection to the earth for both the artist and the art. Learning how to fire pottery without a kiln is not hard and the process is not overly long or complicated. If you have some firewood and a few rocks you have all that is needed to fire pottery without a kiln.
Although individual clays vary in their maturation temperature, most clays will become earthenware ceramics at around 700° Celsius or about 1300° Fahrenheit. This is far hotter than a household oven will reach but a well built campfire can get that hot if you have a place where you can safely and legally build a fire.
Keep reading to see the details of how I have successfully fired pottery without a kiln.
Fire Pottery Safely
The first thing to consider before attempting to fire pottery without a kiln is if you have a place to safely do so. You should have an open area at least 50 feet across clear of burnable materials including grass, weeds, trees or trash.
You will want to have a shovel and water handy while you are burning the pottery just in case it gets out of hand. A bucket of water is good but a hose with a spray nozzle is even better.
The final consideration is legality. If you are in a city or otherwise heavily populated area, can you legally build an open fire? You might want to call the local fire department if you are not sure. In some places a permit is required for any open fires.
Just to be clear, when I say “firing pottery without a kiln” I mean truly without any sort of kiln at all. There are many types of primitive kilns from trench kilns to updraft kilns, even a pit firing is a type of primitive kiln. The firing technique I will describe below involves firing pottery on top of the ground with no structure at all except the kiln furniture and the fuel itself.
The Outdoor Firing Process
The first stage of firing pottery without a kiln is called the “primary fire”. You will need a nice layer of hot coals under your pottery when you fire them, the primary fire is that initial fire used to create that layer of coals. Build your fire with enough good, long burning wood to create a nice bed of coals as if you were preparing to cook a steak. Pine is not good for creating coals but oak, juniper, ash and mesquite are all suitable as are most hardwoods.
While your primary fire burns, set you pottery near the fire so it can warm up. At this stage you are just trying to drive off any remaining moisture in the pots. Be careful not to set the pottery on damp ground, green pottery can wick up water out of damp soil so if the ground is damp set the pots of stones or fired pottery. Rotate the pots frequently so they can get heated all over. Moisture in the clay is the number one cause of broken pottery in an outdoor firing.
When the primary fire has burned down to coals spread them around so there will be coals under all of the pottery being fired. Now place stones on top of the coals in such a way that the pottery can be stacked on top of these rocks. You can use actual kiln furniture if you have it but the old ones used stones and many today try to fire like them too, we will call these rocks kiln furniture too because the purpose is the same. This will keep the pottery from coming into direct contact with the burning fuel which can leave dark spots called “fire clouds”, it also helps to encourage air circulation under and around the pottery which can help them heat up faster and to oxidize better.
Some potters use pieces of fired pottery to protect the pots from coming into contact with the fuel. These slabs of fired ceramics are called “cover sherds”, the prehistoric potters used pieces of broken pots but many potters today create slabs of clay and fire them just for this purpose. If a pot is plain and unpainted then fire clouds may be desirable and you might opt not to use cover sherds, on the other hand if your pottery is decorated with painted designs you may decide to avoid fire clouds which could mar your designs and in that case you would definitely want to use some cover sherds to protect your pots.
So the setting goes like this, hot coals on the ground, stones or kiln furniture on top of the coals, pots on the stones, cover sherds over the pots. Now we are finally ready to start stacking the firewood for our pottery firing, this is called the “secondary fire”.
This is the fire that will actually turn your green pots into ceramic earthenware. You will want a good supply of wood not much bigger than a man’s arm, if you have large rounds they should be split into the desired sizes. The goal is to get it to burn quickly, larger chinks of wood will burn more slowly.
Now stack your wood over your pottery in a teepee fashion, lay the sticks at such an angle that they will not fall over as the wood burns but instead will lay upon the pottery, that is to say do not lay the wood in an overly vertical orientation. Put enough wood on so that you can just barely see the pottery through a few small openings here and there. The photos here should give you a good idea of the amount of wood to use.
By the time you are finished stacking the firewood it may be starting to burn already from the hot coals at the base. If not, you can get it started with some small sticks and leaves or lighter fluid. There is nothing to do now but wait for the fire to burn down, it should not need to be refueled or otherwise cared for if you have prepared everything correctly up to this point. The whole fire from ignition of the secondary fire until the are taking them out of the fire is quite short, about 15 or 20 minutes total.
It can be astonishing to some with no experience in outdoor pottery firings just how fast the process is. The pottery goes through extreme stresses during the firing as the temperature rises rapidly and then cools just as fast, while a modern kiln heats up and cools very slowly to avoid that stress. The trick to creating pottery that will survive such a firing is to use enough temper (or grog), around 20% sand added to natural clay will usually do the trick.
If the wood has all become coals and there are no more active flames then your pottery is done. If you are in a hurry, (who is not anxious to see how the pottery came out) you can start gently and slowly pulling the coals away from the pots to encourage them to cool more slowly. After a little more time pull the cover sherds away if you used them. You are slowly exposing the pottery in stages and letting it cool at a slow pace. The pots will still be too hot to touch, at this point even touching them with leather gloves will leave carbon spots as the gloves instantly burn when they touch the superheated surface of the pot. Be patient. You can wait until the pot is cooler or remove it from the fire with a shovel or some other metal instrument that will not burn on the hot surface.
If you pull the pots from the fire while still very hot, be careful not to set them on a stone or concrete or some other hard, cool surface that will wick heat away and can cause the pot to crack. Instead set it on one of you cover sherds which are already hot, or on sand or dirt which is not as dense as stone.
When the pots are first exposed from the fire any red areas are dark, appearing brown or black and then as the pot cools these areas will oxidize and turn red before your eyes. It is an amazing process to watch a pot oxidize, even after many years of firing this way I am still awed by it.
Firing pottery outdoors is not difficult if you know the basic procedure and it is a fun way to make earthenware. Begin by creating a bed of coals, then stack the pots on top of stones above the coals. Next place pieces of broken pottery strategically to protect painted areas from contact with the fuel. Now stack the firewood around and over the pottery and allow to burn down, when the pottery cools down you can begin to remove from the fire. It’s actually that easy and all potters should try it at least once.
Firing pottery without a kiln has many subtleties and nuances that can take a person many years to perfect. If you are interested in firing this way I suggest lots of practice, you may also be interested in our online pottery firing class. The Southwest Kiln Conference is a good place to see a variety of primitive firing methods practiced, see their website here. Please leave comments below if you have any questions or comments on. the pottery firing techniques covered in this article.