Introduction: DIY Primitive Pottery Firing
Today, ceramics are all around you. The bowls and plates that food is served on, the inside of electronics that I am typing with and you are reading on, and toilets where the contents of those bowls and plates are returned. But have you ever thought of where they came from? Most of the ceramic you own was probably made automatically by machines and fired in electric or gas kilns, but these are very recent innovations that have only been around for a couple hundred years or so. Humanity has been making pottery for tens of thousands of years by using simple wood fires, and today, I will be showing you how to do just that.
Step 1: Dig a Hole
Pretty much as simple as it sounds. You can skip this part all together and just fire your clay in a fire pit like how it was done for a very long time, but a pit kiln like this has many advantages. First of all, the temperatures are much more stable, meaning there is a lower chance of your pottery breaking during the firing process, the walls act as insulation, meaning a higher potential temperature, and you will have more control over things like wind and fuel. The shape of the hole isn't to critical, but the more spread out, the more heat you will lose to the ground. Dig it deep enough for all of the fuel to fit in, but not too deep or there won't be enough oxygen getting in to burn the fuel. My hole is about 1 foot deep (a third of a meter), but you will probably want to go deeper with larger firings. I also added a cinder block to the bottom to provide extra insulation. Ideally, this would be done on all sides with rocks, cement or clay, but you can still get sufficient temperatures without.
Step 2: Insert Greenware
Take your pieces and place them in the hole. Not much to this one, but you will need to consider logs falling as they burn, distribution of the coals, and if they break, damaging adjacent pieces. You can use most standard clay used by hobbyists (except for polymer clays). They are typically stoneware or porcelain, but I think it is more fun and rewarding to go out to a river bank and find your own clay. It will probably break a lot more than commercial clays, but the result will be unique and something you can be proud of knowing exactly where and how it got to be.
Step 3: Adding Fuel
This will basically be built like any other camp fire, the only difference is it is built in a hole, so make sure there is a path for air to get to the underside of the logs. Any kind of wood can be used really, as long as it is dry. The only thing that is really important to this process is the coals; they fall down and make direct contact with the greenware. The coals will need to cover the pottery entirely, keep adding wood until you achieve this. You might want to completely fill the space around, under and on top of the pieces with stuff like straw, dried leaves, or wood shavings. This layer will burn and deplete the oxygen, creating a reducing atmosphere, making the pottery turn a nice black color. You can even try to add chemicals to the fire like copper sulfate or even salt to add flashes of color to your pieces.
Step 4: Cooling
This part requires no labor whatsoever, the hard part is being patient; do not tamper with anything! Even without touching anything, there is a high chance of failure for wood firings. Cooling is the part where most breakage happens. As they cool, they will contract. If one part cools faster, it will of course contract faster, and cause a fracture. These fractures might be violent enough to shoot fragments off that will break other pieces. Depending on the size of the firing, cooling might take from a couple hours to well over 12 hours or longer. Don't be tempted to take the pieces out until they are almost completely cooled down.
Step 5: The Result
If you are lucky, your pieces will all turn out okay, but if there is a high percentage of breakage, it might be because of either your fire, your clay, or just bad luck. Many of my pieces had minor cracks, but were still functional. I would say this was largely successful! Try this yourself, find something that works, and experiment further. Good luck!
Want to know how I found my own clay in nature? Click here!