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Hello again folks!
This is another post in my on going series of practical skill-sharing. It gives me a small opportunity to share with you some of the things I’ve learned over the years, and pass on some hands-on knowledge to you all.
Last time, I talked about Making Clay from Dirt, and also explored a quick way to learn more about your own soil. Alright, so we’ve made some clay, and we’ve made something out of it. The pottery for this for this how-to is made via slip casting, which is a skill I will touch on later on in another post. For now, I’m kinda glossing over that part. Let’s just assume you’ve made some awesome pottery, and now it’s time to fire it.
Pit firing is exactly what it sounds like. You put some pottery in a pit, and you start a fire around it. The pottery inside the pit then goes through a chemical process that turns the raw clay into a ceramic. A ceramic is a fired clay, that has at least partially gone through the process of vitrification, that makes the piece (at least partially) impermeable to water. That’s just a fancy way of saying that the fired ceramic will no longer melt back into mud if it gets wet. The amount of vitrification varies a lot, depending on process, clay, and temperature.
Earthenware, Stoneware, and Porcelain
Ceramics pieces such as bricks, pottery, and ceramic tiles are commonly classed in three different types; earthenware, stoneware, and porcelain. Earthenware is the most common type, and it is made from many different kinds of clay, is porous, (won’t retain liquids), usually non-vitreous, and is fired at a lower temperature than the other two types. It can be glazed (and thus can hold liquids), or unglazed, and is the oldest type of ceramic in human history. Examples of earthenware date back as far as 29,000 BC.
Most clays won’t survive very high temperatures during firing, so stoneware didn’t show up until about 5,000 years ago. Stoneware can only be made of specific clays, and is fired at a higher temperature than earthenware. It goes further into the vitrification process, and as such loses the porousness of earthenware. Stoneware is usually glazed as well, and as such is commonly used for liquids.
Porcelain is fired at the highest temperature of the three types, and therefore porcelain can only be made with very specific (usually kaolin) clays. Porcelain requires great skill and craft to produce, and so is the latest of the three to be invented. Porcelain, for that reason, is often found in “prestigious” items throughout history.
Modern ceramic manufacturing covers the spectrum of all three types, with a variety of glazes and materials. Ceramic tiles, bricks, terracotta flower pots, spark plugs, electrical insulation, and tableware are all made of fired clay.
Animism and Ceramic
As I don’t want this piece to be too long, I will only touch on this briefly here. There is a great deal of animism of working with earth spirits, and clay and ceramics. Just like my first piece on pottery, ceramics are a way of building relationship to the earth as well as to the ancestors. In fact, pottery is one of the key ways working archaeologists differentiate one culture from another. Every people, every culture throughout time has inscribed their own ideas, beliefs, and worldviews into their pottery. In addition, they embodied they working skills and practical experience of their people as well, in working clay and firing ceramics. Moving forward!
Let’s start with materials. For this one, we are going to make pit-fired earthenware, which is the oldest type of ceramic we know of. In short, unfired pottery is put into a pit, and lit on fire. That means the temperatures are low (usually below 800 degrees Celsius, or below 1470 Fahrenheit). It also means there are not many materials needed. For this how-to, I used the following;
- A pit
- Two cinder blocks
- A piece of metal mesh
- Pottery pieces to be fired
- An oven (optional)
That’s it, so lets get started.
Step 1 – Pre-baking (Optional)
Before I get to firing the pottery in the pit, I throw them the pieces to be fired into the oven. First, an hour or so at 400 F, and then I turn up the oven to 500 F for another hour. Even though the pottery is air dried when it hits the oven, the reason I do this is to drive a little more water from the pieces before firing. This is an optional step, but I find it helps a lot with survival of the pieces. In addition, any really bad pieces won’t survive this step, so it helps weed out those pieces too without wasting wood and effort.
(Pottery after pre-baking, ready for the pit!)
Step 2 – Digging the pit, chopping the wood
This is the most straightforward part of pit firing. You need yourself a pit, which is basically just a hole in the ground. Site this away from dry flammable stuff, and find yourself a shovel. For this demonstration I used a pit about the width and depth of a five gallon bucket. It doesn’t have to be huge, as long as you aren’t firing too many pieces. If you already dug a pit for my first tutorial, congratulations, you don’t have to duplicate the effort.
You will also need wood. Not too much since we are starting small, but larger pits = more fuel. Chop chop! Smaller pieces work better in smaller pits.
Step 3 – Prep the pit
(Pit, ready to go)
Once the pit is dug, you have to prepare it for firing. As you’ve might notice, I put two cinder blocks on either side of my tinder and kindling. The reason for this is important. You want the heat to hit the bottom of your pottery. Trust me on this, otherwise you will get only partially fired bottoms. The point of the cinder blocks is to have something to put my pottery rack on top of, so the fire is all around the pieces, and thus heating them from all sides. I didn’t start with a lot of wood in my pit, because you want the temperature to raise somewhat slowly. If you go right to a big, raging fire, some pottery might explode due to unequal heat. It’s a marathon not a sprint.
Step 4 – Fire!
(Lighting fire with the power of the sun! Animism at work… Or play? )
Alright, so now it’s time to light the fire. I like to light my fires with a little convex lens and a box of tinder. If you read my previous post on The Spirits of Fire you might be able to guess why that is. If not, in short in Finnish animism, fire is a child of the sun. There’s practical spirituality there.
Also, once I lit the fire, I had to quickly (yet, carefully) place my rack of pottery onto the fire. That way, the fire was underneath my pottery. Then, over the next couple of hours, I built up the fire and maintained it. There is some finesse here, because you want to maintain a constant temperature, without crushing your pottery. Build the fire up gradually, maintain it at a peak, and then let it cool down slowly. I probably used bigger wood than I should of this time around, though thankfully I didn’t crush anything. Knocked one piece over once or twice though.
Pit fires only get so hot, so overheating isn’t too much of a risk. Once you’ve burned around your pottery for an hour or two, feel free to let the fire die down. Then let the pottery cool for several more hours. It will take a while, so don’t rush it. Pottery likes to explode under unequal heat conditions, which means it warms up too fast, or cools too fast. Be patient. I know, it’s hard. When your pottery is cool to the touch, feel free to remove it.
Step 5 – Pit Fired Pottery, hopefully
Once my pottery is cooled, it’s time to give it a look over. 50% loss rate is about normal, so don’t be surprised if you lose about half your pottery. This is good to keep in mind when you are making and shaping it from clay, not to get attached to any one piece. It may well be the one that blows up. If you really like a particular design or specific pot, make a few of them. That helps to ensure you will get at least one on the other side of the fire.
This is where I tend to ‘test’ my pieces, and give them a good look over. Sometimes there will be broken pieces, sometimes small hairline cracks. I will tend take at least one piece from each batch and get it wet. A little at first, then a full submersion. If it turns back into mud, it didn’t fire completely. If not, congratulations, you have pit fired ceramic! Also, bubbling is totally normal for earthenware, they’re porous after all. Water will drain through them, albeit slowly.
I also want to draw your attention to a couple of details throughout this process. This is where the real artistry of pit firing comes in! Pit firing creates unique ceramic pieces that vary a LOT in color and patterning. The nature of the fire, and the clay, makes each piece one of a kind. Iron minerals in the clay make the rich reds you see in my pieces above. Burning wood and charcoal creates black colors. You noticed I added green grass to my fire, creating more grays/blacks/browns. Minerals, salts, metals, all kinds of materials can be added to the fire to create different colors, especially on white clays.
Some of my pieces have small cracks, or broken bits. I hope to add an extra layer of artistry; by fixing some of those cracks with colored resin. In the tradition of kintsugi, except I’m not using gold… Paints and other things can be added for extra artistry!
Experiment, and enjoy!
As always, thanks for reading!
https://www.upinsmokepottery.com/colorants.html (A great list of colorants for your pottery!)