If you ever played with clay, either in school or as a hobby, you might have wondered what it is and where it comes from. Commercial clay is mined from high-grade sources and then further processed, usually with other additives until a desired composition is achieved. People have been making ceramic objects for almost 30,000 years, and this is obviously not how they did it. In this instructable, I will show you how to find your own clay, straight from the ground and refine it like it was done since prehistoric times.
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Step 1: Locating Natural Clay
To put it in simple terms, clay is essentially just small particles of stone. It can be put into three different categories: earthenware, stoneware, and porcelain. Stoneware and porcelain are more typically used by industries and hobbyists. They are higher quality and will be able to withstand higher temperatures, and make a generally better product. For this instructable, I will be focusing on earthenware clay, which is seen as a lower quality clay. It is generally weaker and fired at lower temperatures, an example is the terracotta that is associated with its use in flower pots. It also happens to be much more porous, so it isn't really "water proof" until you glaze it. Earthenware is far more abundant than the other clays, and it is what I have in my area. Clay is actually relatively abundant in almost all climates. All of the clay I found was located in riverbanks. Look for ledges with a lot of material exposed. You are looking for a change in color or soil consistency. Clay ranges in color from reds, oranges, grays and whites and others depending on the mineral composition. You will definitely know when you found clay when you touch it (or sink to your knees in it). It has a distinct slippery feel that isn't anything like dirt or sand. If it is dry, color is probably going to be your best indicator. To test your sample, add water until it's at a playdough-like consistency and roll it into a long cylinder with an approximately half-inch (about 1 centimeter) diameter and wrap it around your finger. If it begins to break, you might want to find some better clay. It isn't too critical to the firing process, but it will make it harder to work without cracking.
Step 2: Wet Processing
You now have your own clay, but don't get ahead of yourself! You will need to get all of the foreign material out first, or it will cause you trouble in the form of destroying your wares. Natural clay might have small stones, organic material or anything else in it. Any of these can and will decrease the likelihood of success for your ware during the firing, and organic material is worse because it leaves a void in the clay, and might make enough steam to blow up the piece. Many people today like to process their clay in the method I am about to describe, as it will guarantee a sample of almost perfect clay.
The first thing you will want to do is mix your clay with water in a large container until it is completely dispersed and thin enough to be filtered out. Next, pour your slurry through sieves or cloths and leave the larger particles behind. Now that the clay is clean, you need to get rid of most of that water. If you leave container out for a day or two, the clay will settle, leaving a top layer of water that you can decant off. From there, you can just leave it until the water evaporates, or you can strain the water through something like a bed sheet where the clay particles can't fit through. Just don't contaminate your batch, or you will have to start all over again.
Step 3: Dry Processing
Processing my clay dry is pretty much the only way I refine my clay. I like this method because I am very impatient, and waiting for your clay to settle, than letting the water evaporate is very difficult for me. This way is faster and more hands-on. It also adds that "primitive feel" to the work. But the bad news is that it isn't nearly as good at getting all of the foreign material out as the prior method. If you have a fancy art studio with an expensive kiln and tools, perhaps you should skip this step. If you are looking to immerse yourself in the ancient arts, or are just looking for a fun weekend project, keep on reading!
If you gathered your clay dry, congratulations, you can start right away! If you are like me and get yours with more water than clay, you need to dry it out completely. This can be accomplished by leaving some globs of clay in the sun or by a fire. Make sure the inside is dried out to! Now, take a mallet, or a stone, or whatever blunt item you have around, and start crushing it into pieces. Not much technique here, just balancing force so it gets the job done, but you don't lose half of the material as flying bits of shrapnel. As the pieces get smaller, I find it easier and less messy to grind the bits down instead of smashing them. When you have powder, you can run it through a screen to take the larger bits of organic matter out, or like me, just use your hands. Add a bit of water and kneed it until it's plastic, and you're good to go! If you want to increase the chance of success for your pieces, keep on reading.
Step 4: Making the Temper
With commercial clays in commercial kilns, temper is kind of pointless. Assuming your technique is sound, there is a near 100% chance that your pieces won't explode. But, for the primitive potter, things aren't so certain. Temperature fluctuations in a wood fire can be large enough to destroy over 50% of your ware, and that's if you built the fire right! If your clay isn't the best or if you aren't the most experienced potter, there is a quick way to improve the quality and chance of survival for your work: temper.
Temper is just larger particles that is added to your clay body. It works by lowering the rate of expansion from changing temperatures. Think as it as something for the clay to cling to, or like gravel mixed with cement to make concrete. There is quite a range of materials that can be used, from sand, to crushed shells and rocks, and even organic matter (in reasonable quantities). But, if you already have some failed experiments that died in the fire, you can give them new life as temper. Crush up the bits of ceramic until it is composed of powder and granules. Don't feel to bad for your pots, they would have wanted this.
Step 5: Forming the Clay Body
Now that you have everything you need to start making pottery, we need to combine everything we have to make a workable clay body. So, take your powdered clay and add temper too it. You can also just mix it in with plastic clay. If working with larger quantities, form the clay into disk-shapes, sprinkle the desired amount of temper on top, and then keep on adding disks and temper on top of each other and kneed everything together. The only thing you really need to be concerned about is distributing the temper evenly. The amount of temper you should add is relatively case-sensitive. I like to add, maybe 10% or less by volume to the clay, but you might feel the need to add more or less depending on your situation. I would start by testing pieces with varying amounts, or try with none at all. If you get lucky like me, your clay might not need temper to make a decent product.
So, you have some clay that is ready to be formed and fired. You can chose to fire it in a commercial kiln, but you have already done so much out in nature! Why not stick with the primitive theme? You can fire your ware in a simple wood fire! For more detail, check out another one of my instructables where I go over the construction and operation of a simple pit-kiln here.
Thank you for checking out my instructable and good luck finding your own clay!