article from practicalselfreliance
Clay is present just about everywhere, and even soils described as “sandy loam” can contain as much as 20% clay. To the naked eye, it may look like sandy soil, but with a 20% clay content, every 10 pounds of soil is hiding 2 pounds of clay ready for harvest.
Though most soil has some clay content, the yield will obviously be higher if you find high clay soils. Look for areas where the water tends to sit after a heavy rain.
If you’re curious how much clay your soil contains, try doing a test jar. Fill the jar about halfway with soil, add water and stir to completely break up soil particles. After a few minutes, any sand and silt will settle to the bottom. Anything that’s still left suspended in the water is the clay content.
The wet harvest method involves adding both water and soil to a bucket. The soil is then stirred into the water, and allowed to sit for a brief period to allow the rock, sand, and silt to settle out. The clay stays suspended in the water for longer.
The clay and water mixture is then filtered through a fine cloth or sheet. What’s left is a ball of smooth clay.
The wet harvest method is much more efficient and allows gravity to do most of the work. If you have access to plenty of water this is the way to go.
To use the wet extraction method, start by filling a bucket about 1/3 of the way with soil. Add water and use your hands to break up the soil particles as finely as you can get them.
Allow the soil to hydrate for a few minutes, or preferably a few hours. Then use your hands to break up the soil pieces again.
Give the whole bucket a good stir. A shovel works well for this, or a boat oar, or just an arm.
Our soil has so much clay suspended in the water that an arm in the bucket comes out completely covered in the clay slurry.
Once the soil is fully suspended in the water, give the bucket a few minutes to settle. The rocks fell out of suspension almost immediately, followed by the sand.
The silt will take 2-5 minutes to settle down, leaving only the smallest clay particles suspended in the water.
While you’re waiting, get a sheet ready inside a bucket or colander. Anything with a fine weave will do, I’m using an old bedsheet.
The sheet has a relatively loose weave, so I’ve folded it into quarters.
I’ve read in rural India, women who filter water through 7 layers of sari cloth actually filter out cholera. With 4 layers of bed sheet, I was able to filter a clay slurry to completely clear water.
To speed up the process, I gathered the corners of the sheet and hung it from a tree.
In the end, the top inch of clay was still pretty wet and slimy.
After 24 hours, I pulled all the clay out of the sheet, kneaded it together and let it dry in the sun for a few hours. At that point, the texture was just right.
Since it’s not commercial clay, it’ll take a bit of effort to learn how to fire it correctly. The right firing temperature may be hard to achieve, but our next step is to make a primitive kiln in the backyard.
I’ve read that inconsistencies in homemade clay can make it liable to crack during firing and that some potters actually mix in stones to their pottery vessels to help stabilize them. Soon enough I’ll find out when we go to make primitive pottery.