Processing Clay the Easy Way: Water Extraction
(As featured in the January 2008 issue of Practically Seeking)
Today we usually think of clay as being used for pottery
but in truth the uses are almost endless. For thousands of years man has used this substance for a whole host of things, from pigments to medicines. One of the most abundant materials on earth, clay can be found almost anywhere — just look for areas where the ground has broken into a bark like pattern (as on a tree) or areas where water tends sit longer after a heavy rain.
Clay can be extracted from many of these sources quite easily, and whether you plan to use it for pottery or one of the multitude of other traditional uses, the goal is to remove as many impurities as possible and the process is the same. While some clay deposits are pure enough to be used raw straight out of the ground, these are the exception; most clay is found in conjunction with sand.
Many people have never considered the idea that they could make their own clay
Learn more about Harvesting,
Processing and Firing
Primitive Pottery workshop.
or are intimidated by the perceived difficulty of the process. One method, as suggested in many "living with the earth" books, is to pound the dry clay into powder and then winnow (sift) the fine clay particles on to a collecting surface. While this method does work, and in some circumstances may be the only method available to you, it is highly inefficient and requires a huge energy expenditure, violating the primary rule of survival — conservation of energy.
The method I prefer, and teach, is the Water Extraction Method.
The big benefit of this method is that usable clay can be extracted from the most marginal of soils. The clay shown below was processed from soil that was almost 70 percent sand and, using other methods, would have been considered unusable. For this exercise we started with 10 pounds of dirt that had a marginal clay content. It would barely adhere together when pinched between the fingers, but could certainly not be molded into even a basic shape such as a small log.
However, by the time we were finished, we had a little over 3 pounds of high-quality pure clay — more than enough to make several pots.
Step-by-step Instructions for how to Water-Process Your Own Clay:
- Fill a container about one-third full with the soil, then add enough water to fill the container. (Gallon jars or 5-gallon buckets both work well, depending on how much raw dirt you have. Using clear containers can be advantageous to the beginner.)
- Crush the wet mud between your fingers to as small a size as possible, breaking up all the clumps. Once your mixture is as lump-free as possible, allow the material to hydrate for several hours.
- Stir the mixture thoroughly, then allow it to settle for a few minutes. Clay is lighter, and floats above the heavier sediment. Look carefully as the mixture begins to settle and you will see a color change that indicates where the suspended clay particles and sediments meet. This "clay water" is what you want to keep.
- Pour off the clay water into a separate container. Watch carefully while you are pouring and when you see sediment starting to gather on the lip of the container, STOP! Repeat steps 4 & 5 as many times as necessary to extract the greatest possible amount of clay from the sediment. Stop pouring sooner rather than later! You don't want sediment sneaking through into your clay.
- Take the clay water you have collected and repeat the same process of diluting, mixing and settling, and pour this further refined clay water into a third container. This step will help to get rid of the smallest bits of sediment.
- Once you have removed all the sediment, leave the clay water to settle, undisturbed, for at least a few hours (a full day is even better). This allows the clay particles to settle to the bottom of the container.
- After the clay has settled the water should be virtually clear and there should not be any noticeable color change lines within the settled clay. If you see that a sediment layer has appeared below the clay (indicated by a layer of darker, coarser material at the very bottom), repeat steps 4, 5 and 7 until you have removed all the remaining impurities.
- Carefully pour off the suspended water, watching the lip of your container. When clay begins to pour off with the water, stop pouring, set the container down and allow the contents to settle for a few minutes. Continue this process until as much water as possible has been poured off and only clay is left in your container.
- Take a section of old bed sheet, t-shirt or other finely woven fabric, drape it over a bucket and, keeping the cloth secured against the bucket, pour the wet clay into the center. Pull the edges of the fabric together to make a "bag" in which to hold your clay while it dries. Tie the top of the bag closed, pulled snug around the top of your new clay ball.
- Use some sturdy rope or cordage to hang the clay bag some place where it can remain undisturbed for several days. You should see water dripping out of the bottom of the bag as the clay begins to dry. The water should be clear, or have a slight clay-colored tint. If you can feel any grit or see any particles, your bag material is not of a fine enough weave and you are losing clay. Find something tighter and re-bag.
- After two or three days open your bag and check if your clay is still soupy, or if it has firmed up. If you are unsure, scrape a small amount if clay into your hand and if it will form into a ball that retains it's shape easily, you're good to go! If not, re-tie the bag and allow it to hang another 24 hours before checking again. Once your clay has reached a usable consistency it can be removed from the bag and placed into a permanent container, ready to be tempered and molded for pottery, or used for whatever project you have in mind.