How to Use Raw Clay for Pottery

According to the Merriam-Webster Dictionary, clay is "an earthy material that is plastic when moist but hard when fired..." Taking raw clay from the ground and forming it into a usable vessel or tool is a fairly simple, albeit time consuming, task. Many parts of the world have accessible clay deposits available for the informed potter. Deposits vary in quality, some requiring more work than others to prepare.

Raw clay is clay in its natural condition. Some deposits are utterly clean and ready to use while others are gritty and unusable without taking steps to prepare it.

Things You'll Need

• Pick axe or mattock
• Shovel
• 3 buckets, five gallon each
• 12 square feet of wooden board, or cloth such as cotton sheet or canvas
• Kiln

Instructions

Finding Raw Clay

1. Locate a source of clay. Look along the banks of waterways, drainage areas and ponds. Wet clay prevents water from sinking into the ground, thus surface water is often an indicator of clay. Ask around your area. Park personnel, farmers, birdwatchers, hunters and others who spend time on the land are good candidates. Topographical maps also indicate drainage areas and bodies of water.

2. Test your suspected clay in the field. Wet clay should be slick and elastic (bendable). Take a golf ball size piece of moist clay. Remove pebbles and larger detritus by hand. Roll it between your hands until it is pencil thick and seven inches long. If the clay is dry, pulverize it, wet it and knead it, then roll it. Gently tie it in a loose knot. If this can be accomplished without the clay cracking in pieces, then it has the required flexibility. If it fails the first test, add a little water and try again.

   Conduct a second test to determine the quality of the body (strength or consistency). Roll clay to pencil thick and four inches long. Form it into a loop and press the ends together to join. Stand the loop on edge on a horizontal surface. If the loop sags, either the clay is too wet or does not yet contain the desired properties for pottery (pots may slump before they are able to dry).

3. Assess your clay's purity. If the clay is clean and smooth with no grit, you can skip ahead to Section 2, Step 1. If the clay passes the test but needs to be purified, load up bucket #1.

4. Purify the clay. Fill bucket #2 with 3 to 4 gallons of water. Handful by handful, knead the clay in the water until it dissolves. Continue until the water becomes thick, like chocolate milk. Stir the solution one direction in the bucket so that it swirls around like a whirlpool. Immediately pour the solution slowly into the remaining clean bucket. Do not upend the bucket as you pour. The rocks, pebbles and sand that sank to the bottom as the clay dissolved during the kneading process must stay behind in bucket #2 while the solution gets poured into bucket #3.

5. Settle out the clay. Over the next few days, the clay suspended in the water of bucket #3 will sink, leaving a layer of clear water on top. Ladle off this water and add more solution or let it settle out all the way. As you continue, the clay will thicken. When it can be held in your hand without dripping through your fingers, spread the clay out on a board or cloth to dry further. Thinner cloth, such as bed sheet, can handle wetter, drippier clay as it allows the water to pass through while retaining the clay.

Test Firing

1. Make a test piece. Once the clay is a workable consistency (it passes the tests in step 2), you can make a small test pot and let it dry completely.

2. Fire the test piece. If it comes out in one piece, try to break it by hand (wear gloves to protect hands). If the strength of the piece does not allow breakage, then you are ready to start making pottery.

3. Add temper to wet clay. If the fired clay is weak, add temper (ground up, fired clay also called grog, fine sand or eggshell). Add it in measured amounts to allow the reproduction of good mixes. Form the clay into a disk and remove one quarter or less of the disk like you would a piece of pizza. Refill the spot with temper and knead it into the clay. Pre-soaking the temper in water for five minutes helps prevent the clay from getting too dry during the kneading process. Start with 25 percent temper. If your piece crumbles during firing, use less temper. If it cracks and/or breaks, use more.

4. Add temper to dry clay. Pulverize dried, purified clay and form into a circle. A percentage of the dry clay is replaced with temper and then the two can be thoroughly mixed. If you have a good scale, make your mixes based on weight. Add water slowly to the mixture and knead it in. Once the desired consistency is reached, cover the clay with a moist cloth or sheet of plastic and let it stand for 24 hours before using.

5. Wedge the clay. Once the temper is thoroughly mixed into the clay, the air bubbles that get trapped during kneading must be removed to prevent breaking of pieces during firing. This is done by slamming the clay onto your board or table in such a way that it maintains the clay in a lump and not a pancake. Return to the test firings and if the results are not acceptable, change your temper percentage and try again.

Tips & Warnings

• Label your test pieces by engraving them or write down their location in the kiln on paper.

• Breathing clay dust is tough on the lungs and should be avoided.

References

• an earthy material that is plastic when moist but hard when fired