How to Make Raw Clay Usable for Pottery
Naturally occurring raw clay deposits can be found all over the world. If you are fortunate enough to have access to a deposit of clay near your home, you can make that raw clay usable for pottery by purifying it and then tempering it. Purification removes sand and other sediments from the clay. Tempering the clay will make the clay resistant to cracking when it is heated or dried. Temper can be made from crushed shells or crushed pottery.
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Instructions
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Purifying the Clay
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1
Remove any stones, sticks, grass and any other foreign objects from the raw clay.
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2
Put the clay in a bucket. For every one part clay, add two parts water. Knead the clay with your hands, breaking apart any lumps. Then let the clay soak for two to three hours.
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3
Mix the clay and water with your hands. Wait five to ten minutes for the sediment to settle. The sediment that had been mixed into the clay will sink to the bottom, as a darker layer beneath a mixture of clay and water.
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4
Slowly pour the clay and water into a second bucket, without pouring out any of the sediment.
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5
Mix the clay and water with your hands. Empty and wash the first bucket while you allow the remaining sediment in the second bucket to settle for a few minutes.
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6
Slowly pour the clay and water mixture back into the first bucket, without pouring out any of the sediment that has sunk to the bottom. Set the bucket aside for a day to allow the mixture to settle.
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7
Check the mixture after one day. You should see a layer of clear water above a layer of clay. If there is still sediment beneath the layer of clay, repeat Step 6 to further purify the clay. When you are satisfied the clay is pure, proceed to the next step.
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8
Pour out the clear water by slowly tipping the bucket. Stop pouring when the clay approaches the lip of the bucket.
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9
Make a sieve for the clay by lining the inside of an empty bucket with an old pillowcase. Then pour the clay onto the fabric inside the bucket. Slowly lift the clay in the pillowcase out of the bucket, letting the water drain you you lift it.
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10
Tie the end of the pillowcase with a length of clothesline, and suspend it above the bucket. Inspect the clay daily. Remove a handful of clay and mold it into a ball. If the clay does not lose its shape, the clay is ready to be tempered. Remove on piece about the size of a fist and store the rest in one or more airtight containers.
Tempering the Clay
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11
Make some temper by grinding seashells or pieces of broken pottery with a mortar and pestle until the pieces are of an even consistency, small enough to stick to your hand when wet.
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12
Divide a fist-sized piece of clay into eight pieces of equal size. Form each piece into a ball, then flatten them to a thickness of about 1/8-inch.
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13
Form one disk into a shallow cup. If the clay cracks while you work on it, dip your fingers in water and massage the crack from the clay. Then scratch the number "0" into the bottom with a nail. This cup has no temper in it.
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14
Pour some temper onto a board or other flat surface so it as about the same size as one of the disks.
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15
Put one of the clay disks onto the temper, then press it down to cover it wither temper. Turn over the clay and press it down again to coat the other side. Coat both sides of the remaining six disks.
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16
Squeeze the six treated disks into a single ball. Knead the mixture until the temper is worked evenly into the clay. Divide and flatten the clay into six disks 1/8-inch thick. Form one of these into the shape of a cup and mark it with a "10", as this cup is 10 percent temper.
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17
Repeat the above process to create a mixture of 20 percent temper. Form a similar cup from this mixture and mark it with a "20". Then repeat the process again for a 30 percent and 40 percent mixture, with cups made from both these mixtures as well.
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18
Set the five cups aside for a few days. The cup that cracks and crumbles the least represents the amount of temper you should use for the remaining batch of clay.
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19
Mix the remaining batch of clay with the appropriate amount of temper, and your clay is now usable for your pottery project.
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