Things You'll Need
Old canvas sheet
Whether you have accidentally left a batch of clay out for too long and it has dried out, or you have lots of small, dry scraps left over from pottery projects that you don't want to waste, take the time to make hard clay soft and useful again. No matter how hard and dry the clay has become, as long as it hasn't been fired it is possible to soften it ready for use. The method involved is simple but does take some time.
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Examine your clay or clay scraps and determine whether they are bone dry, in which case the clay will be lightweight and porous, or "leather hard," which means that the clay is too hard and stiff to work with but still has some moisture.
Break up any leather hard clay into small pieces with a hammer and chisel and leave the pieces out until they are completely bone dry. This may take a day or two. You cannot re-moisten leather hard clay as it is not porous, so it is important to dry it out thoroughly.
Place your pieces of bone dry clay in the bottom of a bucket. Cover them with cold water so that all the pieces are submerged.
Cover the bucket with a plastic bag and leave it alone for two to three days. Do not stir the mixture or disturb the clay in any way, just let it soak up the water and turn mushy.
When you see that all the pieces of clay have turned into mush at the bottom of the bucket, use a plastic jug to skim the excess water off the top of the layer of mush. Just dip the jug sideways into the water without disturbing the clay mush, take the water a little at a time and discard it.
Spread an old canvas sheet out on the floor, work surface or outdoor area and pour the clay mush onto it. Smooth the clay out with a spatula so that it is a few inches thick.
Let the clay dry out until it is firm enough to use. The drying time will depend on the climate, so take a pinch of the clay every now and then to assess whether it has become workable yet. When it has, store the clay in a covered container to prevent it from drying out again.
After every pottery project, save your scraps of clay in one place. Use this softening method when you have accumulated enough for a whole batch of new clay.