All clays are different depending on the composition and brand. If clay has been exposed to heat or ultra violet rays, it will not soften again. Through a process call conditioning, you can make most any other clay soften and usable for projects again.
Remove one-half ounce to one ounce of clay. You are going to be working the clay in your hands, so choose an amount that you are comfortable working with. You can combine two colours.
Squeeze the clay between your fingers, and then pull it together and roll it in a ball. The warmth from your hands will help soften the clay.
Roll the clay between your hands to make a snake. Squeeze the clay back into a ball once you stretch out the clay. Stretching the clay helps change the texture.
Keep working the clay, kneading and rolling it for at least five minutes. The type of clay will determine how long it will take to soften.
Add mineral oil or petroleum jelly to the clay, if it will not soften after five minutes of conditioning.
Run your clay through a pasta maker at its widest setting to save your hands from the kneading.
Before you condition your clay, put it in a food processor to make it easier to soften.