I have several colors of Kato Polyclay that have hardened in the air. Can I return them to their original texture?
Yes, Kato Polyclay™ that has dried out and hardened can be restored with a clay softener or Kato Polyclay clear medium liquid as along as the clay is not partially cured, which can occur with exposure to heat or high temperatures.
To restore your clay to its original state, carefully cut your polymer clay into small 1/4 - 1/2 inch chunks then place into a mini food chopper/processor dedicated for use with polymer clay. Add a few drops of the liquid polyclay then run the food chopper/processor on a pulse setting and check after about 6 - 8 pulses. If clay is not yet to the desired softness, repeat the process. Once the clay is workable and combined into one unit again, continue conditioning the clay by hand until it is malleable. You can also run the clay through a clay-dedicated pasta machine. Clean the food processor to avoid blending colors the next time you need to use the tool.
If you find you have added too much of the liquid clay and the polymer clay is now too soft, roll the clay into a sheet then place between two pieces of plain copy paper. The paper will leech some of the plasticizer from the clay and return it to a workable state.
If you find your clay has been exposed to heat and is now partially "cured" it cannot be restored to a workable state and will need to be replaced.