Oven bake at 212 - 275℉(100 - 135℃) for 10-30 minutes. Normally 248℉ (120 ℃) requires for 20 minutes of baking to harden it. It does help kids release their creativity. Slice clay into pieces and wrap the clay with plastic film, then soak it in warm water(100 - 140℉/40 - 60℃) for a while.