why the clay dries quckily?

Answer 1

Clay is very porous and lets the water evaporate easily.

Not sure why this question is under painting????

Answer 2

You're using a water-based clay. Oil-based clay, the kind you have to bake in an oven to harden, won't dry out.

To keep your waterbased clay pliable, spray it with water and/or wrap it in a damp paper towl. Then, if possible, cover with plastic. You should wet the clay at least every two days.