I have made regular clay masks. Our district has a policy where we are not
allowed to do the plaster masks right on the face. I have plastic face
forms. I would think the air dry clay would act similar to the regular clay
in the drying. I had some cracking around the sides when it dried if the
clay had been rolled too thin. I had less cracking when I took the maks off
the form while it was still pretty wet. (I let it set for the day). Good
luck!