Pro Art-Jovi Air Hardening Clay. Super soft modeling clay that stays soft in an air tight plastic bag, and hardens when exposed to the air. Air-dries in 24 hours, once hard it can be painted, varnished, polished and cut. This package contains 1/2 pound of Hardening Clay. Comes in a variety of colors. Conforms to ASTM D- 4236. Imported.