Mont Marte Air Hardening Clay is great for many crafting projects. Air Hardening Modelling Clay does not need to be heated is suited. From student to artists and professional modellers, Mont Marte Air Hardening Clay is a perfect choice. This clay hardens at normal room temperature, dries in around 24hrs to earthenware hardness (depending on thickness). This heavy bodied clay is pliable after kneading, and because it is slow drying you can take your time forming it into your desired design.