Sculptors need a modeling clay that is easy to sculpt at room temperature, doesn't dry out
so they can continue to work on the piece for as long as they like, and which holds fine detail.
In 1897 a British art teacher named William Harbutt came up with a modeling clay that could do all of these things. His formula used powdered
chalk, petroleum jelly, and stearic acid. He called it "Plasticine," which is still a brand name today.
Because of its oily composition, it softens when warmed in the hands. Harbutt's original clay was gray, but now oil-based modeling clay is
available in many colors. It is also used by animators for the movable models in claymation films.