Plasticene

Plasticene is an oil-based clay. It is made of the same dry clay body as “wet” clay, but instead of adding water, oil is added. Oil does not dry or evaporate and therefore the clay remains pliable indefinitely. Plasticene cannot be fired and never hardens. It is usually used to make a temporary model from which a mold can be made. From that mold, a casting can be poured in a variety of more permanent materials. You can buy plasticene at an art supply store or you can make your own.
If you buy it, do not buy “hard” Buy either medium or soft, depending on your preference. Mush it a bit with your finger to get an idea of how soft it is. The softer it is the easier it is to work, but the less well it holds detail.
Buy a neutral color, terra cotta, tan or grey. Bright colors, black and white are harder to see detail in and also sometimes bleed on your hands.

Recipe (for 40 lbs of clay)
Ingredients
* 10 lbs microcrystalline wax
* 1/2 gallon #10wt5
* 4 lbs plain automotive grease
* 25lbs dry clay powder (Such as Kentucky ball clay)
Method
1. Melt wax, oil, and grease together. Take GREAT care not to overheat or it may burst into flame.
2. Once melted, stir in clay slowly.
3. Pour into shallow microwave-safe plastic containers, or into a wet plaster mold.