STERO CO 400 Castor oil 40 EO, also known as castor wax, is a hardened vegetable wax produced from pure STERO CO 400 castor oil 40 EO through the chemical hydrogenation process. When hydrogen is added to pure STERO CO 400 castor oil 40 EO in the presence of a nickel catalyst, the resulting product becomes waxy, highly viscous and more saturated. STERO CO 400