(DCO). A castor oil from which approximately 5% of the chemically combined water has been removed and that as a result has drying properties similar to those of tung oil. Dehydration is carried out commercially by heating the oil in the presence of catalysts such as sulfuric and phosphoric acids, clays, and metallic oxides. The commercial product is offered in a wide range of viscosities and analytical constants. Used in protective coatings and alkyd resins.