Balsam Copaiba (B.C.) Medium, 0.5 oz. This is a natural oil derived from the resin of the Copaifera langsdorfil tree of South America. It is a natural substance and is the premiere non toxic, non allergic painting medium. It has excellent working time but will eventually dry, allowing for handling and transport of your painted pieces. It can be modified with clove, lavender, or other oils. Our B.C. Medium is all natural and a medium consistency.