If you use painting medium the paint becomes smoother and fatter. This allows the paint to be smeared out easily and the brush stroke to become less distinct. Adding the medium does not affect the drying time. It does, however, increase the degree of sheen and the durability of the paint film. You can mix the medium with water and it can be applied in the layered painting technique perfectly well. Cobra painting medium is based on vegetable oil, synthetic resin and water.