Painting Medium Artisan Painting Medium is a stand oil based medium, ready made from the bottle. Because of the complex chemistry of water mixable oils, it has been possible for us to formulate a superior medium from a selection of raw materials. This medium thins the consistency of Artisan oil colours and aids fine detail work. It also improves the flow and wetting of the colour. It dries slowly to a flexible film and is good for "oiling out". Oiling out is the application of an oil medium to a painting which has sunk, or lost its oil to the layer underneath.