The purpose of this chart is to give contemporary painters the true secret of the Old Masters: knowledge of working properties. Understanding the physical properties of their mediums can help painters adjust the working properties of their oil paints to satisfy their particular needs. Painters who use a medium only to increase the flow of oil colors can be satisfied with a favorite teacher's medium or one from a book. However, painters who want to explore historical techniques of new ways to make marks need to make custom mediums. They can combine contemporary materials to create the properties of traditional mediums and reduce their exposure to toxic materials. Or they can create a completely new combination to make a unique and personal medium.