I completed my underpainting using only burnt umber and my light medium mix comprised of 40% linseed oil/60% mineral spirits. This mix dries fast and isn’t gummy. Two more layers of paint go on top of the skin so it’s important that they go on smoothly later. The underpainting will show through in the end; I have to get it right! I have purposely done this underpainting rather rough, or structural, with visible brushstrokes to imitate my architectural forms all around her.