Luna 2
After the drawing is finished and I like the design, I paint a light coat of acrylic paint mixed with gesso over the entire canvas. This is done so that when the painting is done there will be only one layer of oil paint. This is so that the oil layer can shrink or expand with no worry of cracking which can be caused by an underneath layer that isn't as dry as the surface layer. Some oil paints are transperant and anything underneath will show through including pencil marks and if the canvas is left white, you will see white brush marks because the gesso can be slick. I always take my time and ask myself if there will be a color painted that will be transperant and then I paint the object that color. I don't usually shade or spend too much time on the underpainting because most of the work will be covered up.