Many artists start oil paintings by first creating an underpainting, which is a simple sketch created with one color. An artist can use an underpainting to develop a drawing, as well as the forms, values,
plains, and edges that are later added to that drawing.
There are no rules for creating underpaintings. An underpainting can be created as a pencil sketch,
pen and ink wash, basic color wash,
or wash-in with raw umber oil paints or acrylics.
I prefer to use raw umber oil paint as my medium for underpaintings. It has very little chroma
(color intensity), which makes it easy
to develop the drawing and values.
raw umber underpainting also serves as
the foundation for the final painting process.