Pastel underpainting, why and how
Why would one bother making an underpainting, as it will be covered anyway with the finished painting?
The number one reason is that the underpainting will influence subsequent layers, in several ways:
a) Careful planning of the values will make it easier to apply the overpainting.
b) The pigments will blend and mix as one applies the colours of the overpainting.
c) If one spaces the strokes of the overpainting, the underpainting will peek through.
d) The underpainting defines warm and cool areas (depending on the type of underpainting).
It also helps to make an underpainting if you are hesitant to start painting on that pristine paper that is staring you in the eye demanding that you don't ruin it.
Paper with outlines only
The above image shows my summer studio, with a piece of sanded paper (Fisher 400) where only the outlines of the subject are drawn. In this case, I used an underpainting made up of near complementary colours (below).
Application of underpainting finished
When the underpaying is applied, a take a disposable washing wipe made out of foam (a foam brush would work as well). I fold it and then use it to wipe in the pastel pigments into the paper. It is best to lay the paper flat when doing that. If the paper is kept upright, the effect is more wiping the dust off. (Very useful when one wants to remove an area.)
Wipe
Wiping
When all the pastel dust is wiped into the paper, I have a relatively smooth base to work on:
Finished underpainting
Then the image is ready for the first applications of the overpainting:
This way, the original colour of the paper will not show up as bothersome white or light spots. Instead, it will have an underpainting that support and enhances the overpainting.


Painting by Salvador Dalí