Work in Progress
An underpainting is a preliminary painting that serves as a base. It is a guide that maps out the composition, shapes, light and dark values, and color choices. When working in pastel, it can be wet or dry. While under paintings are not necessary, they are helpful in achieving what you want to do or envision. They can be useful in creating aerial perspective, which I will get into later as the painting progresses. Some artists will jump right into the production of the work after making a sketch, which I've done in my older works. And that's okay, there's nothing wrong with that. Nothing in art is written in stone---except for "fat over lean" in oil painting.
Pastels can be applied in many ways using different techniques. The underpainting can also be done differently. Water, watercolor, mineral spirits, gouache, pure liquid pigments, and even a thin layer of oil paint can be used to create a wet underpainting. Each offer different effects. For a dry underpainting, you simply rub a thin layer of pigment into the surface. For my wet underpaintings, I like to use water. The effects of water is almost the same as the effects of watercolor. It's okay if colors run into one another or run down the surface, I'm an impressionist painter---not a photo-realist or photographer. Note: certain types of surfaces work best for wet underpaintings. Here I am using UArt sanded paper, much similar to Wallis paper. This paper is heavy enough to handle wet underpaintings and won't warp or buckle. You may see some temporary warping after applying water, etc. It will straighten out and flatten once it is completely dry. Now I am ready to paint.