I'm not an abstract artist, and don't want to be one, but I really love prepping my canvases this way. It's become an important part of my process. I started doing underpaintings because it gave the surface extra sturdiness and more opaqueness. When I started doing outdoor art fairs (almost 15 years ago), the sun would shine through the canvas paintings and you could see all the underlying paint strokes and it didn't look great. So, I started doing a mostly solid underpainting base and it helped. Now, I like to doing a mishmash of colors and mark making, which is a very non-traditional way to do an underpainting.
Here's a list of reasons why I like this process.
1. It eliminates the blank canvas, which can be intimidating.
2. It helps me to use up paint on my palette before it dries.
3. I like to prep a stack of canvases this way so that I have something ready to grad and start painting.
4. Sometimes the shapes, colors and lines helps to guide the direction of the painting.
5. A lot of the underpainting will get covered, but sometimes different areas with peek through adding interest, depth, and texture.
6. It's a fun, playful, no-pressure way to start a painting. You can always paint over anything you don't like.
Below are a couple before and after images.
You can see how the underpainting colors set the tone for the final paintings and where I kept some areas visible.
