Starting with Watercolor...
Each medium has it's strength, and weakness.
Pastel is magic because you can layer color, and even light over dark and dark over light which is something you really can't do with wet media.
However, pastel fills up the tooth or paper and board and makes it hard to layer more on top of it. So what's a color junkie to do?
You could spray a fixative and layer more on top of it-but fixatives darken pastels, and create airborne toxins. I don't use fixative.
Instead, I often start with a pastel underpainting, then wet it with a wet brush. This "melts" the pastel into the board and leaved the tooth of the board clear for more pastel.
Here's an example of an Ampersand Pastelbord with a layer of violet Mount Vision Pastel as an underpainting. Notice how thick the dust is. That dust is pure pigment and it's a shame to waste it! Don't blow it off, instead take a brush and water and wet it. This pushes the pastel deep into the tooth.
The water melts the pigment. This pigment is the same pigment in watercolor-if you use good quality pastel. The main difference is the binders. Pastel companies use different binders; harder pastels are bound with wax, softer with talc and other soft binders. Its the softer pastels that react with water and give you the same effects as watercolor.
Once covered with water, or with alcohol (both work the same), let the surface dry. If you use Ampersand Pastelbord (like me) it will only take a few minutes (this one took 3 mins. to dry). Then your ready to paint as normal.
I do this when I plan to scumble pure color on top of the surface without blending. This keeps both layers clean. The color is rich and intense, with deep chroma. Here's the painting I did on top of this underpainting.
You can see the watercolor underpainting peeking through the layers of color. This technique works well for other mediums as well. If you use watercolor, you are familiar with starting off with a wash and building color on top. If you use acrylic, try starting off with a thin wash of color. Just add more water to the first layer of paint. Oil painters use underpainting to tone canvas, for subtractive painting and for "fat over lean" techniques.
This is one of my favorite techniques for creating loose and painterly pastels. try it on for size and see if it works for you. If you want to try it in person, my Plein Air Adventure Class will be giving it a try this Weds. Feb. 10th, 10am-1pm at Heritage Village in Largo. Be my guest and try this class for free, or just come and watch the demo and go for a walk in a Pinellas County historical treasure!