I like to do an underpainting on most works. My typical application is to use a hard pastel and lay in color in the basic shapes of the composition and then wash with 91% Alcohol. Once that dries – and it does rather quickly, I apply the soft pastels of the painting to the paper, leaving a bit of the color from the wash to peek through in the finished painting. Often the choice of color for the underpainting will be a complimentary color to pastel used on the final application.
I know some folks are using watercolor washes and oil paint washes, so I decided to give at least the oil paints a go for an underpainting. I know it needs to be quite thinned to not fill the tooth of the paper so the thinning substance should be something that expedites quick drying…like Gamsol. One day I was out away from studio and much supply and decided to use what I had. The linseed oil thins the paint very well, but doesn’t dry…for several days! NOT an option! I did have Turpnoid and that dried quickly and seemed to work nicely. I was shooting for some “runs” in the final painting and this achieved that effect. I will say that I put some pastel over the first underpainting once the linseed had dried (left a tacky surface on UArt paper) seemed to work…but my hesitation to judge it is that I wonder if the oily feature will bleed through the final coats of dry pastel. Compared to using the alcohol wash with the oil paint wash…I think I prefer the alcohol wash. Both tests were done on 600 UArt paper. My reason for the preference is I can get somewhat of a “run” with the alcohol and it dries really quickly. The quick dry is great for plein air work. I have also used it on PastelMat successfully. Another day I will use watercolor.