I tried a watercolor exercise that someone posted online – it uses (mostly) random colors to achieve tone. It’s extremely interesting to cross those two things while painting. It’s impossible to completely ignore the effects of color (e.g., yellow highlights seem to really work well, and blue works for shadows even when it’s not really hugely dark). And it’s also impossible to cheat on tone to achieve interesting effects. But, ah, that’s art, right?
I did a pencil sketch of a photo of Gabriel Garcia Marquez, but it was such a good sketch that I didn’t want to use it for the exercise, so I did the exercise freehand in a watercolor sketchbook. I used a #14 flat (about ½”) for most of it, and a #6 round to finish. (I could use the corner of the flat for some details, but it was cumbersome for thin and tight-curving details.)
I chose that brush because the example used it; I had a feeling that keeping the colors chunky would work better. I still wound up with some linear stuff (should have done the nose and mouth creases with the broad side of the flat instead of laying down thin lines…), but it was an interesting exercise, learned a lot of things.
The colors are rather ghostly, but that’s what I had on the palette. I think this is a very good exercise because it forces you to think really dramatically about color and tone at the same time, which I found hard to maintain, but my skills improved as I plowed on, and I was able to fix up some of the worst problems.