Whenever I do a picture, I do a messy sort of pencil sketch, then go over in ink, rub out the pencil lines and paint it. However, I've been looking at some beautiful illustrations by Armin Greder and Freya Blackwood and notice that you can still see the pencil lines (Armin Greder mostly works in pastels, I think). So I had a quick go at just leaving the rough pencil sketch without the ink, then painting it. I really like the look of it. There seems to be more expression or something.
