Learning that Toppi style with those beautiful lines. These are his drawings here: http://www.tumblr.com/tagged/sergio%20toppi Breaking it down, it looks like the hatch lines can go in any direction and they do blend into solid blacks. And also leaving ample solid white areas.
I drew this while sitting a Provence Bakery at Holland Village. A lady nearby was going through math homework with her little boy. The boy looked like he was ready to run off. But he had to solve the math problems on the page first. Waterman EF + Hero pen + photoshop