Line quality in drawing Ronald Searle

We can observe Searle drawing in this YouTube clip (6:16 mark):

Note how he uses his fountain pen unconventionally, upturned with the nib bent. He has a thoroughly roughed in pencil sketch, then works quickly over that in ink, maintaining a spontaneity in the line — ‘stitching’ as he moves his hand, creating that recognizable jagged quality.

 
In the finished drawing the pen lines are contrasted with much bolder lines most likely made with a brush. The dark wash of the night sky contrasts with the figures lit by firelight and makes the figures ‘pop.’ The horse is subtly toned darker as he turns away from his annoying human partner. His drawings hang together with great appeal, creating a satisfying visual experience for the viewer.


http://www.cartoonbrew.com/educational/6-drawing-lessons-inside-story-artist-matt-jones-learned-ronald-searle-138342.html