Circular patterns are used to produce a variety of intensities of shadows inside of a pen and ink drawing. The patterns assist build lighter shadows that progress into darker ones or vice versa. This technique is utilized to make the drawing far more pure and assists build textures like https://how-to-draw-with-ink-pens91320.blogripley.com/35894959/5-simple-statements-about-ink-drawing-for-beginners-explained