Pen and ink, (and also quill nib), is one of the most difficult mediums, along with academic oil painting. The process involves tedious amounts of transparent layers of watercolor, like the method in oil painting called "Chiaroscuro" when used in skin tones, applied by old masters for achieving translucent renderings with contrast and depth. In my personal opinion, pen and ink illustrations are as difficult as oils, because of the fact that an error is permanent and cannot be erased. My illustration work is best summarized as being pop surrealism in a realm in between underground comic books, engravings, and  book illustrations.