It's been a while since I've done a fountain-pen drawing (as you can tell if you look at the ink blob on her nose). I like using a fountain pen, and then washing the ink from the line with a wet brush (or a finger) for shading.
M.C Escher was a brilliant mathematician, as well as an artist. He actually computed the vectors involved in his images, mathematically, then plotted them out to make his skewed perspectives and repetitive backgrounds work out on paper.
I, on the other hand, just tried to copy one of his images in 30 minutes. It's hard enough to try and draw in actual perspective. It's quite another thing to try for this false version.