Working with pen and ink can be quite freeing as the values are simplified by the ink.   The lack of erasing mistakes creates a natural flow and the artist learns to work with the lines he has put down whether good or “bad”.   Phrasing Rembrandt’s quote in sketching terms:  putting down the visual lines you see in ink makes what you do not “know” or “see” more apparent.  Note in the sketch above how few lines are needed to create the woman.   This is a great way to develop your artists’ eye by trying to use a few lines to describe what you are seeing.   Degas’s sketches are also very beautiful with simplified lines creating his ballet dancers.  He often kept “mistake” lines and just drew over them in his sketches.  These days there is a great variety of “pen and ink” type pens that are easy to use without any messy ink refills.    So open up that sketchbook and try out pens for sketching, no pencils needed !