This is charcoal on paper of some vases and is supposed to show contour lines varying in tone to describe a three dimensionality to the form, creating sharper, darker lines as the contour line comes towards you and gradually lighter as the object moves away from you, in this way, trying to avoid a flat appearance of the form. If I were to do this exercise again, I would pay closer attention to the Matisse example below and experiment with some different line techniques he uses for variety such as leaving gaps to suggest form and overlapping lines.
On the right is an exercise from Bert Dodson's Keys to Drawing of copying a master's style and work (in this case Matisse) to get a feel for the simple linear style or contour line style that he uses. His line work is simple, elegant and of most importance to him. Light, shadow, perspective and accurate features were not important. I found this exercise interesting, as Matisse's drawing technique is quite out of my own comfort zone, personally, I'm more practised and comfortable with using lots of tone to convey form.
I'm finding it useful to review these linear techniques and styles to remind myself of the broad variety of drawing techniques and styles and not get too locked into my comfort zone in terms of art creation.