At my last class, one of my students did Purk. And I forgot to tell her she had to do it in the loopy area that we had left for it. It looked great. Then I saw someone else make a Purk that looked like it was on wavy fabric. Unfortunately, I can't find it for you. So, I decided to try and make a Purk that was outside the lines.
Shading Tip: I also discovered that I really like using my black Prismacolor pencil for doing the shading. It's not as shiny as my graphite pencil and doesn't smear as much as charcoal.