Sometimes when I get done with a piece I'm so excited to get started on the shading!! It's like putting the frosting on the cake!! Some people shade as they go - which I do sometimes, and others wait until they finish. I usually like to look at the entire piece when I finish and try to get the feel of it. For me, it makes a difference on my shading. Other times I like how a pattern turns out and I can't wait to shade it and see how it looks completed. I can't believe even with all of the tangles I make, I still get excited about them. In case you have forgotten, I love, love, LOVE Zentangles!! I don't think there's a right or wrong way (after all it's still Zentangling) but to be honest I haven't seen alot of dark shading on a lot of tangle tiles. Of course I have to admit that I'm not a CZT and I haven't had any formal training so I really don't know what they teach you about shading (if anything) during the class. I would love to take the class but circumstances won't allow it right now. Maybe sometime down the road. Hope you do something that YOU totally love, love, LOVE today!!