A sketchbook is a complete piece for me. Whenever I finish a drawing or part of a drawing the first thing I do is start from the first page of the book and flip through to see everything there.
For the most part I am working straight through, but keeping myself familiar with each page and how the whole book flows together brings me in circles of seemingly endless starts and finishes.
You can see what I'm talking about in the drawings this text is sandwiched between. The top photo shows how I originally thought the sketch would end and in the bottom photo you can see how I later decided to switch tools and wrap it up.
Thats usually what is going on in my sketchbooks when you see a shift from markers to pen or pen to pencil or pencil to charcoal and so on.
Can you find the switch in this one? It is a little more subtle than the others.
