The sketch is based on these four sketches that I did on location plus photos I took there, as preparatory work for a large commissioned oil painting. When I was finished with the sketch, I was so glad that the pieces of glassine were already cut and tucked neatly into the book pocket! (Click here and then scroll down that page, to see the glassine pocket and instructions on making one.) That made it super easy to position them over the pages, glue down the edges with a glue stick, and close the book!
Here's what the sketch looks like with the full pages showing, including the border. You can see how the glassine covers get pulled aside to view the sketch. I had to glue the glassine down onto the side borders, so those became partially obscured .