These sketches were done using Sepia and White Cretacolor leads. The faces are pretty small, and I found myself wishing I'd used Prismacolor pencils instead, which can be sharpened to finer points. Nevertheless, the Cretacolors worked okay, and I just kept sharpening them as best I could. I set a timer to quickly sketch the first one. That took 12 minutes, so I kept that time frame when I did the others.
The white on the left side is a sheet of glassine, which folds into the center of the book to protect the pages from one another when the book is closed. (Click here and then scroll down to see how to make a glassine storage envelope in your sketchbook.) I did try spraying with fixative, but the color still rubbed off easily. I'd have to really saturate it in order to avoid that, and I didn't want to lose my lights. Glassine seems to be the best solution for me in a sketchbook.
As reference material for the sketches, I used the book Facial Expressions by Mark Simon. It is intended mostly as a reference tool for animators. As such, most of the expressions in the thumbnail photos of the book are very exaggerated. Still, I find it a useful reference, and each person starts off with a few more normal-looking poses.