I first drew these pumps using water soluble graphite pencils, but I didn't like the results. So I went over them with charcoal. I don't think these two mediums were meant to go together, but I like the results.
Yesterday, I tried out Prismacolor Water Soluble Graphite Pencils (HB, 4B, 8B) in a 5" x 8" Moleskine Watercolor Notebook. Although I have had both the pencils and the Moleskine for a while, I had never used either. One difficulty I had with the water soluble pencils was preserving white areas; it is very easy to go too dark.