I've recently made a sketchbook incorporating some hand-made paper samples attached to old Michelin maps with the intention of trying out different media on different surfaces.
This first sketch of a tree bent by the wind is on a very rough, gelatine sized watercolour paper and I loved the way my parallel pen skipped over the bumps and then washed out to make the shadows.
This second sketch is on an absorbent pastel paper with only a slight tooth and the effect is quite different with the ink soaking straight into the surface causing lovely blooms which perfectly describe the pine leaves. It wouldn't wash out with water at all as the pigment had already been absorbed. I really enjoyed this experiment and now I'm looking around for other combinations to try!