A lot of the artists like drawing on sandpaper. So far, I can't make it work for me. I did list on UART400 with polychromos and BrushAndPencil.com's texture spray.
I did such a bad job on this one, I feel not-so-good about mentioning the reference photo. The photo is *nice.* The photo was taken by T. Fernando from Portugal and posted on Wikimedia Commons.