Everyone that has tried to mark freshly felled timber for milling with a normal graphite pencil, will know that the makings are very difficult to read   However, Stabilo produces a special-purpose pencil, that will mark wet surfaces (and plastic, metal etc). The most commonly available color is black, but it is produced in multiple colors, and I frequently use the red color.   It is called Stabilo All 8008, see STABILO All ? PRODUCTS ? STABILO.COM   It costs about £1/pencil, and is sold i