I've started creating a range of brush-marks which I'm scanning into Photoshop. I have done this using black indian inks. I've just used black as I can digitally recolour these marks easily within Photoshop.
Im Scanning them In at 300DPI so that they will not pixelate when enlarged. Each mark is then being turned into a Photoshop brush so that I can build my own custom brush library from which to work.