Artworks may be left black & white, or the exposed clay areas can be colored. A variety of transparent mediums may be used for color, though the underlying scratches should always remain visible. White clay coated boards can also be covered with other colored media, and then scratched.
Many artists use sharp tools, such as scalpel blades, to scratch away the ink, creating work with exceptional detail and realism. Other abrasive implements may also be used to create a variety of effects. This unique process has attracted artists for its control in rendering intricate subject matter, while remaining highly versatile to those exploring folk art, abstract work, and many other artistic styles.
A useful little article on the technique from the International Society of Scratchboard Artists - click here to view.