Ultimately illustration done by traditional media has to scanned into the digital realm. Some media scans better than others. Generally a flat surface is better than shinny. Watercolor scan and Gouache are excellent. Soft and hard pastels scan well, although in my experience the tooth of the paper is more visible under the scanner, and changes the appearance. Another negative is the delicate surface, it’s easily damaged.
This is why I chose oil pastel, it’s flat and scans well as shown here. The surface is very durable, and can be touched without damage. It can be harder to work with, but with experience it creates wonderful textures. I am very pleased with the scanning.