Julie In Black and White (Watercolor and casein on illustration board, 4x6").
After reading James Gurney's blog entry on his use of casein, I decided to give them a try since they seemed to solve many of the shortfalls suffered by gouache and watercolor. I love them. The paints apply to the paper well and have a great texture. They can be used in opaque and wash applications. It will take practice to handle edges since they dry quickly and are not reworkable (like gouache), but I'll figure it out.
For the above painting I started with a red watercolor wash and then used casein for the black and white.