I painted these astronaut kids a couple of weeks ago. Goauche and india ink on watercolor paper. I really enjoy working in this style. The ink is waterproof once it dries, but I could've painted the kids first and then applied the ink afterwards. It's all a matter of preference. Even though goauche is utilized more as an opaque medium, it behaves like watercolor when you add more water to the pigment.
I think I need to get new nibs. The one I used in these illos is several years old and is starting to fray.
I'd love to work on a children's book using this technique. *hint hint* Any takers?