My minions should know by now I don't think there's any "wrong" in art. And while I'd never condone painting on just any book, why limit your creativity to the inside of your sketchbooks?
Ever since I made the connection – canvas-covered sketchbook ... people paint on canvas ... Hey, I could paint ON my sketchbook – I haven't been able to stop myself. I like this one enough, however, that I wish it was on paper so I could hang it. I could try to recreate it, but it won't turn out the same.
Anyway, I did this by first drawing the image with a black Sharpie marker. Then I watered down liquid craft acrylics (50¢ to $1.00/bottle) and painted the blue background and purple petals. Next, while the paint was still wet, I splattered pink, purple and blue paint. I painted the light and dark orange spots on the butterfly with paint directly from the bottle.
Last, but not least, I went back in with the Sharpie marker to redefine the lines and add the black to the butterfly.
The cover didn't buckle or bend in anyway and since it's acrylic paint, I'm not too concerned about taking the book out and about to draw. After all, once it's completely dry it will be permanent.