I paint it on finger nails...
...on sunglasses (this piece is from my Make 20 Paintings project)...
...on milk bottle tops...
...and on toy cars. I think I've gone too far with the car. It looks okay in the photo, but it's usually viewed from above so it looks a bit strange having a ring of sea around the sky, and I didn't know which direction to paint the clouds. I think an image which is a birds eye view might look better.