I just made a 'double-layer painting' of a pipe-smoking cyborg sailor stearing his iron ship through the waves. Like this:
A: Small box-frame with 3"x3" actual picture size
B: Sea-going craft drawn onto inside of glass with permanent ink
C: Blue acrylic paint and metallic enamel paint over the line-work on inside of glass
D: Cyborg sailor drawn in ink and water-colour on heavy paper (3"x3")
E: Re-assemble frame with sailor inside
F: Mum! I've finished!