Rotating Cube

[Hago Ziegler]

Hi everybody,

I have an animated GIF - it's a rotating cube on transparent background,
consisting of 20 layers. I want to give a wooden surface to this cube.
But: doing this with 20 cubes, each one with 3 sides with
different perspective and brightness every time, is a horrible work. 
  Is there any way to simplify this work?

Thanks,    Hago