After seeing Tony Fisher's Open Petaminx puzzle, I thought of something. Since stickering the inside of an open puzzle is possible, it's also possible to sticker the inside of a puzzle with a fully inclosed core (ie, original Petaminx) Of course, stickering the inside of a puzzle with a fully inclosed core would be pointless, for no one could see what was going on inside. However, suppose someone made a clear Petaminx. Then, it could be stickered from the inside. Using standard, opaque, stickers wouldn't be effective, you couldn't look into the puzzle. Here's my idea: Have you ever seen a one way mirror? They allow you to see through in one direction, but not the other. What if a type of sticker was made that allowed you to look into the puzzle and see all the other colors? I think this is a good idea, but I'm not sure if the injection molding lines would interfere with the view, or if stickers like that are possible to make.

Unfortunately one way mirrors do not exist. The principle of a "one way" mirror is that you have a piece of glass that is partially reflective. If you then look from a dimly lit room through this glass to a very brightly lit room then the light from the bright room will pass through the glass and wash out your own reflection. On the other side of the glass, the reflected light from the bright room washes out the dim light coming through from the other side, giving the impression of a mirror.
So if you were to apply this to a puzzle then you would just need to use transparent stickers.

oh ok, that makes sense. It's to bad "one way" mirrors only work in dark conditions. It would've been really neat.