Wow, this is incredible. I sort of can't believe that that zipper isn't just copied into there from a photo and blended into the whole thing. I know it's crazy to be in awe over a zipper - but I truly think that that part of the drawing is so incredibly realistic that it's just..... crazy good.
The rest of the picture is really awesome as well (though Harry is missing eye lashes.. but maybe that's Radcliffe's fault xD).
Anyway, thanks for sharing the process of making this. I always think it is really fascinating to see how a picture 'emerges' from a sketch.