I should clarify, by stayed behind I mean stayed on the acetate, not the cake!
As with any other multi-chocolate work, I let the woodgrain set up a bit too much before spreading on the next layer (I did dark grain with a white background) so when I went to peel off the acetate much of the dark chocolate stayed behind. Worked fine for my kid's birthday party, but if it's a wedding then give it a go a few time before making the cake! Other'n that, easy & fun. Just cut up acetate (transparency film) from the office supply since my cake was small.