I'm very skeptical about this subject now. I always thought that they did work , having foolishly dabbled with it in my teens like a lot of silly kids. However , after watching Derren Brown's experiment where he manipulated a group of university students into believing that they had in fact made contact with a young woman who had commited suicide as part of a cult pact with fellow students and then later revealed that the dead woman was very much alive , then I am very dubious about the effects of it. As I do not know much about the effects of black magic though , it is an area which I would certainly avoid. I just wonder though how much of it is reality and how much is simply an illusion , caused by our subconscious mind tricking us into believing that the glass is being moved by some spiritual being , as opposed to US subconsciously moving the glass. As I am studying Psychology at the moment , I am more inclined to go with this theory.