I wouldn't necessarily call it 'clean', but it is a nice effect. It requires that you own something else. I can't say too much and risk exposure. It could be done with other things besides bottle caps, theoretically. Again, I can't risk exposure. PM me and I can be a little more specific.
Prohibition is a staple in my act. I absolutely love it. Like previously said, without the risk of exposure, you do have to have an extra something to make it happen. I guess you can call it a gimmick but it's invisible as hell haha.
The method's clever and I've modified the trick to have it possible for the bottlecap to be signed.
Great effect. Requires a gimmick. Definitely worth it though.
I was doing it quite a bit for a while, but have since switched to the classic coin in bottle. Borrow a beer bottle, borrow a quarter--boom. Best reactions I've gotten with any ___ in bottle effects. Do it in clubs and bars all the time, always plays strong.