I tried this during the winter and it does work, if your going to use the chocolate bar method make sure you use the foil lightly otherwise you only scratch the can up which is no good.
A quicker way is to use wire wool or brasso wadding (more fine tools for fire) which should bring that shine up within 5 minutes.
I only had success with a small piece of single ply toilet paper as the winter sun was too weak even for char cloth, but that was on that particular day, it was fun to do though and rewarding and even better when boring the pants off work colleagues about it (Your making it up - think i'll stick with a lighter is the usual dumb bottom reply).
Just thought i would offer some tips from my experience. Good luck i hope you do it cos it's worth doing just the once.
P.S Those numbers didn't affect the experiment