Too bad he's so vague...
As far as I know, only silver and some engineered polymers react to light... well, there are also other products but I've never heard of coffee as a viable alternative.
As for some of the things he does, one of the processes seems to be using part of the xerographic printing process where they put an electrostatic charge on some parts of the paper and make a powdered product stick to it until it is fixed.
