by bmat » Apr 5th, '11, 17:11
Pehaps I am missing something here. So let me see if the routine is the one you are thinking of.
A chalkboard is (actually two) are shown to be blank. They are stacked and given to a spectator to sit on, hold, whatever and then at some point there is a message or prediction or something written on the boards?
If the above is what you are thinking, then you don't need fancy writting implements. What you need are spirit slates, available at your favourite magic dealer.