Now you get your dremel wire wheel or a bronzebrush and work at the rust -clear it out of the pits and and any engraving or stamping. It is never going to be 'mint'! Try and resist the use of any hard abrasives as this makes it look 'restored' - and removes much of the detail from the surface.
BTW - Sorry we forgot to mention that rust removal is messy - whichever method you use. If you think that was bad, try electro-removal. That is REAL messy. (Next time stand the pipe in an old tin or bucket. It saves having to duck when the No1 finds the mess.)