Some type of sheet stock that was punched in the shape of the stars, then possibly gold washed. From a fabrication standpoint, that would be the most economical. I suppose unless there was vulcanite that could resist 2500 F+ temps back in the day. And there were probably little Keebler Elves with tiny little crucibles pouring the gold stars... The rumor I've heard was that Mr. Lee lost his pipe manufacturing facility in an unfortunate schmelting accident.
Because of the mail order success, everyone knows Lee was in with the Bazos family decades ago. This is exactly where he sourced the edible stars in the pipes. ?