What a time it was when iron trusses were a stylistic element in architecture. The best-known example today is the Eiffel Tower. But zeppelins also have an iron framework inside. And Diplomat has now launched a limited edition fountain pen that celebrates just that: the iron truss and the zeppelin. The Diplomat company launched the Aero a few years ago. A fountain pen that reminded me, at least, of a Zeppelin. Now Diplomat is launching another…