You are most enthusiastic about three-dimensional printing in your main leader and briefing on the emerging “additive” technology (“Print Me a Stradivarius” and “The Printed World,” February 12, 2011). You even envisage a revolution in manufacturing. Products are built by progressively adding material, one layer at a time. So far, materials are restricted to plastics, resins, and metals. But the future is open. And the cost of a printer can be recovered by making single objects or limited series of objects, which may decentralize manufacturing to such an extent that there will be no need for factories. Or even urban centers that shadow industrialization. Fascinating prospects, no doubt. But you do not spend much time dwelling on companies that employ three-dimensional printing to produce parts of printers. Even though you mention two of them in passing—one American and another German—you leave it at that. Now, that is where the manufacturing revolution really lurks. Print me a printer rather than a Stradivarius!