That depends entirely on how they do it. If they're careless and let it oxidize it'll be "layered rust". If they do it properly you basically weld the powder

That depends entirely on how they do it. If they're careless and let it oxidize it'll be "layered rust". If they do it properly you basically weld the powder into the shape you want, and you can start with most any kind of steel you want. http://www.metalpowderproducts.com/index.asp?action=materials_ironsteel http://www.metalpowderproducts.com/index.asp?action=material... discusses some of the stuff they do, which includes everything from pure iron to 400 series stainless to tool steels. You probably can't reproduce wrought iron with it easily (true wrought iron has veins of slag in the mix giving it a grain almost like wood has) but the commercial applications of wrought iron is almost insignificant. You still have to heat treat it, and conventional powder metallurgy uses basically dies, but it's a lot more flexible than you give it credit for. Now, whether these guys are capable of the full monty here, as it were, is unknown. They may have been using stainless because their oxidization control is poor and so they need the corrosion resistance. Or maybe they're doing it because it's convenient; hard to say.