 Louis de Geer brought it to Roslagen in Sweden at the beginning of the 17th century, with Walloon blacksmiths.The Walloon process spread to Sweden in the Uppland province north of Stockholm, where it was used to produce a specific kind of wrought iron called oregrounds iron.The source material was pig iron produced by a blast furnace using charcoal and the manganese rich iron ore from the Dannemora mine.