An experimental approach has been used to establish whether medieval ironworking activity could be identified in peat bogs using mineral magnetic measurements. First, magnetic susceptibility and remanence properties were obtained for materials from an experimental iron smelt, in a furnace of medieval design, and from material collected during the excavation of the medieval bloomery at Llwyn Du in Coed y Brenin, Snowdonia. Materials sampled and measured included charcoal, aerial dust, roasted bog ore and furnace dust. A second experiment determined whether small amounts of aerial dust released from the furnace could be detected in accumulating peat samples. Thirdly, mineral magnetic measurements were made on a peat core collected close to the Llwyn Du bloomery. It is argued that the results presented here suggest that it is possible to identify evidence of past ironworking in peat bogs using mineral magnetic measurements, and that the signatures remain well preserved in the peat record even after burial for several hundred years.