Large orange splodges in this Bord na Mona bog indicate the presence of bog iron ore. Photo: OSI Online Mapviewer
Bog iron ore is referred to in much of the archaeological literature on iron smelting in Ireland. It is often suggested as the primary source of iron in prehistory and medieval times but this assertion is rarely supported with scientific analysis (although this has changed in recent times and there are many sites now where chemical analysis of iron slag has indicated a bog source for the smelted ore).
A large orange spread of probable bog ore
The assertion is a logical one, considering the lack of large, high quality mineral ore deposits in Ireland on the scale of those in Britain. Also, bog ore is supposed to be a renewable resource, replenishing over a few decades according to Tylecote, and thus providing a very useful source for small scale iron smelters.
Troweled patch of potential bog ore
Unfortunately very little is known about where and to what extent it occurs in Ireland (more is known about American
and Scandinavian bog ores). Discussions with Conor McDermott, a colleague of mine in the UCD School of Archaeology who had worked extensively in Irish bogs led to a plan to go collecting some of the 'bog iron' he had frequently observed in the field: with the goal of checking its iron content to test if it really is a viable ore and, if it is, of smelting it
Our expedition was very successful, collecting almost 40KG of orange material from the bog (presumed bog ore pending XRF analysis). The material varied from a clay-like consistency to hard agglomerations similar in morphology to iron slag. All of it was very orange, presumably derived from oxidised iron.
Slag-like agglomerations of probable bog ore