EMAP_2012_Report_6_1.pdf (7.3 MB) - The Heritage Council

most likely indicated that the fragments came from bog ore; and possible bog iron ore was
identified from Lough Island Reevy, Co. Down (Gaffikin & Davies 1938, 202). Iron ore has
been collected from the bogs around Clonmacnoise and is believed to have been used for
iron-working at the site (King 2009, 342). Iron-bearing minerals, such as limonite, have been
identified in Cork at Garryduff (O'Kelly 1963, 103) and Oldcourt (Murphy & O’Cuileanain 1961,
90), and ironstone nodules were found at Nendrum (Lawlor 1925, 140).
There is no archaeological evidence for the mining of iron ores in early medieval Ireland and
it is possible that these ore-working areas have been destroyed by turf-cutting or later
bedrock mining (Comber 2008, 239). Early Irish law makes reference to the mining of iron,
for example, the laws of distraint (Cethairslicht Athabálae) referred to penalties for the illegal
digging of someone else’s silver mine or excavating iron or copper ore from his cliff (Kelly
1988, 105).The extracted ore was then dressed, washed, winnowed and crushed with only
the most iron-rich pieces retained for smelting (Wallace & Anguilano 2010b, 70). The large
quantity of iron ore from Garryduff (O'Kelly 1963, 103) suggested to the excavator that it was
derived from nearby ore-bearing surface outcrops. The site also provided evidence for the
roasting of ores and this process involved the transformation of carbonate and sulphide ores
into oxides, the latter of which was more easily reduced in a smelting furnace (Comber 2008,
240). Four large stones with concave surfaces at a palisaded enclosure at Lowpark
specialising in ironsmithing may have been used for crushing iron ore (Gillespie 2006) and a
large slab with a basin in a smelting area at Gallen Priory (Kendrick 1939, 5) was interpreted
as having a similar function. The potential significance of bullaun stones at ecclesiastical
sites, hollows in bedrock and other possible mortars for the crushing of ore at a number of
sites has been highlighted in recent years (Dolan 2009, 16-19). It is likely that iron ore was
found on other sites but was not recognised as such by the excavators (Scott 1991, 154).
2.3.2: Charcoal Production
The iron smelting process required charcoal production and the eighth century law tract, Críth
Gablach, listed ‘a sack of charcoal for irons’ as one of the household possessions of the
mruigfher-class farmer (Scott 1991, 100). Charcoal could be produced in either traditional
earth-dug pit kilns or mound kilns where wood was allowed to slowly smoulder and carbonise
in an oxygen-limited environment (Kenny 2010, 13-14). Control over the amount of oxygen
within the pit allowed the wood to burn slower than in the open air, and thus produce better
charcoal. The most common early medieval form of charcoal kiln was the charcoal production
pit though evidence for mound kilns tend not to survive as well (ibid. 105–6). Charcoal
production pits consisted of earth-cut charcoal-filled pit features, circular, oval or rectangular
in shape, with evidence for in situ burning on their sides and bases. A total of 61 charcoal
production sites were identified in a recent survey. Thirty-two of these were radiocarbon
dated to the early medieval period, of which the majority belong to the period between A.D.
800 and 1200. Typical rectangular pits were 2-3m in length and 1.2m in width while circular
examples were 1.4m by 0.33m in depth. These consisted of small pits in which timbers may
have been placed against a central vertical post, covered by straw, bracken and layers of
earth and turf (ibid. 89). This vertical post was then removed and the resultant hole filled
with charcoal and carefully ignited. The wood was then effectively roasted for several days as
the water and other impurities were allowed to evaporate without the wood actually burning.
Finally, the fire was allowed to die, the kiln was dismantled and the charcoal extracted (ibid.
91). Experimental work has replicated these features in recent years using these methods
(http://charcoal.seandalaiocht.com/). While there has been no synthesis of charcoal specialist
reports oak appears to dominate as a chosen species. This factor evidently influences the
outcome of radiocarbon dates. Other species were also used - at Killickaweeny 1 ash was
used in a furnace (ibid. 101), while at Laughanstown a rectangular pit contained charred
hazel roundwoods dated to A.D. 1020-1190 (2σ) (Seaver 2011, 273). Many of these sites
were discovered isolated from settlement enclosures, sometimes close to features such as
field boundaries and also were occasionally close to features related to iron production (Hull
and Taylor 2007, 25-26, Carlin 2008, 88). The EMAP survey shows that while this was often
the case charcoal production pits were not exclusively distant from the settlement and have
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