Beneath a field on the Kilmacredock Upper side of a townland boundary in County Kildare, excavators found three small bowl furnaces, the physical residue of metalworking that had taken place on a patch of ground measuring roughly eight by eleven metres. No finished objects survived, no tools, no moulds. What remained was charcoal, slag, and in one case a thin frozen stream of metal, just 20mm wide, that had run 42 centimetres from the base of a furnace before solidifying. It is an oddly intimate kind of evidence: the work itself is long gone, but the spill remains.

The furnaces came to light during monitoring of topsoil-stripping along a four-kilometre road scheme, the Celbridge Interchange, between April and December 2001. This stretch of ground runs from Celbridge to Leixlip through a landscape partly shaped by 18th-century estate design, with avenues and woodland arranged around the early 18th-century house at Castletown. The metalworking site lay close to one of the boundary ditches that divided the Castletown deerpark and marked the line between two townlands. Bowl furnaces are exactly what the name suggests, shallow circular pits cut into the subsoil, used to generate the concentrated heat needed for working metal. The three found here were compact, each under half a metre in diameter, with fills dense in charcoal and slag. The largest, Furnace 1, showed signs of having been recut at some point, suggesting repeated use. Furnaces 2 and 3 sat 9.5 metres to the south-west and were positioned so that they adjoined one another. One contained what may have been a plume, a feature associated with the airflow management used in smelting, the process of extracting metal from ore, rather than smithing, which works already-refined metal. A shallow pit nearby may have served for roasting ore before it was smelted. The absence of crucibles or moulds leans the interpretation towards smelting, though the presence of three furnaces leaves open the possibility that both processes were carried out here at different times.