Roughly thirty-five metres south-west of the island's round tower, excavations carried out between 1977 and 1979 uncovered cupric slag, the residue of copper-alloy metalworking, along with a series of stone-filled pits and soil dark with charcoal. It is the kind of evidence that quietly complicates the familiar image of an early Irish monastery as a place concerned only with manuscript and liturgy.

The metalworking activity was found clustered close to two bullaun stones, the bowl-shaped depressions carved into rock that appear frequently at early Christian sites across Ireland, often associated with ritual use or grinding. That proximity is suggestive, though whether it was coincidental or deliberate is not something the excavation resolved. What the soil beneath both bullauns did confirm was further slag and fragments of bone, along with the charcoal flecking characteristic of a working hearth. A pit near the bullauns was radiocarbon dated to between approximately AD 727 and 886, placing the metalworking firmly within the early medieval period when Inis Cealtra functioned as an active monastic community. The excavations were led by de Paor, and the dating was later published by Seaver and O'Sullivan.