This website was made possible by a grant from the Cambrian Archaeology Association
In 2004 the EMRG excavated the site of Thomas Bonsall’s late 18th century water-powered
(overshot 12 feet in diameter water wheel) stamp mill adjacent to the Nant-yr-onnen
steam on Copa Hill, Cwmystwyth.
Here, harder quartz-veined lead ores were crushed. Water was used to lift a series
of iron-shod stamps to crush the ore onto a grate as part of a wet stamping process.
The lead concentrate was collected in a wooden tub beneath.
Cwmystwyth under snow - Stamp Mill excavation site, March 2004 (S. Timberlake)
Excavation of Thomas Bonsall's late 18th-century water-powered lead-stamping mill,
Nant yr onnen, Cwmystwyth. (S. Timberlake)
The excavation of an early lead-dressing mill of this type appears to be unique (see : Timberlake 2007b)