A stone building (15.1m by 5.48m) housing a reverbatory furnace used to dry and roast copper and ochre precipitates from the Dyffryn Adda precipitation ponds (NPRN 91698), part of the Parys Mountain mining complex (NPRN 33752).

The furnace house, or a building on its site, is shown on a map of 1815-1819 and alterations to the building, which include an addition to its southwest corner, a loading ramp on the west side and the furnace chimney on the north side, suggest an earlier building was adapted to house the furnace. Historic ordnance survey maps indicate this building was part of a complex of buildings which included a manager's house and possibly a weighbridge.

The brick-built reverbatory furnace survives, situated at the east end of the building. It measures 6.77m by 3.42m, stands 1.65m high and is braced and secured to the furnace house by re-inforcing bars and tie rods. Running from the furnace is a brick flue 3.12m long leading to a tall circular brick and steel chimney, which produced the draft for the furnace. A loading ramp on the west side of the furnace house brought the copper and ochre to the furnace where it was loaded into two hoppers (charge holes) in the furnace roof. The copper and ochre was then raked onto the flat bed of the furnace, via two access doors in the side wall of the furnace through which the final dried precipitate was also removed. The furnace was fuelled by coal and the fire box, firing hole and ash rake were located at southern end of the furnace, separated from the precipitate by the raised furnace bed, the furnace arch reflecting the heat down onto the precipitate.

The furnace was in use until 1958 following which the building was used by the mine company for storage and offices. The furnace is a Scheduled Monument and of a type now extremely rare in Britain and unique in Wales.

A survey of the reverbatory furnace and house was carried out by RCAHMW in 1999.

Louise Barker, RCAHMW, December 2015.