Rhymney Lower Furnace was located on the east (Monmouthshire) side of the river Rhymney. It originated in about 1803 when the Union Ironworks (NPRN 34143) came into the ownership of Richard Crawshay, Watkin George, Benjamin Hall, Richard Cunningham and Thomas Williams. New furnaces had been constructed a short distance to the south, the output intended to supply Crawshay's forges and mills at Cyfarthfa. In 1804 the works became known as the Rhymney Ironworks and Hall became the sole owner in 1810. In 1824 Forman & Co had created the Bute Ironworks (34140), on the opposite side of the river, and in 1825 purchased the Rhymney Ironworks. Both concerns were then operated as a single works with six furnaces producing 7.608 tons of iron in 1830. Renamed the Rhymney Iron Co., from 1837 there began a large-scale expansion programme with the purchase of several beam engines and the construction of two additional furnaces. Several rail mills may also have been constructed at this time. Output increased to 106.4 tons per week with 10 furnaces operating by 1850 reducing to seven during the 1860s. Rails for export were the main product, with 92 puddling furnaces and seven mills.
The decision to convert to making steel rails in 1876 saw the installation of Bessemer converters, the works able to produce 500 tons of steel rails per week. In 1884 the production of wrought iron ceased. Steel production, however, was unsuccessful and in about 1891 the furnaces and plant were dismantled, though the company continued as a coal mining enterprise.
The works locations are now occupied by industrial estates though it is beleived that buried remains survive.
Source:
L.Ince, The South Wales Iron Industry 1750-1885 (1993), 137-9.

RCAHMW, 21 January 2016