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Blaenavon Ironworks
Blaenavon, Torfaen, Wales, UK
Blaenavon Ironworks
associated engineer
Thomas Hill
James Ashwell
Edward Pritchard Martin
date  1789
era  Georgian  |  category  Factory/Industrial Plant  |  reference  SO248093
photo  furnace interior, by Chris Morris
Blaenavon Ironworks was the first purpose-built multi-furnace ironworks in Wales. It was here that Sidney Gilchrist Thomas perfected the process of dephosphorising iron for steel making. The surviving complex is a World Heritage Site and Scheduled Ancient Monument, and its structures are Grade I and II listed.
Iron ore has been mined in the Blaenavon area from at least 1675 onwards, and most likely earlier. Establishing the ironworks we see today probably started in 1788, when Henry Nevill (1755-1843, 2nd Earl of Abergavenny) leased 4,856 hectares of Blaenavon land to a trio of industrial entrepreneurs from the Midlands — Thomas Hill (c.1736-1824), Thomas Hopkins (d.1793) and Benjamin Pratt (c.1742-1794). It was a far greater area than they needed so they sublet two parts of it. One became the site of Nantyglo Ironworks (built 1792-94) and the other Varteg Ironworks (founded 1802).
The partners invested £40,000 in the new venture. When the ironworks opened in 1789, it had three blast furnaces and employed around 300 men, and was already the second largest ironworks in Wales. The site’s contours had been used to best effect by building the furnaces into the side of a hill so that the raw materials — iron ore, coke and limestone — could be tipped into the tops of the furnaces from high ground. After smelting, the molten pig iron was tapped at the bases of the furnaces on the lower ground and run into sand moulds inside the three casting houses at the front.
By 1796, the furnaces were producing up to 5,576 tonnes of iron per year. Ores, clay, coal and limestone were all conveniently available within the site’s mineral rights. In 1800, a Boulton & Watt steam engine was installed, presumably to blow the furnaces. People were coming here to work from all over Britain and the local population grew as the ironworks expanded. A network of tramways was constructed around the site and housing built for the workers.
Around 1805-10, two more blast furnaces were constructed beside the existing ones and a second engine house was erected. By 1812, the five furnaces had an annual output of over 14,220 tonnes of pig iron.
Despite the downturn in demand for iron after the Napoleonic Wars (1803-15), there was an increase in adit mining for iron ore and coal at Blaenavon. In addition, a wrought iron forge was built in 1816-17 at Garn Ddyrys (SO256118) on Blorenge Mountain, on the Blaenavon tramroad east of Pwll Du Tunnel. Blaenavon supplied the forge with pig iron and coal.
In 1818-21, a tramroad was constructed from the ironworks to the Brecknock & Abergavenny Canal (built 1796-1812) at Llanfoist. The route includes the 2.4km Pwll Du Tunnel (SO245116), the longest tunnel in Britain built for a horse-drawn tramway. It was used to transport limestone from Pwll Du to Blaenavon and wrought iron from Garn Ddyrys to Llanfoist, where cargo rates were cheaper than those at Pontypool.
Some timo before 1819, two rows of calcining kilns were constructed in the north side of the site, above the blast furnaces. They were used to bake nuggets of iron ore, reducing its impurities. Ore was fed into the kilns from a tramroad behind them, and, after calcining, was tipped down into the furnaces for smelting.
In 1836, the running of the ironworks was restructured. The Blaenavon Company was sold and reformed as a joint stock company, the Blaenavon Iron & Coal Company, led by William Unwin Sims (c.1796-1839) with James Ashwell (1799-1881) as resident managing director. After Sims' death in 1839, Scottish industrialist Robert William Kennard (1800-1870) took over as head of the company.
Ashwell remained in post until 1841, leaving with a glowing testimonial, and it was under his supervision that the site’s famous water balance tower was constructed (1839). It was used to raise goods from the casting houses up to the tramroad that connected the ironworks with the forge and the canal. By 1841, 305 tonnes of wrought iron bars, rails and plates were being produced each week at Garn Ddyrys Forge.
The main railway network reached Blaenavon in 1854, offering quicker and cheaper transport of people and freight. Garn Ddyrys Forge in its isolated position, relying on a tramroad and canal for exporting its products, became obsolete. In about 1861, the forge and the tramway ceased operation. Nothing now remains of the forge.
From 1859, new construction was underway. The original 1800 engine house was demolished and replaced by a foundry, the calcining ovens were rebuilt, and a rolling mill and the site’s sixth blast furnace were constructed. In place of of the old forge, a steelworks was built at Forgeside (SO241086) and Big Pit (SO238087) was sunk to supply it with coal.
In 1864, the Blaenavon Iron & Coal Company went into liquidation. The Blaenavon Company Ltd was established in its place, but was bought out by the Blaenavon Iron & Steel Company Ltd in 1870. On the 30th September 1874, Edward Pritchard Martin (1844-1910) was appointed general manager of Blaenavon and held the position for 11 years.
With bulk steel in demand during the Victorian era, a particular problem was vexing scientists. A large proportion of iron ores worldwide contain phosphorus, which makes steel brittle — an undesirable attribute for a structural material. Smelting does not remove phosphorus from iron ore, and the available techniques for making steel using pig iron developed by Henry Bessemer (1813-98), Carl Wilhelm (Charles William) Siemens (1823-83) and Pierre-Emile Martin (1824-1915) did not remove it either. Clearly the phosphorus issue needed to be solved.
Metallurgist Sidney Gilchrist Thomas (1850-85) rose to the challenge and by 1875, he thought he had devised a method of dephosphorisation inside a Bessemer converter. He knew the lining of the converter needed to be chemically basic (not acidic) and able to withstand very high temperatures. This would cause phosphorus to be deposited in the slag (waste material) rather than remaining in the pig iron. Moreover, the phosphorus-rich slag was a valuable agricultural fertiliser.
During 1877 and 1878, Edward Pritchard Martin allowed Thomas and his cousin Percy Carlyle Gilchrist (1851-1935), the chemist at Blaenavon, to conduct large-scale experiments at the ironworks. In his paper Elimination of phosphorus in the Bessemer converter (written September 1878, published May 1879), Thomas described substituting the converter's siliceous lining for durable basic one, adding lime or other basic material to the pig iron and blowing the molten metal with oxygen. The process could also be adapted for use in Siemens-Martin open-hearth furnaces. The 'basic' or 'Thomas' process, as it became known, had worldwide significance. Previously unusable phosphoric iron ores could now be used in bulk steel making.
However, in 1878, the Blaenavon Iron & Steel Company Ltd went into liquidation as a result of the enormous cost of changing over to steel production. The Blaenavon site was purchased for £75,000 by a new Blaenavon Company Ltd, incorporated in 1879. Around 1880, with Blaenavon's No.2 Furnace still producing cold blast pig iron, Furnaces No.4 and No.5 were refurbished to make iron ingots for the Forgeside steelworks.
In the early 20th century, high quality coal was in great demand for steam power generation, and mining it displaced steel making as the local major industry. In 1904, iron production ceased at Blaenavon.
In 1909, Blaenavon’s assets comprised 228 hectares of freehold land, the underlying minerals and the works — two blast furnaces, three Siemens-Martin open-hearth furnaces, soaking pits, reheating furnaces, boilers, a cogging mill, a finishing mill, a steel tyre works, a quarry and three collieries. In 1911, a coke oven and a by-product plant were erected.
During World War I (1914-18), Blaenavon produced shell steel for armaments. Thereafter steel making continued until 1938. During World War II (1939-45), the works produced aluminium and magnesium alloys for the Ministry of Aircraft. In 1947, the coal industry was nationalised and the company lost its coal mining interests at Blaenavon.
The site closed in the 1960s and, though destined for demolition in 1970, was saved for the nation in 1974. Since then, a programme of excavation, consolidation, repair and conservation works has been undertaken. In 1980, Big Pit closed as a working colliery and, in 1983, it re-opened as a mining museum.
In November 2000, the wider Blaenavon area, including the town and the ironworks, Big Pit National Coal Museum, Pwll Du tram tunnel and Thomas Hill's tramroad were designated a World Heritage Site by UNESCO. Blaenavon is also a Scheduled Ancient Monument (Mm200). Since 2008, Blaenavon Ironworks has been managed by Cadw, the historic environment service of the Welsh Assembly Government, and is freely open to the public year round.
The site’s principal structures are Grade I and Grade II listed. Surviving one, whole or partial, include blast furnaces, the water balance tower, casting houses, the foundry with cupola furnace, ore calcining ovens, engine houses and boiler houses, original worker housing, and retaining walls and ancillary buildings.
RCAHMW_NPRN 34134 (main entry), 20853, 67611, 67612, 67614, 67616, 67617, 67618, 67622, 67623, 67624, 67627, 67628, 67631, 309091, 309093, 309095
Research: ECPK
"Blaenavon World Heritage Site Management Plan 2011-2016", 2011, available from http://www.visitblaenavon.co.uk
"Thomas, Sidney Gilchrist (1850–1885)" by J.K. Almond, Oxford Dictionary of National Biography, Oxford University Press, 2004, online edn, May 2006

Blaenavon Ironworks