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of Glengarnock and Stevenston, Ayrshire, originally Merry and Cuninghame
Ore had been discovered in the area in the 1830s but there were doubts about the suitability of local coal for smelting it.
1841 James Merry and Alexander Cunningham, coalmasters and ironmasters, had second thoughts about the black band, mussel band and clay band ironstones in the district. They had not been prepared to take the gamble on using them for, if the coal proved unsuitable, they would have been marooned many miles from the nearest alternative supply. However the situation changed when the Glasgow to Ayr Railway was built along the shore of the Kilbirnie Loch (which could also provide supplies of water). The railway would allow alternative supplies to be brought in if the gamble failed. 
1843 The partners were joined by Alexander Cunningham of Craigends, and Glengarnock Iron Works was founded
The works initially had 8 blast furnaces
By 1872 the number of furnaces had increased to 14. The aim was to manufacture steel plates and angles.
1884 the blast furnaces were reconstructed for a higher output of 250-300 tons per week, and four, eight ton, Bessemer converters (the first in Scotland ), and a steam hammer were installed. At 10 tons, and with a 215-ton anvil, this steam hammer was the heaviest in Scotland. It was installed because there was some doubt whether the Admiralty would accept rolled, rather than hammered, slabs.
1885 The first casts of steel were made early in 1885, and at later date a cogging mill and a 30 inch reversing mill plate mill were installed.
An extensive trade in tinplate bar was developed for delivery to South Wales tinplate mills. This mill also pioneered the rolling of steel joists, which acquired a high reputation among structural engineers. However, tariffs in the United States soon ended the trade in tin plate and the company was the first in Scotland to move into making H-beams for structures and bridges. Most structural work at that time was done with Belgian iron, but the cheap and strong Glengarnock girders soon replaced the imported girders.
1890 Merry and Cuninghame was reorganized into two separate limited companies. One under the original name of Glengarnock Iron Works and the other the Glengarnock Iron and Steel Company. J. C. Cunningham was the chairman and among the directors was E. Windsor Richards, one of the leading iron and steel masters of the day. They led the company into a large trade in sections, rails, sleepers and fish plates.
1892 a new open hearth melting shop was added, with three 25 ton furnaces. The company was registered on 15 June.
1906 the melting shop was reconstructed and three 50 ton furnaces and a 250 ton mixer were built. The mixer was adjacent to the Bessemer plant and served both the open hearth plant and the Bessemer plant. This was a very early example of a fully integrated works. Ironstone was brought from Glengarnock's own pits (No 6 pit was actually inside the works) and it also produced its own coal. With these materials it made pig iron which it converted into steel for rolling into finished products. Glengarnock also used its by-products as a slag mill was installed to grind basic slag to produce phosphate fertilizer.
1913 One locomotive built. 
During the years to 1914 there was a trade depression, with tumbling prices and competition from Germany and Belgium. At the outbreak of WWI all the blast furnaces had been blown out and there was under-capacity working in the other departments.
1914 Listed as coalmasters, manufacturers of pig iron and steel. Specialities: Glengarnock pig iron, steel joists, rails, angles, channels etc.; by-products (Ardeer), sulphate of ammonia, tar, pitch, oil. 
1915 J. C. Cunningham, Glengarnock's ageing chairman, did not feel up to restarting the plant for war demands, so by arrangement with the Ministry of Munitions the works were leased to David Colville and Sons in March 1915, for six months, with extensions in October and in January 1916.
When leased by Colvills, the Smelting Shop at Glengarnock contained one 200-ton Mixer and three 50-ton Open Hearth Furnaces, and the mills were a Cogging Mill, a Bar Finishing Mill and a 12-inch Guide Mill. The whole output was made into Shell Bar, for the British and French Governments.
The Government, after persuading Colvilles to start the idle blast furnaces, had wanted them to use local home ores some of which were to be mined on the Isle of Raasay. This was not so easy. The furnaces were fast becoming obsolete, the workers had become scattered to the services and other industries, and there was an agreement with the Glengarnock Chemical Co for rich gases by using only coal in the blast furnaces, rather that the more economic coke.
1916 The Ministry of Munitions agreed to help David Colville and Sons to purchase the Glengarnock works outright and, by gaining a controlling interest in the Chemical Co relieve them of the fuel contract. The Ardeer blast-furnaces of the original company were not part of the deal.
1916 Once the entire Works were purchased, in July 1916, the Blast Furnaces and Bessemer Plant were put into operation. These consisted of seven Blast Furnaces capable of producing about 2,600 tons of Pig Iron per week, and four Bessemer Converters yielding about 1,400 tons, of Ingots per week. A new Cogging Mill was put down to deal with the output of the Bessemer Plant.
To meet the ever-increasing demand for steel, it became necessary to erect a complete unit consisting of a Smelting Shop containing four Open Hearth Furnaces of 60 tons capacity and two 250-ton Mixers, and a combined 30-inch Cogging and Bar Finishing Mill, with Producer Benches, Re-heating Furnaces, Dead Soakers, Boiler House and Power Station.
1918 In January, melting was begun in this new Shop, and later the whole plant was in operation. The plant was completed just as the war ended, but during the next three years, until the miner's strike in 1921, with its repercussions on the economic life of the country, the plant worked at full capacity. The Structural Department was occupied making and erecting the lighter structure required in these extensions.
The Bye-Products Department, consisting of Ammonia Plant, Chemical Works, and Phosphoric Slag Mill, provided Sulphate of Ammonia and Ground Basic Slag for agricultural purposes, and Oil Fuel for Warships. The total output of these items for 1916-1918 was:- Sulphate of Ammonia, 2,213 tons; Basic Slag, 68,265 tons; Oil, 1,619,050 gallons.
The extensions carried out created a Plant producing 2,200 tons Pig Iron, 1,400 tons Bessemer and 5,000 tons Open Hearth Ingots per week. About 3,000 men were employed.
1920 the Bessemer process was discontinued
1923 the old melting shop also went out of service, with all ingots for both the old and the new mills being made in the new melting shop, from cold pig iron and scrap steel.
The period until 1930 was one of economic stress. In that year Colvilles amalgamated with James Dunlop and Co to form Colvilles and it was decided to centralize pig iron manufacture at the former Dunlop's Clyde Iron Works. This resulted in the blast furnaces at Glengarnock closing down and the old rolling mill was also closed down.
A suggestion was made in the Brassert report that Glengarnock should be closed down, but John Craig of Colvilles disagreed.
During the 1930s the works was fortunate that building was one of the few buoyant sections of the economy.
1936/7 When a general revival of trade came more new plant was installed, and the melting shop capacity increased to 300,000 tons pa. Improvements were made to the new mill to double its output, and a modern cogging mill was installed along with other mill extensions. The two mixers were rebuilt as 90-ton furnaces of the venturi type, thus raising the capacity of the works to 6,000 tons of finished steel per week.
The plant by then also included equipment for the manufacture of steel sleepers, rails and fishplates.
1935 investigations were carried out into fabricating welded girders and a welding shop was opened. The firm was a pioneer in electric welding.
WWII Further expansion took place during WWII, with a third 90 ton Venturi furnace being added to the two built in 1937. The capacity of the furnaces were later increased to 100 tons, and then to 115 tons.
The property covered 764 acres, with the plant occupying 205 acres, the remainder comprising farm land, roads and Kilbirnie loch. Over 30,000 gallons of water per hour were pumped from the loch to a works reservoir 85 ft above the loch level, with a storage capacity of 1.3 million gallons. From this reservoir service water was taken for condensers, mill cooling and open hearth cooling. The furnaces were further protected by 2 hour elevated storage tanks.
Steam was generated from the waste gases from the melting shop and soaker furnaces and was supplied to two turbines of 2,500 kWh and 1,500 kWh.
Glengarnock's melting shop and section mill were amongst the most efficient in Britain and the works had a record for low fuel consumption, due to waste heat boilers and turbo generators that used the exhaust steam from the rolling mill engines. By the 1960s the steam engines had been replaced with electric motors, and the annual capacity was over 400,000 tons of steel ingots.
1961 a £5.5m development was planned for the finishing mill, for rolling flats, angles and sections at thinner gauges and tighter tolerances. Cold cutting also superseded the hot saws, that required allowances to be left for size changes during cooling, and the billet mill was rearranged to allow heavier pieces to be rolled.
1967 Colvilles became part of British Steel.
1978 the open hearth furnaces and cogging mills were closed and the workforce was reduced to 200.
The works finally closed in 1985.