The works initially had 8 blast furnaces
By 1872 the number of blast furnaces had increased to 14. The aim was to manufacture steel plates and angles.
1876 James Merry left. "... James Merry, Esq., of Belladrum, in the county of Inverness, and of No. 68, Eaton square, London, ceased, as on the 15th day of May, 1876 to have any interest in the Companies carrying on business as Iron and Coal Masters, in Glasgow, and at Carnbroe, Glengarnock, Ardeer, and elsewhere, under the names and firms of Merry and Cuninghame, and the Glengarnock Iron Company.
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.
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.
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.
1915 By arrangement with the Ministry of Munitions, the works were leased to David Colville and Sons for restarting to meet wartime demands in March 1915, for six months, with extensions in October and in January 1916.