As far as we know, there was no iron-smelting or malleable-iron manufacture in Glasgow until after 1830. This essay therefore deals with secondary iron manufacture. There was one firm at the beginning of this period, large for the time, making malleable-iron goods. This was the Smithfield Iron Co, established in the early 18th century, which made all manner of iron goods, initially from bar iron imported from Sweden and Russia, but from about 1790 also from locally-made malleable iron. Malleable iron forgings were also made by blacksmiths, working on a smaller scale, either on their own account, or in engineering and perhaps in shipbuilding and road-vehicle making firms. There was also the slit mill, near the mouth of the Kelvin, which cut iron sheet into narrow strips for nail making, generally carried out outside Glasgow.
The other branch of iron working represented in the city was iron-founding. An early foundry was at Camlachie and was initially owned by David Napier. Other early foundries included the Cook Street Foundry of James Cook, the Eagle Foundry of Thomas Edington at Port Dundas, the Rutherglen Road foundry of Claud Girdwood, the Hill Street Foundry of Murdoch & Aitken and the Oakbank Iron Works of John Neilson. All of these, as well as making castings, machined them and assembled them into complete machines. Claud Girdwood was probably the first in Glasgow to make the castings for "fireproof" iron-framed textile mills. The pig-iron used in these foundries probably came initially from Carron, Clyde, Muirkirk, Omoa and Wilsontown iron-smelting works. All of these iron-founding firms were in operation by the 1830s. Immediately after the end of this period, the availability of cheap hot-blast iron resulted in expansion of iron-founding in Glasgow.