Shingling was a production step in the outdated finery and puddling wrought iron production processes where the porous, molten iron mass in the furnace was removed manually for further treatment. The shingling treatment involved hammering the iron to remove slag and close-up surface fissures prior to drawing or rolling the metal into bars. Hammering out of the iron was either done manually or with power hammers and mechanical squeezer mechanisms. In the finery process, this was carried out by a hammerman, and, in the case of puddling furnaces, by a shingler. In both cases, the hot iron was removed using large tongs or hooked iron rods and moved to the shingling stations with large wheelbarrows or via a series of sloped channels.
During the late 1700s and 1800s, bar iron and steel was produced by smelting pig iron in finery and puddling furnaces. Both processes resulted in superior products due to the de-carburization of the iron in the furnace and the removal of impurities in a production step known as shingling. During the smelting process in both finery and puddling furnaces, the iron in the furnace hearth formed a porous ball-like mass that contained a significant amount of expelled impurities in the form of a crust known as slag. The porous nature of the iron meant that the slag not only coated the iron mass, but also filled the many fissures in its surface. This necessitated removal of the slag and closure of all surface fissures during the shingling process.
To facilitate the shingling of the iron mass, it first had to be moved from the hearth to a separate part of the facility. In the case of the finery process, the iron mass, or bloom as it was known, was first consolidated using a water-powered trip hammer and returned to the hearth for re-heating. It was then removed by a hammerman who beat the slag off of the surface and out of the fissures of the bloom with a hammer. This also served to weld close the fissures before the bloom was drawn out to form iron bars.
The puddling process also featured a shingling step that served a similar purpose to that used in the earlier finery furnaces. Here, the molten iron, or puddle ball, was drawn out of the hearth using hooked rods or large tongs and, depending on the furnace design, either pulled down a series of iron-lined channels or pushed in large wheelbarrows to the shingling point. The puddle ball was then hammered manually or with a trip hammer by a shingler to remove all of the slag and close all of the openings and fissures in the mass. In some cases, the puddle ball was squeezed or constricted to achieve the same result using a water-powered machine fitted with a set of large metal jaws.