Appalachian Blacksmiths Association
Antebellum Iron Works in Western Virginia; Part 6
"Wrought iron" is one one the most misunderstood terms in all of blacksmithing. This has to do with the fact that it is was first made by striking with large hammers, and therefore, "wrought" by the human hand. Though this method of iron making has disappeared, the term "wrought" stayed with us because blacksmiths still shape and form their work by striking it with a hammer.
True wrought iron is defined this way: Originally, iron ore was placed in a crude blast furnace with charcoal. The charcoal was set afire and the heat melted the iron from its ore. As blooms [lumps] of molten iron were pulled from the furnace with tongs, they were placed on an anvil and then flattened and squared by striking with sledges. As the iron started to stretch into a ribbon, it was doubled over and struck again. And again and again. The smiths would form the iron into a bar.
The process of continually hammering and re-heating reduced the amount of impurities in the iron bar. It also caused the iron to become layered, or laminated. Wrought iron also retained impurities from the smelting process which are discussed below.
Wrought iron was made by the following processes:
Prior to about 1800, all wrought iron was charcoal iron. Charcoal, iron ore, and limestone were charged in the blast furnace and the charcoal set afire. The iron formed blooms and the blooms were hammered into ingots.
Charcoal iron contained impurities, mostly in the form of silica or carbides. Iron silicate is the predominant impurity. These glass-like impurities form in strands, not unlike fiber optic cable strands. Charcoal iron contains up to 5% silicates. Unlike alloys, the silicates do not bond with the iron. Instead, they remain separate and give the iron a fibrous appearance. Silicates do not oxidize, and therefore, give charcoal iron a high degree of rust proofing. There are works made of charcoal iron that have been exposed to the weather for several centuries and show very little sign of rusting. The silicates also gave the charcoal iron more workability. This allowed the blacksmiths of old to create Repousee or suits of armor which just cannot be accomplished with modern iron and steel.
By the mid-1700's, there arose a need for higher quality iron. The method used to refine charcoal iron was called "puddling." Bars of charcoal iron were heated in a furnace by an indirect coal fire. As the bars melted, a "puddler" (also called a rabbler) stirred the liquid. Impurities (mainly phosphorous, silica, and carbon) burned off and the puddled iron formed pasty balls. The puddler would rake these iron balls together to form a large lump weighing a few hundred pounds. When all of the puddled iron balls had formed and joined to the large lump, the puddler would declare that the iron it had "come to nature" (decarburized.)
At this point, the iron lump was pulled from the tub by an overhead crane with tongs. The large lump of iron, usually weighing 200-300#, was flattened [also called shingled] by a helve or a powered forging hammer. The flattened iron, or shingle, was then fed into the grooved rollers of the rolling mill and reduced to sheets of uniform thickness.
Henry Cort of England invented the puddling process and designed the grooved rolling mill in the 1780's.
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To learn more, read Iron and Steel, by Hans Peot.
See this website for information on "Bloomery Furnaces": http://iron.wlu.edu
this website for information on iron smelting: University of Bradford, England
For the Appalachian Blacksmiths Association, by Dave Allen, Editor
David G. Allen © 2004, 2007