Wednesday, July 05, 2006

On Wrought Iron

(2nd excerpt from 'Defining the Artisan Blacksmith' - under construction)

Wrought Iron:
Is a specific type of iron metal. It is created using a special equipment that results both a distinctive physical structure and also a specific chemistry. All three of these factors combine to a metal that is quite different than modern steel alloys. 'Wrought' in this case refers to the hammering process required to compress and purify the spongy iron bloom that is extracted from a bloomery furnace. There will always be some microscopic layers of silica slag remaining within any wrought iron bar. It is this slag that gives this metal its distinctive fracturing pattern, breaking as short tendrils. "Iron' is the primary element in the metal, and unlike modern alloys, most wrought iron will have few other components. Typically wrought iron has extremely low carbon content, on a grinder the sparks will test as dull red balls. Wrought iron is an ideal material for the process of hand forging. It will remain workable over a wider range of temperatures than modern steels. It will tend to de-laminate as it is worked, requiring it to be re-welded to consolidate the surface (a step not required with steel). Any forge welding is considerably easier with wrought iron, where the slag incorporated within the material tends to float to the surface at welding temperatures, so that often no additional flux needs to be applied.
The modern steel alloys start replacing wrought iron when the Bessemer furnace was introduced about 1855. This new technology not only allowed for greater control in the iron smelting process, it also increased the volume of production by an order of magnitude. Both of these factors made the new steel more dependable in quality and also considerably cheaper than the old wrought iron. By the early 1900's very little of the older metal was still being produced.
The last commercial production of true wrought iron was stopped in 1974. There has been no new wrought iron produced * anywhere in the West since that date.
Any real wrought iron available for sale today will be reclaimed from structures being dismantled. Most commonly the material will be from structural elements from things like bridges. In some cases, larger diameter bars may be reworked down before being sold. A modern industrial substitute is sold, under the trade names 'Electric Iron', 'Rivet Iron' or 'French Iron'. These materials are in fact low carbon content steels, with a carbon content in the range of .05%, but still with the crystal structure of modern steel.
Typically, only small amounts in random dimensions of true wrought iron, often originally created in the 1850's, can be found. Often this collected by blacksmiths as personal stockpiles of these historic materials. Historic wrought iron is treasured for its easy working when hand forged and its better aging characteristics than modern steels. It also becomes an interesting addition to the mix when creating layered steels for knife making.

The term 'Wrought Iron' has undergone a radical shift in its meaning at the hands of popular culture. The term moved from the technical language of the blacksmith into a descriptive term used by antique collectors in the early 1900's. When referring to objects hand forged by blacksmiths in the Settlement / Colonial period, they were correctly described as being made of wrought iron. Eventually however, the definition became less exact, coming be used for any object that was hand forged - regardless of the metal content. Over time (into the 1950's, as blacksmiths disappeared) the term 'wrought iron' has come to refer to 'any piece of metal with a shape that is painted black'. Now objects that are composed of modern mild steel, formed cold, shaped by machine (even plasma cut!), and then painted black - are referred to as 'wrought iron'. This is almost as far from the correct meaning of wrought iron as its possible to get.

( * There are two exceptions. There are a small number of museums preserving the history of technology and industry. Some of these will conduct smaller scale demonstration firings of their historic furnaces. The metal produced is typically kept inside the museum community for restoration work. The second exception are the small group of people using experimental archaeology methods to rediscover what are often ancient and lost smelting techniques. Yields from these test smelters are quite small, typically 5 - 10 kg per firing.)

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February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

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