What Is Wrought Iron?
The term Wrought Iron is specific to the fibrous, hand-refined material that served for millennia as the most used and useful form of iron. It is characterised by its composite structure. In the process of fining, iron and iron silicate were fused together as the metal was worked (wrought) at a white heat under hammers, producing something with a grain structure similar to wood. It is very malleable when heated and very much more corrosion resistant than modern steel. In testament to its endurance, there are still working wrought iron tugs in the States that are over a century old, and HMS Warrior, built in the 1850’s as the first iron warship in the world, has been afloat its entire life.
In its simplest definition ‘Wrought Iron’ is a specific type of iron, and the traditional material of the blacksmith, deriving its name from the word ‘wrought’, which is the medieval past tense of the verb ‘to work’. Wrought Iron literally means ‘worked iron’, which refers to the method of manufacturing the metal by working repeatedly under a hammer. In the past the work of the blacksmith therefore became known as ‘Wrought Ironwork’, a name that has persisted for the art form even though the metal in use may not be wrought iron. Today the common material of the blacksmith is Mild Steel which is a cheap industrial product lacking many of the virtues of its ancestor.
Wrought iron is best described as a two-component metal consisting of iron and a glass-like slag. The slags are in effect an impurity, the iron and the slag being in physical association, as contrasted to the chemical alloy relationship that generally exists between the constituents of other metals. Wrought iron is the only ferrous metal that contains siliceous slag and it is to this slag that wrought iron owes the properties, which are of interest to the conservator and the blacksmith.
There are essentially two types of wrought iron;
- ‘Charcoal Iron’ – made in a charcoal fire and used from the Iron Age to the end of the eighteenth century.
- ‘Puddled Iron’ – made from cast iron in an indirect coal fired furnace and used since the dawn of the modern industrial era.
Historically Wrought Iron has been worked by blacksmiths, using traditional techniques in both forging and construction, to make high end ‘Decorative Wrought Ironwork’. Today however, the term Wrought Iron is becoming debased and misinterpreted, as demonstrated by any Internet search, to cover all ornamental ironwork, including cast iron and mild steel as well as incorporating modern construction techniques. The difference in quality and value is enormous. Whereas it would be unthinkable to repair historic stonework with concrete or cast stone and Portland cement, it is common for historic Wrought Iron to be repaired using mild steel and electric welding.
For those involved in conservation work it is therefore necessary to ensure the correct use of the term Wrought Iron and that both the material and the working methods are properly specified in order to ensure appropriate repairs and like for like quotations. A specification for such work is available free of charge for use in tender documents.