About Wrought Iron

Wrought iron is a very pure form of commercial iron, having a very small carbon content. It is tough, malleable, ductile and can be easily welded. Wrought iron has been used for thousands of years, and represents the "iron" that is referred to throughout history.

Wrought iron was originally produced by a variety of methods today known as a bloomery. Bloomeries used charcoal-heated smelters, typically in the form of small pots or ladles, into which the ore was poured and then covered with a thin layer of charcoal. Air was blown onto the charcoal after lighting it on fire, the heat produced would melt the ore. As the ore melted it would give up its oxygen (ore is iron oxide, or rust), mixing with the charcoal to release carbon dioxide. This way little carbon entered the iron directly. In a bloomery, the fire does not get hot enough to melt the iron completely, so you are left with a spongy mass containing iron and silicates from the ore -- this is iron bloom from which the technique gets its name. The bloom was then mechanically worked to break off the masses of slag and impurities. This process gives rise to the name "wrought", as the iron was pounded and twisted.

The introduction of the blast furnace by Abraham Darby in 1709 changed ironmaking by replacing charcoal with the much less expensive coke. Not only was the fuel much cheaper, but it also could be burned in a "lump" instead of a thin sheet, allowing the furnaces to be much larger. Soon iron prices were dropping rapidly as production shot up. However the product of a blast furnace, pig iron, had very high carbon content and was very brittle. In order to use it in ironmongery, it had to first be converted to a form similar to what the bloom/wrought process produced. This process took time to develop, but by the 1750s a number of oxides had been identified that would react with the excess carbon to produce carbon dioxide, which then bubbles out. Historically, this would be followed by faggoting. Wrought iron which had been faggoted twice was referred to as "Best"; if faggoted again it would become "Best Best", then "Treble best", etc. Faggoting resulted in impurities within the metal ending up as long thin inclusions, creating a grain within the metal. "Best" bars would have a tensile strength along the grain of about 23 tons per square inch. "Treble best" could reach 28 tons per square inch. The strengths across the grain would be about 15% lower.

Wrought iron has been used in building from the earliest days of civilisation, wrought iron door furniture being commonplace in Roman times. The structural use or iron dates from the Middle Ages, when bars of wrought iron would be used occasionally to tie masonry arches and domes. This use of wrought iron in tension guaranteed its use throughout the ascendancy of cast iron in the canal and railway ages, as cast iron is strong only in compression.

The ill fated first Tay Bridge was of cast iron beams tied with wrought iron. The demand for higher dynamic loads in bridges and warehouse buildings, and the ever greater spans of train sheds towards the end of the nineteenth century, led the designers of buildings to acquire the technology developed to build ships of iron, and create beams of riveted wrought iron rolled sections.

By the turn of the century this had led to buildings completely framed in wrought iron, and later steel, girder sections, and cast iron was once again relegated to an ornamental role. Our main concern with wrought iron, however, will be in its application to gates and railings, frequently given an ornamental treatment by the blacksmith. There are wrought iron railings in Westminster Abbey from the thirteenth century, which, in essence display all the characteristics which we have come to know as ~ 'wrought ironwork', although lacking modern refinements such as symmetry and sweetness of line, but the great age of British ironwork, known as the English style began at the end of the seventeenth century. A French fashion for the Baroque style in gates and railings, swept the country houses of Britain, following the import of craftsman by William and Mary, and the greater part of our national stock of good ironwork dates from the early years of the eighteenth century.

After the rise of cast iron as an ornamental medium, wrought iron tended often to take a secondary role, owing to its comparative expense, each piece being made by hand, while castings could be repeated ad infinitum, once the patterns were made. Technically, however, the craftsmen of the age of machines, excelled their forebears, as indeed they must while making mechanical components, so that the ornamental blacksmith work of the nineteenth century displays a perfection of manufacture not seen before nor since. After the introduction of mild steel, cheap because of its ability to be mass produced, wrought iron, and the craft skills associated with it, gradually disappeared in accordance with the general decline of craft standards in the twentieth century, until the last ironworks ceased production in 1974.