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Any old iron

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technical & practice - Far from being confined to the 19th century, the use of metals in construction can be traced throughout the ages

The Industrial Revolution is closely associated with the origin of metals in construction, and International Modernism is synonymous with feats of structural daring indebted to ferrous reinforcement. But neither were exactly new.

The ancient Greeks strengthened their giant stone columns by dropping iron tie-rods through the square, vertically aligned holes at the centre of their stacked component discs: they understood the importance of sealing the iron and fusing metal to stone, achieving both by pouring lead into the gap.

Vitruvius' treatise on architecture, written in about 30BC, was heavily dependent on Greek traditions: one of his few references to metals other than lead is the suggestion that a suspended timber ceiling for baths might be hung by iron rods. This would seem to be the origin of using rods to prop and brace as well as suspend: the church of Santa Sabina in Rome of 422-32 AD retains some of its ferrous reinforcements, and in the east, the tradition of Byzantine hemispherical domes led to the use of both iron tie rods and bands (eg Istanbul, H. Sergios and Bacchus, 527-36 AD).

We generally think of the largest medieval buildings as stone skeletons, devised by master masons who developed structural stonework to its limits in the cathedrals of the mid13th century. But medieval churches were often indebted to ironwork used for cramps and ties. Circa 1000 A.D. , the arches of Trieste Cathedral were augmented with iron tie-rods. Then, in 1117, northern Italy was rocked by an earthquake, which made iron stays a commonplace insurance policy and many of the French and English cathedrals such as Amiens and Canterbury had cause to use tie-rods, too.

Stained-glass windows relied on ferramenta, the iron bars from which the iron-framed windows hung. York Minster has a tennis-court-sized area of metal to frame the surviving 600year-old glass in its east window.

Arch villain Brunelleschi's dome over Florence Cathedral was famously bound by chains to prevent it spreading at the base. The Renaissance penchant for round arches in preference to stronger pointed arches guaranteed the continued use of iron in arcades. Less famously, Sir Christopher Wren's work featured hidden iron rods, probably based on some he had seen at the Louvre in Paris. The floor decks of Hampton Court's royal apartments, built for William and Mary in 1689-94, were threaded with them: after the deadly collapse of the six-month-old walls of the King's apartments in a storm of late 1689, Wren's rival William Talman pounced on the revealed ironwork as evidence that Wren was unconfident of the masonry he had designed. Wren replied that the reinforcement served as an even greater assurance of soundness, while Queen Mary graciously accepted the blame for having been too pushy for completion.

At the same time, one of the most celebrated workers in iron, Jean Tijou (anglicised to 'John Tissue' in books of payment), provided screens of unsurpassed beauty in commissions such as Hampton Court, St Paul's Cathedral and Burghley House.

In the early 18th century, the old House of Commons used iron columns to offer support to its galleries, but this wasn't the first example, being pipped to the post by those propping the kitchen of a nunnery in Alcobaca, Portugal. So, centuries before the Industrial Revolution created an iron icon in the eponymous Ironbridge Gorge, Coalbrookdale, the legacy of the Iron Age had furnished buildings with reinforcement as well as nails, hinges, knockers and knobs. However, it is fair to say that mass production, and the Bessemer Converter, did make a difference.

That difference was the frame. William Strutt used iron columns and brick arches for his father's mill in Derby in 1792-93. But it was the novelist, entrepreneur and amateur designer Charles Bage who three years later logically extended metal components into a system, using both iron beams and columns at Marshall, Benyon and Bage's flour mill at Ditherington, Shrewsbury.

Unlike stone and bricks, iron is local only in as much as the conditions for smelting must be available.

The process of refinement leaves the origins of iron impossible to identify by eye without a manufacturer's stamp. The ubiquitous, fast-track ethos of the transportable iron/steel frame is the major story of the next two centuries, and illuminated by plenty of literature.

Burton's Palm House at Kew, Paxton's Crystal Palace, and Brunel's many bridges are central to the development of mass-produced metal frame components which have come to dominate the conception and aesthetic of large buildings. One need only compare Norman Foster's 1, St Mary Axe with Jules Saulnier's chocolate factory at Noisiel-sur-Marne of 1871-72 to gauge how quickly and completely architects arrived at the externalised metal space frame.

Iron up the competition The story of the skyscraper is one thing, and the ideas that made it practicable can be argued between France, America and the Otis elevator company. Another, less explored tale is the way that the 19th century harnessed metal frames while cladding them in traditional masonry.

Again, it was in the English West Midlands that iron first permeated Gothic revival churches. The vault of Francis Hiorne's church, St Mary the Virgin at Tetbury in Gloucestershire, is held aloft on iron columns more slender than any masonry would allow.

At Calke Abbey in Derbyshire, the estate chapel has chunky cast-iron bar tracery, and the surviving iron windows of Shrewsbury's St Alkmund of 1793-95 offer a thinner version of a late 14th-century tracery pattern (compare with the east window of York Minster, as illustrated). Beaumont in Kent meanwhile, is one of a large number of Regency houses whose sash windows eschewed timber glazing bars in favour of iron.

Reduced to half-inch strips of painted moulding, the effect is of extreme elegance, and perfectly in keeping with Regency iron verandas from Cheltenham to Tunbridge Wells, and with one-offs such as the iron fan-vaulted conservatory once at Carlton House, by Thomas Hopper. George III's abortive and much-criticised iron-framed castle at Kew of 1802-27 was built so solidly it had to be blown up.

One of the most successful reconciliations of different materials is the tower and spire of Big Ben. Loadbearing brick clad in Oxford (now Rutland) stone supports the castiron spire. It is a belated English rival to the medieval town hall towers of Flanders. The iron merely helps it do its job of standing up straight to tell the nation the time. Among the more disappointing Victorian monuments (for the more inquisitive tourists) is Tower Bridge, which purports that medieval stone towers absorb the leverage of its anachronistic steel road plates, whereas, in fact, suspension cables improbably lock into the walls of its fenestrated chambers.

Of course, many would prefer Brunel's curved tubes suspending the railway across the Tamar as a confident, resolved and honest expression of pure engineering design, or the vast box cantilever system of the Forth Bridge for a thrillingly awful essay in Victorian industrial achievement. Even so, it is noteworthy that John Lysaght's Bristol factory, which provided much of the steel for Brunel's work (and even the corrugated metal roofs of houses in 19th-century Australia), consisted of a series of manufacturing sheds hidden behind the facade of a Neo-Romanesque stone office building, internally lined with Royal Doulton's best example of Renaissance ceramics.

The expression or concealment of metals in building has provided a dichotomy full of - well, irony - that remains with us. The earliest metalframed buildings were intended to be fireproof; but heat twists metal and, infamously, steel-framed buildings can collapse as a result. The International Style argued for formal (and, less convincingly, functional) purity but usually hid its steel reinforcement within concrete, while Mies van der Rohe had to clad his expressed universal columns with fireproofing.

All this may be academic: it matters little to the rise and rise of the metal frame, and no polymer or carbon-fibre material is yet economical enough to challenge its supremacy.

But metal construction has undoubtedly triumphed most completely in architectural engineering. The Eiffel Tower, the Golden Gate Bridge, the London Eye: all are hallmarks of the modern age. Imagine any of them in timber.

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