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Iron
production was revolutionized in the early eighteenth century when coke was
first used instead of charcoal for refining iron ore. Previously the poor
quality of the iron had restricted its use in architecture to items such as
chains and tie bars for supporting arches, vaults, and walls. With the
improvement in refining ore, it was now possible to make cast-iron beams,
columns, and girders. During the nineteenth century further advances were made,
notably Bessemer's process for converting iron into steel, Which made the
material more commercially viable.
Iron
was rapidly adopted for the construction of bridges, because its strength
was far greater than that of stone or timber, but its use in the
architecture of buildings developed more slowly. By 1800 a complete
internal iron skeleton for buildings had been developed in industrial
architecture replacing traditional timber beams, but it generally remained
concealed. Apart from its low cost, the appeal of iron as a building
material lay in its strength, its resistance to fire, and its potential to span
vast areas. As a result, iron became increasingly popular as a structural
material for more traditional styles of architecture during the nineteenth
century, but it was invariably concealed.
Significantly,
the use of exposed iron occurred mainly in the new building types spawned
by the Industrial Revolution: in factories, warehouses, commercial offices,
exhibition halls, and railroad stations, where its practical advantages far
outweighed its lack of status. Designers of the railroad stations of the
new age explored the potential of iron, covering huge areas with spans that
surpassed the great vaults of medieval churches and cathedrals. Paxton's
Crystal Palace, designed to house the Great Exhibition of 1851, covered an
area of 1848 feet by 408 feet in prefabricated units of glass set in iron
frames. The Paris Exhibition of 1889 included both the widest span and the
greatest height achieved so far with the Halle does Machines, spanning 362
feet, and the Eiffel Tower 1,000 feet high. However, these achievements
were mocked by the artistic elite of Paris as expensive and ugly follies.
Iron, despite its structural advantages, had little aesthetic status. The use
of an exposed iron structure in the more traditional styles of architecture
was slower to develop.
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