Alchemy and invention.

The symbiosis between metal and architecture has evolved over centuries, with successive eras opening up new technical and aesthetic possibilities through the development of different types of metals.

The use of metals is as old as human civilizatiou. our ancestors knew of just seven metals: gold, silver, copper, iron, tin, lead and mercury. Historically, metals occupied the mysterious realm of alchemy, with its mixtures and secret formulations, and were little understood by those who worked with them. A century ago, aluminium was considered more precious than gold or silver (Napoleon treated his most favoured dinner guests to aluminium cutlery), and the notion that metals could resist nature (for instance, as stainless steel does) was considered fanciful speculation. Yet each era has brought about the discovery of new types of metal, chiefly through the process of alloying (which has its roots in alchemy), whereby a new material is formed from the combination of various constituents. The Ancients experimented with alloys, mixing copper and tin to produce a new metal, bronze, with a lower melting temperature and improved casting properties. (Zinc was also added to copper to produce brass, a gold-like material which could fool the unsuspecting until it eventually and inevitably became tarnished.)

The Romans were the first to use metal as a major building material. The Pantheon had a bronze roof, parts of which survived until the middle of this century; Hagia Sophia originally had a lead roof that lasted 1400 years. Because of their malleability and relative ease of working, copper and lead became synonymous with the complexities of Gothic architecture. Endowed with the rich green patina of age, weathered copper spires and roofs still enliven the skylines of northern European cities. Improved techniques of pre-patination can now bestow an instant, uniform illusion of maturity; Jean Nouvel's new cultural centre in Lucerne (p38) is crowned by a vast, overhanging roof clad in sheets of prepatinated copper. Sheltering a new urban square in its oversailing embrace, the emerald green structure forms a powerful horizontal datum in the lakeside landscape.

But it is iron and steel that have had the most radical influence on architecture. The skeletal structural frame effectively liberated buildings from the inhibitions of the loadbearing wall and trabeated construction. Cast iron, the great material of the Industrial Revolution, revolutionized Georgian and Victorian buildings. Ideally suited to repetition and standardization, the metal's ubiquity defined the British Empire; cast iron bandstands, ornamental gates, fountains, and entire prefabricated buildings (Victorian 'tin tabernacles') were simply plucked from manufacturers' pattern books and energetically exported around the Imperial world, from Durban to Bombay.

In 1851, Paxton's Crystal Palace marked a defining moment in the history of metal and architecture. Employing 3300 columns and 2220 girders prefabricated from moulded cast iron, it set the tone for iron buildings for the next 50 years. In Europe, seminal buildings such as Labrouste's Bibiliotheque de Saint-Genevieve pioneered the use of cast iron internally in Gothicized barrel vaults of prefabricated sections. Yet the metal's associations with mass production and popular taste provoked ambivalence and even abhorrence among the architectural establishment. Frantz Jourdain wrote 'The Institut treated iron with a pious terror that might have been appropriate for a shameful disease'.(1) Ruskin also loathed it - 'No ornaments are so cold, clumsy and vulgar, so essentially incapable of a fine line or shadow as those of cast iron.'(2)

The evolution of iron and steel frames made it possible to build upwards; the heroic scale of American cities was determined by steel-framed skyscrapers. The development of stainless steel at the turn of the century provided an environmentally stable metal that could sustain a polished, lustrous appearance. The Chrysler Building in New York was one of the first buildings to use stainless steel externally, on its sleek, hypodermic pinnacle roof. After the war, the transfer of technology from military and aeronautical industries generated new metal forms. Mies' reductionist structures composed of steel channels, angles, I-beams and H-columns were tautly elegant expressions of a new minimalist aesthetic. Jean Prouve's refinement of industrial detailing and use of lightweight sheet metal have been exhaustively explored by the recent generation of High-Tech architects.

Unlike other building materials, metals yield to the entropic nature of the environment, but can be recovered and reformed. This capacity for recycling gives them some tentative credentials to sustainability. Aluminium, for instance, is very expensive to refine, in terms of energy used to extract the metal from its abundant ore (and the ravaging of the earth's surface to obtain the bauxite in the first place), but can be usefully recycled at a fraction of the original cost. Metal recovered from scrap accounts for around a third of the world's aluminium supply and should play a greater role in future production. Around 75 per cent of copper used in buildings comes from recycled sources. Steel too is becoming greener, with potential for re-use as a structural material. It can be recycled many times, without any loss of its structural strength and although a mass market for used steel has not yet emerged, architects have a potentially influential part to play in selecting and specifying used material if available.

New appropriations of metal continue to evolve. A few decades ago, titanium was considered to be a weak and brittle material only fit for creating pigments in paints. Yet roiled into very thin sheets, its light weight and resistance to corrosion makes it an excellent cladding and roofing material. The new Guggenheim Museum in Bilbao by Frank Gehry (AR December 1997) is clad in an extraordinary shimmering skin of very thin titanium scales. Sophisticated CATIA software, developed by the French aerospace industry, was used to rationalize the metal surfaces of the building established by manual mock-ups, so that even with such complex surfaces, only four standard panel sizes were needed for 80 per cent of the vast surface area. Gehry's imaginative exploitation of the potential of metal generates new paradigms based on the capabilities of electronics rather than mechanics (although ironically the construction of Bilbao relied on the manual metal-bashing skills of workers schooled in the region's traditional shipbuilding industries) and takes its place in architecture's long history of metal alchemy and invention.

1 Architecture and Construction in Steel, edited by Alan Blanc, Michael McEvoy and Roger Plank, London, 1993, E & F. N. Spon, p24. In an essay on Auguste Perret, Jourdain was describing the antipathy the French architectural establishment felt towards cast iron.

2 Seven Lamps of Architecture, 1849; quoted in Cast Iron, edited by Gavin Stamp, London, 1985, John Murray, p7. The splendid image of Smithfield Market (designed in the 1860s by Horace Jones) is by John Gay, whose photographs illustrate the book.