Glass action: glass is one of the most rapidly changing building materials. Future developments will lead to responsive architectures, the nature of which we can only begin to imagine.

'Who, when he first saw the sand and ashes by a casual intenseness of heat melted into metalline form, rugged with excrescences and clouded with impurities, would have imagined that in this shapeless lump lay concealed so many conveniences of life as would, in time, constitute a great part of the happiness of the world?' Dr Johnson, the English eighteenth-century savant, was remarkably perceptive about the nature of glass that, as he pointed out, is a 'body at once in a high degree solid and transparent; which might admit the light of the sun, and exclude the violence of the wind'. (1)

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It is hard for us to imagine a world without glass, but Romans in Classical times could not look out of a glazed window because, even if they could afford glass (which could be cast in quite large sheets), it was too clouded with impurities to see through. Little glass was used in windows (vindauga--the wind's eyes) between the collapse of the Roman Empire and the birth of medieval industry.

Glass really became an important constituent of building in the twelfth and thirteenth centuries, when the Gothic revolution was made possible by the relatively cheap and extensive production of glass in north-west Europe. Painted glass was for religious buildings, where it told Biblical stories to illiterate congregations. But by the sixteenth century, clear glass was used extensively in houses for the rich in Holland and England, creating potentially new forms of relationship between interior and exterior which were increasingly masked by the fashion for Italianate architecture that, derived from a country generally much hotter than north-west Europe, naturally had a much greater proportion of solid to void in elevations than was necessary further north.

Dirt and glass

By the time Johnson was looking out through his Georgian window, a balance had been struck in English architecture that lasted for some two hundred years until the revolution of the nineteenth century, exemplified by Decimus Burton's Palm House at Kew Gardens, London, designed with the great engineer Richard Turner. It was in some senses a celebration of the abolition of the tax on glass in 1845.

Suddenly, glass and iron could be used to enclose very large spaces. The Crystal Palace followed Kew within half a decade. (2) All seemed poised for a great architectural revolution, but it was one that had to wait for at least sixty years to have much general effect.

One of the reasons for the failure of the new technologies to transform architecture (3) must surely have been the problem defined by Lewis Mumford: 'Glass is of all possible building materials the one which most requires a clean atmosphere. Its smooth surface does not absorb dirt and grime, but permits it visibly to accumulate, and in the act of accumulation it loses its own best qualities.' (4)

Mumford pointed out that the roofs of cheap glass and iron in station train sheds of steam powered railways were 'the last place where glass could be used with profit' because 'glass covering became almost as opaque to the sun's rays as it would have been if solid iron or brick had been used instead'. Glass and iron roofs were almost impossibly expensive to clean. He looked forward to a new age of technology in which smokeless cities would reduce the need for washing windows. But the curse of cleaning persists to our own less sooty times. Exciting developments in self-cleaning glass are yet to be tested over a long period, but if such substances can be made extensively and cheaply, it will free thousands of people from the dull and sometimes alarming task of washing glass walls while suspended in flimsy cradles or alpine harnesses.

The other great problem of glass envelopes is their transparency not only to light, but to much of the electro-magnetic spectrum. While the greenhouse effect may be useful if you want to grow palm trees in temperate climates, the phenomenon has completely different results when it is engendered in spaces for human use. The office in which we edit the AR is a standard 1990s British sealed-unit curtain walled concrete slab and column job, complete with the heating and cooling systems common at the time.

Murs neutralisants

We are certainly shielded from the violence of wind and rain, but on hot summer days, little can be done to prevent over-heating and, in winter, we have to spend a lot of money keeping the place above the legal minimum temperature for workplaces. From my desk, I should have a fine view of St Paul's Cathedral through the trees, towers and spires of inner London. But I get glimpses of Wren's great church only occasionally, because the poor people who work next to the glass wall continually lower blinds and louvres to protect themselves from glare, overheating or cold strike. Technology of such buildings has scarcely advanced since Le Corbusier built the Cite de Refuge in Paris in the early '30s, where he prophetically proposed a mur neutralisant which was to have two layers of glass with a void between them in which tempered air would flow to modify differences between external and internal climates. In fact, the building turned out to be something of a disaster because in the end Corbusier could not afford the inner glass leaf, or the ventilation system needed to produce the tempered air. (5) So it overheated in summer, was too cold in winter and had dreadful condensation. Opening windows had to be introduced shortly after the hostel was inaugurated.

At last, murs neutralisants have been realized, and they are becoming ever more sophisticated, particularly in the German-speaking countries (see for instance p52 and p58 of this issue), where a benign combination of humane legislation, sensible investment, and lack of indigenous oil and gas has generated a generation of buildings (mainly offices) that are much cheaper to run than ones like the AR office, and which allow a degree of individual control over the internal climate of the workplace.

Much to be expected

Such advances depend on thorough understanding of building physics and construction, but much else is surely to be expected. Technologies such as low emissivity coatings and fritting are now commonplace, and will doubtless be extensively developed. Combinations of glass and plastics offer many possibilities. Continuing developments in the nature of glass itself, making the material on a large scale structurally efficient, and phototropic or electrotropic could lead to buildings that change with every cloud that passes in front of the sun.

Combined with responsive mechanical control systems of external, interstitial and internal radiation such as louvres and brise-soleil, such transparent skins will give the transition between inside and out astonishing properties that we can imagine only as dimly as Dr Johnson could have envisaged the Crystal Palace. And I will get an ever-changing view of St Paul's in all seasons. P. D.

1 Quoted in Macfarlane, Alan and Gerry Martin, The Glass Bathyscape, Profile Books, 2003, p7.

2 Wigginton, Michael admirably describes the very complicated evolution of glass and iron buildings in Glass in Architecture, Phaidon, London, 1996, pp 33-48.

3 Even Burton built his Temperate House at Kew in 1860 with a masonry Neo-Classical ground level.

4 Mumford, Lewis, The Culture of Cities, Secker & Warburg, London, 1938, p207.

5 See Wigginton, op cit, pp 56.