Glass evolution.

In architecture's historic quest for transparency, the relationship between glass and buildings has evolved through the conquest of technical limitations, presenting the current generation of architects with enriched formal and material possibilities.

The invention of glass took place, it seems, almost by accident, around 4000 years ago in the eastern Mediterranean. Beneath an ancient pottery kiln, the fused silica of pots combined with the alkaline ash of the hearth below. By 1500 BC, moulded and pressed glass vessels were commonplace in Egypt and the skills to make them had spread to Europe. The northward expansion of the Roman Empire lead to the establishment of a thriving glass industry in the provinces of Saone and Rhine, employing craftsmen from Syria and Alexandria. The Latin term glesum (from a Germanic word meaning transparent or lustrous) was used to describe the versatile substance.

Two thousand years passed between the initial serendipitous discovery and the appearance of blown glass, which led to the production of thin transparent sheets strong enough for windows. This marked the beginning of a symbiosis between glass and buildings. As Michael Wigginton notes: 'With this development, new conceptual languages in architecture became possible, which are still being developed and explored; from the simple provision of light and view without a loss of warmth, to the creation of conceptual and technical masterpieces which derived their essential quality from this wonderful material.'(1)

Historically, the relationship between glass and architecture is at its most sophisticated when transcending technical limitations, notably those imposed by load-bearing masonry construction which restricted the width of window openings. The first break with convention was the Gothic exoskeleton; the stone frames and flying buttresses of medieval cathedrals made possible unprecedentedly tall, arched windows composed of myriad fragments of jewel-like glass. Notions of illumination were spiritual as well as literal; the sumptuous, stained glass panels efficiently disseminated Biblical narratives to a largely illiterate populace. The architectural quest for transparency, weightlessness and luminosity began, in effect, with the radiant membranes of coloured light in cavernous Gothic cathedrals.

The next quantum leap occurred in the nineteenth century, with the introduction of the skeletal structural frame, initially fabricated from cast and wrought iron, and latterly steel and reinforced concrete. Such materials were the product of engineering and manufacturing invention associated with the burgeoning industrial revolution, invention that also found expression in the manufacture of glass. During the 1830s, an improved version of the traditional cylinder process(2) began to be used more widely, providing glass of uniform thickness in sizes up to 1m x 1.3m. Until then, manufacturing techniques restricted pane size, as manifest by the intricate divisions of mullions and transoms in windows of the eighteenth and early nineteenth centuries.

Victorian iron and glass technology generated a new architectural language and new typologies - conservatories, arcades, heroic glazed rail sheds and exhibition buildings, notably Paxton's seminal Crystal Palace of 1851 which used over 300,000 sheets of glass. As an iconic expression of materials and structure, its influence on contemporary architects is still evident. Von Gerkan and Marg's vast, barrel-vaulted Exhibition Hall in Leipzig, designed in collaboration with Ian Ritchie (AR March 1996), is clearly a late twentieth-century reinterpretation of the Crystal Palace, using contemporary structural and material technologies of trussed steel arches and silicone jointed glass sheets held in place by cast steel finger fixings.

This century, the notion of transparency has exerted a particularly seductive and tenacious hold on the architectural imagination. Corb's canonical description of architecture as 'the masterly, correct and magnificent play of masses brought together in light' affirmed a new set of values for modern buildings - transparency and dematerialization, achieved through material lightness and spatial interpenetration. The symbolism of glass and metal gradually found new expression in the form of a glass skin, as opposed to glazed openings in a skeletal structure. Gropius' Fagus Factory of 1911 was one of the first examples of a glass facade supported by a thin steel framework; Bruno Taut's polygonal Glashaus Pavilion for the 1914 Werkbund Exhibition in Cologne was made entirely from glass, celebrating its ephemeral, crystalline properties.

The increasing sophistication of glass and lightweight transparent plastics has presented architects with new and enriched possibilities. In the last twenty years, the art and science of transparency has been pushed to new boundaries, by architects eager to exploit new cladding materials and fixing technologies with the same pioneering zeal as their predecessors did in the 1920s and 30s. The seamless, reflecting skin of Norman Foster's iconic 1975 Willis Corroon building (formerly Willis, Faber & Dumas), for example, has a clear historical antecedent in Mies van der Rohe's project for a glass tower of 1922. Mies' monumental, meandering glass wall was intended to exploit the possibilities of inter-reflection and the changing angles of light; over half a century later, it became a reality. With its specially developed curtain walling system consisting of large glass panels hung from the top of the building and the entire assembly stiffened by glass fins, Willis Corroon marked a defining moment in the obsessive architectural pursuit of the uninterrupted, transparent surface.

Architects, engineers and manufacturers continue to evolve ever more minimal ways of configuring glass walls and roofs, notably hanging glazed panels from point fixings. The synergetic combination of a steel structure and the inherently tensile qualities of glass has greatly advanced contemporary ideals of lightness and transparency. Another line of enquiry takes the notion of structural glass a stage further, by exploiting its properties in compression. The outcome is the development of the glass column and the glass beam, used in the all-glass pavilion at Broadfield House Glass Museum (AR August 1995), designed by Design Antenna and engineered by Dewhurst Macfarlane. Exuding a Miesian simplicity and an enviably seamless transparency, the glazed skin is supported by a triple-laminated glass structural frame. Such prototypical projects herald the tantalizing prospect of the ultimate, transparent enclosure.

One important consequence of the increased use of glass in buildings is a more changeable and capricious internal environment. In response to this, the window has evolved from a simple glazed aperture into an architectural skin capable of variable functions. With the advent and continuing refinement of low-emissivity coatings and variable transmission methods such as photochromics, electrochromics and thermochromics,(3) the responsive, multi-layered skin has become a key element in environmental control. Yet the concept of an external skin with multiple environmental functions is not in itself new; Le Corbusier first attempted to devise a mur neutralisant in the early 1930s, for the Cite de la Refuge in Paris. Over sixty years later, Norman Foster designed a modern, high performance version of a mur neutralisant for his complex of buildings at the science and business park in Duisburg (AR February 1993). The seamless skin of the Business Promotion Centre, for example, is an environmentally engineered wall that regulates the transmission of light and heat, prevents the build up of condensation and provides an acoustic barrier.

It seems clear that glass and its attendant technologies will endeavour to evolve still further, enhancing the material's capabilities and intensifying its allure. Many of the buildings in this issue - for instance, Klaus Kada's concert hall in St Polten, (p42) - represent the fulfilment of technical and aesthetic ambitions first postulated by the Modern Movement; yet as the century draws to a close, such ambitions continue to preoccupy architects and manufacturers. Writing in 1931, Gropius presciently observed: 'Glass is the purest form of building material made from earthly matter. It can mark the limits to spaces, it can protect us against the weather, but at the same time opens up spaces, it is light and incorporeal. Although glass as such has been known to us for many years, it is the technical age we now live in with all its modern manufacturing processes that has rendered this substance one of the most valuable materials of our day and of the future. Glass architecture, until recently deemed purely utopian, is now a reality.'(4)