The evolution of the glass envelope goes along with the evolution of architecture as one of the most representative components of contemporaneity, and is the architectural element that most significantly expresses the cultural values of society, and that most prominently displays the sophistication of new technologies.
The most recent examples of glass hybridization to achieve greater functional complexity proceed mainly from energy and environmental agendas: with new proposals for water treatment and reuse through exposure to ultraviolet light; double glazing facades that convert into photobioreactors, aquaponic systems, or synthetic ecosystems; or photovoltaic transparent glass thanks to which the whole enclosure can be used to produce electricity. We can refer examples such as the Solar Enclosure for Water Reclamation and Thermal Control created at the Center for Architecture Science and Ecology (CASE) in New York in 2012, the BIQ House by Splitterwerk-Arup built in Hamburg in 2012, the Vertical Farm by ENEA for Expo Milan 2015, or the Amphibious Envelope by The Living developed in New York in 2015.
The main and most immediate contribution of glass to architecture is its relationship with light radiation, and transparency in particular. These optical properties in combination with a smooth and resistant surface, resistant both to harsh climate and to the passage of time, turn glass into the perfect vehicle for mediation: be it to contain water, algae, frogs, or electrolytes. In this intermediary role, the optimization of natural light control is unmistakably the main reason behind the exploration of the boundaries of glass.
Both light and glass are key themes in architecture. Architects have managed to master the control of light as opposed to matter in order to distill atmospheres and create places. In the architectural realm there are many examples that explore how the excavated mass, the strategically placed opening, lets light make its way in and imbue the space with character, and this has been possible thanks to the right combination of opacity and transparency, light and shade.
Modernity offers however a new reality: for the first time there is a new architecture interested in making itself more permeable to light, increasing its glazed area gradually to reach the whole enclosure: total transparency. That is, the opaque mass disappears and the space is filled with light. This circumstance places us at a sort of ‘zero state’ that offers a total degree of freedom, placing us before an open field for experimentation.
The early 20th century was a favorable time to provide design alternatives to manage the glasslight relationship with precision, involving key figures and episodes in the history of architecture. Frank Lloyd Wright participated actively in the design and development of the pioneering prisms Luxfer, several models of which were patented in 1897. A number of versions of the prisms were used in emblematic works of the American and European avant-garde of that time, like the Stock Exchange Building (1908) by Louis Sullivan, the American Bar (1908) by Adolf Loos, and especially the Glass Pavilion (1914) by Bruno Taut. The Castel Béranger residential building (1890) by Hector Guimard or the building on Franklin 25 in París (1902) by Auguste Perret are two examples of the use of the glass blocks patented by the Swiss Gustave Falconnier. The famous lightness and translucency of the Maison de Verre (1927) by Pierre Chareau and Bernard Bijvoet, and of several glass panes in the projects of Le Corbusier and Pierre Jeanneret, is possible thanks to the famed Nevada lens, by the firm Saint-Gobain. However, only the oil crisis of 1973 – when the energetic reality of glass was categorically revealed and the transparent envelope became unfeasible in sustainable terms – would trigger intensive research in this direction, creating a new discipline: daylighting, or the technical-scientific use of natural light in architecture, which would generate numerous proposals.
Considering all this, the key question is the following: if from the discourse of energy efficiency and sustainability it is no longer possible to secure the first absolute transparency that we reveered in modern thinking, then, with what definitions of partial transparency can we design today?
Densities of Light
We have tried to answer this question since the years of crisis, offering a series of technological alternatives to design with natural light. In this process we can identify three types of partial transparency in connection with three families of technologies, which emerge in each one of the subsequent decades: the glass of geometric light (or of zoned transparency), the glass of diffused light (or of gradient transparency), and the glass of multiple lights (or of negotiated transparency). Each one of these families pursues energy efficiency via all or some of the following functions: optimization in the collection or distribution of natural light in interior spaces, thermal control of light (permitting the entrance of direct radiation in winter and blocking it in summer to prevent overheating), glare control, and the capacity to permit at once visual contact with the exterior and interior privacy.
In the first years, the initial examples of daylighting referred to the optics of prisms exercises of the early 20th century, trying to control propagation of light according to basic principles of geometric optics. Angular light, solidly geometric on the space over which it spreads, describes mathematically calculated paths. These are angle-selective systems, that is, they operate through reflection, refraction, and diffraction to redirect light thanks to basic optical elements liks prisms, mirrors, lenses, louvers, optical fiber, anidolic systems, and holograms. All these systems are made up of three parts, one to capture light, another to manipulate it, and another to scatter light in space. In some systems these three parts can take on a nanometric scale and form just one layer of the glass pane, in others they can traverse the enclosure and massively occupy the building. There is a long list of materials in this family: the multilayer glass format can include films, microreplicated reliefs, louvers, or patterns of varied profiles that can be installed as fixed or mobile elements of the enclosure; the systems to take light to interior spaces inaccessible from the enclosure use largesize components like heliostats, reflectors, optical fiber systems, and vertical or horizontal light pipes. Many projects explore these materials. The renovation of the façade of the SUVA Insurance Building in Basel, by Herzog & de Meuron (1988) is one of the first projects where the new prismatic glass sheets guide the project design. Holographic glass, attempting to provide shade through transparency, fills the roof of the Pforzheim Town Hall in Germany (Auer + Weber + Architekten, 1995), and optimizes electrical production when applied in the rotating louvers of the IGA 1993 in Stuttgart (HHS Planers + Architekten). The imposing light pipes and chandeliers by James Carpenter take natural light through dozens of meters in the Morgan, Lewis & Bockius office building in Washington (2002), and in the restaurant of Royal Albert Hall in London (2002).
In the following decade, the interest in architectural translucency gave rise to new products, most of them subproducts of the search for better thermal insulation. Translucency is understood as a concept that will incorporate subsequent cultural values related with the use of light as atmospheric agent (creating impressions like evanescence, dematerialization or luminescence), and with aspects derived from the evolution of the envelope towards round, smooth, and continuous surfaces that will accentuate different views about lightness and the interior-exterior dialectics. The translucency of light-diffusing glass is achieved through the fragmentation of incident light on multiple beams scattered in different directions. This scattering is achieved including ‘obstacles’ in the transparent glass that will influence the direction of light and the material’s clarity. The glass surfaces used to this end are composed of multilayered surfaces that combine capillary and textile networks, aerogel, view-control films, crystal liquids or temperatureresponsive polymeric gels, as well as physical or chemical treatments of the glazing such as microgeometries, opalizing, matting or frosting. Such use of glazing can be found at the McCormick Tribune Campus Center in Chicago (2003), an OMA work where the envelope is built using Panelite, or the aerogel on the facade of the Yale Sculpture Building and Gallery (2005), by Kieran Timberlake.
From the zoned transparency of the eighties, where the enclosure combined standard glass (clear) and doped glass (distorted visibility), we reach the gradient transparency of the nineties, where clear and doped glass are used with increasing degrees of density. Towards the year 2000 transparency becomes more ambitious, understood as an ambivalent and paradoxical entity, where antagonistic optical parameters can coexist. Pairs of contrasting appearance are made to converge on glass: clear and dark; transparent and reflective; glass that can see but doesn’t allow views; glass that can gaze or be gazed; and glass that permits multiple levels of visibility; in the end, glass that is multi-material, multi-functional, and operates multi-energetically. The concept was developed earlier, around 1981, by Mike Davies, but it wasn’t until this moment that it began to look feasible. In this sense we celebrate the performative, kinetic, interactive, and phenomenological capacity of architecture, that is, to create and detonate potential, mutability, ambivalence, variability: the capacity to host simultaneous states and latent possibilities.
The glass technologies that make these states possible are the sensorized and responsive materials (color liquid crystals, chromogenic materials, spyglass mirrors, and the new generations of photovoltaic cells). All of them specter-selective and nanometric materials; that is, light control means transmitting or reflecting different bands of solar radiation, usually transmitting visible light and blocking infrared or ultraviolet light. Many of these materials are still in prototype phase or limited to small surfaces due to economic or functional limitations. In fact, the roof of the US Pavilion designed by Biber Architects for Expo Milan 2015 is one of the few buildings using smart glass extensively; in this case SPD(Suspended Particle Devices) glass.
The field of contemporary physics is calling more insistently for spatial equality between light and matter, so light has taken a more physical character and matter has become more abstract and ethereal, and shows, as light, its ability to deploy effects. In this context, more levels of conceptual and executive complexity are added to the glass surface. These materials contribute not only with dynamic optics, but actually the implementation of their electronic and chemical components requires decentralizing the composition of their units and limiting size, adjusting therefore to actions like the fragmentation or miniaturization of their parts, in which the basic compositive unit no longer has to be the flat glass panel. This scale harmonizes with the new concept of ornament linked to digital fabrication processes, such as surfaces containing form or a fusion between structure and surface, combined with color, image, and geometric patterns. With the same objective, the miniaturization and fragmentation derived from the inclusion of electronics and kinetic reactions impose a multiplicity of joints on the surface, whose associated optical and mechanical behaviors have boosted research of structural glazing through the maximization of the mechanical properties of the material, preventing the addition of other structural materials.
The most advanced proposals resort to hybrid systems combining technologies from more than one family in one same element, with the purpose of uniting properties and optimizing results. The SmartWrap concept (2003), developed by Kieran Timberlake, firmly established the trend: condensing in the millimetric space of a plastic film the requirements of climate control, lighting, and renewable energy production of the facade, also equipped with an information display. The film combines phase-change materials, solar control via the mass and pattern of the film itself, solar cells, batteries, and organic light-emitting diodes. Along this same line, with its Concentrated Solar Facade (2008), CASE proposes a facade system that combines energy production with thermal and daylight control harmonizing the use of fresnel lenses with new solar sells to produce electricity from a semi-translucid dynamic screen that tracks sunlight. Completed and in use, the west facade of the new Swiss Tech Convention Center (at the École Polytechnique Fédérale de Lausanne campus), by Richter Dahl Rocha & Associés (2014), is one of the few examples we can find outside the prototype circuit. It was the first building to incorporate Grätzel cells, invented in 1988, implemented in an operable system of vertical glass louvers of up to 15 meters in height, providing flexible renewable energy and adjustable solar control.
If the glass of modern transparency was a transitive material – sacrificing its own presence for the sake of transparency –, we see that over the last forty years glass continues to function as a complementary material, with prosthetic elements to fulfill the environmental, structural, and scenic requirements. In its permanent role as ambassador of modernity and contemporaneity, glass is essentially still a means to make other appearances possible...