Porosity is a key topic, or ambition, in the work of Steven Holl Architects. Since Holl’s seductive watercolors first appeared now several decades ago, his architecture has promised an experience of volumes bathed in light and shadow, pattern and color, interconnected both physically and visually in unexpected, geometric ways. For Holl, porosity is a matter of illumination as well as of spatial exploration. In recent projects such as the Visual Arts Building at the University of Iowa, realized by Holl and partner Chris McVoy in association with BNIM, the architectural object is subjected to a complex interplay of light - we might even say it is animated by the lucid. The new Iowa building is furthermore penetrated by a spectacular public promenade that embeds this school for art and art history into its riverside campus. A decade ago, Steven Holl built a remarkable structure for the University of Iowa. That attenuated pavilion in weathered steel is perched facing an escarpment of raw rock and next to a still pool. One limb of the building stretches out as a truncated bridge or pier above the dull water. That first Holl building in Iowa City has a refined postindustrial aesthetic, opening up and deconstructing itself like a Cubist sculpture. Holl’s new building is adjacent, and designed for the same faculty, yet the buildings are not physically connected. The latest project is a compact pile, almost a palazzo in its cubic massing and stacked layers of habitable space. Its outer skin is taut and intriguingly diaphanous. Then you notice the large alcoves notched out of this ostensibly solid massing; they are open to the sky. As with so many Holl projects, the entire building might be understood as a complex vessel. The exterior skin of perforated metal plays games of perception in the changing light and variations in precipitation. Clad in floor-to-ceiling channel glass, the eroded bays capture natural light and reflections of the clouds above. At nighttime, this figure/ground interpretation inverts itself as the outermost walls disappear in the dimness and the bold erosions transition into glowing pavilions or towers of light. You begin to notice many luminous squares arranged in the 3, 5, 8 proportions of the Fibonacci Series. These are windows set within an inner surface and glowing behind the outermost membrane. They shuffle preconceptions of where floor slabs and ceilings might occur within this mysterious, conglomerate form. As you approach the Visual Arts Building, you comprehend more clearly the planarity of the silver/grey metal panels in contrast to the irregular, curving and angled niches carved out of the primary mass. Notice how the exterior skin is organized horizontally (in 16 foot panels) whereas the grey/green channel glass is set vertically, like a taut factory curtain. The detailing is impressive, with one system or family of components meeting the other with geometric precision. They are almost flush. Then, at one of many thresholds to the building, see how the principal skin is assembled with a zinc inner surface and an outer surface made from perforated stainless steel. The many small perforations in the steel mimic or replicate the irregular shapes of the light courts notched out of the palazzo-like form. Holl emerged as the architect-to-watch in 1980s New York with his poetic sense of typology allied to what we might term a New Wave appreciation of craft. These ostensibly distinct concerns - for the urban and systematic versus the idiosyncratic and the experiential - have coexisted in the work of Holl and his team since early investigations at a metropolitan scale and the occasional bespoke interior. In the 1990s, at the Cranbrook Institute of Science in Michigan, or inside Kiasma, the Helsinki Museum of Contemporary Art, small- and large-scale moves did not always achieve ideal equilibrium. Talent can lead to too many ideas. Some decades on, with the Nelson-Atkins Museum in Kansas City and now the Visual Arts Building, Holl’s architecture appears increasingly mature and confident. Entering through any one of four façades, you discover an unexpectedly generous hall opening up through all four stories of the building. It’s almost uniformly white, and brilliantly illuminated, with ramps and stairs and cantilevered terraces juxtaposed in subtly irregular ways. There is some affinity with recent interiors from Zaha Hadid Architects and, further back, the ludic Modernism of Oscar Niemeyer in 1950s São Paulo. There are few if any corridors. The primary pedestrian route cuts through on a diagonal and on a slope to instigate a certain formal tension or energy. Rising up through the building, the notched voids seen on the exterior nudge their way inward as convex pockets of light. Several exterior terraces offer remarkable views across the campus and town. A small penthouse, harboring studios, sits adjacent to an almost flat expanse of glass (a metaphorical pool?) filtering daylight on the light’s descent into the belly of the building. One wonders how art students will treat and engage with the interior and its gleaming whiteness at once strangely warm and cool. The school accommodates art in many guises, from traditional studio practice to new media. As you explore, you gain glimpses of these diverse activities. In addition, there are many offices and meeting spaces for students and professors of art history. In a characteristic Holl move, small staircases supply alternative routes of communication, frequently clustered with built-in benches and a scatter of stools. These more intimate zones service the needs and goals of Holl’s immediate client whereas the central hall is of service to the university in general. The thinness of slabs and the minimal presence of ductwork is due to the incorporation of polyethylene spheres and PEX tubing (for heating and cooling) into the concrete structure. On the exterior, only the southeast and the southwest façades have the stainless steel outer layer. As Holl’s architecture matures and evolves, the figurative and the performative inform one another.