Tuned instrument: Piano's arts museum in Dallas rivals Kahn's in neighbouring Fort Worth in lucidity and the subtle use of limpid light.

Combining a gallery and walled garden, both displaying works in its collection, the Nasher Sculpture Center in Dallas joins Tadao Ando's recent Modern Art Museum of Fort Worth (AR August 2003) in further consolidating the neighbouring cities as a major art destination within the US. The Nasher is also the latest of a family of museums the Renzo Piano Building Workshop has built so that the public might enjoy exceptional private collections of modern art. Like the Menil Collection (AR March 1987) and Beyeler Museum (AR December 1997), its galleries are lit through an all-glass roof, although here all sun-control devices are above the glass that is also the gallery ceilings. Also, while the Menil's external walls are the same grey clapboard as the surrounding bungalows, and the Beyeler's are clad in a stone resembling the streaky red sandstone of Basle, the Nasher does not adopt a material found in its immediate locality. Instead it is clad inside and out in travertine, as is Louis Kahn's Kimbell Museum of Art in Fort Worth (AR November 1978). This, and the top-lit vaulted galleries, suggest a deliberate dialogue with what many deem the last unarguably great American work of architecture, a dialogue set up by a new building that, despite evoking a mythic past, is as light and contemporary in feel as the Kimbell is heavy and archaic.

Since the 1960s, real-estate developer Raymond Nasher and his late wife, Patsy, amassed an outstanding collection of modern art, concentrated mainly on sculpture. Now totalling some 350 works, these were displayed in their house and garden--and some, so the public might encounter and enjoy them, in Nasher's North Park shopping centre. The sculpture centre now allows the public to view these works displayed on a rotating basis, which, along with visiting exhibitions and other events, should encourage regular revisits in a contemplative verdant oasis on the edge of the city centre. Nasher, having met Renzo Piano at the Beyeler opening, entrusted design of the museum to him and the garden to Peter Walker.

The 2.4-acre city-block site is in Dallas' Arts District, across the street from the Dallas Museum of Art and a block away from I. M. Pei's Meyerson Symphony Center, between the sleek, skystriving towers of downtown and a sunken motorway. The design challenge was to create a modestly scaled building that could belong to such a site, bereft of history and consistent contextual cues, overlooked by behemoths and edged by massive metropolitan-scaled infrastructure. Piano's initial instinctual response, poetic rather than rational, was to neither compete with nor conform to this context. Instead the new gallery is quiet and low, and subtly emphasizes the relative newness of the surrounding structures, which thus need not be deferred to, by suggesting his building springs from archaeological remnants that predate them. These remnants of earlier construction, between and around which the sculptures have seemingly been rediscovered, are the parallel tall stone walls dominating the gallery's plan, exterior and interior. (There is an irony here: Kahn advocated architecture that would make great ruins; but the stones of these 'ruins' are flimsy claddings that would soon fall away to reveal a complex mass of steel structure, ductwork and pipes.) Though few would recognize (and none be fooled by) the fantasy that sparked the design, the result is a building that nestles into place. The walls assert a footprint of the scale of the surrounding buildings, yet despite these prominent walls the building has a recessive and delicate grace that contrasts refreshingly with the muscularly chunky buildings that characterize Dallas.

Beyeler's design also grew from the generating gesture of parallel stone walls, although these are capped by an oversailing glass roof and faced internally in white plasterboard. Ranged parallel to the street, the main volume of galleries they define is entered from the lobby, side-on (as at the Kimbell) bringing some cross-axial stability to these elongated spaces. But the Nasher's stone-faced walls reach high above the vaulted roofs, providing anchorage for the tension ties supporting the midpoint of the roofs' curved steel beams. The walls are also perpendicular to the street, offering views from it, through the fully glazed ends of the bays they define, into the garden; and entrance is directly and end-on into one of these bays. Two of the other bays are galleries; the last bay at one end contains a shop, directors' offices and boardroom; the last bay at the other end a cafe and security centre. The entrance bay also gives access to the garden and, via a staircase, to the basement. Like the Beyeler, the building is much bigger than it first appears. In the basement are a further gallery (for works vulnerable to the bright light above), offices, kitchen and an auditorium that can extend through a sliding glass wall to stepped seating outdoors. Ringing this basement, and extending beyond the edge of the building above, is an extensive service area for mechanical plant and storage.

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Outside and inside, the pale neutrally coloured natural materials of the travertine walls and white oak floors predominate, enlivened by the contrast with the white steel roof structure and sun-shading panels, which are clearly visible through the super-white glass roof, and the charcoal grey frames of the fully glazed walls. The travertine is used unconventionally: instead of showing the usual vertically sliced faces of horizontal beds of stone separated by holes, it has been sliced horizontally, along rather than across the beds, and pressure hosed to expose a rough and varied pitted surface. The stone slabs (30mm outside and 20mm inside, where the pitting has been filled) have then been so skilfully matched and mitred as to give the impression of thick solid blocks.

The main street facade is low key; the eye is caught mainly by the contrast between the tall, substantial stone piers and the graceful slightness of the slender steel beams that spring and are suspended between them. (The tension ties justify the height of the walls and reveal these to be curved beams rather than arches. Yet they are the one element of the building that will probably look passe with time: they are too High-Tech and nothing dates as fast as the futuristic.) The relationship between the street and the galleries inside is not as intrusively immediate as is suggested by the open-ended, perpendicular orientation. Planting and porches distance the sidewalk from the glass walls--and the piers stepping forward further relieve any abruptness, not least by introducing a slot of space parallel to the pavement. This interruption enhances the separation and makes more intricate the flow of space. It is easy to imagine Kahn describing these piers as breaking away from the walls to begin their evolution into properly articulate columns that create distance and dignifying decorum; some sense of this is in fact subliminally suggested.

Even the main entrance lacks emphasis, revealed only by the omission of planting in front of it. Once in and past the ticket desk, a cross-axial enfilade of openings slicing right through the building, and the generous stairs downward, suddenly reveal the extent of the whole building, as if offering itself in a gesture of welcome. The immediate impression in the entrance hall and galleries is of the twin touchstones Piano is apt to repeat mantra-like, 'lightness and transparency', here revealed in the weightless roof and the bright light that floods through it as well as in the pervasive presence of sky and garden visible through the roof and end walls. All this, together with the stone walls, recalls a Victorian conservatory or orangery rather than a conventional museum, and is only possible because most sculpture, unlike paintings, is not vulnerable to light.

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Piano's preferred solution of lighting the whole gallery evenly, rather than reflecting light primarily onto the walls where paintings would stand out when seen from the more softly lit centre of the room, is particularly apt for showing sculpture that may be placed at any point between the walls. Direct sun from above is excluded and diffused by cast aluminium panels that rather resemble egg-crates, with openings shaped and angled to admit only north skylight directly. Because Dallas's street grid is angled 45 degrees from north, so too are the openings in the sunshades which reveal differing amounts of sky and create differing patterns as you move around. The sunshade panels span between flanges propped up above the glass from the slender curved beams, which have spotlight tracks along their lower edges. The ends of these beams sit in brackets that swoop down slightly to connect (beneath concealed gutters) with the steel columns within the walls, and so also seemingly sit on the head of the stonework.

The character of the spaces is given not only by the lightness and transparency, as enlivened by the pared and repetitive structural elements and detail, but also by the sure judgement of proportion and dimension. The cross-section of the bays is based on a double square, 32ft (9.75m) between the walls and 16ft (4.87m) to the springing of the curved beams, which rise only another foot at mid-span. This breadth gives a feeling of great generosity and the relatively low ceiling, with only the shallowest curve, gives a contrasting feeling of intimacy. The galleries suit sculpture (and the occasional painting) very well but viewing paintings would be distracted by the views out and movement of space through the galleries.

Outside, the garden is set down a few broad steps from a plinth that extends out from the building. Integrating museum and garden are lines of trees that extend outward from the parallel walls, between which stand various sculptures. Terminating the garden, a planted berm acts as an acoustic barrier to the noise of the sunken motorway, which is further screened by the splashing of a row of fountains that stand out enticingly against the planted backdrop.

The Nasher is a building of great understatement and restraint, and also of the richness that comes from precision: precision in judgement of dimensions and proportions; and precision of engineering, craftsmanship and detail. Designed to show off another art form, it is an architectural instrument so finely tuned as to sing its own song softly in the background, a song so serene that some find it spiritual. (An equally apt metaphor, mechanical rather than musical, that keeps coming to mind is of a purring, highly-tuned machine.) Although it may also seem a slight building, almost as much like a garden centre as a museum, it is so well done, its artfulness raised to the extreme of seeming artlessness, that it enhances and even elevates the contemplation of sculpture.

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