There cannot be many architects who have refused a job on moral grounds. I can only think of one, and whenever an architect accepts a commission that is in some way odious or objectionable, I find myself thinking of him. In 1832, Julius Eugen Ruhl, the municipal architect to the provincial German town of Hanau, refused to design a scaffold for the public execution of a notorious mass murderer. This was in direct contravention of his professional duty to design whatever structure the town needed, and even though a willing substitute was eventually found, Ruhl was duly and severely fined.

But very few architects have the fortitude to be a Ruhl, and the most we can ask of them is to design, as it were, the best scaffold possible, not to question its fundamental rightness. And so if one has moral qualms about the new Barnes Foundation, which opened in Philadelphia on May 18, one’s real quarrel must be with the clients—and, in this case, with the political-philanthropic axis that enabled them to break Barnes’s will, to wrest his great collection of Post-Impressionist and early modern art from its home in suburban Merion, and to recreate it in downtown Philadelphia. About their actions much has been said, and much will continue to be said, but for the moment it is fitting to consider the building itself, and on its own terms.

If one does so, it is instantly clear that the architects, the husband-and-wife team of Tod Williams and Billie Tsien, have performed very well indeed. The project could have gone wrong in any number of ways. The instantly recognizable signature style of a celebrity architect would have overwhelmed the original Barnes, just as a cringing pastiche would have been overwhelmed, in turn, by the monumental scale of its new site on Philadelphia’s Benjamin Franklin Parkway. But Tsien and Williams, who first came to fame with their American Folk Art Museum in New York, are unusual in not having a distinctive signature style. They are known instead for their spatial imagination and exquisite sensitivity in using materials, both of which are on display in their new building, which manages to respect the integrity of the original Barnes even as it presents a bold civic presence in its own right. Only in one respect do they falter, as we shall see, but any architect would have.

The fortune that financed Albert C. Barnes’s impeccable art collection came from argyrol, the twentieth century’s first wonder drug. A silver-protein compound, argyrol ended that tragic cycle by which an infected mother, at the instant of birth, might pass a disease to her own baby. A few drops of argyrol in the baby’s eyes, the passage point of infection, could protect the child. It is the stuff of poetry that Barnes’s fortune and the peculiar art foundation he established shared the same purpose, to bring health and clarity to the eyes.

To design his gallery, Barnes selected that gifted architectural prodigy Paul Cret. Cret was a product of the École des Beaux Arts, and he practiced an intelligent modern classicism, abstracting and simplifying his classical detail and applying it in the form of elegantly sculpted panels to steel-frame construction. Some of the most distinguished civic buildings of the era are his work, including the Federal Reserve in Washington, D.C., the Detroit Museum of Art, and Philadelphia’s flawless Rodin Museum. But Barnes’s building, Cret recognized, was of a different order. A private museum, attached by a passage to the owner’s house, could not be treated as a civic building, with an elaborate sequence of formal spaces. Instead, its character should suggest domestic informality, with rooms of intimate scale and a generous use of warm wood.

As designed by Cret in 1924, Barnes’s gallery was a tasteful French maison de plaisance, two stories in height, built of limestone with a low tile roof. Only its jaunty cubist panels by Jacques Lipchitz suggested the radical nature of its contents. Within were some twenty-four rooms of varying sizes, although none was large except for the double-height grand gallery at the center, with its three great lunettes that Matisse would fill with his painting The Dance.

Here Barnes installed his famously eccentric hanging scheme. There were none of the didactic devices of the contemporary art museum: no labels and wall texts, and no grouping of paintings according to style or chronology (a Franz Hals might sit companionably between a pair of Renoirs). Instead, each wall was organized as a visual unity, forming one of Barnes’s symmetrical and highly idiosyncratic “wall pictures.” Odder still was the way that Barnes hung examples of historic metalwork—hinges, ladles, lock faces—above and between the paintings, to propose subtle affinities in their compositions. Visually charged but verbally silent, the Barnes was not very good for teaching conventional art history but was very good indeed for looking at art.

And for Barnes, this was the point. As a German-trained scientist (and friend of the educational philosopher John Dewey), he found paintings to be as clear as molecules. He had no room for mumbo-jumbo or cant, or genteel aestheticism: the study of art was to be objective: a matter of line, color, and form. To put a sublime Cézanne bather beneath an equally languid iron hinge was not sacrilege but served to make the form clearer, purging it of preciousness or literary meaning.

Throughout his life, Barnes maintained the private character of his gallery. Having been publically humiliated by the reviews that his first exhibition drew in Philadelphia’s newspapers, he closed his collections to anyone but the students of his own art program and any curious tradesman or factory worker who happened to knock at his door (a certain number of whom were academics in mufti, art historians being categorically unwelcome at the Barnes). He continued to bait Philadelphia even in death: When he died in an automobile accident in 1951, his will was found to place his foundation under the control of Lincoln University, a historically black college that to patrician Philadelphia stood on the wrong side of every possible set of tracks. Barnes was advanced in his racial views (he invariably hired black workers, although he insisted on paying their wages to their wives) and believed that Lincoln would be more receptive to progressive views on art and education.

Such was the oyster of an institution that was gradually pried open by successive lawsuits, the latest of which came in 2004 when Lincoln’s own trustees won the right to transform the Barnes into the one thing we can be certain that its founder did not wish it to be: a world-class public museum.

Five years ago, Williams and Tsien received their bracing mandate: the entire institution was to be uprooted bodily, transplanted to another site, and made to serve a vastly expanded program. The original museum would be augmented with additional galleries for changing exhibitions, library, auditorium, the obligatory restaurant and museum shop, and administrative offices, increasing its square footage by a factor of more than seven (from 13,000 to 93,000 square feet). All this must happen without any loss to the essential identity of the Barnes.

The architects correctly recognized that the original museum gallery and its new spaces were two different things, on the order of a gemstone and its setting, and that the gemstone should dominate. Accordingly, the gallery was given pride of place along the Parkway while the new functions, including the entrance lobby, were tucked to the rear in a second parallel wing, making a composition much like two train cars on adjoining tracks. The space between the two was roofed over to form a vast light court that is the spatial heart of the new Barnes and is surely its most spectacular feature.

Nothing is so coveted in the contemporary museum as a festive, hangar-sized courtyard; if museum brochures were honest, each would be prominently labeled as rental opportunity space. This one is unusually grand. It runs the full length of the building, extending well beyond it to the northwest as a roofed terrace. Atop it is a mighty “light canopy” that acts as a baffle to direct sunlight, softening and diffusing it, and giving the visitor the distinct sense of being outdoors. It is from here that one enters the museum gallery itself, as if it were a freestanding building, and in some sense it still is.

The light canopy is the only self-consciously architectural feature of the Barnes, and it rides atop the building as a translucent white block, thrusting deep into space at the northwest end. It is far larger and more prominent than it needed to be—more prominent, in fact, than the original gallery itself—but this must be seen as a concession to the new site of the Barnes. The domestically scaled original building did not have the commanding presence for its monumental setting on the Parkway, and the architects seem to have felt it required something of a grand gesture to hold its own among its haughty neoclassical neighbors, which include the Free Library of Philadelphia and Cret’s Rodin Museum.

If there is a chronic failing of contemporary architecture, it is a certain schematic blockiness, the tendency to conceive of form in graphic terms—how they look in digital presentation—rather than in terms of actual tactile experience. But the great strength of Williams/Tsien is a scrupulous sensitivity to the tone and texture of materials, which the light court shows off in dazzling fashion. The walls are lined with panels of Israeli limestone, chiseled by hand to produce the finely scored surface that Williams jokingly calls “cuneiform.” As one moves around the building, its treatment varies. In the light court, the chiseling is broad in effect, befitting the monumental space; in the museum gallery, it modulates to a more finely rendered scale and is organized into parallel horizontal channels. And where the museum walls emerge from the enclosed space of the light court into the open air the tooling ceases entirely and the color shifts from buff to gray, in deference to the prevailing palette of the Parkway’s neoclassical landscape.

Here and throughout the building, there prevails an appealingly quiet sensuousness of materials—in the patterned mosaic flooring at the entrance, in the lush bronze vestibule opening onto the outdoor terrace, and even in the woven wool panels set among the limestone of the light court as a sound-absorbent material (and quite effectively, for voices can be heard quite clearly here). The Williams/Tsien aesthetic, strangely, is not so much architectonic as textile-like. It focuses less on the expression of weight and support, and the strenuous poetry of structure, as it does on the qualities of pattern and interval, texture and grain. At times, this can lapse into self-indulgence, especially when a more purely architectural expression is required. Along the exterior base of the building, for example, the stone projects to form vertical flanges, suggesting tiny parodies of buttresses. Similarly, bronze strips extend from the upper-story windows, scattered haphazardly across the wall. Here the delight in surface patterning does not serve them well, for the sort of whimsical touches that might be playful on the interior are too fussy to achieve architectural force on the exterior.

In the creation of the new spaces of the Barnes, Williams and Tsien were given carte blanche, but the recreation of Cret’s 1924 building—now called the Collection Gallery—was a vastly more complicated operation. The guiding principle was that the original spaces and hanging scheme were to be maintained exactly as they were, with precisely the same proportions, dimensions, and sequential arrangements. Williams told me that he experimented with enlarging the scale of all the galleries by a certain amount, say 5 or 10 percent, to accommodate the larger crowds, but he abandoned the effort once they noticed that the increasing distance between the paintings threw off the careful balance of object and wall that makes the hanging scheme so memorable (and so weird).

Yet the new gallery is neither a recreation of the original Barnes nor a facsimile of it, but a simulacrum. It scrupulously preserves its empty spaces but not the solid masses that delimited those spaces. These are merely approximated. Moldings, cornices, window surrounds, parquet floors, and baseboards: everything has been simplified and pared down so as only to suggest the original detail. Characteristically, the materials are used well. Tsien has noted how the character of Cret’s Barnes was a mixture of the civic and domestic, in which a display of warm woodwork figured largely. But like most modern firms, Williams/Tsien is somewhat ill at ease with the making of a molding and the art of finely calibrating their profiles to match the temperament of a room. Theirs seem bulky and roughly blocked out, without the sensitivity otherwise seen in their use of materials.

The point is that it is not Barnes’s building but rather his installation that has been moved to the Parkway, and no attempt has been made to reproduce its facades. In place of Cret’s richly sculptural walls, these are highly abstracted, slender planar objects, without projecting elements or cornices. Only the voids of the window openings, cut cleanly through the walls, evoke the ghostly outline of the original Barnes. These unrelieved blank walls, combined with the aloof landscaping and lack of welcoming gestures on the Parkway and Twenty-first Street sides of the building, give it the somewhat aloof and standoffish character of a compound, and, from certain angles, it can suggest an American embassy in one of those high-spirited countries where political donors do not ask to be made ambassador.

The problem is that in its original suburban context, the Barnes was entered from the north, which made this its formal public facade. But in being transposed to the Parkway, while maintaining its interior configuration, the building now turns its back to the public side. Laurie Olin, the architect who collaborated with Williams/Tsien on the landscaping of the building, worked diligently to overcome this. He has opened up a path that gently threads its way to the right of the building and behind it, leading the visitor alongside a reflecting pool to enter the building from the side opposite the Parkway. At the same time, he introduces several right turns into the path, which force the visitor to “slow down” from the tempo of the city.

Viewed purely as a design exercise, Olin’s planting scheme is quite handsome. In one of his most inspired ideas, a tree court is sunken deep into the volume of the galleries, bringing natural light into the underground level where the library is housed. But the terraced landscaping and the row of trees that front the building on the Parkway are not successful. In contrast to the gardens that preface the nearby Rodin Museum, for example, which are delightfully welcoming because the visitor passes through them on the stroll to the entrance, the plantings of the Barnes are not meaningfully integrated into the experience of the building. They have the unfortunate disembodied quality common to the well-tended strips of landscaping before corporate office parks, which suggest affluence and respectability, but do not offer anything like a hearty welcome.

All this is beside the main question, which is how the art looks. The answer, I am surprised and pleased to say, is that it looks terrific. Williams/Tsien have installed louvered skylights in some galleries that never previously had them, allowing for a generous but diffuse play of natural light. Juxtaposed against the well-chosen wall fabric—a straw-color that closely reprises the neutral palette of the original building—the paintings have a fresh vibrancy. At times the improvement in lighting makes it seem that they have been cleaned (they have not been). When seeing how successfully this has been accomplished, one thinks regretfully of the Crystal Bridges Museum, which Moshe Safdie evidently designed for natural light and which its directors unaccountably vetoed.

In one case, the improvement is startling. Matisse’s great liberating work of 1906, Le Bonheur de vivre, had been previously lodged unhappily across from a stair, so it could only be seen obliquely from above or below. Now a slight change in the arrangement of the stairs has given it an intimate new gallery of its own, where it can be seen as never before. Had it been given more prominence over the years, one wonders if it might have had something of the reputation of Picasso’s Demoiselles d’Avignon.

In some instances, alas, there is a loss. The large south-facing French windows of Cret’s building were draped and curtained at two levels, so as to control the light, but in the new curtainless installation the paintings hung between these windows (including Matisse’s chromatically pulsating Le Rifain assis) are lost in the light flooding in behind them. Presumably this can be corrected, and, even if not, one of the delights of a museum lighted naturally is that the art changes along with the light.

The improved lighting will have the inadvertent effect of calling attention to objects that have deteriorated because of too much prolonged exposure to light, such as works on paper. In particular, I was struck by how faded some of Demuth’s elegant watercolors now seemed. I am not sure how this can be remedied, given the mandate to preserve Barnes’s installation. Lower the lighting to the threshold of visibility? Replace the object with a photographic surrogate? There is no easy answer, and it is the unavoidable consequence of the determination to embalm the Barnes, as it were, in perpetuity.

This is perhaps the ultimate paradox of the new Barnes, that it has worked so ardently to make its collection fresh and new and yet has come perilously close in the process to turning it into that deadest of things, a period room. It so happens that the nearby Philadelphia Museum of Art has the country’s finest collection of period rooms, from its Chinese scholar’s study to its Pennsylvania-German living hall, to its Spanish romanesque cloister. These are gorgeously realized, and yet in the end they are disembodied effigies. They are not alive in the way that an actual house can be, even after its owner has died. One thinks of Frederic Church’s Olana or Isabella Stewart Gardner’s original museum, where one sometimes has the uncanny sensation that the owner has just stepped out for a minute and will be right back. One used to have this sense at the Barnes (not necessarily in a pleasant way), but one has it no longer.

A collection is a tangible thing, consisting of so many discrete physical objects, and valued at so many dollars. (The value of the Barnes collection, being subject to market fluctuation, can only be guessed at, but it has been put at between twenty-five and thirty billion dollars.) It is also an intangible thing, as any complex work of human intelligence is, and it cannot be reduced to a utilitarian calculus of visitors per year and tourist dollars spent. If this were the case, then one might simply move Stonehenge to the British Museum and be done with it. (And perhaps lower the Sistine Chapel ceiling as well so that we might get a better look.)

Of course, the moment that the blocks of Stonehenge are disassembled, they are no longer Stonehenge. In much the same way, once the Barnes is moved, it is no longer the Barnes. Each painting may still sit in its precise relationship to each of its neighbors, but it no longer sits in its precise relationship to the world. The genteel parlor-sized rooms of the Cret building were calibrated for its cloistered suburban location, with its distinctive microclimate and for close personal supervision. To take a building of a gently domestic nature and make it function as a civic monument is to put demands on it that it will not be able to meet. The spaces themselves are simply not large enough to accommodate crowds. One can scarcely cross a threshold without stepping too close to an object. If only to avoid theft and vandalism, one can expect a level of security that will be several shades more oppressive than Barnes’s famous rudeness.

If this happens, it will be a pity, because Williams and Tsien have lavished more loving care and intelligence on their building than one usually sees today. I find myself wishing they had been chosen a decade ago to design the expanded Museum of Modern Art. A prediction: When the Barnes hoopla subsides, buoyed aloft by novelty and the fear of offending the cultural funders, there will be a recognition that a cultural crime has been perpetuated, an irrevocable crime on the order of the demolition of Pennsylvania Station, and right under the noses of the city’s custodians. When that happens, there will be a widespread consensus that the move was a tragedy, even as everyone now knows to call it a triumph.