Ten years and $10 million after collectors Jon and Kim Shirley vowed to restore Alexander Calder's Mountains and Clouds (1976/1986), the monumental sculpture's long-missing mobile is returning to the Hart Senate Office Building atrium in Washington, D.C.

The story began in March 2016, when the Shirleys flew from Seattle to Washington for a meeting of the National Gallery of Art's Collectors Committee. Longtime Calder collectors—they donated 48 works, valued at $200 million, from their Calder holdings to the Seattle Art Museum in 2022—they visited the sculpture in the Hart Building atrium. The 50-foot stabile, the "mountains," stood in place. The four "clouds," a mobile designed to hang from the 90-foot ceiling, were gone.

"It was surprising and dismaying," Jon Shirley, former president and chief executive of Microsoft, told ARTnews. An earthquake had forced the clouds down for analysis, and engineers subsequently deemed them unsafe for reinstallation due to structural defects. The Shirleys decided on the spot to spend whatever it took to put them back.

Mountains and Clouds is Calder's final work and the only piece in which he combined a separate mobile and stabile. The largest of the four clouds measures over 40 feet long and weighs nearly one ton. With the mobile reinstated, the work ranks as the largest piece of modern public art in the nation's capital, second in size only to the Washington Monument. "It's one of the most powerful artistic expressions in the nation's capital, and a landmark achievement of American public art," Shirley said.

The sculpture itself barely survived its own genesis. Architects of the Capitol and Hart buildings selected Calder's design in 1975, and Senator Philip Hart of Michigan, the building's namesake, approved it. Calder traveled to Washington in 1976 to approve the maquette; the next day, back in New York, he died. Three years later, cost-cutting on the building's construction slashed funds for the sculpture. New Jersey Senator Nicholas F. Brady raised replacement money from Paul Mellon, the legendary patron and son of the National Gallery of Art's founder. The piece was dedicated in 1987.

The Shirleys stress that the reconstruction demanded more than money. The Calder Foundation, run by the artist's grandson Alexander S.C. Rower, found archival evidence that the mobile had never been realized exactly as Calder envisioned. The conserved sculpture now uses new technologies to bring it in line with the artist's intentions. Shirley credited "a determined team of solutions-oriented senators from both sides of the aisle" and "a devoted interagency group of government staff under the guidance of the Architect of the Capitol" as crucial to the restoration.

Installation began in late August. "Kim and I are looking forward to the moment when the motor is turned on, and the mobile's components begin to move slowly in the way Calder imagined," Shirley said.

Whether the work carries a message for the politicians who pass beneath it daily remains an open question. "Calder was not a political artist," Shirley said. "But the work's symbolic power—its incredible demonstration of equilibrium and the unlikely harmony that can be achieved across different planes—is symbolically potent."