The National Gallery of Art has added 6,430 works from the Corcoran Gallery of Art to its collection in a historic effort that improves its standing as Washington’s flagship art institution while attempting to preserve the legacy of what was the city’s oldest private art museum.

The acquisitions — described by curators as dazzling, stunning and transformative — will dramatically alter the National Gallery’s holdings of contemporary art, sculpture, American paintings and works on paper. And because they are rich with works by women and African Americans, the pieces diversify the National Gallery’s collection.

The accessions are the first to come from the landmark agreement the two institutions signed last summer after long-standing financial problems led to the Corcoran’s demise. The deal allowed the National Gallery to take custody of the Corcoran’s 17,000-piece collection and gave it the right of first refusal to the works. In addition, the National Gallery must help Corcoran board members find homes — preferably in Washington — for the art it doesn’t want.

[Related: Search through the NGA’s list of 6,430 items from the Corcoran Gallery]

More than seven months in the making, the undertaking is unprecedented for an American museum.

“This isn’t something we’ve ever done before. I don’t think anyone has ever done this before,” Director Earl A. “Rusty” Powell III said. “It creates a new sea level for the National Gallery. Every gallery will change.”

The first step in merging the two important collections reveals the challenge of keeping the Corcoran legacy alive. Striking a balance between integrating the works into the National Gallery and spotlighting their Corcoran roots will be difficult.

“It was the original national gallery, a significant, important cultural institution,” said former Corcoran curator Sarah Cash of the now-closed museum. “I feel it is my duty to try to see how I can best steward the legacy of the Corcoran into the future.” Cash is one of 15 Corcoran employees contracted by the National Gallery to work on the project.

For now, the Corcoran will be honored with a pair of “best of” exhibitions on view through May 3. The larger, “American Masterworks from the Corcoran: 1815-1940” features about two dozen favorites, including the paintings “The Last of the Buffalo” and “Mount Corcoran” by Albert Bierstadt, Frederic Edwin Church’s “Niagara” and Frederic Remington’s sculpture “Off the Range.” “Focus on the Corcoran: Works on Paper, 1860-1990” showcases pieces by John Singer Sargent and Jean-Francois Millet.

There are other plans to bring the art to the public. Select pieces will be added to displays in the West Building and the renovated galleries of the East Building when it reopens in late 2016. Others will be featured in two shows planned for 2017 and 2018. In addition, some may be loaned to other museums. Photographs and works on paper will be available for viewing by the public by appointment. None will be sold.

“These are the obvious yeses, the low-hanging fruit,” Powell said, adding that it will take two or three years to complete the project. “It’s a big work in progress. It’s not an end of anything. It’s an end of the beginning.”

Monumental undertaking

Although the court ruling on Aug. 18 set the effort in motion, the two institutions had been talking about potential collaborations for some time, Powell said. “We had several conversations with the Corcoran. What they needed most we couldn’t provide them, which was money,” he said.

There was no “aha” moment, Powell said.

“I sat down and more or less said what we could do,” he said. “Given the fact that this is a new experience for us, everyone will end up with their own opinion, but I think it preserves the collections, it keeps it all in Washington, and it makes it much more publicly accessible.”

[Related: The National Gallery’s great feast: What was gobbled from the Corcoran]

The parties announced the deal Feb. 19, 2014, and signed it June 19. But a month earlier, on May 9, the National Gallery’s Board of Trustees voted to acquire 703 works, pending approval by the courts. It was the first of three votes (the others were Oct. 3 and Jan. 30), and it shows just how eager the National Gallery was to acquire the Corcoran’s treasures.

In July, curators, conservators and registrars began to review the artwork, check their conditions and verify the archival paperwork associated with them. The Herculean task involved some 160 National Gallery staff members working at the Corcoran and its storage facilities.

Some issues were of concern to everyone: the condition of the works, their historical importance, whether they fill gaps or duplicate works the NGA already owns, Powell said.

In some cases, the conservation team worked first, and sometimes the curators and conservators were reviewing the pieces at the same time. The Corcoran’s storage facilities were overflowing, with works filling the aisles and every possible shelf, making for difficult conditions.

Several decisions were made quickly. The National Gallery doesn’t collect textiles, for example, so the Corcoran’s collection of lacework wasn’t considered.

But other works pushed the boundaries. Several Remington sculptures will enter the National Gallery’s collection, firsts for the institution, as will a robust collection of works by late 19th- and early 20th-century American female sculptors, including Malvina Cornell Hoffman and Bessie Potter Vonnoh. Modern art curator Harry Cooper chose works by marquee names — Cy Twombly, Ellsworth Kelly and Jenny Holzer — but also works by artists he had never heard of, including Noah Purifoy, a California assemblage sculptor and founder of the Watts Towers Art Center.

“It was certainly like opening up presents at Christmas,” Cooper said. “There are many levels of learning here, and it’s been great.”

Albert Bierstadt’s “Mount Corcoran” will be on display as part of the “American Masterworks from the Corcoran: 1815-1940” exhibition. (National Gallery of Art, Corcoran Collection (Museum Purchase, Gallery Fund))
Painstaking review

Each department approached the project differently. Mary Morton, curator of French paintings, led a three-member team through the review. They graded each work with an A, B or C and then reviewed the conservation reports of their favorites. She selected 78 of 164 pieces. “If we’re not going to take it, it’s much better to find a home where it will be loved,” she said.

Sarah Greenough and her staff in the photography department faced a much bigger task. Working in teams of three or four, they went to the Corcoran storage for seven hours a day, five days a week for almost six months to make “a first pass” through some 5,800 pieces. Among the acquisitions are a rare, and almost complete, set of Eadweard Muybridge’s “Animal Locomotion” series, seminal pieces by Lewis Baltz and an early work by Sally Mann.

“We reviewed the collection box by box, object by object,” said Greenough, who eyeballed every one of the 1,886 works chosen.

The Corcoran’s collection dovetails beautifully with the National Gallery’s, Greenough said. Although the National Gallery didn’t begin collecting photographs until 1990 — more than 100 years after the Corcoran’s first purchases — the NGA initially targeted late 19th- and 20th-century works because that was “the work that was most rapidly disappearing into other collections,” she said.

The Corcoran has some fine examples from this period — “extraordinary” is how she described a survey album of the American West by Timothy O’Sullivan and William Bell — but its contemporary pieces are especially noteworthy and will bolster the gallery’s collection.

After each department completed its review, the curators presented their wish lists to chief curator Franklin Kelly and Powell. The Board of Trustees then voted to formally acquire the pieces.

“It’s like defending a thesis. This makes sense for our collection and this is why,” Powell said. “It gets down to good old-fashioned connoisseurship.”

No new walls

Like a mantra, the National Gallery staffers repeat that this was the easy part. There are still more than 11,000 works to review. They are the less obvious choices, often by artists who are not bold-faced names.

As they decide what else they will acquire, they will have to figure out how to display their new treasures. “We have all these new works, but we have no new walls,” lamented Nancy Anderson, head of the department of American and British paintings. They will squeeze a piece in here and there, or use a Corcoran work to replace a work going out on loan. But until the East Building reopens more than 18 months from now, there probably won’t be major changes.

And there’s one more wrinkle. The court-approved deal gave the Corcoran School of Art and Design and its two buildings to George Washington University, but it requires the National Gallery to renovate and program a legacy gallery in the iconic Beaux-Arts building on 17th Street NW. Powell said construction can’t begin until GWU finishes its work, and it should take a year. If all goes well, that gallery could debut at the same time the East Building reopens.

“That would be a big kick for everyone,” he said.