William Kelly, the New York Public Library’s director of research libraries, described the restrictions, including the seal on roughly half the personal correspondence in the archive, as complicated but “fairly modest.”

“There’s always a balance in guaranteeing access for scholars, while at the same time being sensitive to the family,” Mr. Kelly said. (Gloria Karefa-Smart, Baldwin’s sister and executor, declined through the library to be interviewed for this article.)

Other limitations — like a seven-year waiting period on any public display of all but a handful of items — seem puzzlingly out of step with current trends at archives, which tend to make as much freely available and visible online as copyright will allow. (The library also declined to let The New York Times photograph anything beyond eight items the estate had approved for display.)

But Mr. Kelly said the restrictions were outweighed by the sheer richness of the archive, which sheds light on how Baldwin navigated different aspects of his identity — gay, African-American, political, artistic.

“I was dazzled by it,” he said, referring to the collection.

The library declined to disclose the purchase price, which was paid with donations from the Ford Foundation, the Knight Foundation, New York Life and three individual donors. (One donor, Mr. Kelly said, contributed the last $500,000.)

For its money, the Schomburg got some 70 boxes of material — about 30 linear feet, in archivist-speak. It spans the full range of Baldwin’s career, from typescripts of his teenage poetry to handwritten drafts of “The Welcome Table,” his final, unfinished play about an imaginary dinner party featuring an ex-Black Panther, a professor and a Josephine Baker-like dancer. (It was inspired by visits Baker made to Baldwin’s house in the South of France, where he spent the last decades of his life.)