Composer Julius Eastman (1940-90) is not having an easy resurrection. But was anything about him ever easy?

His best pieces are acclaimed — though they have provocative, unprintable titles.

Surviving scores have significant information gaps. Like how they fit together. Or what they were titled. Or if they were ever performed.

Under such odds, the current festival "Julius Eastman: That Which is Fundamental" presents 10 of his works this month at the Rotunda in University City, through May 26. Two full rooms of archival materials are displayed at the nearby Slought Foundation. There's more to come in future years, though nobody is sure what or how much.

"As Julius' profile starts to emerge again with articles in the New Yorker and the New York Times, more people are saying, `Oh, yeah, I knew that guy. He did a concert in our space,' " said Dustin Hurt, whose Bowerbird-produced concerts are a significant force in the Eastman revival, starting with a 2015 program of his music and now with the "That Which is Fundamental" festival.

"Black, openly gay, virtuosic, and arrogant" was how Eastman was described Friday by his younger brother Gerry at the festival opening. It was a magnetic combination in cutting-edge circles, but less welcome in the rest of the world.

Born in Ithaca, N.Y., educated at the Curtis Institute, Eastman migrated from one artistic hotbed to another, from the faculty of the University of Buffalo when it was a new-music crucible in the 1970s to the downtown Manhattan minimalist circles in the 1980s. His compositions were performed at fashionable venues, such as the Kitchen, and his famously exclamatory vocal performance in Peter Maxwell Davies' Eight Songs for a Mad King was heard at the New York Philharmonic.

It was a wild time. Mary Jane Leach worked alongside him as a vocalist during that period in 1981: "At 10 a.m., Julius breezed in, dressed in black leather and chains, drinking Scotch," she wrote in an album note for an Eastman recording. "That was my introduction to the outrageousness that was Julius Eastman, who strove to push his identities as a gay black man and musician to the fullest."

Only a few years later, having fallen afoul of addiction, he lost his scores and papers in a New York apartment eviction and, living homeless, was so off the grid that when Meredith Monk wanted him to sing on one of her albums, the Lower East Side had to be plastered with fliers imploring Eastman to call. Then at age 49, he made his way back to Buffalo, where he died.

Eastman's revival began around 2005, with the release of the three-CD set Julius Eastman: Unjust Malaise, on the New World label. Hurt discovered Eastman only several years ago, around the time of Gay Guerrilla, a collection of essays about Eastman edited by Leach and Renee Levine Packer (University of Rochester Press). At that time, barely a single concert of Eastman music could be assembled. Now, Hurt estimates that of Eastman's 50 or so works, 15 are lost. One piece, titled That Boy, survives in a single page of incomprehensible score. Most enigmatic is an untitled choral work that turned up months ago, written for the largest ensembles of his career. It appears to have been performed, but nobody yet knows where or when.

Scholars of centuries-old music are used to exhaustively piecing together enough evidence to yield a performance. Though Eastman's world is more chronologically recent, it's also strangely distant. Gerry Eastman had some scores. A blue suitcase owned by his late mother, Frances, yielded others. Hurt has spent days leafing through endless newspaper clippings in Buffalo, yielding a clue here and there that makes another piece fall into place. Friday's performance of Femenine, for example.

The score to the hour-plus minimalist work has survived, but just last year  an archival recording by the S.E.M. Ensemble in Albany surfaced that allowed performers to fill in the blanks, such as the hazy rhythmic texture established by a set of jingle bells. How could anybody maintain that exact rhythm for so long? One review described a mechanical contraption invented to do the job. Also, Eastman served soup during the performance — while wearing a dress.

Such things weren't all that unusual in the 1970s avant-garde. Nor were fragmentary scores. Acknowledged masterpieces such as Steve Reich's Music for 18 Musicians wasn't fully written down until years after its creation.

The question is whether these musical experiments still speak to the current century, and Femenine, performed Friday at the Rotunda by the Arcana New Music Ensemble, turned out to be as entrancing as anything written during that period by Reich or Philip Glass. Underneath Eastman's incessantly repeated main theme, all sorts of things arose — pianistic storm clouds, wind writing suggesting fantastical plants growing in time-lapse photography, something resembling a Bach chorale, and then, after an hour, a cathartic flute melody.The 1974 recording captures perhaps only 60 percent of the gravitas experienced here live.

Will there be more of the same? Well, scores at the Slought Foundation show Eastman using traditional notation in one score, graphic illustrations in the next. He was always on the move. "Throughout his life, there was a struggle to find a sense of belonging. … In the exhibition, you can see how different he looks in pictures," said Hurt.

The young Eastman could pass for a Bible salesman. But in a somber series of black-and-white portraits, he has a shaved head and long prophetlike beard, with bony bare shoulders. Yet these photos, by Andrew Roth, date from 1980, when Eastman was on the upswing.

His story is that of an unfinished symphony. You don't have the luxury of understanding what's there from the perspective of where it led. Hurt readily refers to Eastman as a creative genius. But will the full range of that genius ever be heard?

Julius Eastman: That Which is Fundamental continues May 12, 19 and 26 at The Rotunda, 4014 Walnut St. Tickets: $12-$25. Information: 267-231-9813. Exhibition through May 28 at Slought Foundation, 4017 Walnut St., noon-5 p.m. Tuesday-Friday, free.