A batch of unreleased recordings by the Velvet Underground frontman was discovered in the Pop artist’s archive at the Andy Warhol Museum in Pittsburgh.

As the New York Times reported, the decades-old tape was found two years ago by Cornell music professor Judith A. Peraino while researching a book about Warhol.

The cassette contains two sides of recordings from 1975, with the first including live renditions of songs from Reed’s albums Sally Can’t Dance and Coney Island Baby.

The second, labelled Philosophy Songs (From A to B & Back) in reference to Warhol’s 1975 book, comprises twelve never-before-released songs along with the fragment of a thirteenth.

Yesterday, Peraino published “I’ll Be Your Mixtape: Lou Reed, Andy Warhol, and the Queer Intimacies of Cassettes,” an article that details the discovery, in The Journal of Musicology.

The songs from Side 2 notably feature phrases from the Pop artist’s The Philosophy of Andy Warhol: From A to B and Back Again, including a variation of a quote that reads “Sometimes people let the same problem make them miserable for years when they could just say, So what. That’s one of my favorite things to say. So what.”

“This tape is Lou Reed working out what he does best, which is figuring out the character of his song, telling the stories, being as brutally honest as he is in many of his writings,” Peraino told the New York Times.

Read also: Lou Reed poems after leaving Velvet Underground set for book

Due to copyright issues, it is unlikely that the cassette will ever get a commercial release. The tape will remain in possession of the Andy Warhol Museum, which will only allow professional scholars to listen to them.

However, the Philosophy of Andy Warhol cassette sheds new light on the tumultuous relationship between Reed and Warhol.

The two artists collaborated in the 1960s when Warhol managed the Velvet Underground for a couple of years. The Pop artist produced the band’s debut album, The Velvet Underground and Nico, which was released in 1967.

Reed notably opened up about his rocky collaboration with Warhol during a joint performance with Kris Kristofferson at New York’s Bottom Line club in February 1994.

Between songs, the musician recalled the iconic artist’s hands-off approach in the recording studio.

“At one point the engineer would say, apropos of something we’d done, ‘Mr. Warhol, is that OK?’ and he’d say, ‘Oh, that’s great.’ And as a consequence of that, we experienced total freedom, because no one would change anything because Andy said it was great,” he recalled.

Reed and Kristofferson’s collaborative performance was captured on the album In Their Own Words With Vin Scelsa, which was released in 2017 as part of the Bottom Line Archive Series.