In 1969, the N.Y.P.D. arrested a group of Black Panther Party members in a series of predawn raids. Twenty-one people were charged with planning bombings across the city and assassinations of police officers. During the many months that the arrested were held, the Panthers fought back, in part, with art—posters, paintings, and flyers. The other day, a curator named Es-pranza Humphrey was inspecting a particularly psychedelic print in a storage room of Poster House, a museum in Chelsea. In the piece’s center was a black-and-white figure with an Afro and a yelling mouth. A spiral of yellow and red squares radiated from an outstretched fist, and fluorescent-pink letters spelled out “Power to the People” and “Free the New York Panther 21.” “One of the women accused was Afeni Shakur, which is Tupac’s mom,” Humphrey said. “She actually ends up representing herself while she was pregnant with Tupac.” The Panther’s public efforts, and Shakur’s jailhouse law studies, eventually helped secure the group’s acquittal.

Humphrey, who was dressed in black, aside from red Nike Air Maxes, was preparing for an exhibition, which opens this month, on the art of the Black Panthers. She was joined by Angelina Lippert, the museum’s lead curator, and Rob Leonardi, the exhibition’s preparator and fabricator. They looked at the poster. Lippert, blond and bespectacled, flipped on a black light. The group went, “Ooooh.”

Humphrey explained that most Black Panther posters—armed figures in berets and leather jackets, often in black-and-white with a single bold color—were printed on the back pages of Panther newspapers, or individually, to be pasted on telephone poles or pinned to bulletin boards. A black-light poster was rare, and had a different destination. “They’re most popular in head shops, obviously,” Lippert said.

People collected them. “The Committee to Defend the Panther 21 got money from really notable New Yorkers, like Leonard Bernstein,” Humphrey said. “He put money into the pool for bail money.”

Leonardi, who wore a blue shirt and nitrile gloves, had mounted most of the posters in the show in what he called a “plexiglass sandwich.” “It reminds you that these are things of the street,” Lippert said. To make the posters pop off the wall, Leonardi had devised a mounting system involving two pieces of wood, a table saw, fine sanding, and something called a “rabbet joint.” He took the black-light poster aside and began stapling plastic archival corners to a plywood board and ripping acid-free tape.