One day in late January 1962, a group of artists — known as the African Jazz-Art Society & Studios — staged a fashion show in Harlem that would change American culture forever.

The event, held in the basement of the Harlem Purple Manor, a popular nightclub on East 125th Street, was called “Naturally ’62” and was intended to promote African culture and fashion.

What made the show revolutionary were the models: a group of nonprofessionals with unabashedly dark skin and natural, unprocessed, curly hair. They were part of the newly formed Grandassa Models, and they were as unlike any fashion plates as the crowd had ever seen.

“It was a pioneering concept, women coming out on stage wearing their hair in a natural state,” former AJASS member Robert Gumbs told The Post. “We didn’t know how the community would respond. I think a number of people came to laugh.”

Yet by the end of the evening, audience members were cheering the models. And the show’s slogan, “Black Is Beautiful” — printed on fliers and posters announcing the event — would become a rallying cry and movement celebrating natural hair, darker skin and African heritage.

The phrase would launch magazines, modeling careers, fashion trends and TV shows, changing the landscape of American pop culture by making it far more open and colorful.

Two current exhibits in New York shine a light on the Grandassa Models and the “Black Is Beautiful” ethos. “This Synthetic Moment,” at Chelsea’s David Nolan gallery through March 10, features the photography of AJASS and Grandassa Models co-founder Kwame Brathwaite, whose images of naturally coiffed black women would influence magazines such as Ebony and Harper’s Bazaar to hire darker-skinned models. Brathwaite’s photos are also integral to the Museum of the City of New York’s 1960s-themed show “Mod New York,” which includes some of the design trends that the “Naturally” shows helped launch.

On Tuesday, the MCNY is hosting a talk with Brathwaite, his son and the Ghana-born designer Mimi Plange about Brathwaite’s pioneering “Black Is Beautiful” work. It’s an overdue celebration of a pivotal moment in New York and black culture.

“AJASS often don’t get the credit they deserve for the way they helped to innovate the culture,” said historian Tanisha C. Ford, author of “Liberated Threads,” about black style. “They were pioneers.”

Brathwaite and his older brother, Elombe, started AJASS in the late 1950s to promote African-inspired jazz musicians as a means of fostering black pride. But after seeing the African Nationalist Pioneer Movement’s Miss Natural Standard of Beauty Contest in Harlem in 1961, they decided to broaden their focus.

They thought the beauty pageant was a great way to show black women that they didn’t need to spend so much time and money trying to tame their natural tresses — and they were particularly dismayed when they saw the pageant’s winner picking up her prize the following week in a processed hairdo.

“We have to do something to have these women feel good about themselves,” Brathwaite said to Elombe. “To have pride in their natural beauty.”

The duo launched Grandassa Models, featuring eight women and two men, who would sport the latest in African hairstyles.

“I was interested in fashion from the start,” Brathwaite, now 80, told The Post. “I did music photography, shooting a lot of female musicians, and fashion was a big deal then.”

“Naturally ’62” would be the group’s coming-out party — and would add fashions inspired by Africa.

It was a bold but risky move.

“You have to realize what the visual landscape was of Africa in the 1950s and early 1960s,” Ford told the Post. “By and large, these images consisted of black folks in Africa in the jungle wearing a loincloth with a bone through their nose.

“This was the representation of Africa that folks across the US began to associate with the continent,” Ford added. Never mind that it was “a very diverse continent with several urban cities and multiple thriving fashion industries.”

That wariness of appearing too conspicuously “African” was why, in the late 1950s and ’60s, most black women had their hair chemically processed or straightened with a hot comb. Even black-oriented magazines like Ebony favored models with lighter, cafe au lait skin and straightened hair.

Black women who didn’t process their hair often faced particular discrimination and taunts.

“Women could get fired from their jobs [for wearing their hair natural] because it was interpreted as being militant,” said Gumbs, now 79, whose sister, Jean, joined the Grandassa troupe. “Even within the black community, people would laugh at [my sister].”

Former Grandassa model Eunice Townsend, who went on to study speech and language pathology after her fashion stint, said, “Blacks had tried to emulate and assimilate into society because we had been outcasts for so long. So for one to step out and do something different, you were sort of ostracized.”

Townsend, who is now 71 and lives in Harlem, told The Post that she had never thought about wearing “Afro-centric” clothes or “being natural” before joining Grandassa, but once she did, the ridicule she faced only made her more defiant.

“Being in the group, it was a big thrill and a change of lifestyle,” she said. “The leader, Elombe, was a real taskmaster, and he made us think about why we were doing what we were doing, so it became a thing of just being proud to be black.”

Grandassa was determined to make “Naturally ’62” the greatest fashion show Harlem had ever seen.

Gumbs designed dynamic posters and fliers featuring the phrase “Black Is Beautiful” — adapted from the teachings of activist Marcus Garvey — in big, bold script. Male Grandassa model Jimmy Abu, a balletic boxer, trained the models on how to strut. The crew members sewing the garments made sure that they were slim-fitting, attractive and modern. Brathwaite, the gifted shutterbug, would document the whole thing.

On Jan. 28, the “Naturally” crew arrived early at the Purple Manor to decorate and go over some last-minute choreography. As the models were getting ready, Gumbs crept upstairs to take a peek out the window.

“There was a line forming, and we said, ‘Wow!’ ” he said. “We knew we had to put on a really professional show so they would just walk away in awe.”

The show opened with an actor named Gus Williams reciting a poem by Garvey celebrating the beauty of black women, followed by music and commentary from jazz singer Abbey Lincoln and her drummer husband, Max Roach. One by one, the models came out in their smart pencil skirts and peplum blouses, their hair undone, dancing to Roach’s syncopated rhythms.

“This was my first attempt at modeling . . . so I was very nervous — until I walked on the stage and heard all the hoots and hollers, and I got courage from that,” Townsend recalled.

“We were very voluptuous women,” she added. “So the audience really enjoyed it, because we mirrored [what they looked like].”

The show was such a hit that they had to do an encore performance immediately after — to accommodate the people who couldn’t fit into the ballroom for the first go-round.

AJASS began to host “Naturally” shows annually — even venturing into other US cities like Chicago and Detroit. Black celebrities, including Miriam Makeba, Nina Simone and Miles Davis, showed up and started talking up the events at their concerts. Blues singer Bobby “Blue” Bland invited the Grandassa Models to open for him at the Apollo Theater.

“The shows became so popular that the hardest thing about them was finding a venue that would fit all the people who wanted to come,” said Brathwaite.

“Naturally ’62” proved far ahead of its time, presaging a larger black-rights movement that picked up steam amid the cultural upheaval of the late ’60s. As the civil-rights, women’s and anti-Vietnam War movements took a more radical turn, said Ford, so did modes of self-expression. And African-Americans in particular began to wear their heritage with pride.

In 1968, James Brown released the rallying-cry song “Say It Loud — I’m Black and I’m Proud.” Essence magazine, devoted to representing black culture, launched in 1970. A year later, the TV variety show “Soul Train” began, bringing black fashion, culture and Afro hairdos into the mainstream. And in 1973, a young African-American designer named Stephen Burrows stunned the Paris couture industry when he brought his coterie of black models, including Pat Cleveland and Bethann Hardison, to strut their stuff at a fashion face-off in Versailles.

While the “Naturally” shows stopped in the 1980s, the “Black Is Beautiful” movement remains as vital as ever. Stars such as Solange Knowles, Lupita Nyong’o and Zendaya often wear their hair naturally, either in a short crop or in elaborate braids — and speak out when fashion magazines lighten their skin or digitally alter their locks. And the year’s most anticipated film, “Black Panther,” out Feb. 16, not only features a black superhero but draws inspiration from African fashion, art and beauty, an aesthetic that its actors have adapted for their red-carpet appearances.

The “Naturally” shows are “a reminder of how even when faced with intense social violence, black people continue to find ways to [express themselves with] style,” said Ford. “They show that black people have long been having our own conversation around beauty and style, and have influenced the most popular fashion and beauty trends around the world.”