A$AP Ferg attends the Tiffany & Co. Paper Flowers event and Believe In Dreams campaign launch on May 3, 2018 in New York City.

When ASAP Ferg was still a teenager in the Hamilton Heights neighborhood of Harlem, he started making crystal-studded pendants. He would sketch designs of characters like Bart Simpson and Mega Man, then hand the drawings over to Earl Harley (also known as "Harley, the buckle man"). Mr. Harley would create the bases for Ferg, who would then add Swarovski crystals and sell the pendants. They cost him about $200 to make; he sold them for about $700 a piece.

A decade later, Ferg, born Darold Ferguson Jr., is hawking pricier gems. This month, he became the first male rapper to appear as a spokesman for Tiffany & Co., the luxury jeweler. Ferg, 29, is not yet a megastar nor the most famous artist in the ASAP crew (that would be Rocky). But in collaborating with him, Tiffany has aligned itself with a princeling of Harlem fashion who aims to honor the legacy of his father, the designer Darold Ferguson Sr., by out-accomplishing him.

During a recent interview at The Blue Box Cafe at the Tiffany flagship store on Fifth Avenue, Ferg was frank about the mutual interest driving the partnership.

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"I feel like we open up doors for each other," he said of Tiffany. "I show them my world, they show me their world."

In working with him, the jewelry brand follows other luxury brands that have sought to reupholster their stuffy brand images by collaborating with luminaries of the hip-hop world.

The conglomerate LVMH Moët Hennessy Louis Vuitton recruited Jay-Z as a brand ambassador for its Hublot watches in 2011, and in the years since, it has been rewarded with hundreds of bars, from his songs and others', testifying to the status of its brands. Virgil Abloh, Kanye West's longtime creative director, was tapped in March as the artistic director of men's wear at Louis Vuitton. And in January, Gucci opened a studio with the Harlem fashion legend Dapper Dan, who worked with Ferg's father and is close enough with the rapper to refer to him as his nephew.

Before Mr. Ferguson Sr. died of kidney failure in 2005, days before Ferg's 17th birthday, he designed T-shirts for stars like Teddy Riley and Heavy D and logos, like the one he created for Bad Boy Records. Also in 2005, Ferg started his own line, Devoni Clothing.

"I always ask my grandmother, when did my father have his first car, when did my father have his first apartment," he said. "That was a way of measuring myself."

Eventually, Rocky, who had known Ferg for years, helped convince him to start making music in addition to designing clothing. A couple of studio albums and mixtapes into his career, Ferg now feels as if he's beginning to reach a new level of fame.

Ferg's love of jewelry is obvious in his music. The first verse of his highest-charting song to date, a remix of his 2018 single "Plain Jane," opens with him decked out in a chain he had made in honor of his friend ASAP Yams, the mastermind behind the ASAP crew, who died in 2015. In a song he created with the actress Elle Fanning, "Moon River," he raps about a Tiffany grill with all gold filling. If such a piece were real, it would be the first grill manufactured by the company. ("I'm a strong believer in talking things into existence and I've gotten everything I wanted so far," Ferg said.)

These days, he cares less about flash. He said he believes in the artistic value of the jewelry he's promoting — referring to himself as a "a walking MoMA installation" — but also understands what it could mean for young people to see him wearing gold from Tiffany & Co.

"I couldn't afford anything in here so I never walked in the store," he said, gesturing at the room. "Kids, I can imagine them feeling the same way, they didn't have anything to connect to."

He imagined what he might say to someone from Hamilton Heights: "I came from where you came from. You could attain this as well."