For more than four decades, this bewildering 5,000-square-foot space in the Flatiron district was where Mr. Brush, who died Nov. 26 at age 75, worked as a painter, sculptor and jeweler. He spent months or years on a single project, which he sometimes shelved for even longer, only selling to collectors who displayed a thoughtful connection to the object — and the ability to pay upward of six figures per piece.

In a city of characters, Mr. Brush was certainly one. Wearing a brown leather apron and steel armored gloves, he frequently went months without leaving his studio, starting every day with a bowl of Cheerios, followed by hours and hours of sweeping. He broke only for lunch — pea soup, always. Most days he worked for 18 hours.

“Daniel Brush is indistinguishable from many madmen in New York City,” a friend, the novelist and travel writer Paul Theroux, wrote in an introduction to an illustrated collection of the artist’s work. “I emphasize the place, because a New York nutter is world-class — something to do with the way the city, so cellular, so like an asylum, an island of vertical compartments, isolates people and intensifies psychosis.”

Mr. Brush spoke divinely of his work, especially with precious metals. “I work with it because I don’t understand it,” he told “CBS Sunday Morning” in 1998 as he melted gold pellets. “I work with it because I like the purple glow that comes off of this as I dream about all of the people that maybe three or four thousand years ago saw the same thing.”

Many of his most famous works were high-wire acts of artistry using tools he made himself.

A piece he called “Second Dome” took six years to make. It has 78,000 gold spheres no larger than a grain of sand drilled into tiny holes. Each gold ball, Mr. Brush once wrote, “is .008 of an inch in diameter, plus or minus .0001 of an inch. I made them all. Individually placed them all. I don’t use tweezers. I use a brush. I pull all the hairs except one, then pick each one up and place it. If you eat pea soup, there’s enough viscosity in your spittle to adhere it to the surface.”

It took Mr. Brush several years to work up the courage to finish the piece by firing it with a torch. “At 30 seconds it succeeds,” he told Departures magazine in 1997, “at 29 it fails and at 31 it melts.”

In addition to his work with precious metals, Mr. Brush was also known for his one-of-a-kind pieces of jewelry.

“Over the past five decades, Daniel has established himself as one of the most innovative artists of our time,” Rahul Kadakia, international head of Christie’s Jewelry, told the New York Times in 2020. “Without outside influences or consideration of the mainstream, he has produced a distinctly singular vision and entirely unique body of work.”

Daniel David Brush was born in Cleveland on Jan. 22, 1947. His parents owned a children’s clothing store. His mother was also an artist and writer, and when he was 13 she took him to London to visit museums and galleries. At the Victoria and Albert Museum, he stood in awe of Etruscan goldwork. “My heart pounded the way it has not since then,” Mr. Brush told Departures magazine. “I was insane to learn how it was made.”

In 1965, Mr. Brush enrolled at the Carnegie Institute of Technology (now Carnegie Mellon University) in Pittsburgh, where he met Lynn Alpert, who goes by Olivia. They married in 1969, the same year Mr. Brush received a bachelor’s of fine arts degree. They then moved to Los Angeles, where he completed a master’s of fine arts degree from the University of Southern California.

Mr. Brush, then an abstract painter, landed a teaching job at Georgetown University. While in Washington, Mr. Brush had solo exhibitions at the Phillips and Corcoran galleries. He sold several pieces but quickly regretted it. “I was so unnerved,” he told the Times, “that I bought every single thing back from every person and I destroyed all the work.”

In 1978, Mr. Brush and his wife moved to New York, purchased a loft in the Flatiron district, and converted it into a combined living and studio space. There, Mr. Brush turned his focus to metals and jewels, crossing artistic boundaries with a steadily growing collection of antique lathes and tools. He read hundreds of books about them.

“I didn’t know how to run them,” Mr. Brush told “CBS Sunday Morning.” “I met an older man, 85 years old. He said: ‘Put the books away. Put the pictures away. Let the machine tell you what it has to say.’ So the machines, with a little bit of my help, made the pieces they wanted to make.”

Mr. Brush never hired a dealer. He and his wife, and then their son Silla, born in 1982, subsisted on a tight circle of wealthy collectors who purchased his work “from warm hand to warm hand,” as Mr. Brush called the transactions. Though Mr. Brush never identified his buyers, some names emerged in articles about him. One patron was reportedly Marsha Garces Williams, a collector once married to actor Robin Williams. Another was jeweler Ralph Esmerian. “CBS Sunday Morning” said the Aga Khan owned a Brush.

In the late 1990s, Mr. Brush’s wife and others in his artistic orbit began gently suggesting that he exhibit his work more broadly. He agreed. In 1998, the Renwick Gallery of the Smithsonian American Art Museum put on an exhibition of his work.

“Brush’s mastery is almost incomprehensible,” Washington Post journalist Hank Burchard wrote about the exhibit. “His golden domes are gorgeous and his jewelry is sensuous. His whatnots (which include a yo-yo and a confection he calls Jelly Bean Suite) are wonderful. His butterflies, bottles and boxes are needful extravagances, exercises in what the artist calls ‘focused frivolity.’”

Burchard’s only lament was that “the Renwick doesn’t supply magnifying glasses to help patrons appreciate the vanishingly small details.”

Mr. Brush is survived by his wife and son. They said he died at a New York hospital but declined to cite a cause.

Though he worked alongside his wife for decades — she made intricate boxes for the pieces he sold — Mr. Brush never employed any assistants or laborers. He never took commissions. He never made the same piece twice.

“I get up and worry about, what’s there to say?” Mr. Brush said at his studio during a 2017 conversation about his work. “Do I have anything to say? Do I know enough? Can I engrave as well as the armourers in Napoleon’s court? I read, I study, I worry. Is it a struggle? Yeah, sure.”