Elton John’s First Auction in 21 Years Has It All: Boots to Banksy.

Elton John is downsizing — and the superstar’s former penthouse residence in Atlanta has been emptied for a series of auctions at Christie’s starting on Feb. 21. The items are expected to bring in an estimated $10 million.

Want the Yamaha conservatory grand piano where the Rocketman plunked the keys of his Broadway shows “Billy Elliot” and “Aida?” It will cost roughly triple what similar models sell for online, with a high estimate of $50,000.

How about Julian Schnabel’s portrait of the superstar dressed in a gown and ruffled collar? The auction house is seeking $300,000.

And the most expensive object, a 2017 Banksy painting of a masked man hurling a bouquet of flowers, secured directly from the anonymous artist, is expected to sell for nearly $1.5 million.

Included in the auction: prescription sunglasses by Sir Winston Eyeware that Elton John owned; a diamond pendant necklace set with round diamond letters spelling “The Bitch Is Back,” estimated at $20,000-$40,000; a Cartier sapphire ring, 18k yellow gold, $50,000-$80,000.Credit…Vincent Tullo for The New York Times

John declined to comment on the auction. (Agostino Guerra, a Christie’s spokesman, cited “long-planned scheduling conflicts.”) However, the singer’s husband and manager, David Furnish, discussed the sale in a recent interview.

“As time went on, the walls got more full,” Furnish said. “Elton never put things in drawers, he bought them to live with his art.”

But the sale of their 13,000-plus-square-foot Atlanta residence, on the 36th floor, for more than $7.2 million last fall gave the couple an opportunity to consolidate their collection of artworks and mementos, which includes the singer’s famous sunglasses, silvery platform boots and one of his first sets of stage clothes — an ivory and gold ensemble made by the textile designer Annie Reavey in the 1970s.

“I met Elton John and we just hit it off,” Reavey said in a 2007 interview in a Nevada newspaper. “I had purple hair, he had green hair. I had rhinestones, he had diamonds.”

The condominium on Peachtree Road symbolized a turning point for the British singer. He bought the two-story abode in the 1990s. It served as his American headquarters during tours and a hideaway for staying sober through the 1990s. But the walls were soon populated with dozens of photographs — part of an extensive collection of images by modern masters like Dorothea Lange, whose Depression-era images of despair include “Migrant Mother,” and the Hungarian photographer Andre Kertesz. John also collected works by Andy Warhol, Cindy Sherman, Robert Mapplethorpe and others that now have museums clamoring for donations.

Above his bed, he displayed “Noire et Blanche,” images by the surrealist photographer Man Ray.

”I love living with my collection,” John said in a video promoting an exhibition of his works at the Tate Modern in 2016. “I’m seeing these wonderful images on the wall that people took a long time ago that still have relevance and still scream out at you.”

When part of his collection was exhibited at the Tate Modern, “what surprised most was its depth,” said Shanay Jhaveri, head of visual arts at the Barbican Center in London. “For someone whose public persona has been so indelibly associated with excess and kitsch, a collection of predominantly black-and-white, modestly scaled Western modernist photographs seemed inconsistent. Perhaps the revelation was this apparent irreconcilability.”

Atlanta was where John cultivated that love of photography, thanks largely to a local gallerist named Jane Jackson. (In 2003, she became the director of the Sir Elton John Photography Collection, which now includes thousands of images.) Some highlights featured in a 2000 exhibition, “Chorus of Light” at the High Museum of Art in Atlanta, are being offered at the Christie’s auction, including works by Irving Penn, Richard Avedon and Andres Serrano.

“The collection was very disciplined,” said Ned Rifkin, who curated the High Museum exhibition and developed a working relationship with the singer. “It wasn’t just about acquisitions but the beauty of having art.”

“I remember there were times he would go to auction and he was genuinely frustrated when he couldn’t get something,” Rifkin, now retired, added. “I’m disappointed to hear he is selling, but on the other hand, he has so much.”

The singer’s husband said it was time to start pruning the collection.

“You have to reach a stage where you can’t just continue to accumulate,” Furnish explained. “Elton hates parting with things. It is a very emotional decision.”

To that end, Furnish has been the one to primarily handle the auction, which is the first time that a major selection from John’s collection has been offered to the public since a 2003 Sotheby’s sale of items from his London home (it brought in $1.67 million.) In 1988, another Sotheby’s auction in London presented a hodgepodge of artworks and oddities — including a Magritte painting of a blue fish wrapped in pearls, a chamber pot and a pair of Cartier silver baskets that John once used as soap dishes — fetching $8.2 million, or about $21 million in today’s dollars.

Now, John and Furnish decided to partner with the auction house’s rivals.

“This was a competitive situation,” said Tash Perrin, Christie’s deputy chairman organizing the sale, who helped broker the deal. “It coincides with Elton closing a chapter of spending his time in the States.”

Perrin said that most of the 900 items being auctioned would have modest prices. Many are being offered for a few thousand dollars, including everything from the portraits by Lange to jeweled rings to Versace dinnerware.

But as recent celebrity auctions have demonstrated, collectors have no qualms about spending gonzo dollars on the knickknacks of their pop idols. Last year’s auction of belongings from the rock vocalist Freddie Mercury at Sotheby’s reach $50.4 million, more than tripling its initial high estimate of $14.2. Bidders fought over everything from a silver mustache comb to cat ornaments and a neon telephone.

During a turbulent market, auction houses have increased their promotion of these celebrity auctions, with the recent sales of items owned by the newscaster Barbara Walters, the fashion editor André Leon Talley, the French actor Gérard Depardieu and the Supreme Court Justice Ruth Bader Ginsburg, each bringing in millions of dollars.

Furnish said the John sale was designed to start their own thinking about the singer’s legacy, as John stepped back from performing to spend more time with their sons, Elijah and Zachary. “That could mean more sales, gifts to institutions, gifts to friends,” Furnish said.

“One reason we have been able to collect is because artists know that when they sell to us, their work is going to a home,” Furnish added. He acknowledged that in the future, “as our sons get older, they might have connections to pieces. We need to elegantly find a way of bringing them into that process.”