Sometime around May 1846, Dolley Madison made her way from her home near the White House to the studio of an enterprising photographer who had begun a quixotic effort to create a daily publication featuring portraits of “interesting public characters.”

The nearly 80-year-old former first lady and reigning grande dame of the capital sat for a portrait draped in a crocheted shawl, her curls peeking out from under her signature turban. But the photographer’s enterprise soon went bust, and the images captured that day disappeared into the slipstream of history.

Now, one of the daguerreotypes made that day is set to be auctioned by Sotheby’s, which is billing it as the earliest known photograph of a first lady.

The daguerreotype, which opens for online bidding on June 12, carries an estimate of $50,000 to $70,000. Emily Bierman, the global head of the auction house’s photography department, calls it “the most important and exciting photographic portrait to come to market since John Quincy Adams.”

By John Quincy Adams, Bierman means the oldest known photographic image of a president — a half-plate daguerreotype that Sotheby’s sold in 2017 for $360,500, including the buyer’s premium. That image showed him sitting cross-legged, trousers hiked up to reveal a pair of “cute white socks,” as Bierman put it.

In the Madison image, what leaps off the tarnished quarter-plate is the delicate filigree of her crocheted shawl, and her direct — and slightly amused? — gaze.

“She’s got this little hint of a smile,” Bierman said. “You can tell she was a commanding and venerable woman.”

The Madison daguerreotype came to light as the sellers, whom Sotheby’s are not identifying, were cleaning out a basement after a relative had died. They submitted a scan to Sotheby’s online estimate portal, floating the idea that it showed the former first lady.

Many people who submit photographs think they have found a lost glimpse of Abraham Lincoln or Jesse James. (“The outlaws in general are very popular,” Bierman said.) Usually, it’s just a random 19th-century ancestor. But looking at the “fairly terrible JPEG,” Bierman said, her senses started tingling.

“Her face is so well known,” she said.

Dolley Madison created the role of first lady as we know it today — that of uber-hostess, and softer face of power. (The title was coined in President Zachary Taylor’s 1849 eulogy, which hailed Madison as “the first lady of the land for half a century.”) The Dolly Madison bakery brand, founded in 1937, played off her elegant reputation, with the tagline “Cakes and pastries fine enough to serve at the White House.”

There are several extant photographic images of her, including two well-known daguerreotypes by Mathew Brady, taken in 1849, a few months before her death. Those images, now at the Greensboro History Museum in North Carolina, surfaced in 1956, when descendants of Madison’s favorite niece found a trove of relics in a trunk hidden inside a wall.

But digging around, Bierman located another, little-noticed daguerreotype of Madison, which was clearly from the same sitting as the one submitted to Sotheby’s. (Daguerreotypes, which are made directly onto chemically treated plates, are unique objects; no negatives are involved.)

That plate, which was discovered in the storerooms of the Maine Historical Society in 1970, showed Madison with the same clothing and the same pose, but with a slightly different gaze and drape of her shawl.

The historical society had attributed the image to Brady. But when Sotheby’s received the newly discovered daguerreotype for evaluation, its specialists removed the plate from the case and found the label of a different photographer: John Plumbe Jr.

Today, Plumbe is best known for three daguerreotypes of the United States Capitol, from 1846 — the earliest known photographic record of the building, taken before it got its marble dome. (One sold at Sotheby’s in 1995, for $189,500 including the buyer’s premium.) In his time, he was famous as an entrepreneur who established studios in more than a dozen cities.

Plumbe, who sold his business in 1847 amid financial ruin, left scant studio records. But in Dolley Madison’s papers, Bierman located a letter he sent her in October 1846, asking if she would allow him to publish a “Plumbeotype” of her image — a reference to the lithographic process he created for reproducing daguerreotypes.

It’s not clear if the Plumbeotype was ever made. But according to a letter preserved in Madison’s papers, she sent one of his daguerreotypes to a friend, Julia Wingate, whose family donated it to the Maine Historical Society in 1917.

It remains unclear how the daguerreotype at Sotheby’s, which is in a matching leather case, came into the possession of the sellers’ relative, who Bierman said had no discernible connection with Madison.

Today, cradled in the hand, it has an intimacy and glow that’s not so different from a snapshot of a friend on an iPhone.

“It’s very different to see a daguerreotype of an important figure behind glass in a museum, under controlled lighting,” she said. “Here you have an opportunity to hold it in the way it would have originally been enjoyed and treasured.”