Portrait of Yarrow Mamout, painted in 1822 by James Alexander Simpson. Is there a picture by the same artist somewhere out there of a woman named Sarah? (Courtesy of Collection of Peabody Room, Georgetown branch of D.C. Public Library)

Go up to your attic right now, or down to your basement, or to your late parents’ storage unit that you still pay for each month even though you’re unfamiliar with its exact contents. Wherever it is you keep things that are ancient and dusty and mysterious, go there immediately and see if an elderly African American woman stares back at you from the canvas of an oil painting.

Because if she does, you may have found one of the world’s rarest paintings.

“It would be the only oil painting of an African American woman who came over on a slave ship. That’s how valuable it would be,” said Jim Johnston.

Jim is a Bethesda lawyer and author. His infatuation with a different oil painting inspired him to write “From Slave Ship to Harvard: Yarrow Mamout and the History of an African American Family,” published in 2012 by Fordham University Press.

Yarrow Mamout was taken from West Africa in the 18th century and sold into slavery in Maryland. He was owned by a Georgetown family but eventually gained his freedom. He was well known in Georgetown, a practicing Muslim who made bricks and owned land. His portrait was painted in 1819 by Charles Willson Peale and displayed in Peale’s Philadelphia museum.

Yarrow was also painted by James Alexander Simpson, a Georgetown painter. Today the Alexander painting of Yarrow hangs in the Peabody Room of the Georgetown public library branch. But in 1825 it hung at Ninth and Pennsylvania NW. We know this because the newspapers at the time were full of mentions of a new attraction: the Columbia Museum.

The Columbia Museum was the creation of an entrepreneur named James Griffiths, a skilled taxidermist, or as he described himself in a newspaper advertisement: “a preserver of subjects of Natural History, viz: Quadrupeds, Birds, Fishes and Insects.”

Griffiths had worked with Peale, whose Philadelphia gallery set the template for the American museum: a compendium of curiosities designed to entertain and educate, no matter your station in life.

Griffiths boasted of more than 1,000 items at his Columbia Museum. What might you see for your 25 cent ticket (half price for children younger than 12)? Here’s a partial list, taken from the National Intelligencer newspaper of the time:

Painting of the Holy Family, copied from Raphael.

Petrified Wood, found in digging a well in this city, 50 feet under the surface of the earth.

One Viper, preserved in spirits.

Wings of a Flying Fish.

Chinese Mariners’ Compass.

Hair ball found in the stomach of a cow.

A Medal representing the Abolition of Slavery, by Great Britain, in 1807.

A Turkish tobacco pouch.

A brass ball found in the tusk of an elephant.

One Sea Gull.

That same list included something more intriguing than a bovine hair ball:

Portrait of Yarrow, a native of Africa, 130 years old; painted and deposited by Mr. A. Simpson, of Georgetown.

Portrait of Guinea Sarah, now living, and upwards of 100 years old, by the same.

The Yarrow portrait is well known, but the portrait of Guinea Sarah was unknown, at least by Jim. Four months after his Yarrow book was published, he heard about it from D.C. artist Mary Belcher , who had come across the mention of Sarah in the National Intelligencer.

Griffiths’s museum failed after about two years despite entreaties to the government to offer financial support to keep it afloat. He went to Baltimore to work at another Peale museum. It’s unclear what exactly happened to the Columbia Museum’s collection. Perhaps the people who had lent the items took them back.

Jim has traced every lead he can think of to find Sarah or learn more about her. Presumably she came from Guinea in West Africa. There is no other mention of her in a Washington newspaper. No census mentions her. (Neither Yarrow nor Sarah was more than 100 years old. It was common then to overstate the age of African Americans.)

The artist Simpson was active in Baltimore, where he painted portraits of many of the top families. Jim poked around up there to see if descendants had the Sarah painting. No dice.

Could the painting have ended up in Peale’s museum, some of the contents of which were sold to P.T. Barnum? The Barnum museum was destroyed by a fire in the 1860s. Jim consulted an inventory but could find no mention of Sarah.

A different, but similarly named, Washington museum — the Columbian Institute — gave its collection to the Smithsonian. Perhaps the Sarah painting was with that. But no, the Smithsonian doesn’t have it.

Jim talked with the daughter of the woman who donated the Yarrow painting in 1935. She was in her 90s and had no memory of Sarah — or of Yarrow, for that matter. “It must have been up in the attic,” Jim says she told him. “My mother was from Alabama. I don’t think she wanted an African American portrait in the house.”

The realist in Jim knows Sarah’s painting was probably destroyed. Fires consumed Georgetown homes with alarming regularity back then. But the dreamer can’t let go of the possibility that it’s out there somewhere.

“You never know,” he said. “Someone may have come across it.”

It would probably look like Alexander’s painting of Yarrow: crude compared with Peale’s masterpiece but recognizable as an actual, specific person. It would probably have the artist’s name on the back. And it might have the name of its subject, too: Guinea Sarah, a woman who may not have been born in Washington but was a Washingtonian just the same.

Twitter: @johnkelly

For previous columns, visit washingtonpost.com/johnkelly.