The Pierre-Auguste Renoir painting that was found at a flea market. (AFP/GETTY IMAGES/THE POTOMACK COMPANY)

The Virginia woman eyed the box of kitsch at the West Virginia flea market and figured she’d discovered a true steal. Surely, she calculated, she could resell that brown leather Paul Bunyan doll to folk art enthusiasts for a tiny profit. As for the rest of the box’s items, she loved the plastic cow. The cow would get displayed in her living room.

But the third item, a painting — with swirls of green and pink, carrying a plaque emblazoned with the word RENOIR — did not excite her so much. She liked only its golden frame and assumed the thing was a fake.

So the woman forked over $7. She drove home. She stuck the box in a shed.

Now, about two years after her random trip to a flea market on Route 340, the woman is selling the painting through the Alexandria-based Potomack Co. auction house, which determined that the piece is a bona fide work by Pierre-Auguste Renoir, the renowned French impressionist. Potomack thinks the painting could fetch as much as $100,000, if not more, when it goes on the auction block Sept. 29.

“When [the auction company] told me it was real, I had to sit down for a minute. I really didn’t believe it. I was like, what? Really? I was a little floored,” said the woman, who spoke on the condition of anonymity, citing concerns that she’d be overwhelmed by the news media. “I can’t tell you what kind of work I do. I am self-employed, and I am well-known for what I do.” She added that her family is French, she works in education and she is thrilled to be selling a Renoir.

“I was just glad that while I had the painting for so long my house didn’t catch on fire and I wasn’t rear-ended by a tractor-trailer or that the birds didn’t tear it up,” she said.

The woman’s fortuitous discovery fills in a mysterious gap in the history of the painting, which dates to 1879 and is titled “Paysage Bords de Seine,” or “Landscape on the Banks of the Seine.” That such a painting somehow wound up in a Shenandoah Valley flea market more than 130 years after its creation exposes an uncomfortable truth about high art: It’s hard to figure out what’s a Renoir and what’s junk.

At the six-year-old Potomack Co., some clients have brought in items on the hunch that one of them could score big. About four years ago, one client showed up with a box of his father’s artwork, and the auction house determined the man had a painting by John D. Graham, a deceased American modernist. It sold for $88,000.

But the Potomack experts said they’ve never encountered a flea market bargain that turned out like this.

“This is definitely an extraordinary case, especially because of the woman’s colorful story,” said Elizabeth Wainstein, Potomack’s owner. “Usually when people have things that we’re able to authenticate, they aren’t pieces by such recognized artists or [of] such historical value. I’ve been in the business for 25 years, and we spend our lives chasing the end of a rainbow like this.”

Renoir’s painting depicts a blurry image of the Seine river, shrouded by green shrubbery and purple and pinkish flowers.

What is known, according to the auction house’s research, is that the French art gallery
Bernheim-Jeune purchased “Paysage Bords de Seine” in June 1925 from a woman named Madame Papillon for 5,000 francs. Anne Norton Craner, Potomack’s fine-arts director, suspects that Bernheim-Jeune, a gallery whose owners befriended Renoir, bought the painting from Alphonsine Fournaise Papillon, who sat for Renoir and is depicted in the piece “Luncheon of the Boating Party,” which is on display at the Phillips Collection in the District.

In January 1926, Bernheim-Jeune sold the painting to Herbert L. May, a lawyer whose family owned a department store in Pittsburgh, Craner said.

Somehow, the painting traveled from May — a man who split his time between Geneva and New York — to the West Virginia flea market. It was there, in fall 2010, that the Virginia woman, who Potomack says is from the Shenandoah Valley, bought it from a person she does not remember. This year, the woman tried taking the painting out of the frame. But she discovered that too many wooden wedges were holding it in place, so she asked her mother for advice. Her mother, she said, suggested that she take it to a dealer.

Hardly an art expert, the woman wanted to find out who could authenticate her flea market painting. She came across the Potomack Co.’s name on the television show “Antiques Roadshow” and made an appointment. In July, she walked through the front door, clutching her Renoir in a tall, white plastic kitchen trash bag.

“Anne just scowled at me,” the woman said, laughing about the fact that she brought the artwork in a Glad bag. “I just bebopped in there, and said, ‘Hey, what’s going on?’ ”

Craner sized up the piece immediately.

“She opened up her trash bag, and the light, the color, the handling — it’s so masterful,” Craner said, recalling the moment. “It did look like a Renoir. There are few artists who capture an image in color in the way he does. He uses the full brush stroke, the side of the brush, the tip of the brush.”

She checked the flea market find against a black-and-white photograph of the painting published by the Bernheim-Jeune gallery. Everything matched, down to the random dot on the upper right corner of the canvas and the painting’s stock number, which was the same one listed in Bernheim-Jeune’s registry.

A couple of weeks later, Craner called the woman to give her final confirmation, and since then, she’s been deluged with interview requests from around the world. The woman, who is divorced and does not have any children, said she’ll attend the auction but keep a low profile. She does look forward to the windfall.

“I’ve been wanting to get some siding and a new floor in my kitchen. I think I’ll be able to do that,” the woman said. “And I’m going to take my mother to France.”