The little Renoir landscape looks so modest and guileless and transparent that a casual observer never would guess at the secrets the painting hides.

"Paysage Bords de Seine" depicts a river and bushes. On that summer day in 1879, a sailboat was skimming along the River Seine. There were trees and clouds. The light was abundant. Viewers even can see the unpainted canvas peeking out from the frame.

That unconcealed quality is what struck senior painting conservator Mary Sebera when she examined the water view for the first time after it was returned to the Baltimore Museum of Art for good on Jan. 31 after a 62-year absence.

"This painting is so open and direct," Sebera said. "There are many places where you can see right down to the fabric. It's not fully covered."

The only fact that museum officials haven't pinned down about this seemingly artless artwork is — well, just about everything.

Why was it painted, and for whom? According to a charming note in the museum's records, Renoir may have dashed off the painting on a linen napkin for his mistress while they were dining al fresco, but that lady's identity remains a mystery.

Another puzzle is who spirited the painting away from the museum between 6 p.m. Nov. 16 and 1 p.m. Nov. 17, 1951, and how the thief — or thieves — got away with the crime for so long.

Finally, no one knows where the artwork was for the six decades before it surfaced with a splash in September 2012. Marcia "Martha" Fuqua claimed she had bought the painting in a box of odds and ends costing $7 around 2009 at West Virginia's Harpers Ferry Flea Market without knowing its true value.

Fuqua, 52, of Lovettsville, Va., fought to retain ownership of the landscape. But last month, U.S. District Court Judge Leonie M. Brinkema awarded title to the museum. The deadline for appeal expires at 11:59 p.m. Thursday. Fuqua's attorney, T. Wayne Biggs, said Wednesday that his client would not bring the matter before a higher court.

Museum director Doreen Bolger said that "Paysage" — which will be exhibited late next month — fills an important gap in the museum's collection.

"We don't have a landscape from the 1870s," she said. "We have a nice group of Renoirs, but most of them are from later in his career. We have 'Child With Hoop' from the mid-1870s, but it's a figure painting.

"At that time, the Impressionists were at their height of exploring nature and atmospheric effects and of painting outside."

Just as Sebera meticulously is lifting the grime from the painting's surface with a cotton swab no larger than a pencil eraser, she and curator Katy Rothkopf also are working together to uncover the painting's past.

So far, they have found just a few tantalizing clues.

Sebera collected powdered fibers that fell from a tiny, slightly frayed area of the canvas and examined them under a polarized-light microscope. She determined that the canvas indeed is linen, as the museum's records claim.

"Linen has a distinct growth pattern that's different than cotton or silk or wool," Sebera said.

"It was a fabric that was commonly used for painting in the 19th century. But the fabric has an unusual weave. What's typically used for paintings is a plain weave, with one thread over and one thread under. This weave structure is more complicated. We don't know what it is yet."

When the painting is removed from its frame and examined in the museum conservation lab's clear, bright light, the weave pattern is visible to the naked eye. The nubby horizontal threads form a stripe pattern that pulls a viewer's gaze from left to right, mimicking the flow of the river in the background.

It's tempting to speculate that the decorative pattern embellished household linens on public display, such as a bedspread, tablecloth … or possibly, a napkin.

"We haven't determined that definitively," Sebera said, "but it's something we're considering."

An appraiser who examined the painting reached a similar conclusion about the landscape, whose value ranges somewhere between $22,000 and $100,000.

"The quick and loose brush strokes painted without definition or resolution gives weight to this theory," appraiser Ted Cooper wrote in a Nov. 12, 2012, report filed in the court case. "Artists often produced these 'souvenirs' of a specific time and place with ready materials at hand."

If Sebera is trying to piece together the painting's history from the raw materials, Rothkopf is chasing the paper trail.

The great Impressionist was in his late 30s and still single when he dashed off the tiny oil. He met the love of his life, the young blond dressmaker Aline Charigot, some time between 1879 and 1881.

Five and a half years after Renoir died, Rothkopf said, the Bernheim-Jeune gallery in Paris bought the landscape for 5,000 francs on June 30, 1925, from a woman identified only as "Madame Papillon."

Though no first name was used, it seems likely that the lady who made that sale in 1925 was Alphonsine Fournaise Papillon, a frequent model of Renoir's and the daughter of the man who ran the Maison Fournaise, a riverfront cafe and popular hangout spot in Chatou, France.

Papillon is the lively redhead in a straw hat leaning over a railing in Renoir's celebrated homage to summertime flirtations, "Luncheon of the Boating Party," which was painted in 1880 or 1881.

"We can feel pretty sure about the identities of most of the people in 'Luncheon of the Boating Party,'" said Eliza Rathbone, senior curator for the Phillips Collection, which owns the artwork.

"Two members of the Fournaise family — Alphonsine and her brother, Alphonse — are among the models." (He's the bearded man in a white T-shirt and straw hat.)

According to the British auction house, Sotheby's, which auctioned off another Renoir portrait of Papillon in 1995, Alphonsine was born in March 1846 and married Louis-Joseph Papillon at the age of 18. She first began posing for Renoir in 1875, and modeled for him often for six years.

Though she seems to have ended up with "Paysage," she may not have been the initial recipient.

Though Papillon is frequently mentioned as one of Renoir's important muses, and though Renoir had well-known mistresses, her name generally isn't coupled romantically with that of the painter.

"I'm stumped," Rothkopf said.

"I've been hoping that the gallery had a big dossier on who she was, but it was a dead end. She could have been a friend. She could have been anybody."

Rothkopf will try to track down the origin of two labels on the underside of the wooden frame. The first is a small white, clearly modern sticker the size of a postage stamp with printed numbers. The second is the ghost of an old label that either has fallen off or been removed. The part of the frame where that rectangle once was fixed is several shades lighter than the surrounding wood.

For Madame Papillon, the sale of the painting wasn't a life-changing windfall. In June 1925, $1 bought between 20 and 25 French francs. According to several online calculators, 5,000 French francs in 1925 was the equivalent of $200 to $250 in U.S. dollars in 1925 — or roughly $2,700 to $3,350 today.

But the French gallery would prove to be just a brief way station for this "Paysage."

Within a few months, the artwork was snapped up by the Baltimore heiress Saidie L. May and her husband, Herbert L. May, for $1,010, or approximately $13,605 in 2014 dollars — representing a nice profit for the gallery on a quick turnaround. The sale to the Mays took place on either Nov. 21, 1925, or Jan. 11, 1926; records conflict. The couple also bought a second painting from the gallery that day, Rothkopf said, a pointillist work by the Post-Impressionist master Georges Seurat.

The Renoir was lent to the museum in 1937 and was bequeathed to that institution, with the rest of May's estate, after the heiress died on May 28, 1951.

May had hoped that the grand building near North Charles Street with the Grecian portico would be the painting's final destination. Instead, it was in residence for just 14 years. According to a police report, the landscape was stolen sometime between 6 p.m. Nov. 16, 1951, and 1 p.m. Nov. 17, 1951, while on display in the exhibit, "From Ingres to Gauguin."

After Fuqua put the painting up for auction in 2012, she said that the Renoir had spent several months bumping around in the trunk of her car wrapped in a white garbage bag. For a time, she said, it was in an unheated shed on a table beneath a cracked window.

Some have challenged that account. But Sebera found nothing in the painting's physical condition to either verify or disprove the flea market tale.

"The painting is a little dusty," she said.

"There is a small area in the upper left corner where the fibers have been disrupted, but it doesn't go all the way through. Overall, the painting is in very good condition. We're looking forward to showing it to the public in late March."

mary.mccauley@baltsun.com