An original Rodin sculpture by Auguste Rodin, a French sculptor of the 19th century. (Astrid Riecken/For The Washington Post)

Elizabeth Tillson remembers little about the green sculpture in her childhood home in Potomac beyond how “creepy” it was. The bronze cast of a woman crossing her legs was “naked and kind of freaked me out,” said the Obama administration IT manager, who also recalls that it sat outside her mother’s study next to the cage holding Max, the family’s pet gerbil.

But Tillson, 55, and her two siblings had no clue who made the sculpture or why they had it in the first place.

Now, after years of dismissing the piece, Tillson and her siblings are selling the sculpture on Saturday at Quinn’s Auction Galleries in Falls Church, with the hope that the winning bid could be as high as $200,000. Why so much? The family just learned that the sculpture that once lived next to the gerbil is a genuine Rodin.

As in Auguste Rodin, the renowned French sculptor who lived from 1840 to 1917, the creator of “The Thinker,” and the artist whose oeuvre fills out entire museums in Paris and Philadelphia, as well as one owned by Mexican billionaire Carlos Slim. Measuring nearly 14 inches tall and set on a stone block, Tillson’s Rodin is one of several versions of “Despair.” And this spring, her family’s “Despair” was authenticated as a piece made by the artist during his lifetime by the Comité Auguste Rodin, a Paris organization preparing a comprehensive catalogue of his sculptures.

The sculpture’s validation surprised Tillson and her siblings, who figured that, since they never asked their parents about the item’s provenance, authentication was a long shot. Family lore has it that their grandfather, the late George Henry Howard, who lived on Park Avenue in New York and served as the president of a large utility holding company, somehow acquired the Rodin before dying in 1960.

They never asked their parents how it came into the family’s possession. Their mother, Elizabeth Mathiasen, a social worker who did a stint at the CIA in the agency’s earliest years, died in 2007; their father, Karl Mathiasen, who co-founded an organization that provides management counseling to non-profit groups, has dementia and can’t provide an answer.

“The piece was never spoken about in the family,” said Tillson, a branch chief in the executive office of the president.

“It was like a piece of furniture,” said her brother, Timothy Mathiasen, 56, the vice president of development for the Princeton HealthCare System Foundation in New Jersey.

“There’s so many things we wish we asked our parents before they got older,” said their sister, Annie Farquhar, 52, the admissions and financial aid director of the Maret School in Northwest Washington. “They were very low-key and very generous in thinking of others. But none of that stuff” — the Rodin and other family art — “was important to her.”

Last year, as Tillson was moving her father into a nursing home, the prestigious auction house Doyle New York told the family it would sell the statue in its September 2013 sale with an estimate of $1,500 to $2,500. The reason for the low value, the auction house said, was that the Musée Rodin in Paris could not authenticate the piece.

The Musée Rodin’s problems: The family’s Rodin bears no mark from the foundry that cast the sculpture; it has no precise provenance; the museum didn’t have records of their “Despair” in its archives; and it only saw one “A. Rodin” signature on the sculpture’s exterior, not a second one that often exists elsewhere on real Rodins.

The grandchildren decided to seek a second opinion and took the sculpture to the auction house in Falls Church.

Matthew Quinn decided that what the Rodin needed was a gentle beating.

Quinn, who helps run his family’s Quinn’s Auction Galleries, wanted to see what was underneath the sculpture, and needed to remove its stone foundation. The 38-year-old, who also moonlights as an appraiser for the PBS hit “Antiques Roadshow,” was searching for anything to help authenticate the Rodin.

Maybe on the bottom Quinn would find the insignia of Rodin’s favored foundry, Alexis Rudier Fondeur Paris? Wielding a rubber mallet and a block of wood, Quinn knocked away the plaster around the bolt that had locked the sculpture into the stone. After the bolt was loosened, he removed the stone base from the sculpture, and scanned its bottom.

He was surprised by what he saw: the raised signature of A. Rodin.

“I was like, ‘That helps!’ ” Quinn said. “I did more research and saw that many Rodins had the raised A. Rodin on the underside of the real ones.”

But Quinn still needed an outside organization’s approval. Instead of seeking out the Musée Rodin as Doyle New York had done, Quinn instead made an appointment to see Jérôme Le Blay, who heads the Comité Auguste Rodin.

So, in late April, Quinn wrapped the Rodin in a flannel sheet, placed it on the back seat of his Nissan SUV and drove from Virginia to the Mercer Hotel in New York, where he unveiled the object to Le Blay, visiting from France.

Le Blay, who has seen 8,000 of Rodin’s works in the past 15 years, looked at the Rodin and gave his answer quickly.

“Within 15 seconds,” Quinn said.

That’s how much time Le Blay needed to know the sculpture was made by Rodin and cast during his lifetime. (Many of Rodin’s sculptures have been cast after his death, with his authorization, but they are generally deemed less valuable.)

In an interview, Le Blay said the raised signature found on the sculpture’s bottom was Rodin’s way to protect against forgeries. The signature is “quite technically difficult” to make during the casting process, and the calligraphy and shape of the letters is “typical” from the period of Rodin’s work around 1910, Le Blay said.

The sculpture’s green emerald patina also matches many of Rodin’s early bronzes, and the stone base was something Rodin commonly used in the early 1900s.

The only thing that frustrated Le Blay, he said, is that he wishes Tillson and her siblings knew how their family acquired the piece. “I don’t think I will be able to find quickly the connection between Rodin and George Howard,” Le Blay said. “I am dealing with this problem every day. Most of the time, you don’t have papers or invoices. They get lost.”

This week, someone from New Jersey placed a bid with Quinn’s above the $30,000 minimum. And seven others — two from London, two from New York and three from the Washington region — have registered to bid by phone. Tillson, who will attend the sale, said she and her two siblings will probably split the money from the sale.

But she hasn’t decided what she’ll do with her share. No more Rodins or scary-looking art, she said. The IT manager is more practical.

“At 55, I would likely put half toward retirement and half toward a trip with my family,” she said, “although I do dream about a convertible, as my car has 140,000 miles on it.”