Imagine being told the big old painting of a 19th-century tavern scene that's been in your family for more than six generations might be worth as much as half a million dollars. Most likely you'd have the same stunned reaction as the North Texas woman does when the first of three Dallas tapings of Antiques Roadshow airs Monday at 7 p.m. on KERA-TV (Channel 13).

The Dallas woman, who asked Roadshow not to reveal her identity, lugged the bulky 1847 oil that her great-great-great-grandfather bought to the Dallas Convention Center on a hot June Saturday last year and waited in line with about 5,000 other fans.

The big find in Dallas was The Illustrious Guest by American artist James Henry Beard. The painting depicts American statesman Henry Clay as a guest at a tavern. Appraiser Alan Fausel of Bonhams gives the painting an auction value of $300,000 to $500,000, which is a surprise to its Dallas owner.

In the series' first show of the 2009 season on Jan. 5, in Palm Springs, Calif., an art expert appraised the most valuable object to appear on Roadshow: a 1937 oil painting by noted American abstract expressionist Clyfford Still. It was received by its owner as a housewarming gift and was conservatively estimated to be worth $500,000.

The Illustrious Guest is extraordinary, says Fausel. "One, because it depicts Henry Clay, a very important person, and, two, it's a historical genre scene," a depiction of everyday life.

Fausel adds that Beard's work, "a lot of little dog paintings," do not command anywhere near The Illustrious Guest's appraised value. "We were stunned," he says, referring to his fellow appraiser Debra Force, a New York specialist in American paintings.

At least one additional work by Beard resides in Texas. Among the State Capitol's important works of art is a silk banner thought to be the only Texas battle flag carried at the Battle of San Jacinto on April 21, 1836.

In addition to Monday's Antiques Roadshow, the episodes on Feb. 2 and Feb. 9 also feature footage taped in Dallas last summer.

On Feb. 9, the owner of an elaborate rocking chair that once belonged to P.T. Barnum will seem familiar to many. Ronnie Claire Edwards played the role of Corabeth Godsey on the TV show The Waltons, from 1974 to 1981; she explains how she came to own Barnum's rocker. Jim Castleberry, also of Dallas, is delighted with his framed Cleveland bicycle poster, which was appraised at between $4,000 and $6,000.

On Feb. 2, Kenneth Johnson of Dallas is featured with his miniature portrait painting of a British abolitionist, appraised at $3,000 to $5,000.

As usual, Roadshow takes viewers on road trips to see interesting collections. Host Mark L. Walberg visits with Gary Busk of Carrollton about his more than 1,000 puppets. The Dallas Museum of Art's silver collection also is highlighted.

The Dallas episodes of Antiques Roadshow will be rebroadcast at 1 p.m. on the Saturdays following their initial showing.