It might be only skin deep, but beauty does not fail to influence the value of a portrait.

Consider two mid-17th-century paintings of English ladies up for auction at the Sotheby’s Old Master sale today. The first, “Portrait of Elizabeth Capell, Countess of Carnarvon” by Sir Peter Lely, is the noted artist’s best attempt to make a homely young woman look attractive. Sotheby’s estimates it will sell between $100,000 and $150,000. “If she were beautiful, the painting would be worth a million dollars,” the co-chairman of Sotheby’s Old Master Paintings department, George Wachter, said.

The second painting, “Portrait of a Lady,” is the work of John Michael Wright, a much lesser artist than Lely, according to Mr. Wachter. It is estimated at between $50,000 and $70,000. “But because the lady in the portrait is pretty, the painting will probably sell for as much as the Lely,” he said.

These works are just two of the 142 lots on sale that the auction house predicts could post overall sales of as much as $11.9 million. “Old Masters is an area where you can still find bargains these days,” Mr. Wachter said.

He pointed to a portrait by Sir Joshua Reynolds that’s estimated to sell for between $100,000 and $150,000. The “Portrait of Charles Blair” is a sketch for a well-known painting hanging in the Metropolitan Museum of Art.

A private West Coast collector is the consignor of a large oil on canvas by Pietro Fabris. His “Villagers Preparing to Depart for the Festival of the Madonna Dell’Arco,” painted in 1773, could fetch anywhere between $300,000 and $400,000. “It’s a snapshot of typically local customs in Naples,” Mr. Wachter said. “We think it might have been painted for [England’s] Duke of Hamilton when he was traveling through Italy.”

One of the most beautiful faces among the Old Master portraiture belongs to the bust depicted in Lot 8, the “Head of a Young Woman, Turned to the Left,” with an estimate of between $20,000 and $30,000. The oval, oil-on-panel portrait measures only about 10 inches by 10 inches and lacks a frame. “It needs some restoration and would do well in a nice frame. There’s some speculation as to who painted it, but it’s undoubtedly from Caravaggio’s circle,” Mr. Wachter said.

There are times that ugly characters can have selling power as well. Take the Copenhagen artist Nikolaj-Abraham Abildgaard’s oil on canvas “A Scene from Danish Folklore, A Nis Eating His Porridge,” estimated at between $15,000 and $20,000.

A “nis” is a type of troll that Danes believe to be a benevolent houseguest if fed enough porridge. “It’s a strange, fun painting,” Mr. Wachter said.

An equally charming lot is Sir Henry Raeburn’s “Portrait of Mr. George Abercromby of Tullibody, Clackmannanshire,” an oil on canvas that could sell for between $15,000 and $20,000. The consignor is a private Philadelphia collector. Mr. Wachter said he wouldn’t be surprised if a Scottish collector buys the painting of the pensive Abercromby. “The Scots are obsessed with Raeburn,” he said.