A key driver of the art market is the continual shift of value toward a previously overlooked or undervalued artist. Francis Bacon has led the way in the last year: A $10 million artist, he soon became a $30 million to $50 million artist, and now may potentially become a $70 million artist. That number will be hard to top. But already the market is gravitating toward another British artist who is rapidly gaining in prominence: Bridget Riley.

Sotheby’s has announced that it will be auctioning “Chant 2” (1967) in its London sales of Contemporary art on July 1. The painting will be exhibited here in New York from May 10 to 14. Estimated at between $4 million and $6 million, the sale is likely to be a dramatic new record for the artist. Her current top auction price is just less than $3 million, which was achieved in February in London when Christie’s sold “Static 2” (1966).

“Static 2” is a work of small black dots on a white background vaguely reminiscent of another high-profile British artist who does well with spot paintings, Damien Hirst. Sotheby’s clearly feels that Ms. Riley’s market, which has been growing steadily over the last two years, is due for a dramatic boost. Nine of the top 10 prices paid at auction for Ms. Riley’s work have been made since February 2006. Prices began to accelerate once she broke the million-dollar mark in February of 2007.

“An artist of her stature in this market should be much, much higher,” Sotheby’s head of Contemporary art, Francis Outred, said. “Works have been sold privately for more, but not much more, than the record.”

Ms. Riley is best known for her black-and-white paintings that cause the viewer to see optical effects. She gained prominence in the early 1960s for these works. Known as a meticulous and painstakingly thorough artist, Ms. Riley made a dramatic shift into color in 1967. “Chant 2” is her first work completely in color. It is also a dramatically large painting — more than 7 1/2 feet by 7 1/2 feet — an increase in scale from her previous work.

Ms. Riley’s artistic gamble was rewarded the next year at the Venice Biennale. There she won the International Prize for Painting for a show that included “Chant 2” and two other important color works. But despite the great fame she garnered in the 1960s, Ms. Riley and her work receded from the forefront of the art world.

Cautious and focused on her art, Ms. Riley continued to produce and sell work that explored her interest in pure abstraction and the interplay of form and color. In 1999, there was a show of her black-and-white paintings at London’s Serpentine Gallery. The next year, New York’s Dia Foundation launched another show of her work. In 2003, London’s Tate Gallery put on a major retrospective. Featured prominently in that show was “Chant 2.”

“The Tate retrospective cemented things in a way for her,” her dealer and the president of PaceWildenstein, Douglas Baxter, said. “It had such authority. It was really just a great, great show.”

These shows appeared in the context of a revived interest in Contemporary art in the U.K. Ms. Riley’s increased stature has increased demand for her work. But the breakthrough seems to have come from collectors seeing her as something other than the godmother of Op Art. “I think what has changed,” a Christie’s expert, Pilar Ordovas, said, “is collectors internationally seeing her and placing her alongside major minimalist works like Agnes Martin.” Her record-setting canvas bears a striking minimalist tone, as well as a price achieved not through competition between British buyers repatriating a national treasure but from bidding by American and European collectors.

To move to the next price level, however, may require more than just a pivotal work from the artist’s oeuvre. The big money comes when an artist begins to appeal to the emerging markets. Ms. Riley has an advantage in her subject matter. Abstraction has universal appeal and doesn’t run the risk of offending sensibilities in another culture. But so far, Ms. Riley hasn’t generated the interest of Russian, Gulf States, or Asian buyers.

It is unclear whether Mr. Outred believes it is simply the quality of “Chant 2” that justifies the estimate or that he has interest from buyers likely to establish a new record. But he remains confident that this picture will perform. Or, as he says in the press release for the painting: “I fully expect it to change the market for her work.”