When Beth Feeback bought two large paintings at $9.99 each from a Goodwill store in North Carolina, the artist intended to paint over them. It’s a good thing she didn’t.

One of the paintings turned out to be the work “Vertical Diamond” by notable 20th century artist Ilya Bolotowsky, and Sotheby’s, the world-famous auction house, has valued it at between $15,000 and $20,000.

Sotheby’s will auction the painting Sept. 21, Feeback said Monday.

Feeback, 45, described the series of events that led her to the painting. She and her husband had gone to display their own artwork April 28 at an art fair in Oak Ridge, N.C. The day was chilly and Feeback hadn’t dressed for the weather. She remembered having passed a Goodwill store on the way to the fair, so she asked her husband, Steve, to watch their things so she could go to the store to find a blanket or afghan to cover up.

She quickly found a throw and a pair of gloves. Then she spotted two large paintings done in red, white and blue.

“I thought they would be awesome canvases. They were $9.99 a piece and I just thought they would be great to just draw on them and paint over them because I didn’t like them as paintings. They were really ‘70s kind of looking, but not ‘70s in that fun, kitschy way, ‘70s in a different way that I don’t really enjoy, so I was like, ‘I’m going to paint big cat heads or whatever,’” Feeback, who specializes in pet portraits, said. “I was going to paint on them and so I bought them.”

She showed them to a friend at the art fair, and her friend spotted labels on the backs of the canvases that read: “Weatherspoon Art Gallery. University of North Carolina – Greensboro.” Her friend told her to find out more about the paintings before she painted them over.

Feeback took the canvases home and they languished in her art studio until mid-June. She nearly painted over them a few times.

“But I decided, you know, I’ll check, I’ll Google these guys. The first one I Google was Bolotowsky. And I Google it and the first thing I saw was the Wikipedia page and I was like, ‘Holy crap. I better get those up off the floor over there,’” she recalled. “And then it just went crazy. When I saw what it was I thought, ‘This painting has got to be worth something, but what do I do now? I don’t know anything about selling a valuable painting.’  We made $200 at the art show that day.”

Bolotowsky was an abstract painter who fled his native Russian and settled in Brooklyn in 1923.  He died in 1981.

On the advice of friends, she contacted Sotheby’s in New York, sending pictures of the painting and the labels on the front and back. They got back to her with the news, and asked her to send them the painting.

She and her husband shipped the Bolotowsky canvas via UPS, insuring it for $20,000, she said.

Feeback said she came close to never having even seen the paintings. The previous owners were a married couple who had bought the paintings at a textile company’s liquidation sale and they planned to put them in the basement of their home, but the canvases were simply too large.