Warhol's brother to sell Campbell's soup can painting for £1m

It is the ordinary snack that turned him into the high priest of pop art. Now Andy Warhol's first painting of a Campbell's soup can is expected to fetch up to £1m when it is sold by the family of his chicken-farming brother, Paul Warhola.

Warhol, who dropped the "a" from his Slovakian surname when he moved to New York from his home town of Pittsburgh, painted Campbell's Soup Can (Pepper Pot) in 1961 and gave it to Paul to celebrate the birth of his son, Marty.

Over the years, each of Paul's seven children took the 20in by 15in canvas to school to show off the talents of their uncle, who rightly predicted that it would "one day be worth millions". Only one other similar-sized Warhol painting of a Campbell's soup can exists. But it is unfinished and belongs to the Warhol Museum in Pittsburgh, making the picture being auctioned at Christie's in New York on 13 November the only one ever likely to be offered for sale.

The iconic painting, which has never been out of the hands of the Warhola family, is believed to have been the inspiration behind Warhol's famous silkscreen "multiples", images of everyday objects such as soup cans and Coke bottles that he printed in different colours. Larger versions now fetch six-figure sums.

But when he painted that first humble tin of soup he had yet to employ the silkscreen process now so closely linked with his work. Instead, he drew the picture by hand from a magazine photograph, labouring for hours to mimic the can's machine-printed precision.

Determined to leave as little trace of brushwork as possible, Warhol, who began his career designing advertisements for women's shoes, meticulously added the bold hues of red, white and yellow on the soup can and used hand-carved stamps to create the small fleur-de-lis decoration.

A Christie's spokeswoman said yesterday: "No image is more American than the Campbell's soup can. It has remained essentially the same in its design since the early 1900s and has been a staple of American pantries for just as long. Warhol's serial images perfectly reflect the consumer-driven society and this painting is one of the earliest examples of his master subject."

Warhol – who survived being shot in 1968 by the fanatical Valerie Solanas, who had once worked at the Factory, his celebrated New York studio – died in 1987 after suffering complications from a gall bladder operation. He was 60.