LONDON.- Thirty years ago, artist Jean-Michel Basquiat secretly signed one of his paintings in invisible ink, says Sotheby's auction house, which discovered the hidden autograph as it was preparing the painting for sale.

Sotheby's experts uncovered the secret this month as they were examining "Orange Sports Figure," which goes on sale Wednesday. The vibrant image of an abstract crowned figure is estimated to be worth between 3 million pounds and 4 million pounds ($4.7 million and $6.3 million).

Basquiat, a graffiti artist who became a 1980s art star, signed relatively few of his canvasses. But Sotheby's said ultraviolet light revealed the artist's name and the date 1982 beneath the work's layers of acrylic and spray paint.

"The signature just popped out," Cheyenne Westphal, head of contemporary art at Sotheby's Europe, said Tuesday.

She said staff were initially "surprised, astonished and puzzled" by the signature, which appears to have been written in the type of pen used to mark banknotes.

"Nobody else probably ever knew about this invisible inscription, and the prospect that he might have left other invisible writings on his canvasses that are only visible under ultraviolet light is very exciting," she said.

Westphal said she knew of no other invisible signature on a Basquiat work.

Basquiat's paintings are often covered in words and doodles. He signed some paintings with a crown, others with his graffiti alter ego SAMO — but relatively few with his full name.

The son of a Haitian father and Puerto Rican mother, Brooklyn-raised Basquiat developed a vibrant style influenced by Picasso and the Abstract Expressionists as well as by the work of street graffiti artists.

His works celebrate icons of black culture, from athletes like Muhammad Ali and Hank Aaron to musicians like Miles Davis and Charlie Parker, and often allude to the legacy of slavery and colonialism.

Basquiat's reputation has soared since his death from a drug overdose in 1988 at the age of 27. "Untitled" sold for $14.6 million at Sotheby's in 2007, and "Untitled (Boxer)" sold for $13.5 million in New York in 2008.

"Orange Sports Figure" is part of Sotheby's contemporary art sale in London on Wednesday.

Westphal said the auction house had not revised the work's estimated sale price in light of the discovery.


Copyright 2012 The Associated Press.