09/30/2011 02:23 am ET Updated Nov 29, 2011

Mysterious Portrait May Be Long Lost Da Vinci

In 1998, a vellum-sheet portrait sold for £11,400 at Christie's. Today, the bidder who bailed at £11,399 is kicking himself. This painting, thought at the time to be a 19th-century pastiche by a German unknown, is now being accredited to one of the great masters of all time, Leonardo Da Vinci. (How much does a long-lost masterpiece go for these days? The Guardian reckons about £100 million.)

Art historian Martin Kemp is the main proponent of the painting's authenticity. The investigation began when Kemp identified the unknown woman in the portrait as "Bianca Sforza, the daughter of Leonardo's patron Ludovico Sforza, Duke of Milan (1452-1508), and his mistress Bernardina de Corradis." He discussed his findings in the book 'La Bella Principessa: The Story of the New Masterpiece by Leonardo Da Vinci.' A key facet of the unfolding mystery was the left margin of the work, which had three holes in it, as if bound in a book.

His suspicions were confirmed when Kemp identified a likely source of the portrait, in a volume of portraits created for the marriage of Bianca Sforza and the duke's commander, Galeazzo Sanseverino, in 1496. The book, now found in the Warsaw National Gallery, appears to have been a wedding gift. Kemp is aware of the astoundingly low odds of ever finding the Bella Principessa page's match. The hunt was basically a wild goose chase for a 500 year old book with a page missing; even if it survived it was unlikely to be found. Kemp recalls the moment when he opened the lucky volume: "Yes, lo and behold, we could identify that there was a page clearly removed. The stitch-holes matched, the vellum matched. It is indeed 1496, it is indeed Bianca and indeed for her marriage. It's uncanny." After such a discovery Kemp was convinced. "Assertions that it is a forgery, a pastiche, or a copy of a lost Leonardo are all effectively eliminated," he said.

Another clue to the mystery is a fingerprint found on the vellum, which Peter Biro, a "forensic art expert," matched to a Leonardo fingerprint on the Vatican. However, this matter has been complicated since Biro received a "scathing profile in The New Yorker magazine questioning the validity of Biro's fingerprint-identification methods for authenticating artworks," including a Jackson Pollock print.

The main opponents of the Leonardo theory are New York experts, many of whom identified it as a German piece when Christie's was appraising it in 2007. One gallery director privately dubbed it a "screaming 20th-century fake". Others are skeptical because there are no other examples of Leonardo working with vellum sheets.

A final mystery presents itself with the question: if the work was made in Italy and sold at Christie's in a German frame, where did the original frame go? Kemp believes "Christie's removed it and put it in a German frame. The Italian frame has disappeared." Christie's refused to comment on the frame.

A mystery that leads back 500 years, the case of La Bella Principessa is sure to continue to spark debate. Maybe that's worth more than £100 million, and maybe not.