How Do Experts Authenticate Art?

Leonardo da Vinci just became even more prolific. An analysis released in the U.K.-based Antiques Trade Gazette claims a small portrait once attributed to a 19th century German artist was actually painted by the Italian master around the year 1500. The surprising revelation is but the latest in a series of cases in which "lost" pieces of artwork were rediscovered through art authentication. But how can experts — who have previously certified works by Caravaggio, Raphael, Van Gogh and countless others — be so sure that a specific painter is responsible for a work of art?

In the case of the da Vinci painting, the authentication was based on physical evidence. Using a high-resolution multispectral camera capable of analyzing the painting on a precise level without touching it, a Canadian forensic-art expert named Peter Paul Biro was able to identify a faint fingerprint left on the canvas. The print was then matched to one on a known da Vinci painting hanging in Vatican City. Carbon dating of the newer canvas matched the painting to da Vinci's period, and an analysis of the style concluded the painter was left-handed, another purported da Vinci trait. Taken together, the clues built a convincing argument for the painting's authenticity.

Absent compelling forensic evidence like a fingerprint, the authentication process becomes a bit murkier. In the past, pieces of art have been certified through a combination of factors, including brushstroke patterns, analysis of the artist's signature, dating of the pigments or canvas used or even the instinctive (but subjective) opinion of academics who have extensively studied an artist's portfolio. A painting's provenance, or its history of ownership, is also important. Being able to trace a portrait back from owner to owner over the course of centuries is no small feat, and it often lends significant weight to a work's legitimacy.

One recent high-profile case that has highlighted the difficulties in authenticating a piece of art is a disputed Jackson Pollock painting, purchased for $5 in 1992 by ex-trucker Teri Horton in a California thrift store. Biro was also involved in that investigation. He matched a partial fingerprint on the canvas to one on a paint can used by Pollock and paint on the canvas to samples from Pollock's studio. Still, despite the forensic evidence, the art community has been reluctant to certify the work. There is no record of the painting's former ownership, and examinations by experts including a former director of New York City's Metropolitan Museum of Art have deemed it inconsistent with Pollock's style. Despite the skepticism, Horton fielded a $5 million offer for the painting (which she declined) and starred in a 2006 documentary about her find, Who the #$&% Is Jackson Pollock?

Cases like these underline the fact that art authentication is a high-stakes game. Da Vinci's portrait has been renamed La Bella Principessa, and its estimated value has been adjusted to about $160 million — a price tag that could result in an unimaginable profit for Peter Silverman, the painting's owner, who acquired it for about $19,000 in 2007.