The foundation offers a 320-page book to back up its claims that it is Leonardo’s, using painting to painting comparisons to justify its attribution.
Martin Kemp thinks differently. The professor emeritus at Oxford University has concluded that the the painting is most likely a copy that came after Leonardo’s was complete. The purported earlier version, called the “Isleworth Mona Lisa,” gives some clues to its late date. As he explains it:
“The Isleworth picture follows the final state of the Louvre painting. It does not therefore precede the Louvre painting.” The original Mona Lisa was changed into its final condition from a previous state; the Isleworth follows its altered and final state.
Secondly, he points out that forensics contradict the likelihood that it is a Leonardo original. “The images produced by infrared reflectography and X-ray are not at all characteristic [of] what lies below Leonardo’s autograph paintings,” said Kemp.
He says that The Mona Lisa Institute’s arguments rely on inconclusive evidence such as 16th century quotes to suggest there was a second portrait.
Alessandro Vezzosi, director of the Museo Ideale Leonardo da Vinci also doesn’t fully endorse their claims, but nor is he as dismissive as Kemp. “I believe it is more than possible that there existed two pieces of art,” he said, but nevertheless regards “The ‘Isleworth Mona Lisa’ [as] an important work of art deserving respect and strong consideration as well as scientific, historic, and artistic debate among specialists rather than a purely media interest.”