The latest biography of Leonardo da Vinci has raised "a puzzling anomaly" in a rediscovered painting that is estimated to fetch $100m at auction next month.
The Salvator Mundi (Saviour of the World) portrays Jesus gesturing in blessing with his right hand while holding a crystal orb in his left hand.
Declared authentic only six years ago, it's to be marketed on 15 November by Christie's New York, which explains it as "among fewer than 20 famous paintings by Leonardo, and also the only one in private hands".
But in a forthcoming research, Leonardo da Vinci: the Biography, Walter Isaacson questions why an artistic genius, scientist, inventor, and scientist revealed an "unusual lapse or unwillingness" to connect art and science in depicting the orb.
He writes: "In 1 respect, it's rendered with amazing scientific precision ... However, Leonardo neglected to paint the distortion which would occur when searching through a solid clear orb at things that aren't touching the orb.
"Strong crystal or glass, whether shaped like an orb or a lens, generates magnified, inverted, and reversed images. Instead, Leonardo painted the orb as though it were a hollow glass bubble that does not refract or distort the light passing through it."
He argues that when Leonardo had accurately depicted the distortions, the hands touching the orb could have stayed the way but peeking inside the orb are a diminished and inverted mirror image of the robes of Christ and arm.
It is all the more vexing, he notes, as Leonardo was in the time "deep into his optics research, and the way light reflects and refracts an obsession."
He filled his notebooks with diagrams of light bouncing around at several angles, he says, wondering whether Leonardo "chose not to paint it this way, simply because he believed it'd be a diversion ... or since he had been subtly attempting to impart a miraculous quality to Christ and his orb".
Some of the world's foremost specialists supported the Leonardo attribution in 2011 when Luke Syson contained the painting into his Leonardo exhibition.
But major scholars have doubts. Frank Zöllner, of the University of Leipzig, wrote in an art journal in 2013 that the painting could be a "high-quality merchandise of Leonardo's workshop" or even a later follower.
Isaacson is very interested in a study from Michael Daley, the director of ArtWatch UK, who said this week: "There is not enough to claim it's a Leonardo. His figural advancement was towards higher naturalism and complexity of posture -- heads turning such a manner, shoulders turning another way, with spins and movement.
"The Salvator Mundi is dead-pan look, like an icon, with no real depth in the modeling. Another unexplained peculiarity is that the figure itself is heavily and uncharacteristically cropped."
Daley also pointed out that the optical deflections appear within an engraving by Wenceslaus Hollar, the 17th-century etcher, from Leonardo's first article, dismissing the suggestion that "Leonardo knew all about the optics, but just decided not to bother."
Isaacson stated: "If you balance the evidence for and against ... then that's a valid purpose, which Hollar wouldn't have distorted the robes if they had not been at the first painting ... If you have a look at the Hollar engraving and, even if it's much different, that counts against [this painting] being original."
He spoke to science specialists in studying optics. Asked whether he would put money into the painting if he had $100m, '' Isaacson explained: "The preponderance of the experts is that it's authentic, and so I would -- but that does not mean that I would be sure."
A Christie's spokeswoman said: "Leonardo's paintings have been known for their mystery and ambiguity. He was familiar with the technicality and attributes of light and astronomy. If the picture had been recreated by him with optical exactitude, the background could have been twisted.
"It's our opinion that he chose not to portray it in this way as it would be too distracting to the subject of the painting."
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