By Stephanie Pappas
The likely Leonardo da Vinci
painting "Salvator Mundi" looks straightforward at first glance: a
depiction of Jesus Christ in Renaissance-era clothing, raising one hand in
blessing and holding a clear orb in the other.
But that orb defies the laws of
optics, creating a controversy over just what da Vinci was using as his
inspiration. Now, a new study argues that the orb may be a realistic depiction
of a hollow glass ball.
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The work has not yet been
published in a peer-reviewed journal, but a preprint of the findings is posted
on the preprint site arXiv. University of California, Irvine, researchers used
a computer-rendering technique to show that the appearance of the orb would
have been physically possible in the real world, if the orb were made of thin
blown glass.
But the paper is unlikely to
settle the long-running debate over da Vinci’s intentions.
"The paper of the sphere is
just one of many examples of scientists making ill-judged interventions in
Leonardo studies based on ignorance of the sources," da Vinci scholar
Martin Kemp, an emeritus professor of the history of art at the University of
Oxford's Trinity College, wrote in an email to Live Science.
The "Salvator Mundi" is
a painting with a dramatic past. It probably dates to around 1500 and was
acquired by Charles I of England at some point in the 1600s. Charles I was
executed in 1659 after a civil war, and in 1651 a mason named John Stone
purchased the painting. In 1660, he returned the artwork to Charles II, the son
of Charles I who retook the throne that year. The trail of the painting then
goes cold until 1900, when it was resold not as an original da Vinci, but as
the work of one of the master’s students.
It wasn’t until 2011 — after
professional conservators got ahold of the painting and repaired sloppy
conservation work that had built up over the years — that art experts
reassessed the "Salvator Mundi" and realized that it was likely
painted by da Vinci himself. In 2017, a Saudi prince bought the painting at
auction for a record-breaking $450 million.
Embedded within the painting is a
persistent mystery. The orb held by Christ contains a few painted sparkles that
look like inclusions within a solid sphere or crystal. But a solid orb would
magnify and invert the image of anything behind it due to the refraction of
light, and the orb in the painting doesn't do that. Christ's robes appear
undistorted behind the glass.
Da Vinci was an avid student of
optics and likely wouldn't have made that mistake carelessly. Art historians
have been arguing for decades about what the orb was made of and whether Da
Vinci deliberately painted it inaccurately. The new paper brings a method
called physically based rendering to the question. UC Irvine computer scientist
professors Michael Goodrich, Shuang Zhao and doctoral student Marco (Zhanhang)
Liang used this method to simulate light in the scene that is depicted in the
painting.
They found that a combination of
dim environmental light, a strong light source from overhead and a hollow blown
glass sphere could re-create the scene in the "Salvator Mundi." The
glass could have had walls up to 0.05 inches (1.3 millimeters) thick without
creating any refraction disrupting the lines of Christ's robes behind it, the
researchers wrote in their paper posted on arXiv. (A hollow orb wouldn’t create
the same magnify-and-flip effect as a solid orb.)
Liang and his colleagues declined
to comment on their work, which Liang said is now under review at a scientific
journal. Kemp was not convinced by the study, however. In a section of his new
book, "Leonardo's Salvator Mundi and the Collecting of Leonardo in the
Stuart Courts" (Oxford University Press, 2020), Kemp traces the context of
the orb from entries in da Vinci’s journals, finding that the artist had a
fascination with rock crystals and their optics at the time the "Salvator
Mundi" was painted. He also lists examples of paintings in which da Vinci
tweaked the laws of physics and light to create a more pleasing composition. In
paintings of the baptism of Christ, for example, the painter and his
contemporaries skipped depicting the refraction of light in water that would
have made the figures' legs look skewed. Da Vinci also painted baby Jesus as
unnaturally large, an artistic way to highlight the Christ child's divinity.
"His paintings were not raw
demonstrations of optical science, any more than they were stark demonstrations
of anatomy," Kemp wrote. In other words, da Vinci was known to use
artistic license in his works, and likely did so with the orb in "Salvator
Mundi."
Leonardo "is not making a
'photographic image,'" Kemp told Live Science. "If he was, all his
'Christ childs' would be the progeny of giants! He is using his knowledge of
natural laws to give conviction to devotional paintings."