Scientists may have solved the mystery behind the glass orb in “Salvator Mundi.”

A group of computer scientists may have solved the mystery behind the glass orb in Leonardo da Vinci’s Salvator Mundi (ca. 1500). Many experts have questioned why the orb in Christ’s left hand does not appear to magnify and invert the material behind it, as it should if it was a solid glass ball. The team of scientists at the University of California, Irvine, claims that this lack of distortion is caused by the fact that the glass orb depicted is hollow, not solid as previously thought.

Art historians have proposed several explanations as to why the orb Leonardo painted does not display the characteristics of a solid glass ball. Walter Isaacson argued that Leonardo deliberately depicted the orb inaccurately, though he also speculated the orb was hollow. Martin Kemp attributed the anomaly to small cavities found in some types of rock crystal and calcite, according to the UC Irvine team’s paper.

UC Irvine scientists Marco Liang, Michael T. Goodrich, and Shuang Zhao used imaging software to produce a digital, three-dimensional copy of Salvator Mundi, then studied how light would pass through various orb types. They hypothesized that the sphere Leonardo used as a model would have had a radius of 2.16 inches and a thickness of 0.05 inches. They also examined Leonardo’s research on light refraction.

“Our experiments show that an optically accurate rendering qualitatively matching that of the painting is indeed possible using materials, light sources, and scientific knowledge available to Leonardo da Vinci circa 1500,” the team wrote in its paper.

In the painting, five lines created by Christ’s folded robes pass behind the orb. Four of the lines converge at the center of the ball, showing no discontinuity or magnification, while the fifth fold is blurred, showing that the artist understood how a hollow sphere distorts straight lines.

Salvator Mundi became the most expensive artwork ever auctioned when it sold for $450 million at Christie’s in New York in 2017. The buyer was revealed to be Mohammed bin Salman, the crown prince of Saudi Arabia, though ownership was ultimately transferred to the Abu Dhabi Department of Culture and Tourism. The work’s current location remains unknown. It was excluded from the Louvre’s current blockbuster Leonardo show, and its unveiling at the Louvre Abu Dhabi has been postponed indefinitely.