Samuel Aranda for The New York Times
UNTIL recently, the Prado’s copy of the Mona Lisa — one of dozens made over the centuries — was not much of a draw. Then, Ana González Mozo took an interest.
Over the last two years, Ms. González, a researcher in the museum’s technical documentation department, has used all manner of modern-day techniques — X-rays, infrared reflectography and high-resolution digital images, among others — to make, and then document, an unlikely finding.
It turns out that the Prado’s Mona Lisa is not just any 500-year-old copy. It was most likely painted by someone who was sitting right next to Leonardo da Vinci, trying to duplicate his every brush stroke, as he produced his famous lady with the enigmatic smile.
When Leonardo adjusted the size of the Mona Lisa’s head or corrected her hands or slimmed her bosom or lowered her bodice, so did whoever was painting the Prado’s Mona Lisa.
“It had to be painted at the same time,” Ms. González said. “Someone who copies doesn’t make corrections because they haven’t ever seen the changes. They can see only the surface of the painting.”