Mona Lisa replicas and reinterpretations
After restoration, the Prado's "Mona Lisa" revealed details covered by previous restorations and layers of varnish.
Furnishings and fabrics were enhanced, as well as landscape and facial features.
It is anticipated that such revelations may offer further insight into Leonardo's original.
Experts at the Louvre reportedly supported the Prado museum's findings.
The Prado replica was subsequently transported to the Louvre in 2012 to be displayed next to "Mona Lisa" as part of a temporary exhibition.
Two nude paintings bearing similarities to Leonardo da Vinci's original were part of a 2009 exhibition of artwork inspired by "Mona Lisa".
Displayed at the Museo Ideale in Leonardo's hometown of Vinci, near Florence, some believe one of the paintings – dating from Leonardo's time – to be the work of Leonardo himself, and it has at times been credited to him.
Other experts theorize the painting, one of at least six known to exist, may be just another copy painted by "followers" of Leonardo.
Scholarly dispute persists as to artist, subject and origin.
The nude in question, discovered behind a wall in a private library, reportedly belonged to an uncle of Napoleon Bonaparte, who owned another of Leonardo's paintings.
Facial features bear only vague resemblance, but landscape, compositional and technical details correspond to those of the "Mona Lisa" known worldwide today.
Speculations about Mona Lisa
In December 2010, Italian art historian Silvano Vinceti reported that the Mona Lisa appears to have tiny letters and numbers in her eyes which are only apparent when viewed with a magnifying glass and shortly afterwards said that the model was Leonardo's male apprentice Gian Giacomo Caprotti (known as Salaì) and that the letters were clues to his identity. The Louvre, pointing out that he had had no access to the actual painting, said that after "every laboratory test possible" in 2004 and 2009 that "no inscriptions, letters or numbers, were discovered during the tests." and that "The ageing of the painting on wood has caused a great number of cracks to appear in the paint, which have caused a number of shapes to appear that have often been subject to over-interpretation".