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
It has for a long time been argued that after Leonardo's death the painting was cut down by having part of the panel at both sides removed. Early copies depict columns on both sides of the figure. Only the edges of the bases can be seen in the original. However, some art historians, such as Martin Kemp, now argue that the painting has not been altered, and that the columns depicted in the copies were added by the copyists. The latter view was bolstered during 2004 and 2005 when an international team of 39 specialists undertook the most thorough scientific examination of the "Mona Lisa" yet undertaken. Beneath the frame (the current one was fitted to the "Mona Lisa" in 2004) there was discovered a "reserve" around all four edges of the panel. A reserve is an area of bare wood surrounding the gessoed and painted portion of the panel. That this is a genuine reserve, and not the result of removal of the gesso or paint, is demonstrated by a raised edge still existing around the gesso, the result of build up from the edge of brush strokes at the edge of the gesso area.