Mona Lisa
Leonardo da Vinci is thought by some to have begun painting the "Mona Lisa" in 1503 or 1504 in Florence, Italy. Although the Louvre states that it was "doubtless painted between 1503 and 1506", the art historian Martin Kemp says there are some difficulties in confirming the actual dates with certainty. In addition, many Leonardo experts, such as Carlo Pedretti and Alessandro Vezzosi, are of the opinion that the painting is characteristic of Leonardo's style in the final years of his life, post-1513. Other academics argue that, given the historical documentation, Leonardo would have painted the work from 1513. According to Leonardo's contemporary, Giorgio Vasari, "after he had lingered over it four years, [he] left it unfinished". Leonardo, later in his life, is said to have regretted "never having completed a single work".
Circa 1504, Raphael executed a pen and ink sketch, today in the Louvre museum, in which the subject is flanked by large columns. Experts universally agree it is based on Leonardo's portrait of "Mona Lisa". Other later copies of the "Mona Lisa", such as those in the National Museum of Art, Architecture and Design in Oslo and The Walters Art Museum in Baltimore, also display large flanking columns. As a result, it was originally thought that the "Mona Lisa" in the Louvre had side columns and had been cut. However, as early as 1993, Zöllner observed that the painting surface had never been trimmed. This was confirmed through a series of tests conducted in 2004. In view of this, Vincent Delieuvin, curator of 16th-century Italian painting at the Louvre museum states that the sketch and these other copies must have been inspired by another version, while Frank Zöllner states that the sketch brings up the possibility that Leonardo executed another work on the subject of Mona Lisa.
Mona Lisa
The first and most extensive recorded cleaning, revarnishing, and touch-up of the "Mona Lisa" was an 1809 wash and revarnishing undertaken by Jean-Marie Hooghstoel, who was responsible for restoration of paintings for the galleries of the Musée Napoléon. The work involved cleaning with spirits, touch-up of colour, and revarnishing the painting. In 1906, Louvre restorer Eugène Denizard performed watercolour retouches on areas of the paint layer disturbed by the crack in the panel. Denizard also retouched the edges of the picture with varnish, to mask areas that had been covered initially by an older frame. In 1913, when the painting was recovered after its theft, Denizard was again called upon to work on the "Mona Lisa". Denizard was directed to clean the picture without solvent, and to lightly touch up several scratches to the painting with watercolour. In 1952, the varnish layer over the background in the painting was evened out. After the second 1956 attack, restorer Jean-Gabriel Goulinat was directed to touch up the damage to "Mona Lisa"s left elbow with watercolour.