<P> 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 . </P> <P> In 1977, a new insect infestation was discovered in the back of the panel as a result of crosspieces installed to keep the painting from warping . This was treated on the spot with carbon tetrachloride, and later with an ethylene oxide treatment . In 1985, the spot was again treated with carbon tetrachloride as a preventive measure . </P> <P> On 6 April 2005--following a period of curatorial maintenance, recording, and analysis--the painting was moved to a new location within the museum's Salle des États . It is displayed in a purpose - built, climate - controlled enclosure behind bulletproof glass . Since 2005 the painting has been illuminated by an LED lamp, and in 2013 a new 20 watt LED lamp was installed, specially designed for this painting . The lamp has a colour rendering index up to 98, and minimizes infrared and ultraviolet radiation which could otherwise degrade the painting . The renovation of the gallery where the painting now resides was financed by the Japanese broadcaster Nippon Television . About 6 million people view the painting at the Louvre each year . </P> <P> Today the Mona Lisa is considered the most famous painting in the world, but until the 20th century it was simply one among many highly regarded artworks . Once part of King Francis I of France's collection, the Mona Lisa was among the very first artworks to be exhibited in Louvre, which became a national museum after the French Revolution . From the 19th century Leonardo began to be revered as a genius and the painting's popularity grew from the mid-19th century when French intelligentsia developed a theme that it was somehow mysterious and a representation of the femme fatal . The Baedeker guide in 1878 called it "the most celebrated work of Leonardo in the Louvre", but the painting was known more by the intelligentsia than the general public . </P>

Location of the mona lisa in the louvre