Frame
Why were the beech crosspieces switched to maple in 1970?
Mona Lisa
Because the "Mona Lisa"'s poplar support expands and contracts with changes in humidity, the picture has experienced some warping. In response to warping and swelling experienced during its storage during World War II, and to prepare the picture for an exhibit to honor the anniversary of Leonardo's 500th birthday, the "Mona Lisa" was fitted in 1951 with a flexible oak frame with beech crosspieces. This flexible frame, which is used in addition to the decorative frame described below, exerts pressure on the panel to keep it from warping further. In 1970, the beech crosspieces were switched to maple after it was found that the beechwood had been infested with insects. In 2004–2005, a conservation and study team replaced the maple crosspieces with sycamore ones, and an additional metal crosspiece was added for scientific measurement of the panel's warp. The "Mona Lisa" has had many different decorative frames in its history, owing to changes in taste over the centuries. In 1909, the Comtesse de Béhague gave the portrait its current frame, a Renaissance-era work consistent with the historical period of the "Mona Lisa". The edges of the painting have been trimmed at least once in its history to fit the picture into various frames, but no part of the original paint layer has been trimmed.