Isleworth Mona Lisa
According to Leonardo's early biographer Giorgio Vasari, Leonardo had started to paint "Mona Lisa" in 1503, but "left it unfinished". However, a fully finished painting of a "certain Florentine lady" surfaced again in 1517, shortly before Leonardo's death and in his private possession. The latter painting almost certainly is the one that now hangs in the Louvre. Based on this contradiction, supporters of the authenticity of the "Isleworth Mona Lisa" claim it is the unfinished "Mona Lisa", made at least partially by Leonardo, and the Louvre "Mona Lisa" a later version of it, made by Leonardo for his own use.
Mona Lisa
At some point, the "Mona Lisa" was removed from its original frame. The unconstrained poplar panel warped freely with changes in humidity, and as a result, a crack developed near the top of the panel, extending down to the hairline of the figure. In the mid-18th century to early 19th century, two butterfly-shaped walnut braces were inserted into the back of the panel to a depth of about one third the thickness of the panel. This intervention was skilfully executed, and successfully stabilized the crack. Sometime between 1888 and 1905, or perhaps during the picture's theft, the upper brace fell out. A later restorer glued and lined the resulting socket and crack with cloth.