Technical analysis and the recent restoration have resulted in the recovery of the original appearance of the work, which is extremely valuable for the way in which it casts light on workshop procedures in Leonardo’s studio. It is the most important version of La Gioconda known to date (see fig.2).
The comparison of the two works and the technical documentation relating to them has also contributed to an understanding of the Louvre painting and to completing the sequence of the known phases of its execution, given that the precision of the images produced during the examination of the Prado’s copy revealed features in the x-rays and infra-reds of the original that had previously passed unnoticed (see fig.3). In addition, data resulting from the comparative examination of the two works confirms what was already known about the way Leonardo’s studio functioned, which has been described by Martin Kemp in his research on the existing versions of the Madonna of the Yardwinder and which are also recorded in a letter from Fra Pietro de Novellara to Isabella d’Este after the former had visited Leonardo’s studio. In his letter Novellara mentions having seen two apprentices making copies as the master was extremely occupied.
The existence of the landscape beneath the black background was detected with infra-red reflectography and from an examination of the surface under raking light before restoration started. It was subsequently confirmed with x-ray. Despite this evidence it was necessary to determine whether the addition of the black substance was subsequent to the execution of the painting, and in that case whether it concealed any damage on it ( see fig.4a - fig.4b).