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.
Salvator Mundi (Leonardo)
Furthermore, the extraordinary quality of the picture, especially evident in its best-preserved areas, and its close adherence in style to Leonardo’s known paintings from circa 1500, solidifies this consensus.
Yet, there are some respected experts on Renaissance art who question the attribution of the painting to Leonardo. Jacques Franck, a Paris-based art historian and Leonardo specialist, who has studied the "Mona Lisa" out of the frame multiple times, stated: "The composition doesn't come from Leonardo, he preferred twisted movement. It's a good studio work with a little Leonardo at best, and it’s very damaged. It’s been called 'the male Mona Lisa', but it doesn't look like it at all."