the London version as a replacement. In line with this theory, it is hypothesised that the Louvre painting was sold in the late 1480s, after some haggling over the final payment. The London painting was commenced in perhaps 1486 as a substitution for the "original" Louvre version, and was not ready for installation until 1508, after prolonged disagreement and negotiation. This explanation, which della Chiesa attributes to Venturi and Poggi, has gained wide acceptance, and is the version of events described on both the National Gallery and the Louvre websites. Martin Kemp dates the Louvre painting to 1483–1490 and the London painting to 1495–1508. Not all authors agree with either the dating or the theory that the Louvre painting was the earlier, was sold, and the London painting done as a substitute. Taylor asserts that the London painting is stylistically the earlier of the two, being more meticulous, in keeping with the product of Leonardo's Florentine training, while the Louvre painting has more in common with the Last Supper and the Virgin and Child with St Anne, including the delicate use of sfumato. Taylor argues that the London painting fulfils the requirements of the commission of 1483 in terms of iconography, and that the iconography of the Louvre painting indicates that it was painted for an entirely different clientele, and gives it a date in the 1490s. Authorship It has always been agreed that the Louvre Virgin of the Rocks is entirely by the hand of Leonardo da Vinci. The Virgin of the Rocks in London has generally been seen as having been designed by Leonardo and executed with the assistants. The Louvre website and various authors suggest that the entire painting is by Ambrogio de' Predis, painted under Leonardo's supervision between 1485 and 1508, or perhaps largely the work of de Predis, with minor intervention by Leonardo. Since the recent cleaning, National Gallery curator Luke Syson has stated that the quality which has been revealed indicates that the work is mostly from the hand of Leonardo, and that participation of members of Leonardo's workshop was almost certainly less than previously thought. Geologist Ann C. Pizzorusso argues that there are geological inaccuracies in the London version, unlike the Louvre version, which mean it is unlikely to have come from Leonardo's hand. Taylor disputes this, drawing attention to the fact that, at the time of writing, Pizzorusso had plainly not seen