Originally Posted by The Batlord

Actually from what I hear Da Vinci used some pretty avant garde painting techniques with the Mona Lisa, but those techniques were also not in line with the more standard at the time techniques that were designed to preserve paintings for as long as possible, so Da Vinci's techniques actually led to the Mona Lisa deteriorating at a far more advanced level than most other artists' works, which is why there are so few confirmed original Da Vinci works today. It's also why the Mona Lisa is never restored, because restoring it would more likely destroy it than clean it.