If the linseed oil in the Mona Lisa ever dries the paint will crack. After 500 years, museum curators aren't overly concerned about it.

In the 1950's, the panel was reinforced with a flexible oak frame. The light oak could have been stained with Minwax, but the conservators decided to darken it with an authentic ammonia fuming process. Of course, the only way to do it right was with horse urine.