@kristenadams Yeah, they were actually initially made as altarpieces and other items meant for churches, so artists of the time worked mostly with wood. I can't imagine how difficult it would be to maintain the life of a wooden piece for so long.
There is some Van Gogh that has been stabbed a few times. I have no idea why, but people just go into the museum and take a knife to the canvas. As if museums didnt already have enough to worry about when it comes to preserving!