I saw a vase in the British Museum when I was in London in 1989 called the Portland Vase. According to Wikipedia the Portland Vase is believed to have been made in Alexandria some time between 20 BC and the year 100 BCE....there is a little plaque on the pedestal that says in 1845 or so some drunk smashed it for whatever reason. I think it took them 8 months to piece it back together. It was an astonishingly beautiful blue and white vase, and of course you could see all the hairline cracks where they had glued it back together.
It maybe back on display, but it's not worth a dime the shape that it is in now.
That was an accident that they should have just choked up and forgot about.