Mark Rothko's Black on Maroon (part of the Seagram Murals) is back on display in London's Tate Modern after an 18 month and £200,000 restoration, after being defaced with a solvent pen in late 2012.
The damage was very significant. It undoubtedly defaced the picture and really ruined it. The question was whether one could remove the damage without damaging the painting. Even the restorers and conservators were uncertain as to whether they could remove the ink and disguise the situation. They've done it brilliantly.
Wlodzimierz Umaniec, the little shit who was sentenced to two years in prison for vandalising the painting, has since apologised for his actions stating "I suppose I wanted to change the art world but of course I did it in a very, very wrong way [...] I'm sure the restoration team has done a wonderful job and I encourage everyone to see the restored picture."
As do I, because the Rothko Room (dimly lit inline with the artists specifications) in the Tate is great and I love it in there.