These are fun. Wish the ones they had there were explained - sometimes they're quite funny, as with the monks complaining in the margins of the texts they were illuminating or copying:
Sometimes this stuff is lost because of fading ink or palimpsest-style erasure - there are multiple efforts on to retrieve such hidden and deteriorating items, which can sometimes yield very important things like lost manuscripts or fragments. I wrote about it a while back, though there's much, much more to know than what I could fit here:
http://www.theatlantic.com/entertainment/archive/2012/03/che...
Sometimes this stuff is lost because of fading ink or palimpsest-style erasure - there are multiple efforts on to retrieve such hidden and deteriorating items, which can sometimes yield very important things like lost manuscripts or fragments. I wrote about it a while back, though there's much, much more to know than what I could fit here:
http://www.nbcnews.com/tech/innovation/multispectral-imaging...