History & CultureHow it works
How to read a scraped-off text after 800 years.
Parchment was expensive, so old writing was washed off and new text written over it. The Archimedes Palimpsest, copied around 950 and overwritten in 1229, was imaged from 1999 to 2008 with ultraviolet, infrared and X-ray fluorescence. Iron in the older ink responds differently from the newer one – over 80 percent became readable.
Useful: Erased rarely means gone: usually only the right kind of light is missing.
Source: en.wikipedia.org