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Centuries ago, writing material could be too valuable to throw away.
Old writing on parchment was sometimes scraped or washed off so the surface could be written on again.
These reused manuscripts are called palimpsests.
The surprising part is that the erased words can sometimes remain chemically or physically detectable.
Modern multispectral imaging photographs the pages under different wavelengths of light, revealing writing invisible to ordinary eyesight.
Researchers have recovered texts that had effectively disappeared for hundreds of years this way.
So an apparently ordinary manuscript can secretly contain an entirely different book underneath the one being read.
© The Walters Art Museum