A new camera can distinguish layers of ink hidden by several layers of ink and paper, and could also be used to analyze paintings:
MIT researchers and their colleagues are designing an imaging system that can read closed books. In the latest issue of Nature Communications, the researchers describe a prototype of the system, which they tested on a stack of papers, each with one letter printed on it. The system was able to correctly identify the letters on the top nine sheets. "The Metropolitan Museum in New York showed a lot of interest in this, because they want to, for example, look into some antique books that they don't even want to touch," says Barmak Heshmat, a research scientist at the MIT Media Lab and corresponding author on the new paper. He adds that the system could be used to analyze any materials organized in thin layers, such as coatings on machine parts or pharmaceuticals.
Also at TechCrunch.
Terahertz time-gated spectral imaging for content extraction through layered structures (open, DOI: 10.1038/ncomms12665) (DX)
(Score: 4, Informative) by Anonymous Coward on Tuesday September 13 2016, @03:52AM
Reading the charred scrolls from Herculaneum is a similar problem, though more difficult because of their geometry. Maybe this terahertz technique would be applicable there. I'm guessing that terahertz waves are easier to generate than coherent X-rays.
http://www.nytimes.com/2015/01/21/science/more-progress-made-toward-learning-contents-of-herculaneum-scrolls.html [nytimes.com]
http://www.nature.com/articles/ncomms6895 [nature.com]