Using a high-tech imaging method, scientists have unveiled details of a Mexican manuscript, dating back from before the Colonization of the Americas, that was concealed under a layer of plaster and chalk for about 500 years.

Ludo Snijders, from Leiden University in the Netherlands, and colleagues used hyperspectral imaging to uncover the secrets of the manuscript called Codex Selden. Also known as Codex Añute, the manuscript dates from around 1560 and originated from what is now Oaxaca in Mexico.

The codex is among the less than 20 surviving codices from the pre-colonial and early colonial Mexico. It has long been speculated to be a palimpsest, older writing documents whose original content has been erased so it can be replaced by a newer manuscript.

The other codices contained colorful pictographs that depicted rituals, genealogies, wars and alliances but the Codex Selden appeared to be blank. The deerskin-made codex was folded accordion-style in pages that were layered with a white paint mixture called gesso.

Researchers began to suspect that there could be more to the seemingly empty pages of the codex after finding that the cracks in the gesso have glimpses of colorful images hiding underneath the chalky outer layer, which was possibly added so the book could be reused.

Scientists turned to several techniques such as infrared imaging and X-ray scanning but these failed to reveal the hidden pictures in detail. With hyperspectral imaging though, they were able to penetrate the layers of the gessos.

The method used information from frequencies and wavelengths across the electromagnetic spectrum and finally unveiled the underlying collection of images inked in yellow, orange and red without damaging the delicate pages.

"Hyperspectral imaging is applied to a Mixtec codex in order to reveal an abundance of never before seen pictographic scenes hidden underneath a layer of gypsum and chalk gesso," the researchers wrote in their study, which was published in the Journal of Archaeological Science.

"Because of the organic nature of these paints, no other technique has been able to reveal them in a non-invasive manner."

Seven pages have so far been analyzed depicting figures representing men and women. In one page of the codex, 27 figures of people were depicted seated and standing. Two of the figures were connected by a red umbilical cord suggesting that they were siblings. Some of the women were depicted having red hair or headdresses and some figures walked with spears or sticks.

The pages also featured what appeared to be a prominent individual represented by a large glyph composed of a twisted cord and a flint knife.

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