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Hyperspectral Imaging Shines Light on Ancient Mexican Text

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Researchers at the Bodleian Libraries have used hyperspectral imaging to reveal never-before-seen pictographic scenes from a rare precolonial Mexican codex that has been hidden underneath a layer of gypsum and chalk for 500 years.

Until now, no other technique has been able to unveil the concealed pictorial narrative in a noninvasive manner. The organic paints that were used to partially create the vibrant images on early Mexican codices do not absorb x-rays, which ruled out x-ray analysis, a technique that is commonly used to study works of art.

Pages 10 and 11 of the back of Codex Selden.

Pages 10 and 11 of the back of Codex Selden. The top image shows the pages as they appear to the naked eye. These pages were scraped in the 1950s during a series of invasive tests which uncovered this vague impression, hinting at the possibility that an earlier Mexican codex lay hidden beneath. The lower image has been created using hyperspectral imaging to show the hidden pictographic scenes that lie underneath a layer of plaster and chalk on the back of Codex Selden. Courtesy of
Journal of Archaeological Sciences: Reports, 2016 Elsevier.

“Hyperspectral imaging has shown great promise in helping us to begin to reconstruct the story of the hidden codex and ultimately to recover new information about Mixtec history and archaeology,” said David Howell, head of Heritage Science at the Bodleian Libraries. “This is very much a new technique, and we’ve learned valuable lessons about how to use hyperspectral imaging in the future both for this very fragile manuscript and for countless others like it.”

The researchers analyzed seven pages of the codex for this study. The results thus far indicate that the covered text and pictorials contain unique genealogic information which may prove invaluable for the interpretation of archaeological remains from southern Mexico.

“After four or five years of trying different techniques, we’ve been able to reveal an abundance of images without damaging this extremely vulnerable item. We can confirm that Codex Selden is indeed a palimpsest,” said Ludo Snijders from Leiden University.

An image created using hyperspectral imaging, which shows the hidden pictographic scenes on pages 10 and 11 of the back of Codex Selden.

An image created using hyperspectral imaging, which shows the hidden pictographic scenes on pages 10 and 11 of the back of Codex Selden. These images lie underneath a layer of plaster and chalk and are not visible to the naked eye. The Bodleian Libraries’ hyperspectral imaging scanner shines white light at an object and for each pixel, it captures all the light that the object reflects back – not just the visible light that the human eye can see, but 900 different wavelengths in the electromagnetic spectrum. Different pigments or paints have different ‘spectral signatures’ or ‘fingerprints’ which allows them to be identified by the scanner. Through high level computer processing, reconstructed images like this one can be created. Courtesy of Journal of Archaeological Sciences: Reports, 2016 Elsevier.

A palimpsest is a document that has been covered up and reused to make the manuscript that is currently visible. The newly revealed manuscript was hidden on the back of Codex Selden, which dates from around 1560 and is one of fewer than 20 known Mexican codices to have survived from precolonial and early colonial Mexico.

The researchers continue to analyze the remainder of the document with the aim of reconstructing the entire hidden imagery, which will allow the text to be interpreted more fully.

Working with the Humanities Division in the University of Oxford, Bodleian Libraries acquired the hyperspectral scanner in 2014 with the support of the University’s Fell Fund. Hyperspectral imaging is now used by Bodleian researchers to reveal hidden text and images and identify unknown substances and pigments with a high degree of accuracy. Researchers have recently used the scanner to clarify the text of the famous Bakhshali manuscript from India, which includes the first use of zero; to analyze the medieval Gough Map, the earliest road map of Great Britain; and to reveal a hidden devil in a centuries-old Armenian gospel-book.

The research was published in the Journal of Archeological Science (doi: 10.1016/j.jasrep.2016.07.019).

Photonics Spectra
Nov 2016
hyperspectral imaging
Methods for identifying and mapping materials through spectroscopic remote sensing. Also called imaging spectroscopy; ultraspectral imaging.
Research & TechnologyEuropehyperspectral imagingCodex Seldenimaginglight-based technologyspectral signatureTech PulseEuro News

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