Researchers at the Georgia Institute of Technology and Georgia Tech-Lorraine used a variety of techniques to look beneath the surface of a 16th-century lead funerary cross. The effort was led by David Citrin, a professor in the School of Electrical and Computer Engineering.
"Our approach enabled us to read a text that was hidden beneath the surface, perhaps for hundreds of years," said Alexandre Locquet, an instructor in ECE and researcher at Georgia Tech.
The study was published in the journal Scientific Reports.
A cross cut from a sheet of lead was found in a burial plot in France, a couple hours away from the Georgia Tech campus. It is a funerary cross that dates to the Middle Ages and has been found in France, Germany, and England.
"This type of cross typically bears inscriptions of prayers or information about the deceased", said the director of the Mus.
The museum lent the cross to Citrin's lab in hopes that it could be used to make the invisible visible. Citrin and his group specialize in non-destructive evaluation and develop techniques that allow for detailed examination of an object's hidden layers without changing or damaging its original form. Although their work often has industrial applications, such as detecting damage to airplane fuselages, the group embraced the opportunity to inspect the cross to further explore their technology's applications for archaeological purposes.
Peeking beneath the veil.
The team used a commercial terahertz scanning device to look at the cross. The scanner sent a form of light that travels over each section of the cross. Waves bounced back and forth from the layer of corrosion to the actual surface of the lead cross. Two different echoes of the same pulse were produced.
The team used an algorithm to process the time delay between the two echoes into a signal. The data showed how thick the corrosion was. The light beams that reflected from the underlying metal were collected to create images of the lead surface.
The insights are interdisciplinary.
The data was gathered during the scanning process, but the raw images were too noisy and messy to read. Junliang was able to process the images in a way that would eliminate the noise. By combining parts of the images that were acquired in different frequencies, he was able to restore and enhance them. The image contained the text.
Vacheret was able to identify multiple Latin words and phrases using the processed images. They were all part of the Pater Noster.
The Pater Noster inscription was confirmed by the team after they worked with a conservationist to reverse the damage on the cross. The team found that parts of the inscription not observable on the original cross were revealed by their images. Their work was able to offer a deeper understanding of the cross and the 16th-century Christianity in France by uncovering additional aspects of the inscriptions that were previously undiscovered.
Citrin said that not all lead objects can be treated this way. We hope our work opens up the study of other lead objects that may have secrets underneath them.
Citrin's group has used terahertz technology to look beneath the surface of 17th-century paintings, and provide insights into techniques of master painters. They are looking at surface coating on Roman ceramics.
Success requires more than just accurate measurement, but also careful data processing and collaboration between researchers from different fields. The team's approach opens new perspectives for terahertz analysis and could produce great boost for the fields of digital acquisitions and documentation, as well as character recognition, extraction, and classification.
Despite three decades of intense development, terahertzimaging is still a rapidly developing field.
More information: Junliang Dong et al, Revealing inscriptions obscured by time on an early-modern lead funerary cross using terahertz multispectral imaging, Scientific Reports (2022). DOI: 10.1038/s41598-022-06982-2 Journal information: Scientific Reports Citation: Terahertz imaging reveals hidden inscription on early modern funerary cross (2022, April 25) retrieved 25 April 2022 from https://phys.org/news/2022-04-terahertz-imaging-reveals-hidden-inscription.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
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