In 2008, a gold-plated pendant was discovered in Mainz, Germany. Researchers believed that the pendant was around 800 years old, and that something was hidden inside of it. However, trying to physically open it could damage the artifact. Therefore, they decided to scan the pendant with a neutron beam.
The research was carried out by a team from Leibniz-Zentrum für Archäologie (LEIZA), part of the Technical University of Munich. They used tomography and Prompt Gamma Activation Analysis (PGAA) with neutrons to scan the interior of the pendant. It revealed five individual packets made of silk and linen, with bone splinters packed in each. They believe the bone splinters were religious relics.
“Neutron non-destructive testing was particularly helpful because we couldn’t just open the trailer and look inside,” explains restorer Matthias Heinzel from LEIZA. “The object and, above all, the locking mechanism have been severely damaged by centuries of corrosion, and opening it would mean destroying it irrevocably.”
During restoration, he discovered a fragment of cord in the pendant’s attachment loop, which on closer examination turned out to be silk. “This is the first proof that this kind of pendant may possibly have been worn around the neck on a silk cord. The neutron tomography at TUM meant we could additionally measure the thread size and the string separations of the textiles inside the pendant,” adds Heinzel.
Neutron analysis makes organic substances visible
In 500 hours of work, Heinzel meticulously removed corrosion deposits from the find. Initial investigations showed that the approximately 6 cm high, 6 cm wide and 1 cm thick pendant was presumably a storage container for religious relics. Since the organic content of the pendant was not visible in the first x-ray images, the researchers turned to neutron tomography, which rendered the individual textile packages inside containing the bone fragments. The researchers determined individual elements of the sample by triggering them with the PGAA to emit gamma radiation.
“We can’t say whether or not these bone splinters are from a saint and, if so, which one,” says Heinzel. “Usually relic packages contain a strip of parchment indicating the name of the saint. In this case, however, we unfortunately can’t see one. As an archaeological research institute of the Leibniz Association, we consider it our duty to preserve the object in its historical authenticity as completely as possible for future generations and to leverage the modern opportunities of non-destructive investigation at the Technical University of Munich.”
There are only three other known relic containers of this type, which are called phylacteries. The term phylactery is derived from the Greek term for safekeeping or protection. Their owners wore them on their bodies, usually hanging them around the neck. The exterior of the gold-plated pendant made of copper shows pictures of Jesus, the four Evangelists, Mary and four female saints in enamel. The researchers dated the pendant to the late 12th century and attribute it to a workshop in Hildesheim, Lower Saxony, in Germany.
The find is in the possession of the General Directorate for Cultural Inheritance at the State Archeological Directorate of Mainz and can be viewed for the time being in the medieval exhibition “AUREA MAGONTIA – Mainz in the Middle Ages” at the Mainz State Museum.
Their research has been published in an article. “Discovery of a 12th-Century Enamelled Reliquary Pendant: Elemental Analysis and Content Visualization Using Prompt Gamma Neutron Activation Analysis and Neutron Tomography,” by Matthias Heinze, Eschly Kluge, Dorothee Kemper, Burkhard Schillinger and Christian Stieghorst, appears in METAL2022 – Proceedings of the interim meeting of the ICOM-CC METALS working group.