Virtual unwrapping of the Bispegata amulet, a multiple folded medieval amulet, by using neutron tomography

Abstract

In recent decades, computed tomography (CT) combined with suitable image processing software has become a valuable tool to enable the reading of texts written on scrolls, which are fragile, damaged, or fused together, without physically unwrapping them. X-ray based computer tomography has successfully been used on scrolls made of soft materials such as papyrus and parchment. Although in few cases inscriptions on thin metal plates that have been rolled up and worn as amulets have been deciphered by using a high energy X-ray source, the readability of writings on of metal scrolls is limited by the high attenuation factor of this type of material.

In this paper, we present for the first time the use of neutron tomography as an alternative to X-ray tomography for studying hidden inscriptions on folded metal objects. It is shown that the method overcomes the limitations of X-ray tomography caused by high attenuation of X-rays in lead objects.

The inscription on the medieval Bispegata amulet, unearthed during excavations in Oslo's Old Town, has been read by using neutron tomography combined with VG Studio software. The amulet was made up of a thin lead sheet with an inscribed text, folded together into a rectangle. The inscription was runic, containing words of religious and magic meaning.