Analysis of metallic archaeological artifacts by x-ray computed microtomography technique.

ABSTRACT

Metallic archeological artifacts have specific characteristics that differs them to the other classes of materials due to the transformations that occurs to them, mainly electrochemical. This way, a process called corrosion takes place, starting at the surface of the artifacts, changing the metals in oxides, sulphates, carbonates or other compounds that may result in substantial modifications in their morphology or the total mineralization. Possibly, most part of the archeological artifacts was already suffering this natural deterioration process, even before the period of time that they have remained buried. A number of techniques can be used for the analysis of these artifacts; however, most of them require physical sectioning, which is a complex time-consuming process. This work proposes the use of X-ray microtomography (microCT), which is a non-invasive and expeditious analysis technique, in order to identify the structures and texture of metallic archeological artifacts under incrustations. A set of artifacts found in excavations in the city of Rio de Janeiro (Brazil) were investigated. They show evident forms of degradation, and the incrustations did not allow to clearly identifying them. Through the microCT results is was possible to evaluate the structure of the artifacts, as well as to quantify the material loss caused by corrosion. Such results provided significant data about these historic pieces, which is important for a precise diagnostic about their conservation state, being a useful tool for preserving the morphology of the collected artifact.