X-ray tomography and aggregated analysis for Bavay treasure bronze statuettes analysis

Abstract

X-ray imaging is one of the oldest technic used in art analysis. X-Radiography is now completed with tomography. Used on bronze sculptures, it gives unrivalled information on state of conservation or fabrication process. The treasure of Bavay, discovered in 1969 in the north of France, is a hoard constituted by 371 bronze objects dated from the 1st to 3rd century AD. Among objects of very diverse shape and function, an exceptional set of Roman statuettes was discovered. Two Mercury statuettes were studied and, apart that they are hollow, their characteristics are very different. The metal walls are thin and even for the Lysippean Mercury and could only be done by the indirect lost wax casting process. On other hand, Indigenous Mercury still own its inner refractory core made of clay, whose shape is a very simple evocation of the statue. Here the direct lost-wax process was used, with first the core shaping, on which wax was directly carved. In some cases, spatial information is difficult to read on flat 2D radiographies, so complementary images are made thanks to 3D tomography. Reconstruction algorithms generate a 3D object issued from 720X-Ray images, showing the internal and the external surfaces. Virtual cutting can show any part of the object, allowing a detailed visualization of the inner parts. For example, Jupiter statue in tomography showed on the inner surfaces metal infiltration and a secondary casting of a lead-tin. Other analysis can be added to tomographic model: the surface 3D acquired with a scanner can add more precision on external surface representation: it was made for the Jupiter statue. In some cases also, photography for surface color analysis, or X-ray fluorescence chemical maps could also be placed on 3D models for a better materials localization.