The Eye of the Medusa: XRF Imaging Reveals Unknown Traces of Antique Polychromy.

The colorful decoration of statues and buildings in antique times is commonly described by the term antique polychromy. It is well-known among scholars but less so to the general public, and its exact form is the subject of research. In this paper we discuss results obtained from the frieze of the Siphnian Treasury in the Sanctuary of Delphi (Greece). We will present the first application of a mobile instrument for macro-XRF imaging for the in situ investigation of antique polychromy and show that it allows one to identify significant traces not visible to the naked eye and not detectable by XRF spot measurements or any other mobile, noninvasive method. These findings allow for a partial reconstruction of the polychromy. Furthermore, we present a novel approach enabling the correct interpretation of artifacts resulting from changes of the detection geometry in the investigation of complexly shaped samples by XRF imaging. This approach is based on the 3D surface model acquired by photogrammetry and fundamental parameter calculations.