Analysis of a wooden statue by non‐destructive X‐ray techniques

Abstract

In this study, the characterization of the “Santa Luzia” statue was carried out through three non‐destructive X‐ray techniques: X‐ray Fluorescence (XRF), Digital Radiography (DR), and Computed Tomography (CT). The wooden statue dates from the 18th century. It was carved in Portugal and is currently located at the Santa Luzia church—one of the oldest churches built in Rio de Janeiro. The portable XRF system used in this study is composed of an Ag target X‐ray tube and an silicon drift detector detector with energy resolution of 122 eV at 5.9 keV. Several spectra were obtained in different regions of the statue. For the DR and CT evaluations, a portable 120 kV X‐ray tube and a 410 × 410 mm a‐Si flat panel detector with a pixel size of 200 μm were used. Individual radiographs of the parts of the statue were acquired and merged into a single image, in order to show its complete radiography. Finally, the CT images of the head of the statue were taken in angular steps of 2 degrees and, after the reconstruction process, the data were analyzed by means of appropriate software. The elements found in the XRF analysis suggest the presence of the pigments lead white, red lead, zinc white, titanium white, vermilion and emerald green. All of them are in accordance with the pigments used by the artists during the statue's historical period. The 3 exceptions were the zinc white and titanium white pigments, which may be an evidence of modern interventions, and the emerald green pigment, which appears to be a repainting of the green region. The radiographic images showed the manufacturing process of the statue, as well as its structural condition. The assembling of wooden blocks, the presence and type of nails and spikes, and regions of different densities were found in the analysis. In the statue's head, the joining of the face with the main part of the statue is clearly visible, and also the hollow glass eye. The CT analysis was able to better detail this section as a spherical cavity in the central part of the head, as well as the presence of a high‐density fragment inside the hole for the fixation of the aureole. The type of glass eye was identified as blown‐glass eye, which is commonly used in devotional statues.