An integrated approach to the conservation of a wooden sculpture representing Saint Joseph by the workshop of Ignaz Günther (1727–1775): Analysis, laser cleaning and 3D documentation

Abstract

This paper reports the conservation procedure applied to a wooden sculpture representing Saint Joseph attributed to the workshop of Ignaz Günther (1727–1775). The component material of the wooden sculpture was identified by observing the thin sections under an optical microscope; the materials layered on the surface were analyzed by optical microscopy, micro-Raman and Fourier transform infrared spectroscopy. The laser cleaning tests were carried out with a Q-switched Nd:YAG system. The surface was examined before and after the cleaning with the aid of a video-microscope, reflectance spectrophotometer and scanning electron microscopy. The steps of the work were documented on a digital tri-dimensional model of the sculpture created by a close range image system in order to carefully register scientific, technical, conservative, and material aspects. The microscopic observation of wood thin sections allows identifying it as lime tree. The analysis of the surface materials highlighted the presence of lead white applied by a siccative oil and barium sulphate. The infrared spectroscopic analysis of the brown surface layer revealed the presence of shellac. The laser cleaning proved an effective method to remove the surface dirt and to reduce the aged protective layer without affecting negatively the wood. The diagnostic analysis carried out prior and during the cleaning process was fundamental to verify the applicability of the laser to the wood surface in order to obtain an efficient cleaning action without secondary damaging effects. In addition, considering the reduced number of laser cleaning examples applied to wooden material available in literature, the documentation of the adopted working process could be a useful reference for the divulgation and sharing of the obtained data.