Use of a versatile instrument for X-ray radiography and tomography of artworks, precious objects and archaeological materials

X-ray imaging is now widely used in the Cultural Heritage field because of its non-invasivity and for the high number of information which can be obtained on the inner structure of an object. A new instrument for X-ray radiography and tomography has been developed by the Physics Department of the University of Torino and the INFN (National Institute for Nuclear Physics). It is based on a microfocus X-ray source, a rotary stage and a linear X-ray detector moved by a high precision mechanics. A frame to fix paintings and larger objects is also available, allowing radiographies on large areas. The possibility to change distances among the analysed object and both the detector and the source makes the instrument very versatile, allowing to analyse both small objects (exploiting a high magnification) and bigger ones (analysing large areas). Moreover many parameters, like X-ray energy, current, integration time and distances, can be optimized in real time, allowing to obtain the best configuration in short time. In this presentation a selection of case-studies will be proposed, showing the potentiality of the instrument on very different kinds of objects and artworks. Painted canvas and panels radiographies will be shown: radiography allows to obtain useful information about the state of conservation, the technique used by the painter (also for authentication purpose) and some basic indication about the pigments (limited to the different radiopacity of various materials). Another field in which radiography is useful is archaeology: radiographies of earth-blocks can show hidden objects before the micro-excavation and can reveal its state of conservation in an absolutely non-invasive way, allowing to decide if it is suitable to remove it from the earth or not. Moreover they can reveal some details of the hidden objects, for example the presence of different materials or decoration obtained with different thicknesses of the same material. Also for gemmology digital radiography is very useful and we applied it to pearls. This technique allows to obtain information on their inner structure and so to understand if the pearl is natural or cultured with a solid bead or beadless cultured, discriminating the market value of the pearl. A third field for which both 2D (radiography) and 3D (tomography) X-ray imaging can give useful information is in the characterisation of objects coming from museum collections. Some examples from artworks and objects from the Anthropological and Ethnographical Museum of the University of Turin will be shown, giving a great number of information on different materials, constructive technique and state of conservation useful both for their valorisation and protection. This work is part of a larger collaboration research project that involves also the Centro Conservazione e Restauro "La Venaria Reale" and the neu_ART regional project.