3D ERT for the study of an ancient wall covered by precious mosaics

The DC electrical tomography (ERT) is still a method scarcely diffused for the study of masonry of recent and ancient buildings, in spite of the very high resolution power of this methodology. The major limitation on ERT applicability on precious surfaces (like masonries or floors with fresco or mosaic covering) depends on the method of current injection: usually it is necessary to drive electrodes (small nails) into small perforations on the surfaces, to obtain sufficiently high current values (to produce good signal to noise ratio). An interesting application of the MYG array (that reduces significantly, compared to other classical arrays, the number of electrodes utilized for current injection) has been carried out on a wall of the fountain room of the Zisa Palace (Palermo, XII century A.D.), covered by a mosaic wall suffering important detachment of tesserae due to internal moisture. The results seem to suggest that ERT investigation with the MYG array has important applicative potentiality in study of precious walls or floors in artistic buildings, because of the low-invasivity and high resolution power as well as velocity of acquisition.