Identification of gilding techniques on Roman marble sarcophagi

Several Roman marble sarcophagi (2nd-4th centuries AD) have been investigated in a first systematic research effort to detect (pigments and) gilding techniques employed in the Imperial Rome. A comparative study was performed on a conspicuous group (no. eighty) of Roman sarcophagi identified in the Vatican Museums, the Capitoline Museums and the National Roman Museum collections. A focused in situ campaign of non-invasive analytical investigations have performed by multispectral imaging, spectroscopic and elemental analysis, followed by aimed micro-invasive techniques. As for the main issue of the gilding and its application techniques, the microscopy still remains one of the most efficient tools for their characterization. Therefore, some micro-samples of three sarcophagi chosen as case studies were examined by means of optical petrographic microscopy (OPM) and scanning electron microscope and energy dispersive X-ray spectrometer (SEM-EDS). The results of archaeological data and scientific analyses show that the leaf gold was applied by two different techniques. In the most attested method, the gold leaf was applied on a ground layer of colour (yellow and/or red ochre, Egyptian blue, etc.); on the other hand, in the other technique, the gold leaf was applied directly onto the marble surface or more probably on top of a thin ground layer of kaolin.