Applicazioni avanzate del laser in fibra per la pulitura di un sarcofago del Museo Pio Cristiano dei Musei Vaticani

The current work examines the front of a double-register stone sarcophagus, beginning of the 4th century AC, conserved in the Pius Christian Museum, Vatican Museum (Inv. 31551). The high relief carved front is what remains of a monumental sarcophagus, found at the end of the XVI century in the cemetery of Praetextatus, on the Appian Way. The sarcophagus was broken to detach the front, used in 1646 in the making of a monument under the portico of the Pantheon and then, after been dismantled, covnered in 1757 in the pontifical collection of Christian Antiquity. The front of the sarcophagus presented several conservation problems and mostly it has been assembled over time in several fragments, using rosin and pins. The presence of ancient restoration treatments, disfiguring, and unstable for the conservation, induces us to research the best methodology for their removal. These layers were overlapped on the marble from a white layer composed by plaster and a second organic one, added with iron oxide pigments. The first cleaning phase, based on the utilization of the agar-agar gel added with triammonium citrate gave good results but couldn't remove the black spots due to previous treatments. We first performed the cleaning tests with a Laser Nd:YAG EOS10000LQS, but the results didn't satisfy our expectations. We decided to test the Infinito Laser, El.En. S.p.A., an advanced fiber laser, extremely selective, in order to test non-interfering characteristic with the surface. The field tests gave excellent results, removing the superimposed layers and respecting the surfaces, as checked with UV and HMI investigations.