Traces of blue pigments on two frescoes in the lower church of San Clemente in Rome In 2009, the Higher Institute for Conservation and Restoration conducted a worksite to examine and carry out essential restoration on the frescoes depicting the Leggenda di Sant’Alessio and the Messa di San Clemente in the central nave of the lower church in the basilica of San Clemente (Rome), dating from the late 11 th century. During the worksite, it was extremely difficult to interpret the composition of the original paint films due to the poor state of conservation of the paintings. However, careful and repeated study of the surfaces made it possible to identify traces of blue pigment on the dark grey background of both walls. In particular, the granules of pigment were localised in micro lesions on the plaster, in surface abrasions and cavities. Two types of blue pigments were identified: natural ultramarine and Egyptian blue, probably mixed together and present in different quantities in the two works.