THE RED CHROMATIC ALTERATION OF WHITE MARBLE IN SACRED PLACES: IS IT A PROBLEM OF CONSERVATION?

The red/orange "stain" on white marble is a chromatic alteration randomly observed on funerary monuments and tomb slabs. The origin could have an inorganic cause (induced by the presence of lead), an organic cause (induced by the presence of microorganisms) or could be due to the interaction between microbes, stone material and environment factors. The case of some marble slabs in Purification Cemetery in Livorno (Italy) is particularly impressive. This paper aims to characterize these red discolourations by means of visual observations, biological and petrographic analysis, and to investigate whether their occurrence can give rise to problems of decay to the marble crystalline structure.