Alteration of marble stones by red discoloration phenomena

Red discoloration on marble showed particular interest between 1980-2000 when red stain phenomena where investigated on different monuments such the facade of the Certosa di Pavia, Siena Cathedral, Orvieto Cathedral, marble cenotaph in monumental cemetery of Pisa etc. Comparative macroscopic observations of the new case studies are presented showing that water plays an essential role in the formation of red stains together with the presence of micoorganisms and a source of lead.