Un'alterazione dei pigmenti nei dipinti murali: la trasformazione dell'azzurrite in paratacamite

Restoration has been carried out in recent years (1992-2002) on important cycles of paintings in Italy (Anagni, Crypt of San Magno; Assisi, Basilica of St. Francis; Orvieto, Chapel of San Brizio and the apse wall paintings; Padua, the Scrovegni Chapel). These projects have made it possible to get a better understanding of the alterations that take place in azurite over time, especially the greening effect. All the cases in question showed widespread transformation of natural azurite into paratacamite. This was observed by means of X-ray diffraction analysis, observation by polarized microscope and scansion electronic microscope, accompanied by X-ray microanalysis.