Vibrational Raman spectroscopic studies of calcium oxalate monohydrate and dihydrate in lichen encrustations on renaissance frescoes

Abstract

Abstract Vibrational Raman spectroscopic studies of the monohydrate and dihydrate of calcium oxalate were undertaken in order to characterize these compounds in lichen encrustations which cause biodeterioration of Renaissance frescoes. Spectroscopic data from the CaC 2 O 4 · D 2 O species provided an aid to the vibrational assignments and indicated that amendment to some literature assignments was necessary. Application of the results to samples of the lichen Dirina massiliensis forma sorediata encrusting certain Italian Renaissance frescoes demonstrated that it is possible to identify the monohydrate and dihydrate of calcium oxalate at a microscopic level.