Appl Phys A (2010) 99: 363–375 DOI 10.1007/s00339-010-5673-5 Degradation of azurite in mural paintings: distribution of copper carbonate, chlorides and oxalates by SRFTIR A. Lluveras · S. Boularand · A. Andreotti · M. Vendrell-Saz Received: 19 January 2010 / Accepted: 1 March 2010 / Published online: 9 April 2010 © Springer-Verlag 2010 Abstract This article illustrates the analysis by synchrotron micro-analytical techniques of an azurite painting present- ing greenish chromatic degradation. The challenge of the experiments was to obtain the spatial distribution of the degradation products of azurite. Copper hydroxychlorides, carbonates and copper oxalates have been mapped by SR FTIR imaging of cross sections in transmission mode. To complement the information, Py/GC/MS and GC/MS tech- niques were applied in order to characterize the binding me- dia and organic materials present as well as their degrada- tion products. Results contribute to a better understanding of the decay of blue areas in ancient paintings not only from the particular point of view of azurite weathering, but also by adding information regarding the oxalates’ formation and their distribution in painting samples. Synchrotron radiation demonstrates its capability for the mapping in painting cross sections. 1 Introduction Azurite is a basic copper carbonate (2CuCO 3 ·Cu(OH) 2 ), a natural blue pigment used since the Fourth Dynasty in Egypt although it became the most important blue pigment during the Middle Ages and Renaissance [1]. A. Lluveras ( ) · S. Boularand · M. Vendrell-Saz Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona, C/Martí i Franquès S/N, 08028 Barcelona, Spain e-mail: alluveras@ub.edu Fax: +34-934-021340 A. Andreotti Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, Pisa, Italy Many paintings became altered by the transformation of blue areas into green and brown. Clear examples of the problematic above described are the frescoes at the Mon- umental Cemetery of Pisa or the Crypt of the Cathedral of Siena [2, 3]. Green shades in azurite blue paintings could be attributed to different reasons depending on their composition: natural green shades of the mineral ore, the use of synthetic green pigments obtained from the corrosion of copper plates ex- posed to vinegar vapours, or the degradation of the original pigment into green products such as copper chlorides. Although azurite presents a natural greenish undertone due to the particles of malachite (CuCO 3 ·Cu(OH) 2 ) and cuprite (Cu 2 O) that can be found associated in nature to the azurite ores [1], the desiderated blue tone could be obtained by purification of azurite from the other phases as it was provided by authors such as Cennino Cennini [4]. Though the synthesis of green copper-based pigments have been re- ported in recipes of Heraclius, Teophilus or Vitruvius [5, 6], the synthesis process products have been already character- ized as mixtures of copper acetates, carbonates and hydrox- ychlorides [7], that is, a different composition from that of the green shaded azurite-based paintings usually character- ized in the literature. Thus, degradation of azurite blue pigment into a green product due to ageing seems to be the cause of the green- ish areas observed in different azurite paintings as the ones cited above. Azurite, although being stable to light and at- mosphere, presents frequent chromatic alterations to green- ish tonalities due to transformation into paratacamite and atacamite (Cu 2 Cl(OH) 3 )[2, 3, 8, 9] and also malachite (CuCO 3 ·Cu(OH) 2 )[1], not yet completely understood. Samples analyzed come from a gypsum shield on top of a door in the Monastery of Santes Creus (Catalonia, Spain) dating from the 1605 AD. The shield is depicted mainly in