title: Green copper pigments biodegradation in cultural heritage: from malachite to moolooite, thermodynamic modeling, X-ray fluorescence, and Raman evidence.
abstract: Moolooite (copper oxalate), a very rare compound, was found as a degradation product from the decay of malachite in several specimens of Cultural Heritage studied. Computer simulations, based on heterogeneous chemical equilibria, support the transformation of malachite to moolooite through the intermediate copper basic sulfates or copper basic chlorides, depending on the presence of available free sulfate or chloride anions in the chemical system. Raman and X-ray fluorescence spectral evidence found during the analysis of the three case studies investigated supported the model predictions. According to the study, the presence of lichens and other microorganisms might be responsible for the decay phenomena. This work tries to highlight the importance of biological attack on specimens belonging to Cultural Heritage and to demonstrate the consequences of oxalic acid, excreted by some of these microorganisms, on the conservation and preservation of artwork.
authors.affiliation: Department of Analytical Chemistry, University of the Basque Country, P.O. Box 644, 48080 Bilbao, Spain. kepa.castro@ehu.es
authors.forename: Kepa
authors.initials: K
authors.lastname: Castro
authors.forename: Alfredo
authors.initials: A
authors.lastname: Sarmiento
authors.forename: Irantzu
authors.initials: I
authors.lastname: Martínez-Arkarazo
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Madariaga
authors.forename: Luis Angel
authors.initials: LA
authors.lastname: Fernández
mesh_terms: D003116:Color; D004396:Coloring Agents / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D003469:Culture; D008956:Models, Chemical; D009942:Organometallic Compounds / Q000737:chemistry*; D019815:Oxalic Acid / Q000737:chemistry; D010151:Paintings; D010209:Paper; D012613:Sculpture; D013052:Spectrometry, X-Ray Emission; D013059:Spectrum Analysis, Raman; D013816:Thermodynamics
chemical_list: D004396:Coloring Agents; D009942:Organometallic Compounds; C520661:malachite; D003300:Copper; D019815:Oxalic Acid