Tracking Metal Oxalates and Carboxylates on Painting Surfaces by Non-invasive Reflection Mid-FTIR Spectroscopy

Abstract

This chapter discusses the potential of reflection mid-FTIR spectroscopy for in situ identification and localization of metal oxalates and carboxylates in paintings. The infrared reflection profiles of the most common metal oxalates and carboxylates are discussed through the direct comparison with reference powders and model samples demonstrating the possibility of distinguishing the nature of the metal counterion. The whole spectral data here discussed represent a unique collection of reference infrared reflection spectra available to conservation scientists for monitoring occurrence and distribution of the most common alteration compounds affecting both ancient and modern paintings. An overview of case studies representing the most relevant situations where metal oxalates and carboxylates have been found in important artworks is presented. This broad vision of the phenomenon, based on the experience matured within the MOLAB transnational access and the ability to probe several points on a painted surface non-invasively, can significantly contribute to progress in the understanding of occurrence, evolution, and origin of such alteration compounds.