Rita Letendre’s Oil Paintings from the 1960s: The Effect of Artist’s Materials on Degradation Phenomena

Abstract

ABSTRACT This paper describes an investigation into the causes of specific degradation phenomena in three oil paintings from the 1960s by eminent Indigenous Canadian painter Rita Letendre. A comprehensive technical study of the paintings was undertaken using a combination of SEM-EDS, FTIR spectroscopy, Py-GC-MS, Raman spectroscopy, XRD, and polarised light microscopy to determine pigments, fillers, additives, paint medium, and degradation products. Compositional factors, including high abundances of manufacturers’ additives such as aluminum stearate and castor wax, have likely contributed to the formation of oil exudates and fatty acid efflorescence. Cross sections illustrated an inhomogeneous distribution of additives and incomplete mixing of components in some colours. This appears to be due to the migration of components over time and also to Letendre’s technique, which included application of thick paint directly from the tube and the addition of extra medium to some impastos. Cracking, lifting, and protrusions in several areas were caused by the crystallization of zinc soaps below the paint surface. FTIR mapping allowed the spatial distribution of crystalline and ionomeric-type zinc soaps to be determined within a problematic paint layer.