FTIR analysis was performed on 74 samples from 21 paintings from IUAM. Most painting samples has several components or layers, and all were analyzed. More than 500 spectra were collected for these components, and interpreted to identify the chemical composition of these components. Model compounds to represent the major organic components of paintings were exposed to various concentrations of DEAE and the products of reaction were analyzed.
Studies on the model compounds showed that DEAE can react with the acidic components of paintings, in particular with the resin acids in natural resin varnishes, and free fatty carboxylic acid in drying oils. However, DEAE does not react with carboxylic esters of glycerol, and therefore is unlikely to react with the triglyceride esters that comprise the major component of drying oils.
DEAE reaction products, specifically DEAE carboxylate soap, was tentatively identified in only one painting, “Peinture” by Soulages. It was found in the ground layer, but in no other layers, including an acidic oil layer on the surface, where the potential for reaction is greatest.
Small amounts of oxalate compounds, perhaps calcium oxalate, were detected in several paintings. One source of oxalic acid and its salts is metabolic by products from molds, fungus, and algae.
The analyses reported here indicate that the IUAM paintings have not been damaged by reaction with DEAE.
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This research was made possible through Grant MT-0424-5-NC-13 from the National Center for Preservation Technology and Training (NCPTT).