Authors: J. Catalano, A. Murphy, Y. Yao, N. Zumbulyadis, S.A. Centeno (presenting), C. Dybowski
To understand the mechanisms and factors that trigger soap formation and the dynamics of the reactive compounds in oil paintings, we used advanced solid state nuclear magnetic resonance (ssNMR) and X-ray techniques, complemented by FTIR spectroscopy. We explored soap formation in model paint films at different relative humidity conditions by 13C NMR and studied the dynamics and mobility of relevant fatty acids and soaps, namely palmitic acid and lead palmitate, in a linseed oil matrix at different temperatures (T) by 2H NMR. The results show the extent of mobility of palmitic acid and lead palmitate in the paint matrix, how they differ, and how they depend on T. Examination with techniques such as solid-state 207Pb, 119Sn, and 13C NMR, and X-ray diffraction provided the basis for interpreting dynamics in terms of the effects of structure and lead ion coordination environments [1-5]. The ssNMR results obtained in model paint samples directly correlate with features of the IR data, so they are useful to further interpret FTIR spectra acquired in microsamples removed from works of art. Also, the ssNMR data sets the basis for minimally invasive NMR studies in microsamples with the development of dynamic nuclear polarization (DNP) techniques. The results will be discussed in the context of their implications for the conservation and preservation of the works of art affected by lead soap formation.
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