A note on the characterization of paint layers by transmission electron microscopy

The application of transmission electron microscopy (TEM) to the study of paint and ground layers in a sample from a fourteenth-century painting is described. The study was carried out on an ultra-thin section cut from a microsample so as to retain the original paint layer structure. The sample had a single ground layer and one, red, paint layer. Analysis of individual particles using electron diffraction identified the major and minor components in the ground and paint layers. The predominant component of the ground layer was shown to be gypsum (CaSO 4 ·2H 2 O), together with some albite (NaAlSi 3 O 8 ), dolomite (CaCO 3 ·MgCO 3 ) and calcite (CaCO 3 ); the paint layer is composed entirely of vermilion (HgS). TEM is a powerful technique, as it allows the complete characterization of the inorganic components in each layer, commencing with a morphological study, then qualitative and quantitative microanalysis by energy dispersive X-ray spectrometry and, finally, the determination of the crystal structure by electron diffraction.