Analysis of pastel and chalk materials

The range of binding media which could have been used in historic pastels encompasses all the traditional painting media, both oil- and water-based, and analytical methods have to take account of this. Suitably sensitive analytical techniques for the analysis of minute samples from pastels, chalks or watercolours have become available only in the last decade. The application of optical microscopy, energy-dispersive x-ray analysis (EDX), Raman spectroscopy, Fourier transform infrared microscopy (μFTIR), gas chromatography (GC) of oleoresinous materials and gums, high-performance liquid chromatography (HPLC) of amino acids, and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), to such samples will be discussed, in terms of sampling requirements and preservation of the sample for a second analytical technique. Other techniques used more in the past are mentioned briefly. The few published analyses of pastel on artworks, together with analyses of watercolour, ‘tempera’ and pastel materials in the Tate Gallery's collection, provide evidence that the extensive literature on the occurrence of pigments in oil paintings and interior decorative schemes can be applied directly to pastel and related materials of nineteenth- and twentieth-century date