Investigation of the binding media of paintings by thermoanalytical and spectroscopic techniques

Differential scanning calorimetry (DSC) has been used to study samples taken from three paintings during treatment in the Conservation Department of the Tate Gallery. The paintings include two from the 16th century: (1) ''Queen Elizabeth 1'' by Nicholas Hilliard (National Portrait Gallery, London NPG 190), (2) ''An Allegory of Life'' (unattributed ca. 1570 British School To 5729) and (3) 19th century, Turner's 'The Opening of the Walhalla, 1842' (Tate Gallery N00533). Knowledge of the type of paint media used is of interest both to the conservator who needs to select the appropriate materials for cleaning the painting and to the art historian for documentation of artists' techniques. In the case of the Hilliard painting it was found that a mixed oil egg medium had been used. With regard to the unattributed 16th century British painting it was found that an oil-based medium had been used. The ground layer contained, as expected, a natural glue. Samples from the Turner painting showed that different regions of the painting had been executed with different materials; the region of the sky was painted predominantly with a drying oil, the lower regions of the painting contained mixtures of oil and resin and in some cases the samples were further complicated by the presence of proteinaceous material and wax. The recorded accompanying weight change gave information on the pigment volume concentration of the samples. In each case measurements were made of both the temperature and the heat evolved during the exothermic reactions. Thermomicroscopy and Fourier transform infrared spectroscopy (FTIR) confirmed the presence of complex mixtures, particularly in the case of the Turner samples.