Fig. 6

a Marten van Heemskerck, The Virgin and Saint John the Evangelist (NG6508.1); b paint cross-section from Saint John’s green robe, showing the underpaint containing long lath-like blue–green particles of copper sulphate, on top of which is a thin verdigris glaze. The ATR-FTIR image showing the distribution of the infrared absorption band in the range 1146–1079 cm⁻¹ shows the location of copper sulphates, while that at 1528–1451 cm⁻¹ shows copper carbonate (malachite) in the few more rounded particles. Images © National Gallery, London