Verdigris pigment: a mixture of compounds. Input from Raman spectroscopy

The reproduction of an old recipe to obtain the pigment known as verdigris leads to a complex mixture of hydrated copper(II) acetates containing neutral verdigris and two varieties of basic verdigris. Since the characterization of such mixture is complicated by the lack of reference standards, we complemented our Raman measurements with Fourier transform infrared (FTIR) and X-ray diffraction (XRD) experiments to perform our analysis, which has been compared with available studies. The spectral analysis allowed us to distinguish the different verdigris varieties, with stretching and bending wavenumbers assigned to the following chemical groups: OH groups (OHhydroxy and OHH2O) (3600-3050 cm(-1)), Cu-O bonds (Cu-O and Cu-OH) (1000-450 cm(-1)) and those corresponding to the acetate group (CH3COO-), i.e. (CH3:3000-2850 cm(-1)) and (COO-: 1600-1400 cm(-1) and 700-600 cm(-1)). Both wavenumbers and Raman intensities were used to quantify the relative compositions of the mixture components. Copyright (C) 2010 John Wiley & Sons, Ltd.