Study by Raman microscopy of nine variants of the green–blue pigment verdigris

The Raman spectra of nine variants of ‘verdigris’ (organo‐copper complexes) synthesized recently by different methods have been measured at room temperature and at 150 K. The spectra are all characterized by a strong band at ca 2935 cm −1 and weaker bands at 3010, 2985, 2935, 1550, 1445, 1415, 1350 and 940 cm −1 at both temperatures; the majority of spectra also feature bands at 220 and 140 cm −1 . The features in the 3000–4000 cm −1 and 900–50 cm −1 regions of the spectra show the greatest differences from sample to sample: those in the high wavenumber region relate directly to the nature of the hydrogen bonding in each sample, while those in the lower region reflect the variations in the Cu–O bonding and crystal structures of each sample. The characteristic bands present in the 900–3000 cm −1 region are sufficient for the identification of a sample as a particular form of verdigris.