Verdigris

Abstract: study demonstrates that resin and fatty acids are able to extract copper(II) ions from verdigris (copper acetate) and verditer (basic copper carbonate). Ligand exchange reactions of basic copper carbonate with fatty acids and resin acids are much slower than is the case with copper acetate. The browning of paint layers is closely correlated with the relative ease of copper extraction; the copper diffuses in the form of fatty acid or resin carboxylic acid complexes. These complexes are formed in the painting layer during grinding of the pigment with binding media containing oleoresin acids, as well as being formed at the interface of this layer and organic upper layers, such as varnishes.

Abstract: 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. Copyright © 2006 John Wiley & Sons, Ltd.

Abstract: Since antiquity, various copper-containing substances have been used as green and blue pigments. Their exceptional diversity, reflecting their various chemical and phase composition, chemical stability as well as their origin, makes their correct identification challenging. The review focuses on copper-based pigments used in ancient and mediaeval works of art, especially in wall paintings and/or related polychromed decorations or statues—siliceous copper pigments (Egyptian blue and green, Han blue and purple, chrysocolla), copper carbonates (azurite, malachite, blue and green verditers), copper chlorides (atacamite-group, cumengeite, calumetite), copper sulphates (posnjakite, brochantite) and—to a lesser extent—copper acetates (verdigris) and other organometallics. Particular attention is given to the necessity of the detailed study of accompanying phases which can serve as useful indicators of natural and/or artificial origin of copper pigments. Factors affecting the stability of copper pigments in wall paintings—salt attack, oxalic acid, alkalinity and heat—are overviewed. A suitable analytical approach based on complemental combination of in situ and laboratory analyses for proper identification and differentiation of copper pigments is proposed.