Copper resinate: preparation, characterisation and study of degradation.
This paper describes a method for the synthesis of Copper Resinate, which disappeared from artists' palettes in the eighteenth century. This was carried out by interpreting ancient recipes following a scientific approach. Its characterisation using Fourier Transform-Infrared Spectrometry and Gas Chromatography-Mass Spectrometry demonstrated that it is a mixture containing copper and oxidised abietic acids, mainly dehydroabietic and 7-oxo-dehydroabietic acids, formed during the preparation of the pigment and the curing of the paint layer. The composition of copper resinate paint layers, artificially aged by U.V. irradiation at 365 nm (UV), heating (T), and exposed to atmospheric pollutants (NOX) in a climatic chamber, was investigated. The combination of irradiation and temperature produced a change in colour along with a significant increase in the recovered amount of 7-oxo-dehydroabietic acid. The identification of copper resinate in a sample from an old painting should be related to the presence of the following resin compounds which are stable in the ageing process: dehydroabietic and 7-oxo-dehydroabietic acid pimaradienic acids. Photo-oxidation of the resin acids co-ordinated with copper seem to be the most probable decay mechanism responsible for the colour change in the pigment.
Colombini
M P
MP
Dipartimento di Scienze Ambientali e del Territorio, Università di Milano Bicocca, P.za Scienza 1, 20126 Milano, Italy. mariaperla.colombini@unimib.it
Lanterna
G
G
Mairani
A
A
Matteini
M
M
Modugno
F
F
Rizzi
M
M
D045784:Abietanes; D003300:Copper / Q000737:chemistry*; D004224:Diterpenes / Q000032:analysis; D008401:Gas Chromatography-Mass Spectrometry; D049669:History, 16th Century; D007558:Italy; D010150:Paint / Q000032:analysis / Q000266:history; D010151:Paintings / Q000266:history*; D010616:Phenanthrenes / Q000032:analysis; D010860:Pigments, Biological / Q000138:chemical synthesis / Q000737:chemistry* / Q000266:history; D012116:Resins, Plant / Q000737:chemistry*
D045784:Abietanes; D004224:Diterpenes; D010616:Phenanthrenes; D010860:Pigments, Biological; D012116:Resins, Plant; C013913:dehydroabietic acid; D003300:Copper; C095375:7-oxodehydroabietic acid