A multi-analytical approach for the identification of aloe as a colorant in oil-resin varnishes.
Aloe plants have been widely documented in artists' treatises dating from the sixteenth to the nineteenth century as a source of colorant to achieve lustrous golden glazes on tin- and silver-foiled objects and warm-toned finishes on musical instruments, such as violins. Aloe extracts contain characteristic anthraquinone and phenolic components which impart a distinctive orange tone and fluorescence to mixtures containing them. Because of the low concentration of colorant in the coatings and its probable degradation by high temperature during manufacture, the identification of aloe in heated oil-resin mixtures represents an analytical challenge. For this reason, the possible presence of aloe in glazes and coatings has been largely overlooked. This paper describes various analytical approaches to the identification of aloe in historic samples, from comparison with results obtained from reference standards and mock-up samples. Complementary analytical techniques including thermally assisted hydrolysis and methylation-gas chromatography-mass spectrometry, high-performance liquid chromatography, laser desorption-mass spectrometry, matrix-assisted laser desorption-ionization-mass spectrometry and surface-enhanced Raman scattering were used. Different chemical markers were identified by the individual methods and the advantages and limitations of each technique for the identification of aloe in oil-resin varnishes are discussed.
Department of Scientific Research, The Metropolitan Museum of Art, 1000 5th avenue, New York, NY 10028, USA. adriana.rizzo@metmuseum.org
Adriana
A
Rizzo
Nobuko
N
Shibayama
Daniel P
DP
Kirby
D000504:Aloe / Q000737:chemistry*; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004396:Coloring Agents / Q000032:analysis*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D013058:Mass Spectrometry / Q000379:methods; D015394:Molecular Structure; D010150:Paint / Q000032:analysis*; D010936:Plant Extracts / Q000737:chemistry*; D012116:Resins, Plant / Q000737:chemistry*; D013059:Spectrum Analysis, Raman
D004396:Coloring Agents; D010936:Plant Extracts; D012116:Resins, Plant