Identification of the natural red dyes and lakes from plants (the madders) and insects (cochineal, lac, and kermes) is typically carried out with destructive methods such as high performance liquid chromatography (HPLC), which can require time consuming and complicated sample preparation and method development. Identification with Fourier transform infrared spectroscopy (FTIR) is usually not possible due to the low concentration of the dye and the presence of the binder, and Raman is generally hindered by fluorescence without a specific instrumental set up. The ability to identify these materials with the non-invasive technique of UV-Vis-NIR fibre optic reflectance spectroscopy (FORS) offers many advantages, as no samples are required and the technique is very sensitive to dyes. There have already been several published studies on the analysis of these red dyes using FORS. While it is sometimes possible to distinguish between these dyes or broadly classify them as of animal or insect in origin, in the analysis of real paintings identification is complicated by the presence of other pigments, the nature of their application, as well as effects of natural ageing. These factors can mask or alter characteristic features in UV-Vis-NIR reflectance spectra. In this study, several of these factors are taken into consideration in order to address the potentiality of UV-Vis-NIR FORS for the analysis of red lakes in paintings. Replicas were prepared using red lakes in several different applications, which were devised to reflect those commonly encountered in tempera painting. The resulting reflectance spectra will be discussed in relation to the different preparations. Lastly, these reference spectra will be compared to those acquired from real tempera paintings.
UV-Vis-NIR reflectance spectroscopy of red lakes in paintings
M Picollo;M Bacci;
2008
Abstract
Identification of the natural red dyes and lakes from plants (the madders) and insects (cochineal, lac, and kermes) is typically carried out with destructive methods such as high performance liquid chromatography (HPLC), which can require time consuming and complicated sample preparation and method development. Identification with Fourier transform infrared spectroscopy (FTIR) is usually not possible due to the low concentration of the dye and the presence of the binder, and Raman is generally hindered by fluorescence without a specific instrumental set up. The ability to identify these materials with the non-invasive technique of UV-Vis-NIR fibre optic reflectance spectroscopy (FORS) offers many advantages, as no samples are required and the technique is very sensitive to dyes. There have already been several published studies on the analysis of these red dyes using FORS. While it is sometimes possible to distinguish between these dyes or broadly classify them as of animal or insect in origin, in the analysis of real paintings identification is complicated by the presence of other pigments, the nature of their application, as well as effects of natural ageing. These factors can mask or alter characteristic features in UV-Vis-NIR reflectance spectra. In this study, several of these factors are taken into consideration in order to address the potentiality of UV-Vis-NIR FORS for the analysis of red lakes in paintings. Replicas were prepared using red lakes in several different applications, which were devised to reflect those commonly encountered in tempera painting. The resulting reflectance spectra will be discussed in relation to the different preparations. Lastly, these reference spectra will be compared to those acquired from real tempera paintings.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.