UV-Excited Fluorescence as a Basis for the In-Situ Identification of Natural Binders in Historical Painting: A Critical Study on Model Samples

Abstract

The fluorescence emission by aged organic binders used in painting is a well-known phenomenon. Several literature studies were devoted to its investigation, both on pure binders and on their mixtures with some pigments. Nevertheless, a systematic study about the real possibility of exploiting such a phenomenon for the non-invasive identification of binders in ancient paintings is still lacking. In the present work, a prototype portable fluorimeter was used to analyze a significant number of model painting samples containing different binders (drying oils, egg yolk, milk, animal glue, and gum Arabic) mixed with various pigments having different hues. The model samples were naturally aged in a period ranging from fifteen to one year. The effects on the spectral pattern due to the different binders, the recipes used to prepare them, and the pigments mixed with them were examined. The fluorescence spectra were corrected for the absorption of the emitted radiation due to the pigments. Finally, the corrected spectra were treated by principal component analysis to determine if the possibility of distinguishing at least the most fluorescent and common binders, i.e., drying oils and egg, existed. It was shown that, even if the technique cannot be effectively applied in the case of mixed or superimposed binders, it allows to put forward at least a preliminary hypothesis when pure binders are used.

Multianalytical Non-Invasive Characterization of ‘Mater Boni Consilii’ Iconography Oil Painting

“…It is possible to better distinguish areas with thinner varnish layers, which can be identified by less intense fluorescence, and areas that show an excess of varnish, identified by more intense fluorescence. As widely discussed in the scientific literature [17], different aging binders have similar fluorescence emissions. The IR reflectography investigation did not reveal traces of either underlying drawings made with absorbent IR material (i.e., charcoal, pencil, or black pigment brush), or traces of pentimenti (Figure 5).…”

“…Fourier Transform Infrared spectroscopy (FTIR) was performed using a Thermo Scientific Nicolet Summit Pro spectrometer with an Everest TM Diamond ATR accessory, with a spectral resolution of 4 cm −1 , placing the painted surface directly in contact with the diamond of the ATR (at the paint loss in the upper left corner), investigating the spectral region between 4000-600 cm −1 . A total of 32 scans were performed on the sample, and the spectrum was analyzed by comparing it with databases and scientific bibliographies [13,14,17,18].…”

Novel integration of non-invasive imaging techniques for the analysis of an egg tempera painting by Pietro Lorenzetti

“…Moreover, the overall fluorescence signal of a paint is strongly influenced by the binder in which the pigment particles are dispersed, especially if the pigment is a weak emitter or does not exhibit any fluorescence. On the one hand, given the strong contribution of the egg binder (fluorescence emission band centred at 510-520 nm [31]), which is present in both the reference samples and the painting, it is reasonable to expect a flattening of the differences between the respective phasors. On the other hand, the different degree of ageing between the reference paints and the examined painting should result in a nearly constant difference in the τ-phase between the painting and the reference samples.…”

Inside the Scriptorium: Non-Invasive In Situ Identification of Dyes in Illuminated Manuscripts by Microspectrofluorimetry and Multivariate Analysis: The Crescenzago Choir Books (End 15th Century) as a Case Study

“…The results of these analyses are shown for some of the reference samples in Figure 2, which illustrates the comparison between the fluorescence spectra acquired on the same mock-up of lake spread on parchment at three different excitation wavelengths: 365 nm, 435 nm and 500 nm. From this comparison it is evident that the best results have been obtained for the fluorescence spectra excited at 500 nm: the bands due to the dyes are in fact enhanced, and the contribution of the binder and the parchment is limited, since their absorption maxima do not lie in the visible region [47].…”

“…Heritage 2023, 6, FOR PEER REVIEW 8 obtained for the fluorescence spectra excited at 500 nm: the bands due to the dyes are in fact enhanced, and the contribution of the binder and the parchment is limited, since their absorption maxima do not lie in the visible region [47]. Consequently, these experimental conditions were transferred to the microprobe by selecting the closest commercially available combination of interference and dichroic filters, respectively centered at 482.5 nm and with a cut-on wavelength of 516 nm.…”