New insights on blue pigments used in 15th century paintings by synchrotron radiation-based micro-FTIR and XRD

Abstract

The blue pigments used on altarpieces in 15 th Century in Catalonia and Crown of Aragon are principally the azurite mineral. To a lesser extent lapis lazuli, also of mineral origin and occasionally, in the background areas, outlining the figures, and for the chromatic ground layer, indigo, were used. Data from several altarpieces belonging to well-known artists of the time is presented. Synchrotron radiation X-ray diffraction (SR-XRD), micro-infrared spectroscopy (µ-FTIR), synchrotron radiation micro-infrared spectroscopy (µSR-FTIR), Raman spectroscopy, scanning electron microscopy with Xray microanalysis (SEM-EDS) are used. X-ray diffraction and infrared spectroscopy in association with synchrotron radiation have shown to be especially interesting due to the micron spot sizes, high brilliance and energy tunability which help to obtain good separation of the signals coming from different phases/substances and their localization in the various paint layers. Examples are presented which illustrate the potential of each analytical technique for the identification of this kind of materials in the 15 th century paintings. The natural origin and composition of the pigments and its distribution in the paint layers are determined and some correlations with other contemporary paintings obtained. Finally, the alteration compounds related to blue pigments are determined in each case.

Raman spectroscopy of minerals and mineral pigments in archaeometry

“…Salvadó et al made a multitechnique microanalysis of the blue paints in different altarpieces in Catalonia and Crown of Aragon from the 15th century, identifying lapis lazuli, azurite and indigo. Veneranda et al identified the compounds constituting a mural painting in the Assumption's church of Alaiza in Basque Country, Spain, and investigated the degradation induced by agricultural activities.…”

Investigation of the Optical, Physical, and Chemical Interactions between Diammonium Hydrogen Phosphate (DAP) and Pigments

“…cm −1 region, which could be linked to an overlapping of Al, Si-O4 tetrahedra symmetric stretching vibration of lazurite and O-Si-O symmetric stretching vibration of wollastonite [61]. The band at 568 cm −1 and the band at 452 cm −1 represent the terminal -O-Si-Obonds bending vibration and Si-O-Si bending vibration, respectively [62][63][64]. The visible spectrum of the lapis lazuli was dominated by an absorption band around 600 nm, corresponding to the electronic transitions for S3 − (see Figure 3g).…”

“…The FTIR spectra showed bands in the 1100-900 cm −1 region that could be assigned to overlapping of Al, Si-O 4 tetrahedra asymmetric stretching vibration of lazurite and O-Si-O asymmetric stretching vibration of wollastonite, as well as bands in the 700-600 cm −1 region, which could be linked to an overlapping of Al, Si-O 4 tetrahedra symmetric stretching vibration of lazurite and O-Si-O symmetric stretching vibration of wollastonite [61]. The band at 568 cm −1 and the band at 452 cm −1 represent the terminal -O-Si-Obonds bending vibration and Si-O-Si bending vibration, respectively [62][63][64].…”

Non-Invasive and Non-Destructive Examination of Artistic Pigments, Paints, and Paintings by Means of X-Ray Methods

“…XRD and SR-FTIR proved to be especially useful. The application of several layers with decreasing particle size, starting with azurite and finishing with lapis lazuli relates these artworks van Eyck's ''Adoration of the Mystic Lamb'' [196]. Synthetic ultramarine shares many properties with its natural form.…”