Mineralogical characterization of the blue pigment of Michelangelo's fresco "The Last Judgment"

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

“…The band at 2040 cm -1 might be assigned to ν(CO) (absorbed carbon monoxide) and may be linked to the purification process followed 17 . The amount of sodalite (sodalite/lazurite ratio=10%) compares very well to the lapis lazuli used by Michelangelo in the fresco of the Last Judgment (12%) 18 and could indicate the same geographical origin 13 . However, the relatively higher amounts of nepheline and quartz (nepheline/lazurite ratio=38%, quartz/lazurite ratio=7%) than in the pigment used by Michelangelo (17% and 4% respectively) may also indicate the use of a less pure pigment.…”

The presence of trapped carbon dioxide in lapis lazuli and its potential use in geo-sourcing natural ultramarine pigment

“…1 shows representative mid-IR spectra for deep blue grains from lapis lazuli hand specimens originating from (a) Afghanistan, which clearly shows the 2340 cm −1 feature, and (b) Chile, which does not show any indication of the same spectral band. The superposition of bands between 1500 and 1000 cm −1 are attributable to the different aluminosilicate, silicate, sulfate, and carbonate minerals present, and although not the focus of this research, they have been studied elsewhere [6,[19][20][21]. The absence of any indication of an overlying doublet from (c) atmospheric CO 2 in both lapis lazuli spectra (a) and (b) confirms the high quality of the instrument purge.…”

“…1(c), it was hypothesized that CO 2 trapped in lieu of (or alongside) sulfur in the aluminosilicate framework of some lazurite specimens could be responsible. This is plausible considering the tendency of sodalite group minerals to contain small neutral molecules such as water [6,13,14].…”

“…Lately, however, other potentially utilized resources of lapis lazuli, especially along the Silk Road, have come to light through ongoing geological and archaeological investigations, thus raising interest in the potential of geo-sourcing of this stone and the pigments derived from it to help elucidate ancient trade routes [3][4][5][6]. Various analytical approaches have been used to identify chemical fingerprints for lapis lazuli from different regions of the world, including Fourier-transform infrared (FTIR) spectroscopy [6][7][8][9], X-ray diffraction (XRD) [6], scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) [9], prompt gamma ray activation analysis (PGAA) [5], and electron diffraction [6].…”

“…Cl − , OH−, SO 4 2− , or S n − ), and neutral species (e.g. H 2 O) are 'enclathrated,' or entrapped [6,13]. The small pore size of the ␤-cage (2.2 Å) when compared to the molecular radius of these compounds or ions insures the enclathrated species remain resident inside the structural framework [13].…”