S. Jorge Villar

Raman spectroscopic studies of a 13th century polychrome statue: identification of a ‘forgotten’ pigment

A Raman microscopic analysis of pigments applied to a 13th century polychrome stone statue of Santa Ana in Santa Maria la Real, Sasamon, Spain, has successfully identified the materials used. The spectral analysis reveals that the stone substrate had been treated with gypsum prior to the application of the pigments. The use of cinnabar, mercury(II) sulfide, in admixture with lead(II) lead(IV) oxide (minium), is a feature of interest; the presence of calcite in the cinnabar could point to a local mineralogical source. The presence of organic compounds in the pigments analysed suggests their use as binding agents or surface varnishes for protection or enhancement of the appearance of the statue. The use of ‘mosaic gold’, tin(IV) sulfide, in place of gold on the hem of the cape, identified by Raman spectroscopy and confirmed by SEM points to the use of a forgotten technology. Our results also suggest a spectroscopic protocol for the identification of tin(IV) sulfide in ancient pigment mixtures in the presence of other sulfide pigments such as orpiment, realgar and cinnabar. Copyright

Spanish mediaeval frescoes at Basconcillos del Tozo: a Fourier transform Raman spectroscopic study

The late mediaeval frescoes in the Church of SS Cosmo and Damian at Basconcillos del Tozo, Castille y Leon, Spain, were studied using Fourier transform Raman spectroscopy. The paintings were only discovered about 3 years ago and afforded a rare opportunity for spectroscopic analysis of pigments and substrata which have not been subjected to cleaning or re-touching over the last 600 years. Although in a polychrome palette, the most common pigments were reds, followed by black, yellow and blue; 20 samples were taken for analysis. The red pigments were identified spectroscopically and a hierarchical application is evident, with pure cinnabar being used for only the most important biblical figures. There is evidence in two of the samples taken of hydrated calcium oxalate, probably arising from lichen colonization, but it is not possible to infer whether this is pre- or post-mural painting. The substrate shows no evidence for the presence of a gypsum plaster. The difference between the red pigments in the paintings is associated spectroscopically with mixtures of red ochre and cinnabar in the figures and also organic coloured resins in the background. There is also some spectroscopic evidence for the inclusion of red lead in figures in the lower panels. Copyright

Comparative Evaluation Of Raman Spectroscopy At Different Wavelengths For Extremophile Exemplars

Raman spectra have been obtained for extremophiles from several geological environments; selected examples have been taken from hot and cold deserts comprising psychrophiles, thermophiles and halophiles. The purpose of this study is the assessment of the effect of the wavelength of the laser excitation on the ability to determine unique information from the Raman spectra about the specificity of detection of biomolecules produced as a result of the survival strategies adopted by organisms in extreme terrestrial environments. It was concluded that whereas FT-Raman spectroscopy at 1064 nm gave good quality results the time required to record the data was relatively large compared with other wavelengths of excitation but that better access to the CH stretching region for organic molecules was given. Shorter wavelength excitation of biomolecules in the blue-green regions of the visible spectrum using a conventional dispersive spectrometer was more rapid but very dependent upon the type of chemical compound being studied; most relevant biomolecules fluoresced at these wavelengths but carotenoids exhibited a resonance effect which resulted in an improved detection capability. Minerals and geological materials, in contrast, were best studied at these visible wavelengths. In general, the best compromise system for the excitation of the Raman spectra of both geological and biological materials was provided using a 785 nm laser coupled with a dispersive spectrometer, especially for accessing the 1800–200 cm−1 wavenumber shift region where much of the definitive analytical information resides. This work will have conclusions relevant to the use of miniaturised Raman spectrometers for the detection of biomolecules in extraterrestrial planetary exploration.

Application of FT-Raman spectroscopy to the characterisation of parchment and vellum, I; novel information for paleographic and historiated manuscript studies.

Raman spectra of parchment and vellum have been recorded and used to characterise materials used in mediaeval (10th century) and later works. These studies support our work on the characterisation of pigments used in historiated manuscripts and provide the basis for future studies of the interaction between pigments, binders and parchment or vellum. Examination of the undecorated parts of the manuscripts or books has been undertaken to ascertain if there are traces remaining of the procedures used to prepare the materials; in several cases, there is spectroscopic evidence for the presence of sulphates and slaked lime, which were used in the preparations of vellums for scriptoria. In one 14th century cantoral, there is evidence for paper being used as backing on the verso side of the vellum, probably from an early repair.

Raman Microscopy of a Mediaeval Spanish Cantoral

A Raman microscopic study of a 14th century Spanish choir book (cantoral) from Burgos has revealed information about the pigments used in the historiated initials, the ruled lines of Latin verse, the musical staves, and the script itself. The predominant red pigment is cinnabar, mercury(II) sulfide, which appears to have been possibly extracted and refined from local mineral sources. The black notes constituting the musical staves are comprised of lamp black. Sparse decoration with blue and purple pigments is also present; azurite is present in both of these, but the purple pigment also shows bands which are characteristic of an as-yet-unidentified organic-based red pigment. The parchment substrate spectrum shows evidence for amide I and amide III bands, with some evidence of degradation.