Dennis W. Farwell

FT Raman microscopy of untreated natural plant fibres

The application of FT-Raman microscopy to the non-destructive analysis of natural plant fibres is demonstrated with samples of flax, jute, ramie, cotton, kapok, sisal and coconut fibre. Vibrational assignments are proposed and characteristic features of each material are presented. Samples were not pre-treated chemically before analysis and were used directly from their respective storage collection; the adaptation of the Raman microscopic technique to the identification of specimens of natural fibres in archaeological burial sites is explored for its forensic potential.

Fourier-transform Raman spectroscopic study of natural waxes and resins. I

Abstract The Fourier transform-Raman spectra of some natural waxes and resins that have been found in preparations of archaeological material have been identified non-destructively. Vibrational assignments are proposed which assist in the identification of the materials used; in one case, a sample of paper impregnated with a wax component, the presence of beeswax was identified. This work forms part of a programme for the characterisation of natural materials, which is addressed in their conservation and preservation.

A critical comparison of some Raman spectroscopic techniques for studies of human stratum corneum

This study evaluates a variety of techniques and sampling conditions for Raman spectroscopic investigations of human stratum corneum. Using a Fourier-transform Raman system and samples of stratum corneum in vitro, we demonstrated minimal inter- and intracadaver variations in molecular vibrations. We have also shown Raman spectroscopy to be relatively insensitive to the hydration state of human stratum corneum, indicating that the technique should be valuable for monitoring the transdermal delivery of drugs from aqueous solutions. The stability of human stratum corneum to near-infrared laser excitation was verified by spectral collection for approximately 1 hr. We have also compared FT-Raman spectra from human stratum corneum in vitro and in vivo. Of the different types of Raman instruments used in this study (visible-light excitation microprobe, visible-light excitation macroscopic sampling, and Fourier-transform Raman), the FT-Raman system provided good-quality spectra with high sample throughput, but systems using visible-light excitation should provide unique information for use in specialist applications.

Fourier-transform Raman spectroscopy of ivory: II. Spectroscopic analysis and assignments

Abstract The FT-Raman spectra of African and Asian elephant and woolly mammoth ivory are reported and comprehensive molecular vibrational assignments are proposed. Since ivory is composed of proteinaceous collagen embedded in an inorganic matrix of carbonated hydroxyapatite, the Raman spectrum of pure natural collagen recorded under similar conditions aids the identification of the vibrational modes. Several bands are identified which could be used for the Raman spectroscopic characterisation of the mammalian ivories studied.

Fourier-transform Raman spectroscopic study of human hair

Fourier-transform Raman microscopic spectra of normal, untreated and bleached hair fibres are presented. Vibrational assignments are made and differences are ascribed to the production of cysteic acid from cysteine. Changes in conformation associated with the disulphide bond in the keratotic component are noted from the v(CSSC) vibrational modes at wave numbers near 500 cm-1. Raman spectra of hair root ends have also been investigated with a diminution in cysteine content being observed. Application of the technique to the biomedical investigation of healthy and diseased hair is proposed.

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

Raman spectroscopic study of 3000‐year‐old human skeletal remains from a sambaqui, Santa Catarina, Brazil

A Raman spectroscopic study of red-pigmented human bones from a 3000-year-old sambaqui burial was undertaken for the first time. Visible (633 nm) and near-infrared (1064 nm) excitation were used to characterize the pigment and its substrate; the red pigment is haematite, iron(III) oxide, which proved to be of a pure form and for which no previous heat treatment processing had been adopted. There is clear evidence in heavily pigmented areas of a ‘limewash’ layer which had been applied to the body of the deceased prior to treatment with ochre. Comparisons made with previous Raman studies of archaeological bone from a separate excavation indicate that mineralization of the present specimens is well advanced, with evidence of calcium carbonate incorporation into the hydroxyapatite phosphatic matrix. Copyright

FT-Raman spectrum of cotton : a polymeric biomolecular analysis

Abstract FT-Raman spectra of cotton in the form of a natural plant boll and as an open-weave surgical bandage fabric have been obtained and comprehensive vibrational assignments of natural cellulose have been made. Comparisons are made with the vibrational spectra of mono- and disaccharides such as α- d -glucose and maltose and with partial assignments for other forms of cellulose.

Raman spectra of oxalates in lichen encrustations on Renaissance frescoes

Abstract The vibrational Raman spectra of lichen encrustations on biodeteriorated Renaissance frescoes have been recorded using a laser Raman microprobe. The major chemical species identified in the encrustations is calcium oxalate. Other vibrational features in the Raman spectra have been assigned to fragments of the substratum incorporated from the biodeterioration process and to organic by-products of lichen metabolism such as erythrin, lecanoric acid and meso -erythritol.