Claude Coupry

Raman Spectroscopic Investigation of Blue Contemporary Textiles

Reference (natural and synthetic) indigo samples were analysed by Raman spectrometry and only indigotin was detected. ‘Jeans’ refers to a specific garment with respect to both the dye, indigo, and the garment cut; from reference spectra of blue-dyed fibres and threads from garments, it is straightforward to observe by Raman microspectrometry the spectra of dyes fixed on threads without chemical pretreatment. On these supports, the spectrum of indigotin shows extra bands assigned to vibrational modes of Bu symmetry, indicating a loss of the centrosymmetry of the molecule and an alteration of its planarity due to the dyeing process.

Fabrication processes of archaeological Egyptian blue and green pigments enlightened by Raman microscopy and scanning electron microscopy

The preparation process of Egyptian blue and green pigments was studied by using scanning electron microscopy and Raman microscopy on archaeological samples. Together they allow the identification of the molecular or crystalline structure of different areas each characterized by their elementary composition or morphology. The main result is the identification of tenorite (CuO), which proves that the syntheses of both compounds were performed in an oxidizing atmosphere. The siliceous areas are always α-quartz; in green pigments, α-cristobalite is rarely observed. In addition, a reference Raman spectrum of cuprorivaite (CaCuSi4O10), the blue crystalline compound of Egyptian blue, was obtained. Copyright

Applications in Art, Jewelry and Forensic Science

Publisher Summary This chapter focuses on the applications of Raman microscopy in art, jewelry and forensic science. As the art objects of interest are unique and precious, it is often desirable to perform the Raman examination directly on them. As is the case for colored compounds, it is often possible to enhance the Raman scattering by pigment samples with the use of the resonance technique. In particular, certain combinations and overtones may be observed which are not detectable in the ordinary Raman spectrum. This effect is often very helpful for pigment identification. The enhancement of Raman overtones by resonance can also aid in pigment identification. For two modern organic pigments, closely related in structure, the Raman spectra are quite similar. Thus nondestructive analyses by Raman microscopy provide information on materials, practices and alterations, information which is essential for art historians, conservators and restorers. For juridic reasons any clue constitutes an element which may be able to provide conclusive evidence. Therefore, it cannot be destroyed, or even damaged, by the analyses employed. Forensic science can then use Raman spectroscopy as an analytical technique, at even microdimensions, which preserves the integrity of the sample. Many different types of sample may be involved, depending on the origin, for example, biological, mineral, and synthetic materials.