Clinical computed tomography and surface-enhanced Raman scattering characterisation of ancient pigments

Sveva Longo,Francesca Granata,Silvia Capuani,Enza Fazio,Fortunato Neri

doi:10.21014/acta_imeko.v10i1.805

Sveva Longo, Francesca Granata + Show 3 more

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https://doi.org/10.21014/acta_imeko.v10i1.805

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Journal: Acta IMEKO	Publication Date: Mar 31, 2021
Citations: 1	License type: cc-by

Affiliation: University of Messina, Sapienza University of Rome

Abstract

<p class="Abstract">A systematic and complete chemical and physical characterisation of painted pigments on wood samples was carried out using multislice X-ray computed tomography (MSCT) and surface-enhanced Raman scattering (SERS) techniques. Inorganic and organic pigments present on the wooden tablets were differentiated by MSCT determinations of Hounsfield units, a semi-quantitative method for measuring X-ray attenuation that, in turn, offers an indirect estimation of a material’s density. However, the MSCT technique is not as reliable as traditional spectroscopic techniques for recognising and classifying organic pigments. Nevertheless, a strength of the MSCT approach was its ability to simultaneously provide a volumetric view of the wood and segment the layers of the specimen using suitable reconstruction methods such as is generally done for biomedical applications. Furthermore, the SERS technique made it possible to identify the type of material present in the pigments (for both inorganic or organic materials) with a high spatial resolution, even pigments in mixtures or those applied directly on the investigated wooden support. The combined MSCT and SERS data obtained through this systematic investigation constitutes the basis for the assembly of larger reference databases that will ultimately support the development of long-term conservation protocols.</p>

Highlights

The identification and characterisation of pigments provide essential information for the dating, authentication and conservation of wood-based objects and for the study of art history in general [1], [2]
A systematic and complete chemical and physical characterisation of painted pigments on wood samples was carried out using multislice X-ray computed tomography (MSCT) and surface-enhanced Raman scattering (SERS) techniques
Clinical MSCT was applied to the investigation of pigments painted on a wooden support

Summary

Introduction

The identification and characterisation of pigments provide essential information for the dating, authentication and conservation of wood-based objects and for the study of art history in general [1], [2]. Different methods are used to describe inorganic and organic pigments due to the intrinsic limitations of the techniques: X-ray fluorescence cannot provide a definitive elemental signature; Fourier transform infrared spectroscopy is limited by the interference of binders and extenders [3] and high-performance liquid chromatography [4] requires relatively large samples (0.5–5 mm in diameter). In the last few years, portable Raman setups have regularly been used to study a wide variety of materials, including paper, in order to follow degradation processes or create spectral reference libraries of organic and inorganic pigments. Some laser source wavelength is absorbed by specific pigments, leading to extensive fluorescence backgrounds, which obscure the weak Raman signals, or in worse cases, cause photo-degradation of the sample, preventing pigment identification [5]. Surface-enhanced Raman scattering (SERS) addresses these difficulties since the presence of noble metal nanoparticles induces a giant amplification of the Raman signal [6]

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