Some practical aspects of pigment analysis using Raman spectroscopy

An artwork often is a complex, multilayered and multicomponent system build-up. Chemical interaction between these components and layers, which age over time, influenced by environmental conditions, can lead to reactions that alter the visual impression, the integrity and the materials of an artwork. Conservation science is thus confronted with alterations at different interfaces and levels such as for example the pigment–environment (e.g. Cato et al. 2017), pigment-binder (Fig. 1, Ferreira et al. 2015) and the varnish-environment (e.g. Soulier et al. 2012) interface.
To learn more about these phenomena, our current strategy is minimally invasive, combines the complementary techniques of infrared imaging (ATR-FTIR-FPA), Raman spectroscopy and scanning electron microscopy (VP-SEM, SE/BSE/EDS), applied sequentially to micro-samples. This combination not only covers a wide range of materials, but also delivers morphological and 2D stratigraphic information from minimal amounts of sample material.

With respect to pigment identification on micro samples, Raman has many strong advantages in tracking down pigment traces, both inorganic and synthetic organic pigments. It probably even may be called ‘THE’ technique, when it comes to synthetic organic pigment detection and identification (e.g. Scherrer et al. 2009). Yet, in many cases, Raman cannot rely on simple routine measurements. This presentation gives some insight into non-standard behaviour at the laser-pigment interface and possible approaches to retrieve a useful spectrum.

Literature References
Cato E. et al. (2017). J Raman Spectrosc 1-10.
doi.org/10.1002/jrs.5256
Ferreira E. et al. (2015). Herit Sci 3(1): 1-11.
doi.org/10.1186/s40494-015-0052-3
Scherrer et al. (2009). Spectroc. Acta Pt. A-Molec. Biomolec. Spectr. 505-524. doi.org/10.1016/J.Saa.2008.11.029
Soulier et al. (2012). Z Kunsttechnol Konserv 108-117.
https://www.hkb.bfh.ch/en/conservation-and-restoration/consulting-services/