Raman Spectroscopic Analysis of Art and Archaeological Materials
Authors: Edwards Howell G. 
Published: March 2015

The application of Raman spectroscopic techniques to the analysis of artworks and objects recovered from archaeological depositional environments has provided novel data about their composition and degradation, which has been proved essential for their curation, conservation, and restoration particularly in the case of a range of biomaterials and pigments that have been subjected to biodeterioration. This article will describe the analytical information available from such studies, illustrated with examples of real‐world case studies covering pigments in rock art and frescoes, textiles, mummified tissues, hair, skeletal fragments, resins, ivories, and corroded items. The article will conclude with a consideration of the future application of portable Raman instrumentation for screening artworks in museums and churches and archaeological items at excavations and in the field to assist archaeologists in the preservation, storage, and damage conservation of artifacts and cultural heritage.

The analysis of artworks and archaeological artifacts differs from other analytical projects because of several unique features that need to be considered: access to the artwork is often severely restricted with security issues, the burial environment can induce chemical and physical changes to an artifact that sometimes cannot be predicted or appreciated until the excavation has commenced, and the emergency treatment carried out by archaeologists on‐site to stabilize an artifact can obscure the acquisition of subsequent analytical information in the laboratory. In addition, the changes in chemical composition of the products being studied due to external events have then to be correlated with the original starting materials, and in the case of ancient artwork and archaeological biomaterials such as textiles, resins, and adhesives, this may require parallel laboratory aging studies to be undertaken and evaluated analytically. For mummified human remains, the desire to understand mummification rituals and processes must be tempered with the knowledge that one is dealing with a deceased person and ethical considerations should always be foremost appreciated. The application of Raman spectroscopic techniques to the analysis of archaeological artifacts was first realized when long‐wavelength laser excitation was available in conjunction with microscopic sample illumination, specifically 1064 nm excitation in the near‐infrared region with a sample footprint of about 2 µm. The reason for this was twofold, namely the suppression of fluorescence emission that was particularly prevalent with objects exhumed from their depositional environments and the opportunity to interrogate heterogeneous specimens at the micron level; the fact that this operation could also be carried out nondestructively and provide analytical information from the presence of organic and inorganic components in the same sample without necessitating their mechanical separation was particularly favorable for this application. This article describes the analytical information that can be obtained from the Raman spectra of artworks and archaeological artifacts through the illustration of case studies across a wide range of materials such as mummies and human skeletal tissues, pigments, textiles, resins and waxes, glasses, ceramics, metallic corrosion, stone encrustations, wall paintings, historiated manuscripts, easel paintings, and cave paintings from prehistoric to more modern times. Wherever possible, the influence of the Raman spectral interpretation on the historical knowledge is highlighted.