Characterisation of a portable Raman spectrometer for in situ analysis of art objects.

During the last decades, Raman spectroscopy has grown to an established analytical technique in archaeometry, art analysis and conservation science. Mobile Raman instruments were designed to be used for in situ characterisation and identification of inorganic and organic materials in art and archaeometry. This research paper aims to point out several aspects that need to be considered when selecting a mobile Raman spectrometer for in situ archaeometrical studies. We describe an approach to evaluate these parameters and apply this to a dual laser portable Raman spectrometer. Twofold characterisation of mobile Raman instrumentation for art analysis: (i) investigation of spectroscopic characteristics such as (amongst others) spectral resolution, spectral window, signal to noise ratio and limit of detection; (ii) evaluation of specific properties that are useful for mobile studies in archaeometry. These include options for easy positioning and focussing, the ability to reduce laser power on the surface of the art object and the working distance between the probehead and the artefact. Finally, the research was completed with field tests by studying the pigments of a mediaeval wall painting.

Provenance determination of Vinica terra cotta icons using self-organising maps.

In the Vinica Fortress, Republic of Macedonia, 50 undamaged terra cotta icons and 100 fragments, all dated 6th-7th century, were found. In order to determine the provenance of these unique terra cotta icons, the mass fractions of 19 different chemical elements were previously determined in ten fragments of the terra cotta icons and thirty three samples of clays from eight different sites from the region. Due to the dimensionality and complexity of the experimental data, the archaeometric results were treated with self-organising maps (SOM). The results obtained using SOM were compared with the ones obtained using principal component analysis. Both chemometric methods revealed that Vinica terra cotta icons were made from clay from Grncarka, 2.5 km South-East from the Vinica Fortress.