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It is assumed that the unique wall mirrors found at the Archaeological Park of Pompeii (PAP) are made of obsidian. To contribute to the knowledge of those archaeological artefacts, this work proposes in situ elemental analyses in collaboration with PAP seeking to determine, in a total no-destructive way, the composition and provenance of the main mirror preserved at the House of Gilded Cupids. Comparing the geochemical composition of this black glass with that of obsidian samples collected from the main Mediterranean sources, both X-ray fluorescence (XRF) and laser-induced breakdown spectroscopy (LIBS) confirmed an incompatible content of many key elements. LIBS in-depth analysis excluded the potential relation between the higher concentration of Ca and Mg and the presence of alteration products. In addition, XRF analysis missed the detection of Rb, Y, Zr and Nb, which are widely recognized as the elemental fingerprints of obsidian sources. Combined with the detection of a high content of strontium (500–700 ppm), the in situ elemental data proved that, rather than made of obsidian, the analysed mirror was handcrafted by the fusion of coastal sand. Waiting to extend this study to the other mirrors found at Pompeii, the results here presented indicate the history of these unique artefacts needs to be rewritten. [ABSTRACT FROM AUTHOR]

Mosaics, one of the most important decorative artworks in the Roman culture, were usually elaborated with a set of tesserae joined with lime or others binders to form geometric or figurative decorations. The identification of both substrate and colored compounds of the tesserae is a challenge for chemists and archaeologists. In this work, two mosaics present in the House of Gilded Cupids from the Archaeological Park of Pompeii were analyzed in situ by non destructive techniques. Raman and Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopies were used for the molecular and mineralogical characterization, and hand-held energy dispersive X-ray fluorescence (HH-EDXRF) spectrometry and Laser Induced Breakdown Spectroscopy (LIBS) for the elemental analysis. LIBS in-depth analysis was performed to obtain insights about the thickness of the pictorial layer determining that the thickness of red and orange pictorial layers was higher than 140 μm. The results showed that white tesserae were mainly composed by calcite, while local black colored volcanic rocks were used to manufacture black tesserae. Red and orange tesserae were composed by a calcite-based matrix with a hematite pictorial layer applied over it. Orange color was obtained by diluting hematite in the calcite matrix. Principal component analysis (PCA) of the XRF data was performed to observe differences and/or similarities between the analyzed mosaics; the samples projection of the PCA showed clear groupings. [ABSTRACT FROM AUTHOR]

The House of Gilded Cupids (Regio VI, Insula 16, 7, 38) was unquestionably one of the most important residences of Ancient Pompeii, where important archaeological artefacts such as mural paintings, mosaics, sculptures and lalariums were rediscovered. This work characterizes two wall mirrors that, together with those recovered from the House of Efebo and the Domus of Euplia, represent the only ones found in the archaeological site of Pompeii. The 2015 and 2016 expeditions of the Analytica Pompeiana Universitatis Vasconicae project performed an in situ multi-analytical study, using only portable non-destructive analytical techniques. Molecular data provided by Raman spectroscopy suggested obsidian was the reflective matrix for both mirrors. Elemental data provided by energy dispersive X-ray fluorescence and laser induced breakdown spectroscopy (LIBS) systems were concordant with Raman spectroscopic results, enabling the detection of Ca, K, Al and Na as the main elements included in the Si matrix characteristic of obsidian igneous rocks. The LIBS data confirmed the presence of obsidian hydration layers. All techniques were used to investigate the degraded white and yellow crusts of the mirrors. Gypsum (CaSO4·2H2O) and nitrocalcite (Ca(NO3)2·4H2O) were identified in the white areas and gypsum and goethite (α-FeOOH) in the yellow crusts. LIBS depth profiling on the white crusts found a layer of nitrocalcite on top of the gypsum layer. Gypsum and goethite were proposed to form after partial dissolution of the mortars patches (with high iron contents) used in modern restorations around the mirrors, followed by a reprecipitation on the surface of the mirrors. Nitrocalcite was proposed to form after the attack of atmospheric NOx on gypsum crusts. These results represent the first analytical work focused on the study of these unique mirrors and provide the knowledge needed for defining more adequate conservation treatments. [ABSTRACT FROM AUTHOR]