Raman microscopy as a tool to discriminate mineral phases of volcanic origin and contaminations on red and yellow ochre raw pigments from Pompeii

Raman microscopy is a molecular technique that is able to detect compounds that are present in the samples at minor/trace levels thanks to the precise focusing on particles of interest. The detection will also depend on the Raman scattering of the measured compound. Moreover, due to the nondestructive character of the measurements, this technique is one of the most used when samples under study belong to the arts and archaeological fields. Among the different archaeological sites in the world, Pompeii is one of the most important ancient cities. In this work, Raman microscopy—supported by X‐ray diffraction—has been used to detect traces of mineralogical phases of volcanic origin and contaminations in red and yellow ochre pigments. These samples were buried for thousands of years and recovered from the archaeological site of Pompeii in their original bowls. On the one hand, regarding the characteristic mineral phases of volcanic origin, the obtained results showed the presence of langite [Cu 4 (SO 4 )(OH) 6 ·2H 2 O], jarosite [KFe 3 (SO 4 ) 2 (OH) 6 ], atacamite [Cu 2 Cl (OH) 3 ], and anatase (β‐TiO 2 ), a polymorph of titanium oxide found in igneous rocks. On the other hand, contamination compounds such as Egyptian or Pompeian blue (CaCuSi 4 O 10 ) and huntite [Mg 3 Ca (CO 3 ) 4 ] were also identified. Some of the compounds identified by micro‐Raman spectroscopy could not be detected using X‐Ray diffraction and vice versa. Therefore, it was corroborated the necessity of using more than one unique technique in order to obtain a complete information about the molecular composition of the ochre pigments under study.