In situ X-ray fluorescence-based method to differentiate among red ochre pigments and yellow ochre pigments thermally transformed to red pigments of wall paintings from Pompeii
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Most of the magnificent wall paintings from the ancient city of Pompeii are decorated with red and yellow colors coming from the ochre pigments used. The thermal impact of the pyroclastic flow from the eruption of Vesuvius, in AD 79, promoted the transformation of some yellow painted areas to red. In this work, original red ochre, original yellow ochre, and transformed yellow ochre (nowadays showing a red color) of wall paintings from Pompeian houses (House of Marcus Lucretius and House of Gilded Cupids) were analyzed by means of a handheld energy-dispersive X-ray fluorescence spectrometer to develop a fast method that allows chemical differentiation of the original red ochre and the transformed yellow ochre. Principal component analysis of the multivariate obtained data showed that arsenic is the tracer element to distinguish between both red colored ochres. Moreover, Pompeian raw red and yellow ochre pigments recovered from the burial were analyzed in the laboratory with use of a benchtop energy-dispersive X-ray fluorescence spectrometer to confirm the elemental composition and the conclusions drawn from the in situ analysis according to the yellow ochre pigment transformation in real Pompeian wall paintings.
KeywordsRed ochre Yellow ochre Color transformation Dehydration process Arsenic traces X-ray fluorescence spectrometry
The authors thank the Naples National Archaeological Museum for the permission given to extract samples of raw pigments contained in the original bowls. Moreover we gratefully thank the “Soprintendenza Pompei” for the permission given to analyze in situ the wall paintings in the houses studied. Iker Marcaida and Marco Veneranda are grateful to the Basque Government and the Ministry of Industry and Competitiveness (MINECO) respectively, which funded their predoctoral fellowships. This work was funded by the Ministry of Economy and Competitiveness (MINECO) and the European Regional Development Fund (FEDER) through the project DISILICA-1930 (reference BIA2014-59124-P).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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