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In situ micro‐Raman spectroscopy (μ‐RS) of rock art paintings in open‐air rock shelters entails several difficulties: sunlight, wind, dust and crusts that mask Raman signals from the pigments and any other component of the paint recipe. These problems have been considered in the present work. Special attention has been devoted to the presence of crusts. Five rock art sites in the eastern Iberian Peninsula with outstanding difficulties to be analysed by this technique have been the object of this study. In situ energy dispersive X‐ray fluorescence and diffuse reflectance infrared Fourier transform spectroscopy using portable instruments have provided important help. Moreover, microstratigraphic studies by μ‐RS and scanning electronic microscopy combined with energy dispersive X‐ray spectroscopy of micro‐specimens from the painting panels have revealed the distribution of the different components. Dolomite and calcite are dominant minerals in the rock substrata. Whewellite, gypsum, calcite, clay, dolomite, α‐quartz, anatase and haematite have been found on the surface of the painting panels or forming stratified layers in the crusts. Haematite and amorphous carbon have been detected in red and black pictographs, respectively. Copyright © 2014 John Wiley & Sons, Ltd.

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This work presents the results of field Raman analyses, assisted by a hand-held energy dispersive X-ray fluorescence spectrometer, for the experimental determination of efflorescence from walls and wall paintings of two Pompeian houses, one with many luxurious decorative elements (House of Marcus Lucretius, Regio IX, Insula 3, House 5/24) and a more modest building (Regio IX, Insula 3, House 1-2). Both exposed and protected rooms were measured in different year seasons, spring (May 2010) and summer (September 2011 and 2012) and considering different orientations. Chemical attacks of acid gases (CO 2 , SO 2 and NO x ) on the original compounds of the mortars, biominerals formed by the biological colonizations as well as direct rain-wash of the newly formed salts can be considered the three most serious problems of the archaeological remains from Insula IX 3 of Pompeii. Also, infiltration waters from the ground contribute to such decay. The walls and wall paintings exposed to the rain-wash are the worst preserved, probably as a result of a continuous cycle of CO 2 , SO 2 and NO x acid attack to the original carbonate materials, involving loss of plaster. This severe decay was not observed in the rooms covered by roofs although those walls affected by infiltration waters from the ground showed decaying because of the action of the efflorescence on the carbonate materials acting as the binder of the mural painting remains in the houses of Pompeii.

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