Characterization of an unusual black patina on the Neang Khmau temple (archaeological Khmer area, Cambodia): a multidisciplinary approach A. Casanova Municchia, a * F. Bartoli, a S. Bernardini, a G. Caneva, a G. Della Ventura, a M. A. Ricci, a T. Boun Suy b and A. Sodo a In the archaeological Khmer complex (Cambodia), an unusual black patina covering both the exterior and interior walls of the Neang Khmau temple, has been observed during a recent conservative survey. In fact, it is present over all the four facades of the temple, covers a relevant part of the vertical surfaces protected from rainfall and is also homogeneously distributed on the interior of the mon- ument. The upper and the lower areas show, on the contrary, a relevant lichen growth. The temple was built by using laterite bricks, a natural material common in tropical areas as a weathering product of pre-existing rocks. A preliminary investigation on the patina samples together with ecological considerations excluded a biological origin of the black alteration, thus prompting a more detailed study. In this work, we have investigated the physico-chemical origin of this unusual patina by identifying its mineralogical and chem- ical composition. Raman and FTIR spectroscopies, SEM-EDS, micro-XRF and XRPD have been applied to characterize the alteration products. Analyses have been performed both on single fragments and on polished cross sections collected from all four temple facades and from one area in the temple interior. Optical observations of the cross sections have evidenced irregularities in the thick- ness of the patina. Raman and FTIR spectra have revealed that the black layers are mainly composed of manganese minerals (hollandite, romanechite and manganite). This peculiar alteration pattern is interpreted as because of the tropical climatic conditions of Cambodia. Indeed the variation of wet and dry seasons favours the migration of iron and manganese ions and their successive immobilization in regions not directly subject to leaching. Copyright © 2016 John Wiley & Sons, Ltd. Additional supporting information may be found in the online version of this article at the publisher’s web site. Keywords: patina; stone deterioration; archaeological site; manganese oxides; laterite Introduction The archaeological Khmer area is one of the most important archaeological sites in Cambodia, as it contains the ruins of two cap- itals of the Khmer Empire (Angkor and Koh Ker), belonging the 9th to the 15th century AD. The area was left in a state of neglect for cen- turies, and only since 1993, thanks to the UNESCO participation, the international community and the Cambodian authorities have planned restoration works and scientific and conservation projects, aimed at preserving and adding value to this impressive archaeolog- ical park. The entire area includes about 40 main monuments in the Angkor region and remains of about 76 temples in the Koh Ker area. All monuments were built using sandstone, laterite and bricks. [1–3] Recent studies of the temples record the observation of various forms of deterioration of the stones. [4–8] The most common are bio- deterioration processes because of microorganisms and plant colo- nization (bacteria, cyanobacteria, algae, lichens and higher plants), because of the climate and lush greenery of the area. The associ- ated damage is visible as a coloured bio-patina ranging from green, to pink and black on the walls of the temples. [9–12] The danger of the biological colonization is extensively discussed in the literature. [13] On the other hand, several studies have evidenced deterioration patterns because of chemical/physical causes, such as weathering processes of sandstones bricks because of wet–dry cycles, [7] or to efflorescence of salts related to bat guano. [2] Many monuments in the Archaeological Khmer area are affected by anomalous and uninvestigated stone alterations that are worth addressing. This paper focuses on the characterization of an unusual black alteration observed on the exterior and interior walls of the temple Neang Khmau, in the Koh Ker area. Black alterations are generally because of biological colonization, which is heavily recurrent in tropical countries, or natural black to brown thin layer enriched in iron/manganese minerals (desert varnish) [14,15] or to an accumula- tion of pollutants (black crusts) and, last but not least, to a chemical modification of the original material. [9,16] Distinguishing among these alteration patterns is mandatory for the correct conservation or restoration treatment, although this task is often not easy and requires a multidisciplinary approach. A preliminary investigation of the samples object of this study, excluded that the black alteration of the Neang Khmau temple was because of a biological colonization. Thus, we used a multi- methodological approach combining Raman and FTIR spectros- copies, scanning electron microscopy coupled to energy dispersive (SEM/EDS), micro-XRF and powder X-ray diffraction (XRPD), with the aim of addressing the origin of this patina. * Correspondence to: Annalaura Casanova Municchia, Università Roma Tre, Dipartimento di Scienze, Viale G. Marconi 446, Italy. E-mail: acasanovamunicchia@uniroma3.it a Università Roma Tre, Dipartimento di Scienze, Viale G. Marconi 446, 00146, Rome, Italy b Authority for the Protection and Management of Angkor and the Region of Siem Reap (APSARA), Siem Reap 17251, Cambodia J. Raman Spectrosc. (2016) Copyright © 2016 John Wiley & Sons, Ltd. Research article Received: 14 January 2016 Revised: 18 May 2016 Accepted: 24 May 2016 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI 10.1002/jrs.4969