## 5 Conclusions  
Several non-invasive and micro-invasive analytical approaches were used to identify pigments and binding mediums used in the Burmese wall paintings at Me-taw-ya in Myanmar. The use of EDXRF data for the pigment identification may be more complicated when dealing with the altered ones, due to the advanced state of decay of the wall painting in an archaeological context, as in the case of the Me-taw-ya temple. Using PCA, the association of mercury with chlorine or arsenic suggests two degradation mechanisms of mercury related respectively to the darkening of vermilion, or its adulteration with an As-bearing pigment. The Raman spectroscopy performed in situ revealed two forms of oxalates, weddellite and whewellite, suggesting traces of organic compounds. In addition, only at one point was the orpiment agent, even if the widespread detection of arsenic in the paintings remained unexplained. Conversely, Raman spectra acquired on paint samples were useful to identify hematite and vermilion for the red paints, with carbon black probably in lampblack form for the blackish areas. An FTIR-ATR analysis performed directly on the painted surface of the micro-samples showed calcite and quartz and a primer layer composed of clay minerals, together with oxalates detected both on the plaster and on the paint layer. The possible use of Neem gum and honey was demonstrated as the binding medium in the paintings by GC-MS analysis, confirming 'a secco' technique. It is interesting to highlight that the Neem gum is extracted from the bark of this endemic tree, characterised by antisceptic properties probably against the attack of termites and ants to which the paintings are often subjected. For the same purpose, we argue that Neem oil together with animal glue were added to the plaster used in the temple. PLM and SEM-EDS analyses allow us to corroborate the previous findings of the technique of Burmese painting: a lime-based plaster mixed with an organic binder together with quartz, feldspars, Fe-based compounds, Ti-oxide, and silicates (i.e., homblende, albite and muscovite) was used in support of the murals at Me-taw-ya. Moreover, a primer layer composed of clay minerals together with As-based compounds was applied. These latter compounds were found with different arrangements mainly in the primer layer, in which it seems to be its major component and it could justify the high As-levels revealed also by EDXRF and its uniform appearance. Therefore, its presence cannot be uniquely ascribed  
Figure 10: Sample MY31: (**a**) BSE-SEM micrographs; (**b**) EDS spectrum of the primer layer. to the alteration of As-based pigments. Further analyses will be carried out in order to ascertain the nature of the As-based compounds. The following is available online at [[https://www.mdpi.com/article/10.390/app112311441/s1](https://www.mdpi.com/article/10.390/app112311441/s1)]([https://www.mdpi.com/article/10.390/app112311441/s1](https://www.mdpi.com/article/10.390/app112311441/s1)), Figure S1: X-ray characteristic peaks of the main elements in the MY samples. Conceptualization, M.L.A. ; Data curation, M.L.A., M.V., P.H. and G.G. ; Formal analysis, M.L.A., V.M., M.V., A.C., P.H., N.E. and G.G. ; Funding acquisition, M.L.A. ; Investigation, M.L.A., V.M., M.V. and G.G. ; Methodology, M.L.A. and P.H. ; Project administration, Y.M. ; Resources, K.L. and Y.M. ; Supervision, M.L.A. ; Validation, M.L.A. and K.L. ; Writing--original draft, M.L.A. ; Writing--review & editing, M.L.A., V.M., M.V., P.H. and G.G. All authors have read and agreed to the published version of the manuscript. This research was funded by BEN 123456I, Benelli Arte, Urbino and DISPEA Project, University of Urbino, CUP H31I18000020005. The authors would like to thank [PERSON] and [PERSON] (National Heritage Conservation, Florence, Italy), the restorers that were working on the Me-taw-ya temple, for their support. We thank [PERSON] in supporting Raman analysis.