CHAPTER 15: Analysis of the Degradation of Medieval Mural Paintings in the Open Air Abandoned Church of Ribera, North of Spain

This work concerns the study of the conservation state of the church of Saint Stephen in the village of Ribera de Valderejo (Alava-Araba, Basque Country) and of the wall paintings preserved inside of it. The town is located in a rural area and it is in a state of abandonment, therefore, in these environmental conditions the preservation of artworks is complex. In order to propose the best conservation and restoration method, original pigments, new materials employed in modern times, building materials and decay products were characterised first using Raman spectroscopy and X-ray fluorescence portable devices and subsequently, some collected samples were analysed by laboratory techniques. Raman spectroscopy and a scanning electron microscope, coupled with energy dispersive X-ray spectroscopy allowed us to clarify issues about the mural paintings, in particular, the presence of a black tone and a highly toxic product such as magnesium arsenate used as a biocide product. In addition, ion chromatography was applied to the study of the soil and the river water to ascertain the ions that can be present in water infiltrations. Raman analyses were necessary to obtain a characterisation of different carotenoids (β-carotene, zeaxanthin and astaxanthin) and salts efflorescences (nitrate and sulphate salts) present on the wall and on the mural paintings. In addition, due to DNA extraction, two fungi genus (Cladosporium cladorporioides, Mortierella alpina) and two bacteria genera (Streptomyces sp., Bacillus amyloliquefaciens) were identified.