Ca-oxalate films on the stones of the medieval architecture: the case-study of Romanesque Churches

Traces of Ca-oxalate films were found on the stone surfaces of stones of some Sardinian medieval Churches of the ‘Giudicati’ period. The study aims to define their distribution and microstratigraphy on the different architectonic stone elements and to clarify their precise roles as result of probable ancient conservation. Ca-oxalate films show a variable color from greyish, to rosy or yellowish and generally they are present on the decorative architectonic elements of monuments. Their thickness is variable (10-50 m) owing to the roughness of the stone surfaces. XRD analyses performed directly on the collected microsamples and on powders gently scraped from their surfaces revealed calcite+weddellite (type 1) in some of them and calcite+weddellite+whewellite (type 2) in others. Preliminary observations at the polarizing microscope showed two different micro-stratigraphies.