Model study of the constituents of wall painting degradation patinas: The effect of the treatment with chelating agents on the solubility of the calcium salts

A model study on the application of chelating solutions on superficial calcium degradation patinas of wall paintings is presented. For this purpose the solubility of calcium sulfate, carbonate and oxalate in aqueous solutions of the Ca2 + chelators EDTA and citrate, was evaluated. Both the obtained solutions and their insoluble materials were analyzed by several analytical techniques. These studies revealed that the treatment of solid samples containing calcium sulfate and carbonate as the models of painting patinas resulted in higher solubilities of calcium sulfate and carbonate over that of oxalate. Moreover, our investigations confirmed the higher capacity of EDTA to chelate Ca2 + compared to that of citrate. All these results were interpreted and discussed on the basis of speciation models, solubility products of the salts and formation constants of the calcium complexes in solution. Finally, we report the characterization of a sodium calcium double citrate salt formed as an unexpected product in the treatment of the calcium sulfate with citrate. Overall our results suggest that the low solubility of calcium oxalate prevents its dissolution upon treatments with chelators, and that the capacity of citrate to dissolve the calcium salts is lower than that of EDTA irrespective of the duration of treatment

A multi-analytical approach applied to the archaeometric study of mortars taken from The Forty Martyrs rupestrian complex in Cappadocia (Turkey)

Mortars and plasters from the Forty Martyrs rupestrian complex (Cappadocia, Turkey) were characterized by means of different and complementary analytical techniques, in order to achieve evidence about the raw materials and the production technologies employed in the site dwelled by some of the first Cappadocian Christian communities. The investigated area is constituted by rooms directly hewn in the volcanic deposits named “Fairy Chimneys” and included in the UNESCO World Heritage List. Archaeological studies attributed different uses to the rooms, i.e. chapels, storages and wineries. The multi-analytical approach means to confirm or to retract the archaeological thesis and to highlight probable differences in the production techniques of the stone materials .In this regard, textural and compositional data of the binder and the aggregate fractions were collected by optical microscopy and electron microscopy coupled with microanalysis. Pigments and binder composition was investigated by Fourier transform infrared and micro-Raman spectroscopy. Lastly, probable traces of organic residues were identified by gas chromatography coupled with mass spectrometry. The obtained results allowed for identifying variations in the technical and compositional characteristics of mortars and plasters which can be related to different uses of the rooms constituting the rupestrian complex. Keywords