The work performed till the end of 2008 was centered on fragments with painting layers (either from the second or the fourth Roman style) and mortar fragments without any remaining of pigmentation.
Two main degradations were observed in red layers, leading to some darkening processes. In the particular case of red layers with cinnabar (HgS) two decaying compounds were detected, elemental mercury (Hg) that gives the blackish shade to the red layer, and calomel (Hg2Cl2), a white compound that is formed after the reduction of Hg(II) in the presence of chloride. In the case of layers with hematite (Fe2O3), a thin black layer was observed at the microscope revealing the uniform presence of magnetite (Fe3O4), a degradation product that can be formed by reduction of hematite with SO2 gas (a typical compound of the modern atmosphere around Pompeii), together with gypsum (CaSO4.2H2O) and possible (para)coquimbite (Fe2(SO4)3.9H2O).
These results were submitted to the consideration of the Scientific Committee of the RAA2009 Congress (5th International Congress on the Application of Raman Spectroscopy in Art and Archaeology) that was organized in Bilbao by our IBeA research group. These results were accepted as an Oral Communication. Later on, it appeared our first publication in the special issue devoted to that Congress.
The samples having only the arriccio and intonaco mortar layers were analyzed in 2009. The results shown apart from the expected calcite, quartz and puzzolanic (silicates like diopside MgCaSi2O6,a typical compound of volcanic stones) compounds, the presence of several degradation compounds, namely gypsum, niter (KNO3), mirabillite (Na2SO4.10H2O), epsomite (MgSO4.7H2O) and weddellite (CaC2O4.2H2O). The experiments of the soluble salt test confirmed the presence of dissolved chloride, sulfate and nitrate anions, in agreement with the compounds detected by Raman spectroscopy.
The results obtained from the mortar samples were submitted in June 2009 to the Historic Mortars HMC2010 Congress (Prague, September 2010). Our work was accepted as an Oral Communication, being also published in a dedicated book.
The chemical explanation to justify the presence of the decaying compounds lead us to consider a generalised impact of the surrounding high polluted atmosphere (high presence of SOx and NOx acid gases in a marine aerosol environment of the Naples metropoli). But to extract this conclusion from the few number of samples was considered too risky. That’s why we checked the posssibility to perform field analysis directly on the walls of the House of Marcus Lucretius. And at this moment, the APUV project started.