X-ray spectroscopy solves mystery of red Pompeii paintings

Artists in ancient Pompeii painted the town red 2,000 years ago with a brilliant crimson pigment made of cinnabar (HgS) that dominated many of the doomed city's wall paintings. The eruption of the volcano Vesuvius showered the neighbouring towns in pumice and ash, and the Villa Sora, in Torre del Greco, remained buried until just 20 years ago, which is when excavation work started. In the remains of the house, the distinctive red colour of the wall frescoes has turned black in many places. The origins of this darkening degradation have not been clearly identified yet and remain a major issue for curators. At ESRF, by aid of micro X-ray fluorescence and absorption spectroscopy, scientists analyzed red cinnabar paintings coated on a sparry calcite (CaCO₃) mortar exhibiting different levels of degradation. The results indicate two possible degradation mechanisms; formation of HgCl₂ and CaSO₄ through reaction with NaCl and SO₂ from the environment, respectively. For more information, see the paper, "Blackening of Pompeian Cinnabar Paintings: X-ray Microspectroscopy Analysis", M. Cotte et al., Anal. Chem., 78, 7484-7492, (2006).