The Red into Black: Roman Wall Paintings at Pompeii

For years, archaeologists and art historians have wondered why the wall paintings discovered at Pompeii and other Roman sites turned from a vivid red to black so quickly--within 20 years of their exposure. The frescoes were originally painted in cinnabar, a poisonous substance and the principal ore in mercury called mercury sulfide. Cinnabar has a bright crimson coloration in its natural state; and the rapid change in color to flat black was recognized and lamented by the Roman writer Vitruvius , who commented in the first century AD that the application of a 'punic wax' prevented the color change. According to a new study reported in Analytical Chemistry this week, the reason that the color changes has to do with exposure to chlorine--probably from the sea--and subsequent calcite sulfation, resulting in a black layer 5 microns thick hiding unchanged cinnabar.

A research team at the European Synchrotron Radiation Facility led by Marine Cotte believe that the calcite deposits are probably related to the exposure to climatic and atmospheric conditions. Further tests are in the works, but progress on this may have implications for future preservation (and maybe restoration?) of Roman wall frescoes.

• European Synchrotron Radiation Facility
• ESRF Press Release
• Roman Archaeology
• Pompeii, various and sundry bits of info and links to some great websites
• Recovering Pompeii, from PhysOrg.com, more information about the chemistry involved
• Cinnabar, from About's guide to Geology Andrew Alden

The photo is of a blackened wall fresco at the Roman site of Oplontis, and is credited to Mario Pagano; the article in Analytical Chemistry, which I have not read, is:
Marine Cotte, Jean Susini, Nicole Metrich, Alessandra Moscato, Corrado Gratziu, Antonella Bertagnini, and Mario Pagano. 2006. Blackening of Pompeian Cinnabar Paintings: X-ray Microspectroscopy Analysis. Analytical Chemistry 78 (21), 7484-7492.