Using LIBS, the researchers were able to study the ions in the paintings in situ.Ivan Vdovin / Alamy Stock Photo
Volcanic material ejected by Mount Vesuvius has preserved the ancient Italian city of Pompeii for nearly 2,000 years, providing a time capsule of life in the Roman Empire. But findings from researchers led by Maite Maguregui, at the University of the Basque Country in Spain, show that debris may also be causing degradation of Pompeii’s priceless murals.
Salt accumulation is a known threat to these artworks. The ions responsible for salt formation have generally been found in groundwater. However, pyroclastic materials produced by volcanic eruption are rich in fluoride ions, which also form salts, but such ions are difficult to analyze with portable instruments.
To measure the ionic impact of volcanic debris, Maguregui’s team turned to laser-induced breakdown spectroscopy (LIBS). LIBS offers a portable solution to interpret the distinctive emission bands produced by different molecules after laser illumination, and can readily discern fluoride from other ions. “This has been applied by NASA’s Mars exploration studies, but never in the field of cultural heritage,” says Maguregui.
LIBS offered a new perspective on Pompeii’s murals. “The first surprise was seeing fluorine everywhere,” says graduate student Silvia Pérez-Diez. Further analysis at selected sites allowed she and Maguregui to determine how fluoride-based salts might form. “When those paintings are excavated, some remains of volcanic materials are there, and humidity or rainwater can leach these ions and promote crystallization of salts,” says Pérez-Diez.
These findings reveal a hidden factor that could confound efforts at preservation and restoration, since these crystallized salts can degrade some of the paints used. Now, Maguregui hopes to profile Pompeii’s fluoride accumulation more extensively.
