Invisible Varnish Found Guarding 37,000-Year-Old Paintings in French Cave

ARDÈCHE, FRANCE — Scientists say they have found a hidden reason that the Paleolithic paintings of Chauvet-Pont-d'Arc Cave have lasted some 37,000 years: a thin, invisible mineral coating that may have shielded them from the ages.

According to a report in The Debrief, the work was led by researchers from Sorbonne Université and France's National Center for Scientific Research (CNRS). The team built a portable instrument using ultraviolet fluorescence spectroscopy, which can examine cave walls from as far as 2.5 meters away, sparing the fragile art any contact.

By comparing how limestone and calcite deposits respond to ultraviolet light, the team identified a translucent calcite layer over charcoal drawings on the Panel of the Horses, which visitors meet on entering the Skull Chamber. The researchers suggest the layer may act as a natural varnish. They add that where the deposits grow thicker, the coating could obscure parts of the paintings.

The team also reports an unexpected orange fluorescence beneath certain charcoal markings and near smears left by ancient torches. Laboratory experiments lead the researchers to believe the signal may come from limestone or calcite exposed to heat. That, they say, raises the possibility that the artists sometimes drew with very fresh charcoal, perhaps still hot or burning.

Lead researcher Dr. Philippe Walter described the approach in a statement as "much like forensic investigation." The cave, according to the report, was sealed for many thousands of years by natural collapses, and the findings were published in the journal ACS Omega. The authors say the method offers new ways to monitor and preserve such delicate sites.