Tucked away inside a limestone cave in southeastern France lies some of the oldest artwork in existence. Known as Chauvet Cave, the site is so historically important - and fragile - that its location is kept secret and locked behind a huge steel door. And now, researchers reporting in ACS Omega have devised a technique to safely investigate these artworks and understand the natural varnish that has protected them for centuries.
We examine every piece of evidence to decode the techniques of prehistoric artists and understand how the paintings have been preserved over time." - Philippe Walter
Adapted from ACS Omega 2026, DOI: 10.1021/acsomega.6c05061
Somewhere around 37,000 years ago, a group of Paleolithic people entered what is now Chauvet Cave and left behind detailed artwork of local fauna, including cave bears, cave lions, bison, and horses. The drawings were sealed off by an ancient rockfall and left undiscovered until the 1990s. Several decades later, a lot can still be learned from these ancient works of art, including how the cave's geology may have contributed to the artworks' preservation. To study cave walls without damaging them, researchers have used UV fluorescence spectroscopy, which reveals fluorescent mineral deposits invisible to the naked eye . Philippe Walter and colleagues wanted to use the technique to noninvasively investigate these ancient drawings. Their focus was on mineral deposits that have formed atop the charcoal-based drawings and the techniques used to create the art.
Due to the fragility of prehistoric footprints in front of the artwork, the researchers set up a portable spectrometer on a protective walkway around 8 feet (2.5 meters) away from the cave wall. A beam of UV light was shone on the wall, and the resulting fluorescence from the mineral deposits and pigments in the artworks was analyzed by the spectrometer.
Adapted from ACS Omega 2026, DOI: 10.1021/acsomega.6c05061
"Our methodology is much like forensic investigation: We examine every piece of evidence to decode the techniques of prehistoric artists and understand how the paintings have been preserved over time," says Walter.
The researchers' analysis revealed that:
- Mineral-carrying water flowed over the wall's limestone surface, leaving behind thin layers of calcite. That calcite glowed blue under a blacklight, revealing a natural varnish covering parts of the artwork.
- Some areas displayed an orange fluorescence, which could be from hot charcoals or burning materials, like a lit torch, being rubbed against the wall to create the drawings.
These results showcase the careful interaction between humans and geology that allowed these artworks to be preserved for tens of thousands of years. Walter and team anticipate that the technique also has applications from forensic science to monitoring biofilms onboard the International Space Station - a project already underway.
The authors acknowledge funding from the French Ministry of Culture, the French National Centre for Scientific Research (Centre National de la Recherche Scientifique), and Sorbonne University.
One of the authors is a founder of Lumentis, a company developing imaging instruments for historical artwork analysis.
