Prehistory · c. 35,000 BC · Chauvet Cave, Ardèche, France
Natural calcite varnish may protect 37,000-year-old Chauvet Cave art in France
Ultraviolet scans taken from 2.5 metres away show a thin, see-through mineral layer over the charcoal drawings, and suggest hot charcoal, perhaps from torches, altered parts of the wall.
Chauvet Cave, France A thin natural coating of calcite covers parts of the charcoal drawings in Chauvet Cave in southeastern France, and may have protected them for tens of thousands of years. Researchers found the coating with ultraviolet light, without touching the walls. Ice Age people made the drawings about 37,000 years ago.
The team was led by Philippe Walter, and the first author is Y. Boulard. They published the results in the journal ACS Omega in 2026. The French Ministry of Culture, the French National Centre for Scientific Research (CNRS) and Sorbonne University funded the study.
Chauvet Cave holds some of the oldest art ever made by people. Its painters used charcoal to draw cave bears, cave lions, bison and horses. A rockfall later sealed the entrance, and nobody saw the drawings again until the 1990s. Officials keep the cave's location secret, and a large steel door locks the entrance.
Measured from a walkway 2.5 metres away
The researchers used UV fluorescence spectroscopy. The method shines ultraviolet light on a surface and measures the glow given off by minerals and pigments. It picks up deposits the human eye misses.
Prehistoric footprints and soil still lie on the floor in front of the art, so the team could not get close. They set up a portable spectrometer on a protective walkway about 2.5 metres from the wall. They used a custom system built for the harsh conditions inside the cave.
Telling the coating apart from the rock is difficult. Limestone and the calcite left by dripping water have nearly the same crystal structure. Older tools such as X-ray fluorescence and Raman spectroscopy struggle to separate them. Under UV light, however, tiny organic impurities trapped in each material glow differently.
The team built a model of the decorated wall. With it, they separated the calcite signal and worked out how the layers are stacked.
A veil over the Horses panel
On the Horses panel, the readings showed a see-through calcite veil over the charcoal drawings. Mineral-rich water flowed across the limestone and left thin layers behind. These layers glowed blue under UV light.
The veil works as a natural varnish. Knowing it is there helps conservators judge how stable the paintings are today.
The coating is uneven across the cave. In the Alcove of the Lions it varied from spot to spot. There the charcoal drawings themselves changed how calcium carbonate built up on the wall.
The team also saw patches of orange glow near some charcoal marks. The authors think hot or burning charcoal altered the calcium carbonate and produced the colour. A lit torch rubbed on the wall could have done this. The idea still needs confirmation. That will require studies of how the charcoal burned and how heat changed clays with different amounts of iron oxide.
The method has a limit. The amount of glowing impurities differs from place to place, which makes it hard to compare layer thickness. The results are therefore approximate.
Walter compares the approach to forensic work, in which every piece of evidence helps explain how the artists worked and how the paintings survived. The authors treat the rock, the pigment and the coating as one system. They say the findings will guide decisions about protecting the caves and limiting access.
The technique also has uses in forensic science. A project already under way uses it to track biofilms aboard the International Space Station. One of the authors co-founded Lumentis, a company that builds imaging instruments to analyse historical artwork.
Sources (1)
- Natural varnish may protect 37,000-year-old Chauvet Cave art, UV scans show (Archaeology News)
Paper: Y. Boulard et al., ACS Omega (2026). DOI: 10.1021/acsomega.6c05061
Spotted a mistake? Tell the editor about a spelling error or a fact that is wrong. We correct stories openly.
Readers' picks show on the front page.
.jpg){kind=link}
BisonsPoursuivisParDesLions.jpg){kind=link}
Comments
House rules. Stay on the subject, be kind to other readers and say where your facts come from. No advertising and no personal attacks. The editor reads along and hides comments that break these rules.
Loading comments…