Treatment agreed to remove fungus from prehistoric art

New clusters of black fungus are spreading over treasured cave drawings in France, scientists warned, as they announced a bacteria-killing recipe to protect the remarkable Palaeolithic paintings.

The stains are the latest biological threat to the Lascaux cave drawings, considered one of the finest examples of prehistoric art, since their discovery in 1940.

The caves were closed to the public in 1963 after green algae and other damage appeared, but despite restricted human access they have suffered occasional bouts of fungus-related stains.

This July, caretakers noticed new black spots covering some of the drawings, the Lascaux Caves International Scientific Committee said at a two-day meeting this week.

Samples were taken, showing that the stains were caused by two fungi called ulocladium and gliomastix that developed on top of a sublayer of existing bacteria, said Michel Clement, the French Culture Ministry’s top architecture and cultural heritage official.

Targeted biocides, or substances that kill bacteria, were tested on the samples and submitted to this week’s meeting. The panel approved the use of localised biocides to treat the affected areas.

Afterwards, the caves will be closed completely for three months, Mr Clement said. Currently only a few people, chiefly scientists, are allowed to enter the cave and only at carefully regulated intervals.

The climate control system installed in 2001 will also be modified or replaced, the panel announced.

The cause of the new bacteria was unclear.

After the climate control system was installed in 2001, moisture stains appeared that were treated with fungicides, antibiotics and the spreading of quicklime. Those treatments ended in 2003.

The scientific panel also reviewed studies suggesting global warming may be affecting the caves.

The average natural temperatures inside the caves – registered by the climate control system – have risen 0.9 degree Celcius since 1981, said Marc Gauthier, president of the committee.

The temperature inside the main cavern is kept at a constant 12.5 Celsius (54.5 Fahrenheit). More than 50 control instruments also measure air pressure and humidity and warn of other changes affecting the natural balance that existed in the cave before its modern discovery.

Carbon-dating suggest the murals – of bulls, felines and other images – were created between 15,000 and 17,500 years ago in the caves near Montignac, in the Dordogne region of south west France.

A replica of the main Lascaux cavern constructed about 200 metres from the original is a big tourist attraction.