Greek scientists use lasers to clean Acropolis

In the past two and a half thousand years, the temples of the Acropolis have suffered fire, bombing and earthquake. Now, scientists are trying to save them from a new modern enemy - pollution.

Standing on a hilltop at the centre of Athens, a city of four million people, the Acropolis' elaborately sculptured stones have fallen prey to a film of black crust from car exhaust fumes, industrial pollution, acid rain and fires.

A team of Greek engineers and restorers are using an innovative laser technology system to clean the surface of the ancient monuments, uncovering colours and ornamentation hidden for decades.

"It is very serious," said Maria Ioannidou, director of the Acropolis Restoration Service, of the pollution. "It destroys sculptural, structural and painting details. One of our aims is to regain these cultural details using new technology."

For years the team tested 40 different methods, including mechanical and chemical processes, to find the safest solutions to restore the white of the marbles without losing detail.

The winner was the brainchild of Crete's Foundation for Research and Technology, which created a system that uses two laser beams of infrared and ultraviolet rays simultaneously.

These rays have been used separately to clean ancient marble, but it was found that one left a yellow tint while the other left a grey one. The new system blasts off layers of black film leaving the marble details intact, without discoloration.

But it is a risky process.

"If you remove something you cannot put it back in place, so we must be quite sure that we remove unwanted pollutants and leave... all the information on the original surface," said Evi Papaconstantinou, the chemical engineer in charge of the team.